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CG Chipmunk mods

Old 05-09-2006, 09:28 AM
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RVM
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Default CG Chipmunk mods

I am planning on building a CG Super Chipmunk here soon. I built one years ago and remember that there was quite a bit I wanted to change about it, but got out of the hobby before I could build a second one. Of course, I may just get an ARF or something since my building skills seem to have deteriorated. [sm=tongue.gif]

I'd like to use the best of everything in this plane. At the first of next year I want to start getting into 35%-40% planes and figure I should start familiarizing myself with all the latest gear early. Chipmunk should be a good place to start. Anyway, does anyone have any mods they've done that have really improved the plane?

This is my list so far from what I can remember about the kit and what I've read here:

Robart Hinge Points
Fiberglass cowl, wingtips and the bottom center wing part
Two aileron servos, no flaps (first one I built had flaps)
I'd like to try rounding the bottom of the fuselage if I can do this without adding weight or sacrificing strength
Generally building the plane lighter, though I'm not sure the best way to do this without compromising structural integrity
Pull-pull rudder (used this on my first one), though not sure of servo placement this time around
Increasing rudder and elevator surface area if this would be beneficial
Generally replacing all hardware with the kit


I am going to use a Saito .91S for power. I hope this will give unlimited vertical if I can build the plane light enough.
I am going to switch from my heavy NiCd rx batteries to LiPo. I think I'll need a voltage regulator for this to bring it down to 6v. I'll also use a MPI miracle switch, so I figure I can use their regulator. Anything else that I need to know to run LiPos?
Going to use my JR 811 servos and 770 rx paired to my JR 9303 tx.
What would be the best fuel tank? I was thinking one of the round Slimline (I think Slimline makes them) would be ideal for this plane.
Ball links are a must to eliminate slop - DuBro ball links any good?
Sullivan pull-pull for the rudder.
What would be the best pushrod setup?

Any other comments or suggestions are very much appreciated!
Old 05-09-2006, 10:26 AM
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captinjohn
 
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Default RE: CG Chipmunk mods

I had one with a Saito .80 in it. I loved that plane. I bought it used and flew the pudding out of it. Low inverted passes and inverted figure 8,s ...split S......stall turns....tail slides...was lots of fun. Even vertical dive spins where great...untill i spun it from to high getting to much momentum in the spin...it did not quite come out in time. If only there would have been a 6 foot low spot in the field it would have made the last loop-out command!!!!! Capt,n
Old 05-09-2006, 03:36 PM
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nickj
 
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Default RE: CG Chipmunk mods

I built two, one with flaps and one without. I liked the no-flaps better. Terrific plane either way. I ran an ST .60 in both, very fast but not unlimited vertical (overrated, IMO). The Saito might do it with the right prop.

Personally, I wouldn't go LiPo with the Rx battery. NiMH would save some weight without the extra hassle of charging LiPos. As for the tail feathers, they seem huge already, and I never had trouble knife-edging the plane. In fact, I'd be leery about any mods. I was happy with the stock wing belcranks and the wire-in-tube pushrods. They seemed simple and sturdy, and the planes came out nice and light. The only thing I might do is beef up the landing gear. Just a little.
Old 05-09-2006, 05:08 PM
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Default RE: CG Chipmunk mods

I was hesistant on increasing the elevator and rudder surface area as well. However, I still definitely want to do away with the bellcranks. I would prefer absolutely 0 slop in all my control surfaces.

Other than charging LiPos is there any downside? I really know very little about them and there isn't a "basics to Li Po battery use" article anywhere that I can find.
Old 05-09-2006, 05:35 PM
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Default RE: CG Chipmunk mods

Two things about LiPos I've heard, but can't confirm:

If you crash, LiPos can be damaged, and become immediately unusable. And the damage may not be evident, so. . .
LiPos don't cycle as many times as NiCads or NiMH.

Lots of people at our club fly with LiPos, and they seem unconcerned with either of these.

I won't put up an argument in favor of bellcranks. But they worked for me.
Old 05-09-2006, 11:36 PM
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Dynamo
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Default RE: CG Chipmunk mods

A must do is to replace the landing gear. The gear provided with the kit is way too weak. You'll end up having to bend back the gear after every landing and punching holes in the wing covering on every bad landing if you have wheel spats on.
Old 05-10-2006, 12:21 AM
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RVM
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Default RE: CG Chipmunk mods

Should I replace it with more wire gear? Is there a better option?
Old 05-10-2006, 11:10 AM
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donkey doctor
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Default RE: CG Chipmunk mods

Hello; I agree with everything I read here. The landing gear need s constant attention. I will replace it with a centre mount aluminum gear the next time it bends. It amazes me, and anyone else watching, how slow this plane can fly. I have a Saito 80 on mine, and I think that it's just about perfect for it.
Old 05-10-2006, 12:30 PM
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Default RE: CG Chipmunk mods

What would you mount the gear to? Would you replace the ABS fairing on the bottom of the wing and make a plywood mount?


ORIGINAL: donkey doctor

Hello; I agree with everything I read here. The landing gear need s constant attention. I will replace it with a centre mount aluminum gear the next time it bends. It amazes me, and anyone else watching, how slow this plane can fly. I have a Saito 80 on mine, and I think that it's just about perfect for it.
Old 05-10-2006, 12:40 PM
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Default RE: CG Chipmunk mods

What about Li-Ion batteries?
Old 05-10-2006, 05:34 PM
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Default RE: CG Chipmunk mods

Anyone know if moving the rudder and elevator servos to the back would throw balance off terribly with the Saito .91S on the nose?
Old 05-10-2006, 06:02 PM
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Default RE: CG Chipmunk mods

Most wing-mouted LG wires bend back after awhile. Thicker LG wire, that's not a bad idea, along with beefier blocks in the wing. I wouldn't switch to a one-piece, though. Wouldn't look right.

I've never heard of anyone using Lithium-Ion for the receiver. Just a guess, but you might not be able to draw enough amps from it.
Old 05-10-2006, 07:42 PM
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jamsam
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Default RE: CG Chipmunk mods

I have mine all framed up and now finish sanding. I have a couple gripes/mods that I'll pass along:

I read about the landing gear so I beefed up the blocks and epoxied a brass tube into the torque block so the thick music wire has a better bearing surface. I hope it's OK - I'll just plan on making every landing soft. Yea, right. . . .

I couldn't see the logic in the plastic wing tips and belly pan. I made balsa tips and a built up balsa belly pan that both should be easier to cover.

I didn't like the rudder pushrod exit coming out the top of the fuse, so I'm trying to add an arm coming out the side of the fuse (opposite from the elevator pushrod) and connecting it to the wire that's between the tail wheel and rudder. Not sure how well this is going to work out, but maybe it'll look a bit nicer.

I stuck w/ the ABS cowl. Heard all the horror stories, but didn't want to spend $ on a glass cowl. I just took my time trimming and joining the halves and I think it looks OK. ABS wheel pants came out OK too, but not sure how well these will work out on our grass strip.

The canopy that came w/ my kit was not formed properly. CG promptly replaced it, but when I later found defective wood and notified them, they didn't reply. The sheeting is some oddball thickness (5/64" I believe?).

You cannot soak the balsa sheets that bend along the top long enough. I didn't try the alcohol trick though. . .

I'm using flaps just because it should be fun. Dual aileron servos for the wing. OS 61FX up front.

The comments on the Rx batteries seems risky to me. I'd suggest just sticking w/ your stock batteries.

I really enjoyed watching Art Scholl fly when I was growing up. So I'm looking forward to a little nostalgia when I get this in the air.
Old 05-10-2006, 10:06 PM
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preich
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Default RE: CG Chipmunk mods

I finished my CG Chipmunk after an 18 year hiatus. Yes believe it. I started it 18 years ago. Built the wing and fuse, then shelved it in favour of raising two kids and putting them through college.

I too read about the LG problem. I call CG and talked to a great old guy there who built 3 of the prototypes in 3 weeks back then. (I say old...he's probably my age!) He told me about a LG mod they made that was probably not included in mine. I cut out some of the shear webbing and sure enough, the triangle stock bracing was not there. I added that and beefed everything else up that I could. One of the major weekness was in the ply included in the kit for the gear torque blocks. The ply was not 100% laminated. I drilled several 1/64 holes through the ply and soaked in thin CA in an effort to stiffen things up. I bought new 3/16 wire and made a new set of gear bent an addition 10-15 degrees to put the axles ahead of the LE. This helps the nose over problem. I added robostruts, silver soldering the entire assembly, ie strut, adapted and gear wire, instead of using the set screws. I'm hoping these mods take care of the gear issues. At least make it a little more robust.

The bellcranks worked out fine for me and they looked good and solid, but I scrapped them in favor of dual servos. I bought a computer radio and want to fool around with the flexability of two.

I powered mine with and OS 91 surpass 4 stroke swinging a 14X7 prop. I mounted it inverted and used a slimline pitts style muffler. (great piece of hardware and a great company to deal with) Using a remote headlock, it can be completely cowled in. But, I cut-out the cowl around the head to allow a conventional starter cell. Cowled in, for cooling, it just look too tight to me.

I built mine with flaps. You guys that built with flaps then without....Why did you loose the flaps second time around?

I think Art Scholl was a great guy and a great pilot. But, I think the Pennzoil scheme is just too tired. I finished mine in the Steve Oliver Oregon Aero SkyDancer scheme. (Formally the Pepsi SkyDancer) It's one of a kind and every bit as eye-catching.

Next stop is the Great Planes Super Chipmunk 1.20 ARF with smoke for me. Problem is it can ONLY be had in a Pennzoil scheme. I called GP and inquired about special ordering it uncovered and was told it can't be done. Even the replacement wing and tail group arrive from the vendor covered. I'll either have to strip it and re-cover it or live with it.

On the battery, I'd stick with a high capacity NiCad or go NmH. LiPo's there are more trouble than you stand to gain in weight savings or capacity. Even if you used 5 digital servos, I'd think a 1200 mAh NiCd would give you plenty of flight time between charges. I run Lipos on small electric park flyers and they are finicky, expensive and delicate.

Hope that helped.
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Old 05-10-2006, 11:07 PM
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Kwigen
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Default RE: CG Chipmunk mods

I've been flying my CG SC for several years with no problems with the gear. I too had read about possible weakness where they mount in the wing so I added balsa doublers to each rib where the blocks glue to the ribs. Also I doubled the rib at the anchor point. The gear doesn't like rough fields so keep your taxi speeds slow.

It is a beautiful bird in the air and is my favorite flyer. OS .61fx, flaps, two wing servos, and if I was building another I would mount the rudder + elevator servos near the tail.
Old 05-10-2006, 11:15 PM
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Default RE: CG Chipmunk mods

I built a no-flaps version first, then flaps. If (when) I build a third it won't have flaps. The flaps were a cool gimmick, but did nothing for flight performance. They'd slow the plane down for landing, but the plane was slow enough without them. And they add weight. I liked the handling of the no-flaps plane more.

The ABS cowl and wingtips worked fine for me, but the wheelpants never did.
Old 05-11-2006, 08:56 PM
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Default RE: CG Chipmunk mods

I think doing a built up belly pan and wingtips might be a bit out of my league. Well, the belly pan might not be so bad, but dunno how I'd get the shapes right and identical on the wingtips. Does anyone know if the belly pan is available in fiberglass as well? Or, for that matter, where I can order a fiberglass cowl? If anyone can give any good tips or instructions on how to go about building the belly pan and wingtips I think I'd like to try that.

I've got a 2400mah NiCd pack now, which would be too heavy. I might look into ordering a 1200 or 1400 nicd or nimh pack for the Chipmunk if Li-xx batteries are that much of a hassle.

Moving the elevator and rudder servos to the tail might be a more effective way of positioning them, and if I remember my first Chipmunk clearly there was plenty of room to move the battery pack around to adjust the balance. I won't add any lead (dead) weight. :P

I really like the Slimline inverted Pitts muffler. If I do that I may, if weight permits, add an onboard glowplug ignition system.

Will 1/8" Robart hinges work in the ailerons of the Chipmunk? I am not sure if they'd be long enough, or maybe even thick enough.

Thanks for all the great input so far!
Old 05-11-2006, 09:03 PM
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RVM
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Default RE: CG Chipmunk mods

Anyone have any experience with Fiberglass Specialities?
Old 05-12-2006, 06:52 AM
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Default RE: CG Chipmunk mods

On my first Chipmunk I used the stock ABS cowl and pants, On my just finished second one I used Fiberglass Specialities parts.
Very nice, they look better and are lighter. Just be sure to get all the pin holes filled before you paint.

Dennis
Old 05-12-2006, 07:49 PM
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jamsam
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Default RE: CG Chipmunk mods

Wing tips: Using the plastic wing tip as a template, trace out the overall shape of the tip onto a sheet of 1/32" ply. Then stack/glue a few 1/4" thick balsa pieces onto the ply part to generate the thickness of the tip. Now hopefully you have a small disk sander - Otherwise, well, it's a bit more work I suppose. Anyway first get the airfoil shape of the tip, then with the balsa tip and plastic tip side by side on the bench, carefully try to mark the front to back curvature of the plastic tip onto the wood tip. The ply part will get glued to the wing. Using ply stiffens the trailing edge - otherwise balsa alone will break.

By using a stack of 1/4" parts, you can use the visible lines at the glue joints to help create a consistent/symmetrical tip. When done w/ the shaping, use a dremel tool to hollow out the inside to save a little weight.

Belly Pan: Mount the wing to the fues with some wax paper at the fwd and rear fues. Actually this was pretty simple to build a box to conform to a belly pan. Did require some careful fitting, but once done, looks much better than the plastic. Just need to plan out how you're going to work around the wing attach bolts.

Hope that helps. . . .
Old 05-12-2006, 08:01 PM
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RVM
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Default RE: CG Chipmunk mods

Thanks for the tips jamsam! Got any pics?

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