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Foam Board Jenny

Tench745

Well-known member
#1
Hello again all. I decided I should post my Jenny build to the forum. Alas, I have no in progress photos, but a few good ones of the completed model.
Jenny 1.jpg Jenny 2.jpg Jenny 3.jpg Jenny 4.jpg Jenny 5.jpg

I've done a few high speed taxi tests (Something you do on a full size airframe that so few modelers seem to duplicate.) and decided my rudder throws were too high and possibly elevator throws as well. My port wheel began to come off and the maiden had to be pushed back. Rain and strong-ish winds since.
 

Tench745

Well-known member
#5
Well, I attempted another maiden today. The plane made it into the air for all of maybe three seconds before nosing in. I'll let you all see for yourselves. Apologies for the shakiness. My dad, a commercial pilot and flight instructor, was my camera operator.

The damage isn't bad, loose firewall, scraped nose, loose upper wing. I did get to fly my FT flyer while I was there, but got blown downwind further than I thought on approach, smacked a tree and stripped the rudder servo.
Time to break out the hot glue. :)
 

Tench745

Well-known member
#7
I believe it was mostly operator error. Full up elevator, not released in time, coupled with too much aileron. I've never really flown 4 channels before.
 
#8
Full up on take off is bad... That certainly could be it. If you can, always get enough speed for the plane to start to lift off on its own; but then you probably already know that... Maidens give me the jitters too....
 

Tench745

Well-known member
#9
Finally maidened yesterday.
After a quick stint with the glue gun the Jenny was patched up and ready to try again.
Strong winds were forecast for the next afternoon, so I got up early(ish) and headed down to the park. I opted for a hand launch this time, put it to about 2/3 throttle and let her go just as the wind was kicking up. She flew beautifully. The wind started gusting to 15-20 so I brought her in for a landing, the elastics in the gear weren't strong enough so the gear struts dug in and ripped off. It was a short flight, maybe all of five minutes, but she handles well on low rates and has more than enough power.
Looks like I figured the CG and the throws and everything right. Glad I did my taxi tests though, it was far too responsive on the first test so elevator and rudder throws were reduced at the servo. Tricky business that, since the servos were mounted directly below the top wing's center section.
Now that I've maidened her I added fore and aft flying wires on the struts to help hold the upper wing's position, added windscreens and rebuilt the gear with stronger rubber bands. I hope to get her up again before the snow flies, but with the weather here this time of year it doesn't look good.

Sorry I have no video this time, Dad didn't come because he figured it'd be too windy for me to get her airborne. I seem to fly better alone anyway.
 
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#10
Congratulations on the maiden. It really looks like a Jenny. Have you thought about how to make the curved parts under the wings that the Jenny had to keep her wing tips from touching the ground in a bad landing or if the pilot turned too sharply while taxiing? I think they go right under the struts.
 

Tench745

Well-known member
#11
Indeed I have. There are a couple ideas in my head. I could do piano wire or small diameter aluminum tubing, it'd save a good bit of wear and tear on her wingtips I'm sure. I got a first coat of paint on her last night and a pair of windscreens made up which I'll be putting on as soon as I'm finished with paint.
 

Tench745

Well-known member
#14
When I built this I used Elmer's foam board, it was heavy and needed quite a bit of clay in the nose to get it balanced. Over the winter I changed out the tail surfaces for identical ones built of Adams foam board. This allowed me to remove all the nose weight.
I've also switched to a 9x4.7 prop for a little more thrust with less speed.
I decided to dig in to the mechanics a bit more, had to remove the wing to access the servos just forward of the cockpit and reduced the throws so flying at full rates will be easier. Everything is assembled again now.
The landing gear was modified again. On my last flight the axle bent about 20degrees on landing. The initial rubber band suspension I installed wasn't strong enough, so I switched to a zip-tie in the middle of the axle, but this was not enough support.
The newest iteration has two zip-ties about half way out from the center and outboard of that it is wrapped with rubber bands. This seems to have good spring and enough support not to fold again. It's warm and calm today, so we'll see soon. :)
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Tench745

Well-known member
#16
Well, the good news is the landing gear is strong enough. The bad news is...





DSCF2329.JPG
I've got to stop flying on that hill...

She's so heavy that at anything more than one tick below full throttle, she starts to settle. I was testing throttle settings, brought it down to about 3/4 throttle and she settled a lot more than I was expecting. I went to throttle back up, but she just wouldn't come.
I think I hit LVC on by battery. I was at about 7 minutes of flight time and theoretically at full throttle I only get 6.5(ish)minutes of flight time. The ESC is set to cut throttle to half at LVC, and if that's what happened there's no way I could've kept her off the ground.
Looking at it afterward, I don't know. The ESC should have cut off at 3V per cell and here at home I'm reading 3.8V per cell. So maybe I just stuffed my Jenny into a hill through bad piloting. How very scale!

Ah well. Time to rebuild.
 
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Tench745

Well-known member
#19
Beautiful bipe, Jamboree. I actually spent all of yesterday reviewing the Jenny, stripping electronics, etc.
I decided to go back to the source, got a good 3-view of the JN-4D, plugged it into autocad and realized why the last plane looked so, off. Basically, for a 35" wingspan the fuselage should be about 18" nose to tail-post. My crashed Jenny had a 28" fuselage nose to tail-post.
For that size fuselage, the wingspan becomes something closer to 52."
So, I spent yesterday completely redrawing everything for a 52" wingspan JN-4D, checking it against the 3-view and published specs, and then cutting it out of DTFB. Today will see the continuation of that work. Pictures to follow.
 

Tench745

Well-known member
#20
The rebuild is well underway. I say rebuild, but the only thing the same between the two is going to be the electronics. Almost every single piece has changed size or shape from the original plans to make her more scale. PDF files of my build will be available once I'm sure everything goes together if anyone is interested.
First pic shows the minimal under-camber airfoil I'm trying.
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Here's a comparison between the old and new. Fuselages and tail surfaces are almost the same. The old fuse was much more tall and narrow than the new one. I always thought it looked funny. The wings are significantly larger on the new build too, actually to scale. Jenny was a big bird.
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