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Super Chipmunk "conversion"

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Super Chipmunk "conversion"

Old 08-28-2009, 12:59 PM
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Mr Cox
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Default Super Chipmunk "conversion"

Just thought that I would share something a bit more positive than pictures of chinese engines that don't work...

I've had this ARF for quite sometime and is looks like it will soon be finished. I like the way the super chipmunk looks and got the ARF made by Goldberg, as it has a better looking engine cowl than the other ones do. Not much to report about the assembly. I've strengthen the front and mid part of the fuselage using triangular pine and epoxy. This added about 0.5 oz I think but made things a little stronger. A Hayes 061 mount was modified to take the 074 and to have a lower weight. Thunder tiger 2.5 oz tank fits well and are fairly lightweight too.

All up weight now seems to end up around 19oz (with a 750mA battery, landing gear and a pilot, so there is some room to lower it further). It is listed as 22 oz on electrics and with the Norvel 074 it should be fine, I think/hope...

The engine and muffler will fit inside the cowl (without the spring starter), but I'll run it without the cowl first to see how it likes to run inverted. The all important decals need to get on there too.

Here is some data:
Super Chipmunk 400 (by Carl Goldberg)
Wingspan: 38"
Length: 28 1/2"
Wing area: 230 square inches
Weight: 22oz (3S lipo, 400 engine) 19oz with Norvel 074

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Old 08-28-2009, 10:10 PM
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flyinrog
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Default RE: Super Chipmunk

I have one of those,,built it but never quite finished it..had the Tiger 400 with a norvel .074, great flying plane,,got some radio or battery hit and totalled it...bought the super chipmunk to try the same thing, but left it brushless, havent flown it yet,,sure would like to try the .074 in it, so let us know how it goes, I'm not a fan of inverted engines...Rog
Old 08-30-2009, 09:29 PM
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ChicaWolverina
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Default RE: Super Chipmunk

Cool, but DO uninstall the engine and take everything out of the forward compartment and use 3 or 4 heavy coats of clear dope cut by 50% with thinner and then...

Really though... please don't just take it out in that condition or it will be wasted after a few flights because you didn't complete the conversion.


><
Tomasina
Old 08-30-2009, 10:18 PM
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Default RE: Super Chipmunk

That's a nice model Mr. C!
How has your Summer been so far?
Old 08-31-2009, 02:29 AM
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Mr Cox
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Default RE: Super Chipmunk

Summer has been good here, a bit windy but that's just good practice. My regular field is very flat with only tall grass and bushes so one can just play around and come in from almost any direction (not over the pit of coarse). I visited a friend of mine and their field was a bit different though, quite narrow with several of trees. Almost lost my most trusted plane there (shown in my avatar, can't remember what is was called...). I went inverted downwind and out of site behind a few trees. I just kept full elevator until it came out on the other side with a nice climbing angle and got a loud "wow" from one of the younger pilots...

Tomasina, don't worry this is not my first plane and I'm planning to put a hatch in front (rather than a solid fire wall) and fuel proofing of coarse.

The only thing that worries me a little is the inverted engine, I'm not a great fan of those either. All the oil tends to end up at the head. This is what stopped me last winter from finishing it. A horizontal mounting would have been better for the engine but that would not clear the cowl. I'm might get some well needed practice on my inverted flying though...
Old 08-31-2009, 02:52 PM
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Default RE: Super Chipmunk

This will be a slow build but I just thought I would post a few tips on weight savings. Most of you here probably know this already but I'm still surprised sometimes at how much weight that can be saved by just being a bit careful.

First up are the wires and switches. By not using a commercial standard switch and Y-harness (at 17g in total), but instead soldering the servo wires together directly and using a smaller switch (at 5g in total, including a charging lead), there is a weight sawing of 12 grams.

Second tip is to have a look at the tank. Lightest option would be a bladder but I kind of like the simply operation of standard ones.
The weight of a standard 2 oz tank is around 31g, while a lightweight tank and light clunk (home made in this case) will only weight about 17g (shown here is a 2.5oz one from TT, but there are also other without the large rubber stopper and brass tubes etc). Another saving of 14g.

These two simple measures alone then saves about 12+14=26g or almost 1oz!
This is without having changed any of the functionally at all...

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Old 08-31-2009, 05:47 PM
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Default RE: Super Chipmunk

Very good!

It is a beautiful model and you are thinking not only in conversion but in a very conscious coversão.
Old 09-19-2009, 02:53 PM
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Mr Cox
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Default RE: Super Chipmunk

Okey, everything is ready now, I just have to run the engine inverted and then it is ready for a testflight. I've put a thin balsa hatch in the front and also fueled proofed the hatch and front with epoxy. There is plenty of space for the radio installation and I choose to put the swith inside the canopy, since it is so easy to take on and off.

Total weight as shown below is about 18.5 oz (18.9oz with the cowl).

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Old 09-19-2009, 06:50 PM
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Default RE: Super Chipmunk

Looks outstanding Mr Cox! You do immaculate work.....do you also build furniture?

The forward hatch is something I've never seen before and in this case it looks like a great idea.
I'll bet when you bring this model outside it will make the dark clouds run off in shame and make the birds sing...it might even fly half way decently, too
Old 09-19-2009, 11:05 PM
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Default RE: Super Chipmunk

Ilike it !!!!
Old 09-20-2009, 10:45 AM
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Default RE: Super Chipmunk

Maidened today, it flies really well, starts from grass at what feels like half throttle and just sits there until it is picked upp. Rolls are a breeze and the inverted flying is excellent. Made a few large turns over the field inverted and at half throttle, I'm really pleased with this one!

The inverted engine was no problem at all, I just have to change the way I usually fuel. Filling until fuel comes out the exhaust will effective flod the engine...

I used an APC 6.3x4 which spins at about 16500 rpm when maxed out on 10% Nitro (I think I have an extra shim in there too). It ran a little rich on the low end, might add an air bleed to fix that.

I'm still stoked by the performance, just have to finish the cowl now...
Old 09-20-2009, 03:00 PM
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Default RE: Super Chipmunk

Just thought I would add some settings data in case someone is interested in getting one for glow or even electric...

I reduced the controltrows of the ailerons and elevator to about 1/4" and 3/8" respectively by trial and error, this turns out to be about half of the recommended throws. I don't run much expo so that could be a reason.

CG is right were they recommend it 2-1/2" behind the leading edge, i.e. the rear part of the wingspar. I didn't play with this at all as it seemed fine to me. The elevator does have a tiny bit of downtrim when I look at now. I have put in about 2° of downtrust by guessing (the firewall had none) and I might increase that a little the next time.

I didn't use the stock wheels and wheels pants, instead I've put on 2" lightweight wheels. This worked well on our rough grass, it only needs a little up elevator when starting from a stand still or taxin slowly, to avoid tipover (this is standard I think). I have seen other comments on week landing gears, but I didn't have any problem. On the contrary they seemed quite springy and nice just like on a larger plane.

I made four flights today and had no misshaps appart from the pilot loosing its cap...
Old 09-20-2009, 03:13 PM
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Default RE: Super Chipmunk

Very nice, Mr Cox. I like that there are a few of us actually converting smaller lecky models to glow. Most folks think that's backwards these days! I'm putting the finishing touches on my Electrifly Fokker DVII with an OS .10 and hope it works out as nice as yours did.
Old 09-20-2009, 04:04 PM
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Default RE: Super Chipmunk



What a beauty Mr. Cox! Did you fly it with the cowl of decide against it?

TeeBee,

I been wondering whatever happened to that Fokker?I can't wait to see the final pictures.

KP

Old 09-20-2009, 04:23 PM
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Default RE: Super Chipmunk

I didn't want to alter the cowl before I had desided on the orientation of the engine. Turns out it works just fine inverted so now I'll start to make some went holes in the cowl.

I would really like to keep the spring starter though, they are so convenient to have, but the stock one will not fit inside the cowl.
I have a few ideas and might try to make something similar to the later springs from cox which are not grabbing the prop it self but rather the thrust plate.
Old 09-21-2009, 05:44 AM
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Default RE: Super Chipmunk

Hang in there, KP. I'll post some pics as soon as it's done.
Old 09-21-2009, 02:26 PM
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Default RE: Super Chipmunk

Mr. Cox!
Please post weight figures for engine mount. How much it saves going from 074 to 061 one? If I need mount for 061, can I use 049 one in the same manner?
What servos you used here? Will HXT500 6g servos be enough for plane under 20oz?
Thank you,
Kostya
Old 09-21-2009, 04:22 PM
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Default RE: Super Chipmunk

I used the Hayes 061 mount, it should also fit the 049 as they have the same case dimensions. I don't have any unused mount left and I did that modification last winter so my memory is a little "weak". The mount is fairly beefy and also has a support for a nose gear that I didn't need. I'm guessing the weight might have gone from about 15g to 10g, so nothing spectacular but it is all the little places that count in the end.

Choosing servos are a little tricky, there is such a jungle out there...
This is one place where one might be tempted to save a little more weight but will then loose both in precision and, what's even worse, also in safety...
So it is always a compromise, too light/weak and you might risk the whole model, too strong and you'll need a larger battery etc.

I don't like to go much below 8-9g servos (or below 1 kgcm torque) except for on the throttle where a failure is not fatal (unless you are also in an awkward position when it fails). On this model I'm using Cirrus 9g servos. It is the first time I've tried these ones so I can't really say anything about their lifespan yet, but they are quick and precise for their size. I just wish the manufacturers would also give a typical current draw, as this seems to vary a lot. A buzzing servo will certainly draw a lot of current...

I don't have the HXT500 myself, but some people seem to like the HXT900 ones. They are 9g and 1.6 kgcm (?) and it sounds to me like a better/safer match.
Old 09-21-2009, 11:39 PM
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Default RE: Super Chipmunk

Thanks alot for your advice. I have good experience with HXT500s with 20oz electric foam Extra. People use them successfully with 400 size helicopters. I've noticed that glow power guys often tend to use heavier servos, 9g at least. I think I'll try to build my Tiger Sport with HXT500s and run couple of tanks during engine breakin and see if increased vibration cause their degradation.
Interesting facts about Hayes engine mount. Did you compare Hayes with Dave Brown mounts by weight? I never seen any of them and need to choose lighter one to order. Can I save weight if I make it from hardwood or plywood?
Thank you,
Kostya
Old 09-22-2009, 11:04 AM
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Mr Cox
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Default RE: Super Chipmunk

ORIGINAL: combatpigg

Looks outstanding Mr Cox! You do immaculate work.....do you also build furniture?
I wasn't quite sure if this was a joke or not, all I've done here is to make a hatch on an ARF. Compared to your own beautiful scratch builds I do feel a bit ashamed...
I don't really build any furniture but I do like to make things out of regular wood too.
Old 09-22-2009, 11:15 AM
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Mr Cox
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Default RE: Super Chipmunk

Salat, I haven't compared the weight to Dave Brown mounts, don't think that I have any of those actually. The lightest plastic mount I have seen are from ACE, for the cox TeeDee engines, might hold the 061 after some mods but they are quite hard to find...

The lightest would be home made wood mounts if done carefully and incorporated into the firewall area during the build. Brodak also has some pre-made in plywood but they are a little weak around the screw holes and I've dropped an engine using those...
Old 09-22-2009, 10:40 PM
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Default RE: Super Chipmunk

Mr Cox, Hayes makes 2 types of mounts, long and regular. Which one you used?
Thanks,
Kostya
Old 09-23-2009, 01:17 AM
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Default RE: Super Chipmunk

I've used the Hayes NV06 which is meant for the Norvel 061. For an AP wasp I actually shortened it a bit too.
Old 10-22-2011, 11:36 AM
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Default RE: Super Chipmunk

I really love the way this plane flies, it is perhaps the best all-round 1/2A I've ever had...
Tried to make a little movie today but one can't really see the plane in the air, just thought I would share it any way.
The engine is fully cowled, but I've left the wheel pants off since our field is quite rough. Might make a more sturdy, and a taller, landing gear for it too.

[youtube]http://www.youtube.com/watch?v=trSCx-6zlAo[/youtube]
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Old 10-22-2011, 11:48 AM
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Default RE: Super Chipmunk

Here a a few more images of the engine installation. I'm using a norvel springstarter that grabs a custom propdriver, cox style, so that all can stay behind the cowl. A few primitive baffles are enough to guide the air flow around the cylinder.
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