Stuka Stunt Main Forum · 14 of 14 known posts recovered
thanks guys
Mike
Michael Schmitt
Dave Day
Website: http://www.iroquois.free-online.co.uk
Leonard Neumann
I would also dry fit the nose parts to see if your FP may be too wide as well. In your situation, I'd rather replace a couple of formers and make the fuselage wider, than have to chop off parts of the mounting lugs. Also, check around some about that FP -- according to our host, the 40 is less tractable in an inverted mount than is the FP 35. I further suggest that you should consider a tank closer in capacity to 5 Ounces, as well. That's the size I am using with an FP 40 I've been running lately (on a profile).
.
Kiwi
**
The older I get, the better I used to fly!
You may want to try the engine setup (i.e. engine, muffler, prop, fuel, venturi, etc.)you want to use in your Nobler on one of your existing planes. You could measure the fuel loaded accurately with a syringe and get a pretty accurate feel for the fuel consumption for your setup. This would give you some comfort in choosing a tank capacity for your Nobler.
I've also read that Leonard favors the .40FP for profiles but not for upright/inverted use. Therefore, if you want to use an OS .35 FP I would gladly swap you one of my OS.35FP engines for one of your Byron .40FP engines.
DennisV
P.S. Good luck at the St. Louis contest this weekend.
Mike
Michael Schmitt
Another thought: Why not use a Fox .35 with a hemi head, stuffer
backplate and $ 50.00 crank? I really want to see one.
Best of luck in St. Louis. Remember its not like its Green Bay.
Dick
Ron B.
F4Fguy
If you built it stock with 1/8 doublers,the ARF tank will be too wide.Build the one on the plans,or use a plastic clunk.
re(2)above:If you leave out the firewall former,the crossgrain balsa will help restore the beam strength,but will cause a serious loss of torsional strength.
re(4&5)above:As they say,your results may vary.My old,iron sleeve,home brew 35FP is very happy on an 11-5 modded Zinger,and does the pattern plus 5-6 laps on 3 1/4 oz of 5%-70%-25% fuel.On a full 4oz tank,I consistently overrun.It's also happy no matter what the mounting position.
Ron B.
Interesting comment. We have been building planes from scratch this way for years. I consider the nose bullet proof. Even with a molded top "block" and the cowl underneath there is no way that thing is going to twist. Now we do take the mounts all the way back to the wing, so the engine mounts become a crutch. But if one builds it this way, I see no problem.
Leonard Neumann
Ron B.
F4Fguy
Leonard:
After reading your comment above,I devised a crude but,effective experiment.I built a balsa mockup consisting of a tube with one fixed bulkhead at one end,and a removeable one at the other end.Two "motor mounts"are installed allowing a torsional load to be applied.A series of pics is attached to show the arrangement and the results.
(1)General view,showing the torsion boxwith one end clamped and weighted to the bench.
(2)The open ended(one end)box with no load,note the "pointer" zeroed on the Al bar.
(3)Same as(2)with wieght on the pointer,note the deflection re zero above.
(4)No load with front bulkhead in place,zeroed.
(5)Front bulkhead in place with same load as(3)above.
Note that,for the same load,the torsional deflection is 100% more without the bulkhead.Note also the front bulkhead is not glued in place,but merely slid in.
With what you devised there, I would have assumed the same. How long was the box from the point where it is clamped in the rear to the point where it is clamped in the front? We were talking a Nobler setup that is about 8 inches in front of the wing and the engine mount area is about 2 1/2 inches. You should have your half inch cross grain balsa glued between these motor mounts from that point all the way back. This is the crutch and this is the key. But we are not done.
Let's do this the hard way, with a modern stunter and a longer nose. How about 3 1/2 inch engine area and 6 1/2 inches for the tank area (ten inch total). The fuselage sides are carried all the way to the front. They are lined with 1/32 plywood doublers that actually extend to behind the wing. Carry them to the middle if you want to. Make the motor mount crutch so that the back 6 1/2 inches is cross grained balsa. This makes a solid, rugged crutch. Fuselage sides are glued to it. An inch and a quarter below the crutch there is an eighth inch tank floor installed. You omitted this. There is also a big more structure above and below the fuselage area. You omitted this. But, in all fairness, there may (probably) be a removeable cowl on the bottom which adds no rigity. But the real point of omission is the tank. Not only do we have that balsa crutch between the motor mounts from right behind the engine extending all the way to the wing (and the rear bulkhead) but there is a metal tank wedged solidly between the mount and the "floor" that you did not install in your example. The motor mount crutch, in and of itself, makes that nose solid, but once you wedge that tank below it with fuselage sides lined in plywood, some tyhpe of gusseting at the corners, and that tank wedged in place in the compartment with the bottom floor you also omitted, you have full strength and then some right on up to and beyond the area where the bulkhead would have been. Put a partial bulkhead above the tank if you want, but this thing is solid. And any twisting motion will not be applied to the very front as in your illustration, but at the motor mounts. This, on the PA series of engines, for instance (extreme case) would carry the torque nearly 3 inches behind the front. Still, build the box as I describe. Or modify yours. Make the distance from the point where it is clamped solid at the rear to the front no more than 10 inches, make sure the rear of the box cannot twist (the wing is holding it together if nothing else) make sure the cross grained balsa extends all the way up to a point no less than 3 1/2 inches from the front. Put in a tank floor. Wedge a tank in (oh, did I forget the plywood doublers?) and then try your twist. I would be interested in seeing how much force it does take. I have never seen ours as anything less than rock solid.
Leonard Neumann
Leonard:
I wasn't trying to start a pissing contest.I was just trying to illustrate a principle.The most important loads on the nose of a stunter are the torsional reaction loads from the power plant.the best way to minimize the effect of those loads is to add bulkheads to the torque box formed by the front end structure.It's the most structurally efficient,and the most weight efficient.Certainly you can add fill between the mounts.But this is not as structurally advantageous as the front bulkhead.It's good for damping vibration,but that's another question.In any event the demo wasn't intended to be quantitative.Qualitatively,a bulkhead is much more effective than anything you can install parallel to the walls.The way to improve front end stiffness and strength for a given weight,is to increase the section modulus in the direction of the forces applied.That is what the firewall bulkhead does.It's interesting to me that even as a teen,George Aldrich recognized or intuited this in the original design of the Nobler.
Ron B.
Leonard Neumann