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BF-109 Swapperschmidt

#1
I posted an article to show people the design I was working on. But I thought a thread would be more appropriate for discussion and minor updates on my progress. I do intend to release the plans once I'm satisfied with the construction.

http://www.flitetest.com/articles/swappable-axis-warbird-prototype

After seeing the sneak peek image of the flitetest warbird I decided it needed a rival. You simply can't have a war with only one side. Once I decided what to build I set off designing a plane. Design cues were taken from previous builds by flitetest. As of right now the first prototype has been built and flown.

The wind was gusting to 17mph, hardly the kind of weather you maiden a new design in. But, no guts, no glory. She got off the ground ok but the plane seemed to want to dive on me. I trimmed in some up elevator and got it to level off nicely. That was the only trim I had to give it. Roll rates were nice, perhaps a little fast for a warbird but close. Since I was concerned that the plane was nose heavy I tried some inverted flight. I had to give it some elevator but not nearly as much as I expected. It actually felt about right. It was getting pretty cold so I came in for a landing. I didn't have enough power and accidentally landed in the snow. The landing gear I put on was something I had cooked up real quick because I wasn't going to maiden a prototype hand launching in 17mph wind. I really only expected the gear to hold up for takeoff and maybe a landing or two. It turned out to be far stronger than I anticipated. The gear and plane showed no damage in the impact with the snow. Since it's proven it's self strong enough this landing gear design will be in the final plans. All together the plane handled well and even cut through the wind better than expected.

I have already made several design changes and will be building the second prototype in the coming weeks. I am also working on a canopy. Considering how well the maiden flight went I hope to have it perfected and plans released before too long.

I realize the front of the fuse is a bit off. My glue wasn't hot enough and it cured before I got it set right. This will be fixed on prototype two.
_____

I have since finished #2 and made some tweaks to the design for #3. The weather is horrible here so #2 didn't stand a chance. I will finish #3 before the weather breaks so I decided to try #2 instead of just tearing it apart with no flight time on it at all. Needless to say 17mph gusting over 20mph winds made the flight very short. I might as well have thrown a tissue in the air. As for design changes, I changed the rear of the fuse a little to get it closer to the real thing and removed the faux air scoop because it looked silly. I think the fuse looks more sleek and true to the real thing. I also made some changes to the way I mounted the tail feathers and added supports(which the real plane has) for strength.
 

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Foam Addict

Squirrel member
#2
Looks good!
I am working on a 2 foot long blu-spit, but I like DTFB better than FFF.
Very nice design!
I look forward to a flight vid!
EDIT:Cockpit?
 
#4
I think I have the plans pretty much done. I need to tweak the building technique a bit still. The cockpit is a little off but I pretty sure I know how to fix it. I need to finish and test fly this one. Then I'll build one more and do a build video, then pretty up the plans. It's all built with supplies from the dollar store and it isn't too hard to build.
 

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glydr

How many letters do we ge
#7
Agree - it looks like a 109 tail (small). Just concerned that some 'poetic license' might be required to help it fly better.

I'm sure it will be ok.

Great subject by the way, love the aircraft and your rendition in foam-board is inspiring!
 
#8
I was a little concerned when I built the first prototype. But the plane flew well. The elevator had plenty of authority but I didn't test the rudder much.
 
#9
I just put the newest one in the air. It seemed to have a mind of it's own, it felt very unstable. The first one seemed to fly good but maybe I was mistaking some of it's instability for wind. I'm going to try increasing the tail feathers 20% and see if that helps. Good news is I think I'm getting the CG narrowed down and found that a 24g motor is too underpowered for it. It will fly but not that great. I may try that motor again once it's finalized but it just didn't have the power.
 
#11
when you say a 24gram motor, what kv rating is that?

the build is looking really good mate. loving watching this thing come together
 
#12
I tried it with the 24g 1300 Kv hextronic running an 8x6 prop on 1000mah3s. Once I get the plane flying good with the dst-1200 I'll probably revisit the 24g. But as it is it seems like the 24g only has enough to get the plane airborne and not much else. So you could fly it on the 24g motor but it probably won't be much fun.
 
#13
Ok, went for another test flight today with the larger tail. The plane is still acting funny. Flying level the plane wants to pull left, I assumed this was just torque roll. When I pull up the plane pitches right, the harder I pull the harder it goes right. I thought maybe the elevator was flexing under the stress but the control horn is on the left side. If that was the case pulling up should make it go left. I put a popcicle stick in there any way to strengthen it but it still does it really bad. I'm at a loss here if anyone has any ideas I'm all ears.

On a good note when I trimmed it and let off the stick it tracked nice and straight. And the rudder has plenty of authority.

P.S. I tried to get some video but it didn't pan out :(
 

Foam Addict

Squirrel member
#15
That sounds like the symptoms are flex.
Brace your Horizontal stab. heavily, and that should help the problem the problem.
I have had a few planes that had awful coupling, and usually this solved it.

"If that was the case pulling up should make it go left."

It could still roll right due to the aerodynamics of the elevator.

Is there a way that you could swap the elevator horn to the right and rudder horn to the left? this should reverse the problem if it is flex, but if it remains the same it my be a built in problem dealing with the rotating air coming off the prop.

This would be very very helpful.
Hope this helps.
 
#16
flex would certainly explain it and you're right it could be some strange aerodynamics involved. I was thinking of putting a camera on the plane pointing at the tail tomorrow. that might help me see what's going on. swapping the control horn shouldn't be a problem either.

I've been spending a lot of time handling the plane since I got back. After reading your post I plugged a battery in, propped the tx so it was giving full up, then pushed down on the elevator to see what happened. After doing this a few times and looking all over I saw the vertical stab move. It isn't a lot, but it doesn't take much and it's in the direction that would make the plane turn right. This may be the culprit. I'm going to try some bracing and fly it tomorrow to see what happens.
 
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#17
I reinforced the tail and took it out for another flight today. I put a camera on the plane facing rearward. It only caught the vertical stab but that didn't appear to be flexing, atleast not to me. Unfortunately it wasn't pointing down enough to see the horizontal stab. Still I did get some video on the plane and from the ground. Maybe you'll see something I don't. Oh and outside loops didn't seem to have the problem.

you may want your sound turned down, the onboard video is loud.

 
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#18
just to let everyone know(if anyone is following) I haven't given up yet. I have a new fuse built, I've moved the horizontal stab down to connect with the fuse to give it more support, and I realigned it to make sure there was 0 incidence. If this works I have some ideas to take it back up to it's proper location.
 
#20
the rudder worked really well so the plane turned hard and started to nose down. when I tried to pull up it started spiraling to the right. which is the issue I'm trying to fix. If I pulled up the plane would roll hard right, and I mean uncontrollable hard right. everything I did with the elevator up to that point had been very light movements. If you watch the takeoff again you'll see the right wing dip, that's from pulling up. then you'll see the left wing, that's me over correcting a little. basically everytime I would pull up at all I was struggling to keep it level. hopefully the next one will fly good and I'll know it was in the tail. if not it may be some kind of weird tip stall thing from the design of the wing(but I doubt it).