OT Stunt Engine Design

LAST EDITED ON Jan-23-04 AT 06:06 PM (CDT)
 
Here are some screen shots of an engine I intend to built for an OT stunter, probably a Humungous or a Lil' Moe. Its based on a design by Andrew Coholic he calls the AJC Skyburner .65, and was intended to be a sparker. It was inspired by the Edco Skydevil. I'm using his casting modified and myown internals.

I am retiming it and making the necessary changes to get the weight down and make it easy to change the CR, hopefully shimless.

What do you think?

>Here are some screen shots of an engine I intend to built
>for and OT stunter, probably a Humungous or a Lil' Moe. Its
>based on a design by Andrew Coholic he calls the AJC
>Skyburner .65, and was intended to be a sparker. It was
>inspired by the Edco Skydevil. I'm using his casting
>modified and myown internals.
>
>I am retiming it and making the necessary changes to get the
>weight down and make it easy to change the CR, hopefully
>shimless.
>
>What do you think?
>
>Randy Ryan
>AMA 8500
>SAM 36
>I fly 'em all and love it!

I am thinking the bottom engine is going to have a little trouble with fuel draw.

Seriously, since I don't know anything else about it, my only suggestion would be to make it so you could change the ventur.

Also, since this is a double exhaust, are you going to run it like they used to do in the "old days" (you know, the last century) with no muffler? Might be loud. Might be interesting to watch.

Leonard,

You'll notice in the leaky shot that the ventui is a seperate piece. I do intend to run it unmuffled like wayback when crankshafts were chipped from solid Italian marble.

Seriously too, I will probably have a contingency plan in place to muffle the beast if it proves to be too obnoxious. But don't you just love the asthetics of the twin stacks?

Randy Ryan,

Glad to hear you will at least initially run this engine open exhaust. Oh man, it would sound so cool! I'd even be tempted to install open-end megaphones

However, you're due for a big old pile of unsolicited advice the second or third time you show up with this engine unmuffled.

So I say skip the mufflers, that's too easy. Twin tuned pipes simply must be bolted to this motor. Or maybe one tuned pipe fed by a 2-into-1 header.

Side benefit: We're repeating ourselves on this site when it comes to many issues. Your home-brew, dual-stack motor could easily prompt massive debates.

Suggested topics:

1) One header and pipe on a dual-stack engine. Will this work? If not, why not?

2) Two headers and two pipes on a dual-stack engine. Will it work?

3) A 2-into-1 header with a single tuned pipe, can it be made to work?

4) Two headers, two pipes on a dual-stack engine. Can one pipe be timed for grunt, the other for top end?

5) Will you make me a spare engine so I can (claim to) be doing some testing?

Here's a Cross Section.

Dan, I like the dual header idea, I could use a Roberts 3 line setup to switch from pipe to pipe!

Ain't no spares, yit!

Randy, I hope I can one day buy something from you - you're living history! It would be an honor to own something you made. It'll be a while yet before I could even afford to pay what something like that would be worth (if a price could even be put on it!), and at least that long as well before I'll have the skills to actually put it to good use, but I can at least dream...

(I hope that's a "licking lips" smilie, and not a "sticking tongue out"...)

Tim

Thank you so much Tim, your compliments are appreciated very much.

What a beauty, just outstanding, nice blend of designs.Thanks for sending in the pix.You're inspiring me to dust off my old Atlas lathe.Yup a real dandy effort. Jim Sofra

Would look better with a RED head!
Humor..God's gift to us to keep us from making sausage out of each other daily.

LAST EDITED ON Jan-24-04 AT 00:03 AM (CDT)
 
But Joe, gentlemen prefer blondes! So do slobs like me!!

Thank you Jim, I'd have to build this one just to be able to look at it!

Randy,
What an interesting post.
More details on timing would also be welcome.

Here are a few initial observations for interest's sake:

I like the one piece cylinder and fins which give strong support from the fins in maintaining cylinder shape and the efficient transfer of heat to the fins.

Similarly I like the cool transfer part of things at the rear and the hot exhaust at the front where the most cooling is happening.

They look like very big diameter big and little ends. If you are pressing in phosphor/bronze inserts these should be very cool running and long wearing. Keeping the reciprocating mass down might be a little challenging but I note the piston has a ring so perhaps you are using an alloy piston.

It seems you will have a ball bearing main and a bushed front end. I like this idea too as it makes a great seal around the shaft intake and supports the (big) shaft over a considerable length. Making a good fit is important of course and therefore an interesting/enjoyable job.

All the best with the project and I hope you keep us up to date with progress and a performance report.

Tim Gee.

>Randy,
>What an interesting post.
>More details on timing would also be welcome.
>
>Here are a few initial observations for interest's sake:
>
>I like the one piece cylinder and fins which give strong
>support from the fins in maintaining cylinder shape and the
>efficient transfer of heat to the fins.
>
>Similarly I like the cool transfer part of things at the
>rear and the hot exhaust at the front where the most cooling
>is happening.
>
>They look like very big diameter big and little ends. If you
>are pressing in phosphor/bronze inserts these should be very
>cool running and long wearing. Keeping the reciprocating
>mass down might be a little challenging but I note the
>piston has a ring so perhaps you are using an alloy piston.
>
>It seems you will have a ball bearing main and a bushed
>front end. I like this idea too as it makes a great seal
>around the shaft intake and supports the (big) shaft over a
>considerable length. Making a good fit is important of
>course and therefore an interesting/enjoyable job.
>
>All the best with the project and I hope you keep us up to
>date with progress and a performance report.
>
>Tim Gee.

Hi Tim,

The timing is being worked out, I am comparing several of my nicest runners and will time this engine accordingly.

The rod is muscular, but it and the piston are both aluminum so the mass should not be a problem. Some thing else you can't see (because it isn't there yet) is the bypass cavity and the holes that will be necessary in the piston skirt to allow transfer. That will remove yet more reciprocating mass.

It is indeed a rear ball bearing, if the casting had the material available it would have a front BB as well. Super Tigre used a setup like this though and it worked well as did a number of other engine manufacturers. The main issue here, besides fit, is concentricity of the bores. With the bushed rod and BB this should be a long life engine accept maybe the ring, but that's an easy part to change.

The other feature, which is not yet illustrated, will be an external compression ratio adjuster. I won't detail it here as it may be patentable.

Thanks for your comments, I'll probably be starting on this next, when the Vivell diesel is finished. I'd like to have a prototype bolted into something for testing this spring.

Hi All

The repo Edco Skydevil on petrol, spark and about 11*6 is a niiice sounding engine. A little bit of sub piston induction made them get up and go. But may be not for stunt.

Nice project.

John Quigley

Hi John,

This engine will only look vaguely like and Edco.

Sub-piston inducion is used on Orwick 64, Super Cyclone, Anderson Spifire 65, Cunningham Blue Streak 64, (not to mention all the Cox engines)..For all out 2-cycle run, which is what the old engines did for a living, this extra air intake is supposed to neutralize any residual vacuum left in the crankcase just before the intake port closes for the transfer cycle.

I once had a discussion with local "experts" about the advantages of sub-piston induction. So I taped the 4 induction holes on my Orwick 64 and did an A-B comparison test (same prop, fuel, etc.) I could detect very little change on the electronic tach, but since the needle had to be peaked for each run, maybe I missed something.

And it might be mentioned that sub-piston induction is not allowed in the F2D rules (one way of circumventing the 4mm venturi rule).

That looks fantastic! How did you ever get to the point of building your own engine? I modify the timing on an FP-40 with a Dremel and think it's a major accomplishment and then I see something like this! It would really be neat if someone (hint, hint) would write a series in Stunt News showing us the steps of designing and building their own engine. In our club (NVCL)we have almost a half dozen members with their own little lathes or mills (and one guy with the full-blown computerized everything that makes stuff for NASA!) I suspect that their are a lot of PAMPA members with interest in what you are doing.

Scott

Hi Scott,

Thanks for the compliment. Building my own engine is just something I enjoy doing. For years I've been restoring, converting and building engines that are either old timer or replica type and I decided I'd like to try a stunt engine.

Don't know about an article in SN, I suppose I could photo document this project and submit it, never know what might happen. Anyway, I just finished the Vivell diesel I have been posting and will make test runs tomorrow, then I am going to dig into this stunt engine. I have timing research yet to complete, but I can probably have that done in an evening if I just sit down and do it.

Thanks again,

Dear Randy:

Actually, the stunt guys would probably be very interested in this. There is a regular column in Stunt News that covers engines. That column regularly reports on stunt engines, how they perform, how to modify them, etc. A series of pictures of the engine at various states of its construction would be very interesting as I don't recall any previous submissions on original design and constructed engines. Of course, if you took it to John Brodak's contest and he saw it, he'd probably want to do a production run on it......

Anyway, I think it's a great project that you are doing. Some day....

I have started getting the first installment of an article on this engine for SN. I will submit it and see what happens from there. This could be fun!

Randy,
You should definitely submit the article. If you do it in sections, it would be great. Or the complete article at once, doesn't matter.
My suggestion: Anodize the head RED!! LOL!! For OTS, maybe ST 46 or 60 timing?? Good solid 4-2 break.
Bill <><