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.