Unicorn

UAV Research at the University of Minnesota

August 3, 2007

Today we took a small field trip to do a couple systems tests.

Here is the basic setup with Paw, Troy, and Brian:


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Here is a closup of the Unicorn airframe with all our instrumentation:


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Here are some pictures of the flying area:


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Here are some pictures of the Unicorn in flight:


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Senior Telemaster Early Flights

While rummaging around my hard drive I stumbled on some early footage of our Senior Telemaster flying. This footage includes some of my earliest successful autonomous flight using the original MNAV sensor head (now discontinued.) There isn’t anything especially great about this footage, other than I love the way the Telemaster looks in the air, especially it’s “scale” take offs and landings. These videos date back to sometime in mid-summer 2007.

The following movie includes some take offs, landings, and some early autonomous flight. One thing that is purposely highlighted in this video is an MNAV firmware bug that would cause the servos to go hard over full stop and send the UAV spiraling out of the sky. Fortunately we could quickly flip back into manual mode and manually pilot the aircraft to safety. Eventually I personally tracked down the firmware bug and fixed it. (Now we no longer use the MNAV in our UAV work.)

Here is a second movie showing a segment of successful autonomous flight.  The Telemaster is flying a bowtie — or figure 8 — pattern.  This is interesting to me because it offers a visual reference for the “quality” of our early MNAV based autopilot system that we can compare our current system against.

Sig Rascal 110 #1 Instrumentation

MicroGear and the Xbow MNAV

March 5, 2007

Paw finalized the RxMux assembly after I verified everything worked.

March 3, 2007

Today I ground tested my RxMux manual override board and everything appeared to work great.

February 20, 2007

Flight testing the MNAV, Stargate, and Maxstream again.


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In our test last November, we had problems with our gps antenna connection. We made an attempt to fix that issue, but have been waiting through about 40 days of brutally cold weather here in MN to find a flyable day. Finally today the weather and our schedules matched up so we put in 2 very nice test flights.

The MNAV worked well. The secured gps antenna connection held up well though all RPM ranges, taxiing, take offs, landings, and some relatively agressive in flight maneuvers. Everything seemed solid. That is great news because it lets us move on to more interesting things.

In addition to just collecting the data, I fed it into a running copy of FlightGear in real time so you could visualize a synthetic view of the real world flight on the computer. This includes the world position, attitude, and flight surface deflections. It’s very cool to see the virtual view on the computer match exactly what the real world airplane is doing as it happens.

This synthetic view will be useful for a number of things down the road. For example, we can click anywhere in the synthetic view and get back the real lon/lat/elevation of the ground point we clicked on. Now imagine that we have overlaid live video on top of the synthetic view in a way that matches the two views "conformally".

The synthetic view also gives us the ability to highlight obstacles, restricted airspace, target routes, approach paths, other uav’s in the air, etc.

Takeoff …

Roll …

Fly by …

Loop and Landing …

November 22, 2006

First flight with the MNAV, Stargate, and Maxstream on board

First, no crashes to report!

Here are some observations.

1. We powered everything on and it all worked at the field (including gps.) Then we did a test flight with the MNAV and radio modem *off*. We landed and then powered everything back on to do engine on tests. From that point on … with engine running or not running we were unable to get any gps lock. We were pushed into a corner with battery life so we couldn’t sit around and wait 30 minutes to see if the gps could find itself. So we flew without gps and collected attitude, airspeed, pressure altitude, and transmitter stick inputs; the gps never came to life in flight. Dang, no gps data. 🙁 We need to investigate this further, we don’t think it was an antenna connection issue since we *very* carefully secured that. I’ve observed in the past that the MNAV gps can be a bit persnickety, and the MNAV hides all the nmea strings so we can’t see if the gps is seeing zero satellites (antenna problem?) or seeing a few satellites but is lost and trying to find itself.

2. I was really underwhelmed with battery life for our maxstream radio modems and the MNAV/stargate. We were running standard 9v batteries for the maxstream and a 3.7v lipoly (1320mah) battery for the stargate. We got maybe 20 minutes out of everything before the batteries died. I’d really like a bit longer life for a better safety margin when we fly with the system in the critical control path.

So the two main technical issues for us to iron out are (a) figure out what happened with the gps … probably just needed to let it sit for a while longer to find itself and (b) we need longer battery life for a bit more comfortable safety margins. A 10-15 minute flight with 20 minute total battery life is pushing things a lot tighter than I’m comfortable with.

3. We did collect attitude data. I don’t have a very good sense as to the quality of the attitude data, and without location/gps to go along with it, it doesn’t really make sense to replay it in flightgear as a visual sanity check … that was what I was hoping to do. We don’t have an absolute truth reference, but when you replay the flight you can visually catch a lot of abnormal things that wouldn’t show up in the plots.

4. The pitot tube dynamic pressure system seemed to work and yield plausible results. Top speed for the day with our Rascal 110 was about 90mph. Throttled back cruise was maybe 35-45 mph. Approach speed was about 35 (makes sense since I didn’t change the elevator trim between cruise and approach so speed shouldn’t change too much if I’m flying hands off.) Touch down looked like in the neighborhood of 25 mph. (Units converted from m/s to mph indicated, not knots.) Sense since, not knots … how do I stumble into this clumsy english?

5. static pressure/altitude data seemed plausible. The minimum/ground value for the day was 738, max altitidue was 1230, so we kept it under 500′ AGL. Actual field elevation is close to 900′ so these values weren’t calibrated for local weather conditions and that is expected.

6. We updated the demo code to log transmitter stick inputs (and onboard battery voltage) as well. Those seemed pretty good overall, but there are several places where the servo channel data glitched out. The system didn’t register this as a complete transmitter off situation, but the data would get really noisy: 1-3 values at the high end, 1-3 values at the low end, 1-3 correct values, repeat. There is one particular stretch of about 7-8 seconds where the data got *really* noisy and bad. We never flew very far out, so I really didn’t want to see this kind of noise in my data. Makes me very nervous, makes me think that I could easily fly out of range and not be able to recover control in time to save the airplane, if the MNAV is in the critical control path. I didn’t try to fly especially far away, but at the same time we didn’t have gps working so I can’t know what the cutoff range is. We might be able to filter the transmitter data to help things out since there are clearly some good values in the midst of the noise, but still, not what I wanted to see. We’ll need to think very hard about a safe way to proceed. Aside from the one ugly 7-8 second stretch, the other drop outs seemed much more momentary and probably wouldn’t hurt us too bad.

So that’s where we are at. We need to figure out why our gps refused to work. We need to get some bigger capacity batteries. And we need to solve our MNAV interference/range issues before we can proceed on to autonomous flight.

November 18, 2006

Pictures of the MNAV and StarGate mounting detail


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MaxStream Xtend Radio Modem


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GPS Antenna and Ground Plane


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External Power Switches


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Adding and Routing the data and power cables


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Power and data for the MaxStream radio modem


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Packaging everything together


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Installation in the fuselage


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Sig Rascal 110 #2 Results

Sig Rascal 110 #2 – UMN UAV Project


IMG_4073 Purchased August 24, 2005.

This is the second Rascal 110 purchased by this project. It comes with a Zenoah G26 gas 2-stroke ignition engine. The engine seems to be a very nice match for the aircraft. With an 18×8 prop, it will idle at about 1800-2000 rpm and tops out at about 7000 rpm. This isn’t quite the 10k rpm that our OS 1.60FX would turn (with the same prop) on our first Rascal, but it is more than enough power for this aircraft.

October 25, 2006.

Pictures from our morning at Jensen field. We were flight testing to collect data from our 3-gps carrier phase differential attitude determination system.

Warmups on the ground …


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Fly by’s …


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Landing approaches …


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Some of the ground crew helping out …


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Taxiing …


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Closeups of the instrumentation …


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Detail of one of the wing gps antennas mounted internally …


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Overview of the airframe …


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July 11, 2006.

Here is an article written about our project: sensor-0517.pdf.

Here are the raw (color) photos.


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May 31, 2006.

Today was a beautiful day. Temps in the upper 70’s. Wind about 5mph out of the N and NE. Our mission for today was to collect good MIDG data. We have had problems with our aerocomm radio modem link so Greg rigged up a little gumstix unit to record the data directly on board. We lose our real time link for this, but we get solid data with no drop outs. We want solid data for another little adventure.

This was our first outing of the season. We put in two flights today and the Rascal flew beautifully. The engine ran great and was rock solid. I even spotted my landings on the runway, although with the extra weight, she rolled out a little long onto the grassy area which is no big deal. The Rascal handles mowed grass with no problems.

Here are a couple new pictures of the Rascal with Greg and I.


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December 12, 2005.

Movie time.

Here’s a word of explanation. On 10/26/05 we did a test flight and captured the live video stream from the onboard camera as well as the data stream from the onboard IMU/GPS/INS unit. (See the entry for 10/26 below.) We replayed the data stream in FlightGear with overlayed instruments (this can also be done in real time as the data is captured) and saved that out as a movie. Then we edited the two streams together in two different ways: side by side, and blended overlay. The result is interesting. You can see at the start of the flight where the IMU was pretty far out of whack … as much as 5-20 degrees off in yaw. But as the flight progresses you can see the error diminish and later in the flight the match can be quite good.

Both videos are about 50Mb to download. You will need DivX6 to play them. Linux or open source people might find they can play these with xine or mplayer. Windows people might need to go download the DivX6 runtime codec from http://www.free-codecs.com/download/DivX6.htm.

Blended Overlay

Side by Side

November 30, 2005.

Minnesota! This here is what we live for! We put up with above freezing temps, oppressively humid summers, terrible mosquitos for a few months of the year, and high taxes, but days like today are the payoff: Standing outside in +20F temps (and often colder) freezing our butts off or playing hockey, or both. 🙂

Today we flew Rascal #2 at Jenson field. Temps were about +20F. Winds were some where between calm and very light. We probably had about 2″ of snow on the ground … right on the borderline for operating with wheels. The first takeoff run was a little “S” shaped and we had one nose over on a landing (zero damage) but other than that everything worked fine as I adapted to the conditions. We also tested our new video capture hardware.

Just look at these picts and see what you folks in sunny warm climates are missing out on. Oh yeah, and these pictures look dark for good reason. The sun barely cracks the horizon up here this time of year. And when the sun is up (or not up) it’s usually cloudy.


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November 11, 2005.


img_3142 Here is a diagram of some of the Rascal 110 dimensions.

October 26, 2005.

Today we flew Rascal #2 at Jensen Field. Weather was perfect, winds were light and out of the east. Our primary goal was to test the live video and live synthetic view right next to each other to verify they track each other as they should since both reflect live data. We also practiced flying over specific objects and buildings to see if we could recognize things from the live video in flight.

Here are two pictures taken nearly at the same time. The first is from the onboard video camera, the second is the FlightGear based synthetic view:


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October 17, 2005.

Paw and Greg fixed our radio modem / RC system interference problem so now we get excellent range checks. We setup down at “Jensen field” in Rosemount, MN.

Here is a picture of the field and the row of hangars:


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Our ground station is basically setting up our equipment on a picnic table in the shade:


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Here are some pictures of our aircraft posing:


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Results:

Our wireless video camera refused to work so we flew without that. Our primary objective though was to flight test our “synthetic visual system.” This consists of a MIDG-II IMU/GPS/INS transmitting data to the ground via an aerocom radio modem. On the ground we have some custom software that reads the MIDG-II binary data and sends the results over to FlightGear for real time rendering. Ted built us a “photo-real” model of the area that was compatible with FlightGear.

We were disappointed with the data rate we were getting (maybe 5hz.) This prevented us from doing any serious flying under the hood. But I think we validated our approach and when we track down our data rate issues we will have a very powerful remote piloting tool.

I made a short movie of an approach and touch down. I replayed the data on my laptop so it is smoother than in real time because the replay code can easily interpolate between data points. I pointed my little digital camera at the laptop’s screen and here is the result, low quality, but you can see things in action. Notice the live working instruments at the bottom of the display. We are landing to the west and have a pretty stiff turbulent wind coming from the NW and rolling over the hangers. I’m not showing off my piloting skills here, but the touch down was nice ad gentle. 🙂

Click on the following “text” link to view the movie:

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October 3, 2005.

All our instrumentation was moved over to Rascal #2 so today we flew a series of test flights to make sure the plane flew well with it’s payload. We couldn’t pass the range check test with our radio modem on so we scratched our heads for a while, but couldn’t come up with any clever ideas so we unplugged the power and grudgingly continued with no telemetry data.

We were very happy with the aircraft’s performance and handling with the load. We seemed to be getting solid video with our patch antenna. We also wanted to put more time on our buddy box/safety pilot system so we did one flight where we switched off control to each other.

Finally, happy with how everything was working, we walked over to the ground station and took turns flying “under the hood” with video only. Our camera points 45 degrees down which gives a good view of the ground, but not the horizon. We were able to hold a reasonably straight line via video alone, but turns were very difficult because you couldn’t see the horizon to get a good judge of bank angle and pitch angle. This is where the synthetic view would have been really nice … but no telemetry data.

Next up is to figure out our interference problems and get back to where we can fly with telemetry turned on.

September 26, 2005.

Friday and today we have been working on extracting our instrumentation from Rascal #1 and testing it to verify everything still works after our crash. We need to do a bit more testing, but we are reasonably confident at this point that everything survived intact (minus our radio modem which had it’s antenna sheared off.)

Today I continued to modify my MIDG-II replay software so I can read the live incoming data directly from the serial port and pass it to FlightGear. This gives us a live, real time, synthetic view that should match the real aircraft very closely. This should allow us to insert things like restricted airspace, important objects, mission goals, flight route, etc. into the synthetic view. We even have the capability of setting up a virtual ILS for our landing approach. Our sensors are not good enough to allow us to do a full stop landing, but they could assist us in lining up and flying most of the approach.

In addition, the synthetic display can be viewed from inside a live virtual cockpit with working instruments, from a chase plane, or from a tower view. This should be really cool!

September 21, 2005.

After crashing Rascal #1 we decided to take Rascal #2 up for it’s maiden flight. Everything worked great and the plane flies just as beautifully as Rascal #1. I think we get a lower idle and more braking action from the prop on approach, so Rascal #2 is easier to spot in on the landings. Also, there is much more fined grained precision on the low end of the throttle range with the G26 which means a notch up or down of power actually gives you a notch up or down of thrust. This makes controlling the rate of decent on approach work just like the text books say it should. (With smaller glow engines you typically have poor precision on the low end and seem to have not enough or too much power on approach with no fine grained control.)

One small bit of strangeness did occur in our 2nd flight. I think we had the idle set a little too low so when I pulled power for a slow fly by, the engine quit . I was downwind, but way to high to make a good approach to the runway. I kept the wings level and touched down on the extreme far end of our mowed grassy area. I bounced back up and sailed into the farm field (alfalfa???) bounced one more time in the field and the nosed over and went tail high. Zero damage, not a scratch, but it ended up *inches* from where Rascal

Sig Rascal 110 #1 Rebuild

Sig Rascal 110 #1 – UMN UAV Project

Next steps …

  • Come up with a better solution for securing the tank.
  • Redo top nose cover job?
  • Cut and fit cowl.
  • Purchase replacement windshield (?)

October 20, 2006.

This morning I re-maidened Rascal #1. I had to work through some minorhardware issues, but the structure and rebuild all held together well,and the airplane flew straight and true and as good as it ever has.I’ve very happy with the outcome, and very glad to have this airplaneback on active flying status.

October 19, 2006.

This evening I ran the engine for the first time after the crash. Everythingseemed to perform well. I think I may try to re-maiden tomorrow if the weather is ok.

October 2, 2006.

The battery and reciever and crystal arrived today. I tested to makesure they all work. I brought the aircraft home this evening andmounted the receiver, battery, and volt-watch unit. I still need to secureantenna. I’m running out of things I can think of todo before test flying!

September 29, 2006.

Begin putting the damaged right wing back together. I epoxied thewing joiner box back together so it is secure again and then a rebuiltand sheeted the first inboard section of leading edge back to the mainspare. Finally I sanded and covered it and (tada!) the wing is done!


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We are *really* close to being ready to fly! Just waiting on thereceiver and battery now. I will cut and fit the cowl after wesuccessfully test fly and after I’ve regained my confidence in thisengine.


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September 28, 2006.

Mixed up some epoxy and sawdust and used that to fill in the shatteredend of the right wing strut. I sanded this down to shape, redrilledthe hole, and threw a quick coat of white paint on it. Good asnew. 🙂 Here are before (damaged) and after (fixed) shots.


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September 27, 2006.

Installed the engine and muffler.Reassembled and installed the main gear. Cleanedup the wings in advance of inspecting and repairing them. Inspected thedamaged wing strut and determined it is fixable.


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September 26, 2006.

I recovered the front of the fuselage in white monocote. The top of thenose didn’t turn out nearly as well as I had hoped so I may cut that offand redo. We ordered a receiver and battery. I reinstalled the tailwheel assembly and the canopy.


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September 25, 2006.

Test mounted the engine and rigged the throttle linkage. Next step is tocover the front of the fuselage.

September 22, 2006.

Worked on installing the fuel tank. Routed the throttle linkage housing.

September 19, 2006.

Secured the front wing support (where the wing dowls plug into.) Gluedin forward cabin support rods.

September 18, 2006.

Epoxy seal/paint the outside firewall.Filled in some of the gaps/cracks with balsa filler.

September 15, 2006.

Today I glued in the top nose support stringers. Then starting with thecracked up nose sheeting from the original, I drew a rough template of theshape the sheeting needed to be. I transfered that to 1/16th sheeting anddid some test fitting and trimming. Finally I squirted it up with windex which was what I had on hand and the sheeting pretty much melted around the curve …cool. 🙂 The final results looks better on the left side than on the rightbut I guess that just means I need to do a little filling and sanding.


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Posing with the cowl and the cabin support rods.


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September 14, 2006.

Reinforce left front nose side splice internally with some hardwoodsquare stock.

Finished sheeting both sides of the front fuselage (i.e. sides of the nose.)


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September 13, 2006.

Reinforce wing leading edge bulkhead reinforcements. I’m compensating herefor an earlier mistake where the bottom portion of these reinforcments didn’tget clamped in where they should have been and thus there is some ugly gaps.It will be non-visible when the fuselage is all sheeted, but I just wanted tomake sure it’s solid structurally.

I installed (and tack epoxied) the engine mount blind nuts onto the backside of the firewall. These are a horrible pain to deal with once everythingis sheeted in … probably the hardest part of assembling the stock Rascal.So they are installed now and I don’t have to worry about them later.


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Finally, I cross sheeted the bottom of fuselage forward of the main gearblock. This adds a surprising amount of rigidity to the nose section whichis what I was hoping/planning. I also attached the original sheeting to therear of the main gear block. (Little details …)


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September 12, 2006.

Today I spent a few moments fabricating and installing the firewall sidereinforcements. I also fabricated the nose top stringers.


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September 11, 2006.

Today I glued in the main landing gear block and supporting structure.I also dug around the shop and found the hardwood stringers I’ll needto support the balsa sheeting on the top of the nose section. When Itest fit the cowl, she’s actually starting to look a bit like her oldself again! Maybe there is hope after all. 🙂


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September 8, 2006.

I spent a few more minutes fiddling with the fuselage. I foundseveral cracks and splits in the cabin roof where the wing dowlsinsert, specifically the sheeting forward of that.

I also secured several more cracks and splits in the bulkheads andvarious places I found them. I epoxied the split off pieces back ontothe landing gear mounting block.

I glued the cracks and splits in the right side forward nose section(shown in test fit configuration in IMG_3993 in the Sep. 7 entry.) Ifinalized my scheme to splice in the left side nose piece to theoriginal. It will involve a number of doublers, some beefy squarestock, and a big mess of epoxy.

Finally, I began to reassemble the nose section.


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September 7, 2006.

A week ago I scored a new replacement cowl from a very kind fellow modellerwho was willing to donate his spare to the cause.

Today I did some work gluing the split clamshell that was the fuselage backtogether. From the wing trailing edge foward split out like a big clam shell.From the wing leading edge forward is just splinters. After today I shouldmostly have the wing leading edge back to the tail all fixed up and solidagain.

Yes, it still looks pretty ugly, but an amazing amount of rebuild progresshas actually been made:


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May 30, 2006.

Today I made a replica of the fuselage bulk head that is between thecabin and the firewall. I also started tracing out the piece for the leftside of the nose (which exploded in the crash.) It is important to get thesize and shape just right so the firewall has the proper amount of right anddown thrust. I think I’ve got it, but it’s something I have to be carefulabout. I’m not 100% sure yet how I will fit/splice the new piece into theold one, but once I figure out how to get the side pieces glued on in a structurally sound way, I’m home free for this rebuild I think.

The replacement firewall:


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The replacement rear fuel compartment bulkhead:


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The replacement "instrument panel":


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The replacement left side of the nose area:


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May 26, 2006.

I pieced together the shattered bits of the original firewall and usedthat as a pattern to trace out a new firewall. The firewall is two layersof 1/8" light ply, so I made two copies, and sandwiched them together withepoxy.

My goal is to use the original bits as patterns to build new pieces when theoriginal is just too shattered. There is still some thought that needs togo into how best to proceed in some areas, but I’m making progress.

May 19, 2006.

Happy birthday to me. 🙂 I spent the evening cleaning up the engine.The dirt was surface only, nothing even made it into the carb. The carb wasslightly shielded by the cowl and the engine wasn’t running when it hit.There was a small amount of dirt/grit inside the veturi, so I popped offthe carb and blew everything out from the backside with carb cleaner. Hopethat doesn’t attack the rubber gaskets (not to mention my fingers.) Thealuminum spinner appeared to have no damage, the engine seemed to turn well,the motor mount was 100% intact. The only thing that shattered was thefirewall. I’m going to have to build me another one of those.

May 17, 2006.

Some of the parts fit together, some don’t. Some pieces are just not thereanymore.


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May 16, 2006.

Today I started laying out the parts to try to piece them together. I madea lot of progress figuring out what goes where, but haven’t glued anythingback together yet. Some pieces I can probably glue together and use, butsome of the more load bearing structures I’ll glue together to make a formand then reproduce the part.

For what it’s worth, the left side of the front fuselage got compressedand exploded into bits. The right side of the forward fuselage is"reasonably" intact. This would indicate that the aircraft had some rightlateral motion when it impacted the ground. That is the direction the tailswung around after impact and it was the right wing that ripped off.

After staring at the pieces for a few minutes today, I believe this Rascalcan be rebuilt and will fly again, but it will take some effort. It won’tbe a completely trivial rebuild.

September 26, 2005.

Until further notice, Rascal #1 is offline. We are transfering all ourinstrumentation and cameras over toRascal #2.Follow that link to the most current interesting info.

September 21, 2005.

Today we flew 3 very nice flights testing out a new patch antennafor our video system. The new antenna seemed to yield much better results thanwe were getting before. Plus we had determined that the ground transceiverfor our radio modem link had also been interfering, so we put some goodseperation between the radio modem transceiver and the wireless videoreceiver and that all worked much better.

The video was working well so the next thing we wanted to try was havingme fly by video only (using a buddy box system and a safety pilot.)Take offs and landings would be done visually as per standard R/C procedures. The fly by video would only happen during a short segmentof the flight.

Shortly after take off (with maybe 75′ altitude) the engine sputteredand died. I thought I had plenty of altitude to turn back to the fieldso I initiated a turn. By my recollection I stayed off the elevator toavoid any chance of stalling, so the nose dropped substantially duringthe turn. However, once I got pointed down wind and tried to roll out ofthe turn (still with 20-30′ of altitude) the plane was unresponsive anddove straight in at a pretty sharp angle. As you can see there wassubstantial structural damage.


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img_2936Case of dumb thumbs? Did Iride full elevator all the way into the ground? I didn’t think so at thetime, but the consensus of the audience was that I stalled it in. Buthere is my thinking: 1. TheRascal is nearly impossible to stall, 2. I am aware of this issue and I*thought* I was intentionally staying off the elevator specifically toavoid this mistake, and 3. the plane seemed completely unresponsive inthe final one or two seconds.

But I also don’t trust my recollection and I know my mind can play trickswith me. I am hoping we have good MIDG data from this fateful flight.I am hoping that I can compare the planes directional vector with it’sorientation to get an estimate of velocity and alpha. I don’t think Istalled it in, but I’m hoping the data can shed some light on what reallyhappened. We don’t have a way to record control inputs or indicatedairspeed, so we may never know for sure what happened. Just so I don’tforget, wind estimate for the time of the crash was 5 mph out of the south.The MIDG will give me speed relative to the earth, not speed relative tothe local air mass.

Update (Sep 23, 2005):

  • For some unexplained reason (and this has never happened to us before) our MIDG didn’t have a gps solution for the final flight. This means we had no position or velocity data, only attitude data.
  • The attitude data clearly shows the take off, climb out, and turn back to the field.
  • Our engine died during the climb out before the turn. But during the 180 turn back to the field, the nose immediately drops to between 10-15 degrees pitch down. This supports my intention to lay off the elevator during the entire turn so that gravity would keep the aircraft above a safe airspeed and eliminate the risk of stalling.
  • Because of data buffering and the fact that when the main gear departed, it sheared off our radio modem antenna, I believe we lost the last second or two of data. Our wonderful video capture software automatically deleted the video for us because it detected too much snow (after the crash.)

Conclusion:

Note that I am speaking unofficially here, and from the perspective ofthe pilot in command with an ego to defend. Whatever the evidence,the conclusion will be that it was not my fault. 😛

I believe I properly executed my plan to turn back to the field withzero elevator input. The resulting natural dive during the turnshould have kept the airplane at safe flying speed since it naturallyseeks an equilibrium. This aircraft is *very* difficult to stall andin all previous stall tests, stalls were slow, required a tremendousamount of forced up elevator, they were gentle not sharp, and somelimited control authority was always preserved even during the stall.This makes it hard for me to believe that I could have been in a stallregime, and even if I was, I would have expected different behaviorfrom the aircraft. I believe I had sufficient and safe airspeed.However, when I tried to roll out of the turn and pull out of the diveI had nothing. The plane gave no response and continued to divestraight into the ground.

My conclusion then is that given my recollection of the control inputsand my intentions (supported by the attitude data) combined with myunderstanding of aerodynamics and my specific knowledge of theparticular flight characteristics of this aircraft, I believe theaircraft maintained safe airspeed throughout the 180 turn backmanuever, and very likely I over compensated and gained more airspeedthan needed through the turn/dive. Based on my understanding of thespecific characteristics of this plane, I find it highly unlikely thatI was any where close to the stall regime. The more likely scenariois the relative orientation of the plane’s R/C receiver antenna to theground transmitter, combined with the interference patterns of the twoon-board transmitters (1 for video and 1 for data) put us in atemporary "dead" zone. Unfortunately our close proximity to theground when this occured meant that we were unable to fly through thedead zone and recover … we hit the ground first.

I think I can rule out pilot error in the direct operation of theaircraft, however there are still higher level issues we have controlover that likely contributed to the crash. Specifically engine tuningprior to the flight. We did run up the engine on the ground beforetake off and it sounded perfect, but perhaps we missed something.Also we were using a buddy box system for the first time on thisflight. Did that contribute in any way? Crashes seem to always be along sequence of events where the initial problem leads to, but is notthe source of the final crash. What else could we have done prior tothe flight, with the setup of the airplane, the setup of the buddy boxsystem, the setup of our instrumentation, our flight plan, etc. tohave prevented this crash? Are there things we can do to ensure morereliable engine operation?

This big Rascal can be rebuilt and will fly again.

Sig Rascal 110 #1 Flying

Sig Rascal 110 #1 – UMN UAV Project


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Project started March, 2005.

I am involved with the University of Minnesota Aero Dept. on a UAV project. My part of the project involves assembling the airframe as well as being the chief test pilot.

June 7, 2005.

Today we flew the Rascal 110 on it’s maiden flight! Winds were about 10-ish out of the SE, gusting to 15+. It was a bit on the windy side and the gusty cross wind was tricky, but we managed.

Posing at the start of the day …


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img_2547 Curt at the controls …


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img_2551 Turning final …


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img_2552 Ready for another flight …


img_2553 Greg at the controls …


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img_2560 Still in one piece at the end of the day … 🙂


img_2561 The Rascal is a big beautiful flying airplane. It’s a tremendous floater. Even at 1/4 throttle, the tail comes up quickly on the take off roll, and it’s airborn soon after. We powered the Rascal with an OS 1.60 FX 2-stroke. That is plenty of power and she can sure fly with a lot less engine, but the airplane is big enough to handle all that extra power just fine. It will go unlimited vertical, but just barely. It was a bit tricky to handle in the gusty cross-wind, really wanting to weathervane into the wind, but I’m sure with some practice and more flight time I will get a better feel for how it handles on approach. It’s a great flying aircraft and should be able to carry quite a load.

June 16, 2005.

Today I made two very short flights with the Rascal. Both ended early with the engine quiting. I safely dead sticked both times, but I wasn’t in the mood to practice dead sticking today. I couldn’t get the engine to run reliably, even after a fresh glow plug so I gave up for the day. I’m going to rip the cowl off and play with it at home to see if I can figure out what’s going on. No clouds, barely any wind, temp in the mid-70’s, other than engine proplems, it was a great day for flying. 🙁

The prop got damaged on the trailing edge midway between the center and the tip during the maiden flight, so today I was flying with a new prop. I went with an 18×8 (instead of the original 18×10) to try to get more “braking” action on landings to counteract it’s tendency to float forever. I’ll have to wait to get the engine running reliably again before I know how much this will help.

June 18, 2005.

Today I put in 3 really good flights. I yanked the cowl at home and ran a tank through in my front yard which I think cleared out the cobwebs. I think it was still a little tight from being so new and I was a bit off on my needle valve adjustment last Thursday. But today I had the engine running great. It pulls the Rascal through the air authoritatively and allows you to do *big* beautiful maneuvers. I probably ran 60+ oz of fuel through the engine today.

July 2, 2005.

Today we tested a simple telemetry system consisting of a Garmin Etrex GPS and an AeroComm radio modem. The aircraft flew great. The telemetry worked great. The GPS worked great and we got WAAS correction. Everything went pretty much as good or better than expected. From the data collected the max speed we hit with the Rascal 110 was 88.9 kts and I suspect that was with the wind which was running 5-10 kts at the surface. The Rascal can cruise comfortably at 25 kts and can lollygag and putter around at maybe 15-ish or even a little slower. But fire up the throttle and she get’s up and goes.

Last minute tweaks and engine tuning before a flight.


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img_2658 Slow fly by and final approach.


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img_2660 I also hacked together a system to load in the gps track, interpolate/smooth the 0.5hz data to 60hz and fake roll/pitch, then blast the result to FlightGear via UDP packets. The result is a virtual replay of our flight and it turned out pretty reasonable for a linear interpolation. FlightGear provides a working virtual instrument panel (AI, ASI, Alt, DG, and VSI) as well as a working HUD and a 3D sythetic world view.

These are virtual views from the flight playback. Notice the working instruments in the virtual cockpit view. Oh, and it’s flight gear so I tuned in a nearby VOR station. 🙂 If we recorded control inputs we could animate yoke, pedals, and control surfaces in FlightGear as well.


Virtual-UAV-01 We can also do external chase views and include a HUD if we like.


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Virtual-UAV-04 Here is a plot of a portion of one of our flights.


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August 5, 2005.

We had to scrub today’s tests due to radio interference problems (eventually traced back to the receiver.) Our intention was to test the newly installed wireless video system with two cameras. One pointed straight down and one pointed forward 45 degrees.


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August 24, 2005.

Today we did 3 really nice flights to test our MIDG II IMU and our 2 camera, 2 channel wireless video system. We think we got excellent looking data back from the MIDG and it appeared to work *very* well. Unfortunately, our wireless video was really bad. We are going to have to do a lot of work on the video system to get it up and running satisfactorily.

We bought a second Rascal (RTF). This one is powered by a Zenoah G26 2-stroke gas engine.

Update: I worked over the weekend on parsing the MIDG binary data and feeding it into FlightGear. The result is a really nice animation of the 3 flights. The 50hz data rate on the MIDG captures a lot of the subtle nuances of the flight, dutch roles, wind gusts, twitchy thumbs, and even does a good job capturing aerobatic maneuvers–loops, rolls, wing overs, etc.

Sig Rascal 110 #1 Construction

Sig Rascal 110 #1 – UMN UAV Project


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Project started March, 2005.

I am involved with the University of Minnesota Aero Dept. on a UAV project. My part of the project involves assembling the airframe as well as being the chief test pilot.

November 3, 2004.

It appears that our small UAV project got funded here at the U of MN. Hooray! I get to be paid (for a short time) to build and fly R/C airplanes. We plan to purchase our first hardware in early February ’05 and immediately work on assembling and test flying the airframe .

February 24, 2005.

U of MN UAV project update: We have done the initial airframe, engine, and R/C gear order. A couple items were backordered so we don’t have any fun toys to play with quite yet. The airframe will be a Sig Rascal 110 running an OS 1.6 2-stroke engine. Initially we will hand fly it (perhaps using an onboard camera rather than direct line of sight?) but eventually we will develop autonomous capabilities as well.

April 4, 2005.

Installed ailerons, aileron servos, linkages, and routed servo leads. The wings are essentially complete. Here are some pictures of the different pieces:


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April 6, 2005.

Here are a few pictures of some of the toys hanging around the Aero work shop:


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May 2, 2005.

Installed OS 1.60 engine into the Rascal with special ordered beefier engine mount.

May 4, 2005.

U of MN UAV project update: I cut, fit, and installed the cowl today. I found an 18×10 prop (in the recommended range) floating around the lab and slapped it on temporarily. Yikes … it is big! I will have to make one more opening for the mixture adjustment. It looks like we will need to special order a spinner for this beast. I also took a heat gun to the wings and fuselage and shrunk out most of the wrinkles.


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May 6, 2005.

Today I bought a larger tank (24oz) than stock and fit it. I haven’t locked it in place yet, but that’s [hopefully] a quick thing. I also glued in the fairings which provide a bit of extra support for the horizontal stabalizer where it attaches to the fuselage. Next up is installing the elevator and rudder servos in the tail. Here are a couple pictures from inside the cabin.


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May 9, 2005.

Today I installed the rudder and elevator servos in the tail of the Rascal. This minimizes the length of the linkage used (thus reducing slop and the risk of flutter.) I then attached the horizontal and vertical stabalizers and the additional two fairings on the top side of the horizontal stab. Then I attached the elevator, tail wheel, and finally attached the rudder. Next up is the rudder and elevator linkages.


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May 10, 2005.

Today I fabricated and installed the rudder and elevator linkages. I also installed the springs that attach the rudder to the steerable tail wheel. After that I turned my attention to the inside of the aircraft and installed the onboard radio on/off switch and the throttle servo and linkage.


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img_2529 Then I assembled and installed the main gear. The Rascal wheel pants come completely finished, even with blind nuts already installed. It’s about a 10 minute job to assemble and attach the main gear, wheels, and wheel pants, including taking them out of the baggies.


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img_2530 With the main gear installed, the Rascal can now stand on her own, so it was time to pose for some pictures.


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img_2519 Now I add the wing.


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img_2523 I almost forgot about the cowl.


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img_2525 And I might as well put on a prop while I’m at it.


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May 11, 2005.

Items completed today:
Installed the side windows.
Installed a new prop (appropriately drilled out for our shaft diameter.)
Secured fuel tank.
Installed an extension to the receiver on/off switch.
Initial balance tests indicate that we might come out pretty close with no added weight.

May 12, 2005.

Items completed today:
Pad and secure battery and receiver.
Route the receiver antenna.
Touch up and shrink covering in a few areas.

May 13, 2005.

Today I checked the control surface throws to verify they matched the manufacturer’s recomendations. I also moved the battery as far forward as possible to put the aircraft in balance. I think we are now balanced with no need to add additional dead weight. With the exception of final checks, this plane is ready to fly.

May 19, 2005.

Today we fired up the brand new OS 1.60 FX 2-stroke engine and ran 24oz of fuel through it. The engine behaved well and pulls *very* strong. The next big step is the maiden flight. I will be gone most of next week so we will likely shoot for a day the week after next weather permitting.

May 30, 2005.

Fit and installed new spinner. We still need to get all the right tools so I can properly tighten everything up. Right now a couple pieces are only finger tight, but they look good.

June 6, 2005.

New pictures … all ready for her maiden flight tomorrow (weather permitting.)


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Stabilization

Roll/Pitch Stabilization System

Pictures of the FMA Direct Co-Pilot installation …


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The FMA Co-Pilot has some complexity to it, so it’s important to read through the manual carefully to get it setup properly, and to get it calibrated properly at the field before flight. The manual explains quite a bit about how it works, and what it can and can’t do. It’s important to understand these things so you know the devices limits and what you can expect. I mounted my sensor on the centerline of the fuselage immediately behind the trailing edge of the wing. This gives me good visibility left/right and makes for a very clean installation. Exhaust comes out the bottom-left of cowl so it’s fairly protected from residue. I pick up more bugs there than anything else.

I discovered that you have to be very careful and precise with the field calibration procedure, otherwise it will try to drive the aircraft into a bank and the plane will be constantly turning. Conveniently, my transmitter trim still works with the Co-Pilot device activated, but one caution, if your aircraft is trimmed for normal manual flight and you activate the co-pilot and it is not perfectly calibrated, you need to retrim. That can lead to (possibly substantial) trim changes with the device on versus off … it’s workable, but you have to be aware of it.

I setup the Co-Pilot so I could turn it on/off and adjust the gain with my “flap” channel. That worked well, and I found that with my big, slow Kadet Sr. I could fly with the gains dialed to full max just fine. Initially I only activated it altitude, but eventually I tried flying lower, and even landing with it activated. It worked so well that I eventually did takeoffs and touch and goes as well as landings. I observed no ill tendencies and it seemed to help make my landing smoother because it can compensate for gusts more quickly than I can (and I was able to practice this because the winds were getting gustier as my test progressed.) With the co-pilot activated, it wants to drive the wings level and sort of tries to hold pitch. But it still passes through your manual inputs “additively” so you are able to fly fairly normally and override the stabalization controls.

Ok, so the big question after playing with the co-pilot for a few flights is “how will it work as a UAV stabalization system?” My answer at this point is, yes very well for many applications and airframes. However, it’s not perfect and it’s not magic. The Kadet is big and slow, so even with the gains dialed up to max, it can’t keep the plane perfectly level all the time. It is highly sensitive to the field calibration procedure, so you need to perform that carefully, then ensure that you are well trimmed before cutting it loose to do anything on it’s own. It does do the job though and keeps the plane reasaonably stable. With the system activated, it is very safe. You can input full rudder deflections and while I do observe some banking, the system holds it’s own and limits the bank to 10-20 degrees and keeps everything under control. Note that this is a “simple” proportional controller so it can’t cancel out all errors or biases, but it produces a “stable” system. That’s why it can’t hold the wings level against rudder input, but with neutral rudder it does just fine.

I think I’m happy enough with the co-pilot to move forward and start looking at getting my flight computer running.

 

Overview

EGN Project Overview

My first goal is to have fun and use this as an outlet for a few ideas that have been bouncing around in my head. I have a life long love of aviation, airplane models, and computers so I would like to mix these together a bit.  I have an FMA Direct CoPilot IR stabilization system that I plan to use to keep the aircraft self stable. Notice that this is instead of any type of gyro/accelerometer/IMU unit. An IMU typically reports orientation as input to a flight computer which then does mathemagic to calculate servo positions to keep the plane level. This IR unit does all that itself in a$100 unit. The downside is it can only hold the wings level, the upside is that is usually exactly what we want to do.

I also have a small flight computer, a First Robotics Minicontroller. This has a CPU and can drive servos directly. I hope to attach a GPS, do a small amount of crunching and then drive the rudder servo to steer the aircraft to a waypoint (such as home.)

I also hope to use this to do some sort of aerial photography … either wireless video, or digital stills, or both.

Beyond that it would be fun to add a radio modem to pass telemtery information to a ground station and perhaps pass commands back to the onboard computer system. I could envision some integration with FlightGear to use that as synthetic vision or overlay the live camera view on top of the synthetic view.

I am funding this project on a hobby budget. So I plan to scrimp and save, reuse existing equipment, buy off of ebay, etc. and only move as fast as my spare funds will allow. My goal is to build a self stable, self navigating R/C aircraft for under $1000 total cost.

Safety

Let me just say a brief word about safety and politics. I understand the AMA is concerned about UAV projects. They don’t want irresponsible behavior ruining the hobby for everyone else. I plan to always operate this aircraft under the constraints of the AMA safety code. (i.e. always in visual and radio range, always within the R/C model altitude limits, always with a human pilot able to assume manual control at any instant.) I also understand the FAA doesn’t really know what to do with UAV’s yet and has no immediate plan for fitting them into the USA airspace. Again, I plan to operate this aircraft entirely as a R/C model aircraft which the FAA is not interested in regulating.

Throughout this project I plan to pay keen attention to safety issues, fault tolerance for the onboard systems, safety for the pilot, safety for the aircraft, and safety for everyone else. I know I can’t control every aspect of every circumstance, but I wish to be very thoughtful, and very considerate of a wide range of safety issue so that (1) the aircraft itself is fault tolerant as much as possible, (2) the on board intelligence will be able to detect some problems before the pilot on the ground and take steps to minimize or avoid damage to the aircraft, and (3) I will operate the aircraft so that if something does happen, it will happen as far away from any person or property as possible.

I believe this approach is essentially restating the spirit of the AMA safety code with fewer specifics.

Construction

EGN Construction Log


img_2376 Please note: these entries are arranged in reverse chronological order with the newest entries at the top.

Maintanence Tasks

 

  • Engine installation.
    • Need to enlarge the cowl openings a bit for better engine access.
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  • Radio installation.
    • Need to fashion better strain relief for the antenna where it exits the fuselage.
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  • Apply decals.

May 13, 2005.

This project is officially moved over to active flight status!

May 11, 2005.

Today I threw on about 10.5 oz of lead up front to balance the airplane. I think we are just about ready to top off the batteries and go fly!

May 9, 2005.

Sealed gap (on one side) between horizontal stabalizer and fuselage. Balancing: now that pretty much everything is in place, I have done some initial test balancing. I have 4 3/4 oz of stick on lead in my inventory, but I think I will need a bit more than that in the nose for it to balance right. I always hate adding dead weight, but what can you do. I think the remote servo in the tail + the tail wheel is what did it to me. That said, the Kadet starts out with such a light wing loading that a few extra ounces should be unnoticable.

May 8, 2005.

Today I installed a remote fuel valve, as well as a 12×6 prop and the spinner. I screwed on the cowl, and tighted up the muffler. I then bolted on the wing and set it outside for some pictures …


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May 7, 2005.

Today I finished off the main gear installation. The aluminum main gear was special ordered from TNT landing gear. I wonder if I should have ordered two so I could install floats someday? 🙂


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img_2478 I also padded the receiver and battery, and routed the antenna out the bottom of the airplane and to the rear. Finally I cut out and installed the side windows. It looks like she may come out a tad tail heavy, but I haven’t put the prop and spinner on yet. We are getting close to being ready for the maiden flight. It’s down to a few details now.

May 2, 2005.

I had previously mounted the tail wheel and tail wheel servo, but I needed to rig up the pull/pull spring/wire system. Today I bought some thin piano wire and did just that. It’s not perfect, but looks fine from 10′ away and is solid structurally so I guess it will do.

April 23, 2005.

Maisy expressed interest in being chief test pilot …


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April 23, 2005.

Last week I glued on the tail surfaces. Yesterday and today I installed the cabin servos. I then constructed the elevator and rudder pushrods, and installed them. The provided hardware/wire for one end of the pushrods broke when trying to make an “L” bend. Fortunately I had some replacement wire pushrods laying around that worked out just fine, probably better.


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img_2436 I also fabricated and installed the throttle pushrod and connected it to the engine.

April 10, 2005.

Today I glued in the elevator and rudder hinges and then test fit the tail surfaces.


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img_2429 The tail surfaces are glued on with epoxy and care must be taken that the horizontal stabilizer is aligned with the wing (when viewed from behind), and also that it is perpendicular to the fuselage (when viewed from above). It should only require a small amount of balancing and leveling to achieve this, but 5-min epoxy means I have to work quickly. I also purchased a micro servo and tail wheel assembly for my tail-dragger conversion. I plan to plug a “Y” harness into the rudder port of my receiver and run two servos. A standard servo will control the rudder surface, and a second micro servo mounted in the tail will control the tail wheel steering. The servo will be linked to the tail wheel with springs so it won’t need to generate (or endure) a lot of torque.

March 6, 2005.

Today I drilled a new throttle pushrod hole. I filled all the extraneous left over fire wall holes (I moved the engine mount up, The throttle push rod had to move, and I am not using a nose wheel.) I also left two holes/routes (temporarily sealed) back to the main cabin if I ever want to install a larger tank. Finally, I sanded the cowl cutout so it is nice and smooth.

February 27, 2005.

For this project I have chosen a 4-stroke engine. This has caused me a fair amount of grief. With the default upright mounting scheme, the throttle arm is dead center with the tank; not exactly ideal. My final solution is to mount the engine upside down to the bottom of the motor mount arms, and move the mount up by the height of the arms so the thrust centerline stays the same. This keeps the motor mounts from needing to extend above the top of the firewall. This also puts a lot more of the engine inside the cowl and lets me use the original nose wheel push rod for the throttle. I need to be a bit careful about tank height vs. carb height, but we’ll see. I might want to add a pressurized fuel system to avoid this problem and allow me to install more fuel capacity.


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September 18, 2004

I’m a little hung up on an engine mounting problem. This kit is setup to mount a 2-stroke engine upright, and everything is laid out perfectly for that. I’m trying to install a 4-stroke engine, and *everything* is in exactly the wrong spot for that … no matter what I come up with. Here’s a page I setup to describe my problem. Kadet Senior ARF 4-stroke mounting problem.

September 9, 2004.

Today I took a few minutes from the daily grind and finished installing the aileron servos and linkages into the wings. For all practical purposes the wings are now finished and flyable. Here are some various pictures of the wing:


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IMG_1955 Just to reference the size of this model, I’m about 5′ 9.5″ tall (1.77m for people outside the USA.) The wingspan is about 6′ 8″ (2.03m).


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IMG_1957 And finally, here I am testing the fit of the wing with the fuselage:


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July 14, 2004.

My engine arrived today. I purchased it off of ebay … a Magnum 61 four stroke, but was sent an ASP 61 four stroke. As best as I can tell they are the exact same engine from the same manufacturer, but the instructions are in Chinese. You get what you pay for I guess. Here are online Magnum 61 instructions. Just Engines sells ASP engines and parts.

July 12, 2004.

Today the flight pack arrived. I purchased it new from Tower Hobbies to match my existing transmitter brand and frequency. I also purchased an extra servo (one servo per aileron) and the necessary 24″ extension cables and a “Y” harness. I needed the aileron servos and extension cables to start construction so now I’m ready to begin.

July 1, 2004.

I purchased the airframe from rcuniverse.com “new in box” for about $50 less then I could get it from any hobby shop. It arrived today. Yikes! It’s huge! Much bigger than I expected!


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