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Author Topic: de havilland chipmunk  (Read 323 times)
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simpsd
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« on: May 18, 2020, 12:40:52 PM »

I have not built a new stick and tissue model in quite a while ... then came covid19 and I went back to working on a de havilland chipmunk I started a couple years ago.  It is from plans I found online and scaled up. This is my first attempt at covering a model with 1/32 balsa sheeting.  I had so much trouble reconstructing the wing saddle I almost gave up. I think it will come in around ten ounces. I've put an e flite 300 in it. I have a hobby king receiver with self stabilization I was thinking of using (never tried self stabilization but this might be a good place to try it out.  Here are some pictures of the progress.
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RalphS
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« Reply #1 on: May 18, 2020, 01:23:19 PM »

Interesting build.  What span is it?  Unusual to see banded on wings these days.  Looking forward to seeing it progress.
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simpsd
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« Reply #2 on: May 18, 2020, 02:49:37 PM »

The wingspan is 33 inches.  I still use banded on wings partly because I am sometimes rough on my planes. I drag wing tips on landing and other mishaps. The first R/c plane I had was a Carl Goldberg Jr Falcon. I cartwheeled that so many times! I wonder if I'd ever have got the hang of r/c flying if I tore wings out with each bad landing. I don't love the way it looks but I guess I'm kind of blind to that sort of ugly feature of my planes. What do you use on models of this size? It would have made this build a lot easier if I had just glued the wings on.
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atesus
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« Reply #3 on: May 18, 2020, 03:02:40 PM »

The wingspan is 33 inches.  I still use banded on wings partly because I am sometimes rough on my planes. I drag wing tips on landing and other mishaps. The first R/c plane I had was a Carl Goldberg Jr Falcon. I cartwheeled that so many times! I wonder if I'd ever have got the hang of r/c flying if I tore wings out with each bad landing. I don't love the way it looks but I guess I'm kind of blind to that sort of ugly feature of my planes. What do you use on models of this size? It would have made this build a lot easier if I had just glued the wings on.

On RC gliders I used to use nylon break-away bolt(s) which come in many sizes. They shear off rather easily in the event of a mishap. I'm not sure if the ones you buy at the hardware store would work as well. Here's a sampling of the kinds Tower Hobbies carries:

https://www.towerhobbies.com/cgi-bin/wti0095p?FVSEARCH=nylon+bolt

Great looking plane. Sheeting looks great.
--Ates

 
--Ates
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simpsd
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« Reply #4 on: May 23, 2020, 09:28:49 AM »

I'm thinking of putting an orange ORX RX3SM self stabilization receiver I got a few years back from Hobby king. It has six channels. Standard pins.  I have never used self stabilization. Does anyone have experience with these type receivers and is it a good idea for a model like this (33' span approximately 11 oz)?  The DH Chipmunk  is coming along well - more pictures soon.
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billdennis747
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« Reply #5 on: May 23, 2020, 10:21:57 AM »

I'm thinking of putting an orange ORX RX3SM self stabilization receiver I got a few years back from Hobby king. It has six channels. Standard pins.  I have never used self stabilization. Does anyone have experience with these type receivers and is it a good idea for a model like this (33' span approximately 11 oz)?  The DH Chipmunk  is coming along well - more pictures soon.
I don't  know but here is Steve Glass's free flight Chipmunk with self-stabilisation on aileron.
https://www.youtube.com/watch?v=THDlmSBAqh4
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Konrad
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« Reply #6 on: May 23, 2020, 12:02:29 PM »

I have used the HK Orange gyro'd RX. I have a RX3SM in front of me.

Not sure what you are asking. I generally don't like gyros in my models.

One needs to ask what does one want the gyro to do.

I set mine up to be helpful in turbulent air. But I found the model responded too much like an RC flight simulator cartoon.

I've also set them up to aid in the post stall of "3D flight". There they do make a huge difference.

Will they correct for improper flying (poor RC skills)? no.

Do they work? Yes.

I don't know how software savvy you are. But if you are old school like me  the RX I have uses switched and pots to set the RX parameters.

As the Chipmunk has a very classic lay out I don't this gyro's will be of any real value. Not unless you set the CG real far aft. But it doesn't look like you are setting up the model for super responsive controls.

So the short answer is I wouldn't use the gyro's on your Chipmunk. They are one more thing to screw up while trying to set up a model.

All the best,
Konrad
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Cut it twice and it's still too short!
Konrad
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« Reply #7 on: May 23, 2020, 12:09:39 PM »

If going with nylon bolts make sure the wing is free to leave the fuselage (not help captive by the wing opening of fairings). There is nothing special about the nylon bolts from Tower or any other big box hobby distributor other than price.

If going with nylon bolts go as small as practical with you model I'd look at a set of 6/32 maybe even 4/40 screws. I use some 4/40 screws as anti rotation (skewed) pin on my 3 meter gliders.

All the best,
Konrad

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Cut it twice and it's still too short!
simpsd
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« Reply #8 on: June 02, 2020, 03:08:35 PM »

So It wasn't (isn't) finished yet but I flew it anyway. I don't know if I'll get this one to fly well or not. I've had others that at first seemed unlikely to fly well, ones that with trim and balance changes, prop changes, etc have eventually flown well. I'm not optimistic about this one. It does take off and fly. The turns once established are ok. I just add in a bit of rudder in the direction of the turn - no adverse yaw problems. The plane just seems surprisingly slow to respond, sort of sluggish, encouraging more input then finally almost over-responding (Is That tail heavy behavior?) Also it seems to drop faster when the power is cut back so landing seems faster and more difficult than my other planes of the similar size and weight. There was a little wind around and that may have been responsible for some of the difficult flying. Anyway, the only safe direction to take off at my little ball field was with a tailwind this morning. On probably the fifth or sixth take off I pulled up a bit steep and early. The right wing must have stalled (I didn't build in any washout) and it went down to the right and snapped the horizontal stabilizer.  Also I'm not happy with the covering and color (I'm running out of tissue choices and my dope supply is old and thick. I should have been patient and ordered some fresh materials)  If I get it flying well I think I'll spray it white and go from there. Here are some pictures.
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Re: de havilland chipmunk
Re: de havilland chipmunk
Re: de havilland chipmunk
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TimWescott
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« Reply #9 on: June 02, 2020, 10:49:15 PM »

Slow to respond and then over-responding could be the self-stabilization.  Before I did anything else I'd try a normal receiver.

The excessive drop on throttle-down is either not enough downthrust, or the CG is too far forward.

Persevere!
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Konrad
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« Reply #10 on: June 03, 2020, 03:46:51 PM »

Slow or poor response to the rudder is a key indicator of not enough dihedral. Do add washout. (All these small RC planes have needed more that I thought) Most of my Orange gyro'd RX's are stick priority. That is the gyro is NOT fighting the commanded input. Add a bit of down thrust. I assume you have down and right thrust, if not add it.

Too nose heavy will actualy result in the plane's nose coming up as the speed increases (plane dropping).

All the best,
Konrad
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Cut it twice and it's still too short!
simpsd
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« Reply #11 on: June 04, 2020, 12:25:35 PM »

Thanks a lot for the suggestions.  I am responsible for a bit of confusion here. I forgot to say that before I flew it I swapped out the self-stabilization receiver for a regular one.  So the good news is it is flying a lot better now. The biggest changes I made were I replaced the elevator servo which I think was too small for the job. I also worked on removing the friction from its pushrod. The servo was overworked and not moving fast enough and I suspect it was worse under the loads put on it in flight. Now the elevator responds more quickly and travels further with power to spare.  Second I caught one of the aileron servos misbehaving. At random occasions, it would stall and stick in whatever position it was in.  In the process of removing that servo, I disconnected it from the Y harness and noticed it unplugged rather too easily. Turns out the connector was faulty or damaged and not always making a good connection. So servo problems fixed, I put in a 4 gram heavier 3cell battery and went down to the field and Wow it actually flys pretty nice.  I don't think it will be my favorite but damn good. Now I have to decide if the color/covering is good enough or paint it white and start fresh.  I know that will make it a little heavier but ....hmmm
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simpsd
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« Reply #12 on: June 04, 2020, 12:37:50 PM »

I meant to add in the post above that originally the thrust line was very close to the datum so there was little or no down thrust. As a further tweak, I may try another washer between the motor mount and the firewall. As far as washout goes, is there a good way to add that to a wing mostly skinned with 1/32nd balsa after it is already made?
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Konrad
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« Reply #13 on: June 04, 2020, 01:52:09 PM »

As I assume it was built with CA (plastic) it won't take to kindly to steam or heat. So I think you might want to look into adding a stall strip (something to make the LE of the wing root sharp). The idea is to get the root of the wings to stall before the tips.
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Cut it twice and it's still too short!
simpsd
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« Reply #14 on: June 04, 2020, 03:22:59 PM »

Hmmm. Stall strips I remember seeing those on real airplanes, so they work on models too. I made this model a bit old school all with yellow waterbased wood glue. I might have used some CA here and there if I'd had any. Mine all hardened up in the bottle.  I really have to put together a supply order. I don't particularly like working with CA glues but there are times when they make things easier. So a little twisting in steam might get me some washout.  I think I'll fly it some more and then decide if it is a worthwhile risk to take with the wing. I'm just pretty happy now that it is flying reasonably well.
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Konrad
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« Reply #15 on: June 04, 2020, 04:03:42 PM »

Great news about using yellow glue. To my mind the risk is greater not adding the washout.

All the best,
Konrad
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Cut it twice and it's still too short!
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