Choosing an engine for a Sig Chipmunk.

I have an old Sig Chipmunk kit from the 1970's and am thinking about useing an O.S. Max .35s for power. Is this engine likely to be suitable for a Chipmunk in the medium weight range. I had planned on using a Fox .35 as shown on the plans, but I think the Fox might be too marginal in power. I would appreciate information from anyone who has flown the Chipmunk with the Max .35s or the Fox .35 or both..............TD

TD,
For a period correct power system, the OS 35S should do a very good job! Just keep it as light as you can, which you already know. A good Fox 35 will do the job, also. Of course, you will get a bunch of posts telling you what "new" engine would be better, and they probably would be, but your question was about the OS 35S and Fox.
I have flown both engines in question, and a good straight, light Chipmunk will fly just fine with either. IMHO, the OS 35S, overall, is a little stronger than all but the best, or reworked, Foxes.

Bill <><

Disclaimer: I am niether a NATS Champion, engine reworker, engine producer, column writer, Hobby Shop owner, rockeet scientist, nor otherwise. Just an old Advanced flier.

>
>Disclaimer: I am niether a NATS Champion, engine reworker,
>engine producer, column writer, Hobby Shop owner, rockeet
>scientist, nor otherwise. Just an old Advanced flier.

That just loves model building, flying, and communicating about it too! AND who happens to know quite a bit about it as well.

Oh yes, the L&J, Woolard, and Denny modified Fox 35's will outpreform a stock OS .35S. I don't know about OS .35S's being modified, but these guys could probably do something for the umph of an OS too!

BTW just got of the Tower site and bought me a good ole LA.46 before they get discontinued there!

>
>BTW just got of the Tower site and bought me a good ole
>LA.46 before they get discontinued there!
>

Jim,

Is there some reason to believe that they will no longer be available from Tower, or will no longer be manufactured?

Thanks,

Andy,

I saw a post somewhere maybe not here on SSW but maybe at flight lines that Tower was going to discontinue the LA .46. I don't know if that post was accurate but I just thought I would ACT in case it was accurate and my chance of obtaining one disappeared!

Sounds like a perfect choice. I've had one and it flew pretty good on the Fox. Still, a little more power would have been nice. Watch that it doesn't get nose heavy, although a little bit doesn't seem to hurt their flying characteristics too much.

Some of the best flying Chipmunks I've seen use a bit more power. The Chipmunk is slightly larger than the typical 35 size airplane, so a bit more power is not bad. Bill Calkins had one powered by a ST46 that was nice. The Milwaukee club has several Chipmunks in their stable powered by stronger engines. I think Jim Krueger uses an Aerotiger 36 and Mike Woods an OS 40FP. John Paris flies one powered with a 40 (I think). Perhaps some of these gentlemen will give their opinion.

Fred

>Some of the best flying Chipmunks I've seen use a bit more
>power. The Chipmunk is slightly larger than the typical 35
>size airplane, so a bit more power is not bad. Bill Calkins
>had one powered by a ST46 that was nice. The Milwaukee club
>has several Chipmunks in their stable powered by stronger
>engines. I think Jim Krueger uses an Aerotiger 36 and Mike
>Woods an OS 40FP. John Paris flies one powered with a 40 (I
>think). Perhaps some of these gentlemen will give their
>opinion.
>
>Fred

Fred is right about flying mine with a 40. Double Star with a smaller spray bar and one head shim to be exact. Nice combination. I would imagine a strong 35 stunt would work well on a light airplane.

If you already have an OS 35-S, by all means try it out. Wonderful, Fox like engines minus the Dreaded F__ Disease, and maybe 20% more power.

If not, err on the safe side for power, and try an OS 35 FP.

I built and flew mine in the 70-75 era with a then new Fox .40 stunt engine. It was plenty of power for the 4,000 to 6,000 altitude I was then flying at. However, I never really broke that engine in and it flew better wtih an OS Max .35 III. I personally would not use the Fox .35 in it. There are better engines with more power and the weight differene is minimal compared to power output. Just to stiffle the Fox lovers, I have 8 of them and do use them, but in OTS and samll Classic planes. The Chipmunk will do better with a more poerful .35 or a .40.

You did not state if this is the CL-3 (Jim Van Loo) kit or the redesigned Super Chipmunk CL-19 kit... If it is the Jim Van Loo, the plans show the Fox with a prop extention to clear the cowl. If you go with an OS FP or an LA a prop extention is not needed, The MAX-S is shorter (Like the Fox) and may not fit as clean as an FP/LA. I am getting ready to build a CL-3 kit as soon as I clear my building board of a Ringmaster and Sterling Hellcat.

I will be using the OS .46 LA for my Jim Van Loo Chipmunk (CL-3)
This will be my first full body stunter!

It is my understanding that some of the 70's kit have a tendency to build a little on the heavy side, so if you are going to use what you already have I would think that the OS MAX-S would give you enough peformance. Then if later on down the road you want to upgrade to a LA .40/46 it will be an easier switch.

LAST EDITED ON Dec-11-03 AT 07:47 AM (CST)
 
My kit is the CL-19 Super Chipmunk. I have started bulding on the oldest one (obtained in the 1970's). The other is still in plastic wrap (got it from Tower Hobbies 10 or 12 years ago for $32.95 when they were reducing their control line stock).
Thanks for the information shared in the above posts.
Sounds like the Max .35-S is going to be my best bet on the old Chipmunk. If I find I need more power, I suppose I can go to a Max .40FP, since they are so readily available on the Bay. Probably have to get an R/C version and do the conversion..................T.Durrill

The LA 46 has my vote. The best Chipmunk I had was powered by a Como 40 and for what ever reason that engine seemed to have more power than any of my other 40's. The only down side to the Como was it was a bulky and heavy engine. On the subject that the LA 46 is going to be discontinued. PLEASE TELL ME IT AINT SO.......

TD,
I would use the Max S 35. If you find it needs more power, the Brodak 40 is a drop-in replacement & weighs the same.

Phil: Prop extensions really aren't a problem. You just put it on, and make sure everything is tight. The weight increase is pretty trivial. You do have to make the prop hole a bit bigger to accept the new hollow prop nut, true. But this is done quickly.

Currell,

My cousin, Hawk Hawkins, gave me a prop extention set up for a Fox when I visited him a few weeks ago but I have not had any reason (yet) to try it out. My thinking was that for the CL-3 kit a stronger running engine might be beneficial to performance and, oh by the way... you won't need any extra gadgets. But I see that the plane in question is the CL-19 kit and I believe that you can mount a Fox with no problem, with or without an extention. I have no reservations using an extention, I just don't want to if I don't need to.

But truth be told, I am a newbie and all can give is what I have (re)learned in the last 1 1/2 year or so since returning to the hobby. I do have both the CL-3 & CL-19 kits and can only compare kits/plans since I have not built or even flown one (yet!) I also will only comment on those things in which I have direct experience with. I was convinced by a number of friends that it would be a waste of money to buy and run Fox engines. I got one on eBay (50th anniv) for $32 like new in box with a Super Tigre NVA (Installed upside down) and now have three because I have found them to be easy to work with and reliable. I am just breaking in a L&J on a Twister, and have not flown it yet with that engine, weather permiting maybe this weekend... I am just now learning the beginer pattern and hope to be at a contest this summer... Probably running OS engines or the L&J, we'll see.

In any case, thank you Currell for your contributions to this (and other) forums... I try to read postings here every day, and have learned a tremendous amount in a short time...

Got a modified 40FP in the cl-19 to cl-3 conversion I'm currently campaigning. It weighs 44 or 45 ounces and has no problem with power. My plane is stock kit wood with a few ounces thrown in for the "way late in the building process" conversion, building a new plane would have been WAY easier, just wanted to do it. Also added all the adjustable stuff and a standard removable from the front tank box and engine crutch construction. Oh, that was fun AFTER the fuse was already built.

Swinging a 11x5, 60 eye to eye lines. Nose heavy as heck, doesn't really seem to mind, as stated above. Got a 3" bellcrank, a 4" wouldn't hurt, would change that if starting over.

Tools

Sorry can't comment about the engines you asked about. As popular as this plane is, I've never seen another cl-3 flying. Only have seen 3 other Chips at all.