Mars mods for OT stunt?

I'm building a Mars for old time stune and I'm "fussing" with the engine mounting arrangement. I've posted a couple of other questions aboult this: thanks to all for the help. I'm planning to mount a Fox .35 with the back plate screws as on the original but my question is about engine orientation. The original was un-muffeled, side mounted. I'm struggling with getting enough width to accommodate the 2" wide fuel tank and get clearance for the exhaust and muffler. I've also thought about using a Thunter Tiger 25 (runs better than the Fox when side mounted...) but it is slightly shorter (engine c/l to the bottom of the exhaust port) than the Fox .35 and would require some nose surgery to get muffler clearance (also, my Fox is getting a wee bit "tired"...). I've seen pictures of a Mars somewhere that had the engine mounted inverted. This would address two issues: 1) The muffler clearance, and 2) the deaded Fox "burp". BUT is this type of modificaton OT "legal"?

I'm not sure I would go this route: I think it might look out of place to have the cylinder head sticking out the bottom of the nose
...just considering options before I start hacking balsa...

So, my questions are 1)Fox vs. Thunder Tiger, and 2)side mount vs. inverted (or some other orientation...). What are your thoughts?

I would think that you could reorient the engine without causing problems with it being legal. (Someone else may correct me here, if they like). After all, what if you put in a Wankel, or an inline engine? Obviously the "cylinder" orientation would need to be different.

On the use of the TT 25, however, how about using a tongue muffler? Even with the Fox that may be an answer to your problem of getting enough tank width, although, with either, I would think a 1 3/4 inch wide tank would work just fine. To me, the use of a tongue muffler on some of these old time and classic ships that didn't use a muffler originally is an obvious solution to a problem. You maintainn the same exhaust width, and it extends straight out of the cowl. It is much lighter and leaves less mess on the airplane.

Ah, ha! thanks for the info: a trip to the Brodak site and I found the 1 3/4inch medium tanks. in uniflow plumbing too.

Yeah, the tongue muffler looks like they way to go. Certainly not as ugly as the big fat expanion muffler hanging out of the side of the fuselage.Even with that I'll need to pull in the sides a wee bit: the Fox is just a bit over 1 inch from the engine c/l to the bottom of the exhaust port and the mounting flange on the tongue muffler is a bit wider than the exhaust port. So this needs to be dimension to the outside of the fuselage (duh...). The TT is a bit less than that. The fuselage sides are 1/8 with a 1/16 ply doubler, so the 1 3/4 wide tank should do the trick.

Ron,

I also built a MARS a while back. Beautiful flier! Mine weighed about 30 oz with a baffle piston Fox.25. I did the backplate-bolts through the firewall thing, and found problems similar to those you mentioned.

I would still do it that way... On US engines, backplate bolts are either 3-48 (older, smaller Fox, possibly others) or 4-40. For non-US engines, I hope you have a good contact with a fasteners supplier...

It is possible, and only a few-cuss-words-awkward to get the engine in and secured using Allen head bolts/small L-shaped key.

Mine loosened up the firewall after a dozen or so flights. I may rebuild it someday... recommended: a realy solid tie-in of firewall to doublers and sides. An idea for how to do this in a pretty cramped engine bay -- pad the firewall back a bit, say 1/8 to 1/4", with a 5-ply spacer or two behind the engine's backplate. ...just enough larger than that so the bolts won't split out the plywood piece(s).

That leaves room to work around the head and exhaust stack, and not compromise the actual firewall structure. . On mine, I had to carve away some of the structural firewall to get a fit. Not a good thing, that. The removable hatch only covered the center fuselage area, and the engine slipped in a la model without removable cowl... like foot into slipper?

Hatch ran full length of the tank bay. Occasionally the tank had to come out to allow keying the Allen bolts in solidly. Nose gear separately mounted to firewall, NOT held on by clips under the backplate bolts.

The baffle .25 was plenty adequate, and (with a few of my touches) did not shake much. MARS was smaller than the Chief and T-Bird, with a thinner airfoil, meant -- like the SMOOTHIE -- for windier days. Doesn't need tons of power...

Not all Foxes burp when side mounted. As to the tank width. Brodaks has them 1 3/4"wide. They are the former Taffinder tanks. Hope this helps some.

I have seen two Mars'....both extremely heavy and a real chore for a Fox to drag around. I believe the OS wouldn't be that much more powerful.
I would rethink powerplant before doing a bunch of work dedicating the plane to the motor.

See Ya

The Palmer "Mars" has always been my favorite. I have so far built a Chief 1, a Venus, a Smoothie, and in progress is the Palmer/Goyet HighBoy. I don't see an inverted engine as a violation of the OTS rule, as long as the cheek cowls are in place. Check with Lou Crane on Mars. I think he has a soft spot in his head for that plane also.

Mr. srark
Did you build A MARS?
If so, how did it do?
I built a take apart for vsc. about 10 years ago
Weighed about 42 with a veco 35 side mounted.6 bolt TCC.
Never been flown.
Trimmed just like Palmers. Sure looks nice on the wall

I have a Mars kit from Saturn Hobbies in Australia. I see no reason that the airplane can't be built light (35 oz) and powered by a Fox just like the original. The trike gear may be a little more drag, but this is not a large heavy airplane. Putting a heavy engine on it will make the airplane nose heavy and require tail weight. This increases the overall weight, making the wing loading high. I would suggest the Fox 35 or a light moder 25 and keeping the airplane light. Larry Foster has eleminated the "burp" on his Foxes, and increased the power enough that is ideal for the Mars. Smoother than stock too, so it is a great match.
Steve
The older I get, the better I used to fly!

Any normal-size stunter, no matter how elegant or beautiful, built for a Fox or OS 35, must come in under about 32 oz. Otherwise, you will have a brick on your hands. This often means selecting light wood, or changing the internal construction.

Some folks would have you believe that a Nobler should be heavier! I can't accept that. I built a Nobler from a D**** kit with Fox35. It was a turkey (I didn't own a scale then, but I know it was heavy). I ended up giving it away.

Remember, you can always add ballast, but a heavy plane is a lost cause.