Posted by Bryan Cuervo on October 4, 2009 at 4:00pm
After my last UAV project went up in flames (literally!) I’ve shifted gears and designed a dedicated autopilot (AP) test vehicle. She is a tailless plane with removable wings for transportation and has plenty of room in the fuselage with easy access.
For the autopilot, I’m using Bill’s UAV DevBoard with a modified AileronAssist code for handling the elevons. This modification is a work in progress by Ben Levitt and he is including a lot of great features. You can check out the latest versions of the code here. The tailless had her first autonomous flights this weekend and I’ll be posting all of the flight logs on this blog. So far, I’m really pleased with the AP’s performance. Not only does the DevBoard and software perform well, but Bill also provides a wealth of information on the theory of his methods as well as the “how to” to get the hardware and software installed and running. I know this is beginning to sound like a commercial for Bill’s stuff but if you do a search on this website, you’ll find nothing but praise for Bill and his accomplishments. And to top it all off, he’s always willing to immediately chime in and help whoever asks for assistance.
Hi Andy,
I used the pink, Owens Corning, extruded foam I picked up from Home Depot, hot wired the MH60 airfoil and vacuum bagged one and a half layers of 6 oz standard weave fiberglass with WEST system epoxy. I don't have spars. I just let the wing skin take the load from the 3" long wing joiner boxes and, so far, everything has held up just fine.
My fuselage length and CG works for placing my 3200 mAh lipo in the nose. If you shift all that weight to the CG, you'll need to move the motor as far forward as you can.
Currently I'm at 11.5 oz/sq ft wing loading and 85 watts/lb power loading with max throttle set to 326 watts. I wanted the power loading a little on the high side for my hand launches but it turns out 85 watts/lb is still a little more than I really need. I would probably go with 75 watts/lb next time (smaller motor) and save a little weight. It's amazing how much power these little, brushless motors put out.
I like your idea of increasing the wing span and adding flaps for slowing the wing down but I've gone back to adding winglets (smaller). You can get away without them since there is wing sweep and if you move the CG farther forward but then your efficiency suffers.
A 4 inch wide fuselage will give you plenty of room and I'm also working on a blended wing body for my next wing. Looks a lot sexier although it's a real pain to make.
The only "show stopper" I see is placing the battery at the CG. This means you'll have to add more weight in the nose and then you've defeated your goal for keeping wing loading down-----unless you are already planning on adding useful weight (camera,etc)---
How are you going to make your fuselage blend into your wings?
Bryan, I'm ready to move forward with my wing/uav and your project is basically a perfect match to what I've been envisioning. For the benefit of myself and others who might be inspired by your design (or Jaron's, or Curt's...) I'd like to share my plan and get your feedback. Perhaps you can review this from an "if I did it again" point of view.
Your wing seems to have to fly a bit fast because the wing loading is a bit high. I'd like to use the same sweep/airfoil/washout you are using, but take the span to 72". That still leaves me with 36" wings that can fit in the proverbial trunk, and will yield slower speeds with similar payloads. I think I'd like to go with 1.3 lb EPP, and two carbon tube spars - I think that is what you did. I'll wait and see if I need to glass a portion of the wing, but I suspect I'll have to if you did - especially with the greater span.
I'd like to add flaps so I can experiment with the flight speed envelope and yaw control, and push Ardupilot in the realm of yaw control without winglets or any other vertical surfaces.
Overall, I think 350 Watts and a 9 or 10 inch prop should be enough power.
Has your fuselage been adequately wide and long for your gear and W&B? I would take a similar approach in length and try to position the battery at the CG so I can use different batteries (lipo and A123s). I think I'll go a bit wider to 4 or 4.5 inches to give me more room, and I might make the fuselage more of a 'blended wing body' style.
Based on your description of editing, maybe I AM doing it right :-) I'll take a look at the other software, but the utility that comes with the PhotoMate887 is pretty good, and has track editing capability. The problem, as I'm sure you know, is that you end up with big blob of tracks all in one area, and it's hard to pick a particular spot to split the track. I think all these software packages will pretty much assume you're going to have a single line to edit.
Speaking of editing, I'm thinking about posting a thread on the UAV section at RCG, since it allows me to edit posts as needed. I also much prefer their format to the DIYDrones site.
Wow Rusty,
That looks great!
To edit my tracks, I open them in notepad and delete the coordinates I don't want in the final picture. This is tedious and I have to delete some, look at the results in GE, delete some more ------
Ricardo found some online software that is supposed to simplify this but I can't find the link right now. When I do, I'll let you know------just found it (that was fast!) here.
I managed to make a few laps before dark, and here's the logger results. This is with Ben's code, and a combination of what Bryan set for parameters, and what I thought it would be for my plane. Altitude hold was not on, and neither was crosstracking. The GPS was the 406.
It was really pretty tedious to edit the track, so I must be doing it wrong :-)
Bryan, your attention to detail is not wasted here. I also read about the tail volume ratios but I ended up erroring on the side of to large. I am betting the washout you have added into your wings is what is holding your stability with small vertical stabs. I am running drooped winglets (extending below the wing center line) to help with stability as my wing has no washout. Looking at your results i think my next set of wings for my uav wing will have some washout built in (one of the great advantages of break down designs).
You're plane is just too "pretty". You need some raw blue foam, and hot glue :-)
I'm enjoying the testing details, and probably won't be adding any of my own this weekend, since it's currently raining. I really did want to test the GPS logger, and it might still happen. Just depends on the weather.
For the anal retentive types (like me), I had read on RC groups that the ideal vertical tail volume ratio for our planes was 0.020 to 0.030. My original winglets had a value of 0.019 which is on the low end but they were still big enough to get in the way during transportation and were more prone to break. Based on what was learned in the recent test flights, I cut the original area down about 25% which yields a ratio of 0.014 and I predict she'll still fly just fine.
Modified winglets.
Curt,
I also thought she would have been a lot more skiddish. I have 20 degrees of wing sweep and had the CG a little more forward than usual. Apparently, that gave me enough yaw stability.
With this knowledge, I've cut my original winglets to about half the original area and have them reattached.
Comments
I used the pink, Owens Corning, extruded foam I picked up from Home Depot, hot wired the MH60 airfoil and vacuum bagged one and a half layers of 6 oz standard weave fiberglass with WEST system epoxy. I don't have spars. I just let the wing skin take the load from the 3" long wing joiner boxes and, so far, everything has held up just fine.
My fuselage length and CG works for placing my 3200 mAh lipo in the nose. If you shift all that weight to the CG, you'll need to move the motor as far forward as you can.
Currently I'm at 11.5 oz/sq ft wing loading and 85 watts/lb power loading with max throttle set to 326 watts. I wanted the power loading a little on the high side for my hand launches but it turns out 85 watts/lb is still a little more than I really need. I would probably go with 75 watts/lb next time (smaller motor) and save a little weight. It's amazing how much power these little, brushless motors put out.
I like your idea of increasing the wing span and adding flaps for slowing the wing down but I've gone back to adding winglets (smaller). You can get away without them since there is wing sweep and if you move the CG farther forward but then your efficiency suffers.
A 4 inch wide fuselage will give you plenty of room and I'm also working on a blended wing body for my next wing. Looks a lot sexier although it's a real pain to make.
The only "show stopper" I see is placing the battery at the CG. This means you'll have to add more weight in the nose and then you've defeated your goal for keeping wing loading down-----unless you are already planning on adding useful weight (camera,etc)---
How are you going to make your fuselage blend into your wings?
Your wing seems to have to fly a bit fast because the wing loading is a bit high. I'd like to use the same sweep/airfoil/washout you are using, but take the span to 72". That still leaves me with 36" wings that can fit in the proverbial trunk, and will yield slower speeds with similar payloads. I think I'd like to go with 1.3 lb EPP, and two carbon tube spars - I think that is what you did. I'll wait and see if I need to glass a portion of the wing, but I suspect I'll have to if you did - especially with the greater span.
I'd like to add flaps so I can experiment with the flight speed envelope and yaw control, and push Ardupilot in the realm of yaw control without winglets or any other vertical surfaces.
Overall, I think 350 Watts and a 9 or 10 inch prop should be enough power.
Has your fuselage been adequately wide and long for your gear and W&B? I would take a similar approach in length and try to position the battery at the CG so I can use different batteries (lipo and A123s). I think I'll go a bit wider to 4 or 4.5 inches to give me more room, and I might make the fuselage more of a 'blended wing body' style.
Any show stoppers in my plans so far?
Based on your description of editing, maybe I AM doing it right :-) I'll take a look at the other software, but the utility that comes with the PhotoMate887 is pretty good, and has track editing capability. The problem, as I'm sure you know, is that you end up with big blob of tracks all in one area, and it's hard to pick a particular spot to split the track. I think all these software packages will pretty much assume you're going to have a single line to edit.
Speaking of editing, I'm thinking about posting a thread on the UAV section at RCG, since it allows me to edit posts as needed. I also much prefer their format to the DIYDrones site.
Cheers,
Rusty
That looks great!
To edit my tracks, I open them in notepad and delete the coordinates I don't want in the final picture. This is tedious and I have to delete some, look at the results in GE, delete some more ------
Ricardo found some online software that is supposed to simplify this but I can't find the link right now. When I do, I'll let you know------just found it (that was fast!) here.
I managed to make a few laps before dark, and here's the logger results. This is with Ben's code, and a combination of what Bryan set for parameters, and what I thought it would be for my plane. Altitude hold was not on, and neither was crosstracking. The GPS was the 406.
It was really pretty tedious to edit the track, so I must be doing it wrong :-)
Rusty
You're plane is just too "pretty". You need some raw blue foam, and hot glue :-)
I'm enjoying the testing details, and probably won't be adding any of my own this weekend, since it's currently raining. I really did want to test the GPS logger, and it might still happen. Just depends on the weather.
Rusty
Modified winglets.
I also thought she would have been a lot more skiddish. I have 20 degrees of wing sweep and had the CG a little more forward than usual. Apparently, that gave me enough yaw stability.
With this knowledge, I've cut my original winglets to about half the original area and have them reattached.
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