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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