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.