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Author Topic: Rotating engine adjustments  (Read 276 times)

Offline Shorts,David

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Rotating engine adjustments
« on: May 12, 2022, 08:06:17 PM »
I'd rather ask and save thirty minutes if possible. I'm going lean on the insides and rich on the outsides. My engine is mounted sideways. So I raised the tank all the way. Still have a milder but noticable problem.
Question. If I rotate the engine and mount it upside down, it lowers the venturi. So, it seems like this will help solve my problem quite a bit. Any input?
Fp 40, 11*5 or 11*4 prop. Oriental with a black plastic engine mount. Thanks

Offline Dave Hull

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Re: Rotating engine adjustments
« Reply #1 on: May 13, 2022, 02:47:36 AM »
That's a large change. The factory hole in the case on the OS .40FP is about 14mm (.55") "above" the engine mounting pads. If you kept your engine thrust line in the same place, you would be moving the nva discharge orifice by essentially that amount.

If you are pretty close, you might find the difference further reduced by using muffler pressure, and using a uniflow tank. You did not say what your baseline was, so....

If you want to rotate the engine, look carefully at your mount. At least on the Dave Brown mounts I have used, the hole pattern is not square, therefore your bolts won't line up except in the orientation it was initially drilled for. Not so simple as unbolt and rotate for testing.

You also did not say how much you did move the tank, and whether just a bit more might get you there? If this is an Imitation front end, then I can see the problem of the tank thru the fuse.

One thing to consider--if you are not allergic to plastic tanks, as some people seem to be--is a Sullivan clunk setup where you can move the uniflow point up or down and not have to have the tank body centered perfectly.

With a firewall mount (plastic R/C mount) you must be aware that you are trading one problem for another. You will also be moving the orifice laterally by 14mm. The engine may tolerate this ok, or it may not. I worked on one OPP (Other Person's Plane, gifted to me) that used an R/C mount and sideways engine. With the fixed, internal tank (no access) you couldn't set it lean enough on the ground to get a flight setting that wasn't stupid rich. Yup. Had to cut into it and get the control line engine/tank relationship back. On this one, I chose to keep the tank inside the fuse of a heavily modified Fancy Pantsy, but rotate the engine to vertical. The little OS .25FP just couldn't handle that much lateral offset on what for it, seemed to be a fairly wide tank.

If you simply cannot bring yourself to move the tank further, then you might try what I had to do once on another OPP:  I took the R/C mount off, and made a donut shaped "butch plate" out of 1/4" aircraft plywood. It had two sets of holes. One set lined up with the blind nuts buried in the firewall. Flathead machine screws (countersunk) went there to hold on the plate. Then I drilled another set of holes to attach the mount while relocating the engine thrustline--and therefore the nva--to establish the correct tank height. I intentionally offset it a bit so that some shims under the engine lugs were required. I made up a number of these so that I could tune the setup without endlessly making and remaking the butchplate. Worked out fine, considering what I started with: a plane that would fly great upright and on the insides and would instantly go rich and die inverted or on any negative-G maneuvers....

Good luck with whatever solution you find,

Dave

Offline Lauri Malila

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Re: Rotating engine adjustments
« Reply #2 on: May 13, 2022, 09:10:17 AM »
I'd rather ask and save thirty minutes if possible. I'm going lean on the insides and rich on the outsides. My engine is mounted sideways. So I raised the tank all the way. Still have a milder but noticable problem.
Question. If I rotate the engine and mount it upside down, it lowers the venturi. So, it seems like this will help solve my problem quite a bit. Any input?
Fp 40, 11*5 or 11*4 prop. Oriental with a black plastic engine mount. Thanks

The problem is not caused by tank height, so you cannot expect good results by trying to fix it with tank position. These will help, but not fix the problem completely:
 -Less load.
 -Higher operating rpm/leaner operating setting.
 -Hoter plug.
 -Higher (if possible without detonation) CR.
 -Lower viscosity oil in fuel.

I didn't quite understand your last idea, about rotating the engine, do you mean you have an RC-engine mount and you can rotate it? If so, you'll find the best running symmetry when cylinder is tilted down somewhere near 45 degrees. But you'll have to move the fuel tank down accordingly, to keep tank centreline near spraybar. L

Offline Reptoid

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Re: Rotating engine adjustments
« Reply #3 on: May 13, 2022, 02:10:27 PM »
The problem is not caused by tank height, so you cannot expect good results by trying to fix it with tank position. These will help, but not fix the problem completely:
 -Less load.
 -Higher operating rpm/leaner operating setting.
 -Hoter plug.
 -Higher (if possible without detonation) CR.
 -Lower viscosity oil in fuel.

I didn't quite understand your last idea, about rotating the engine, do you mean you have an RC-engine mount and you can rotate it? If so, you'll find the best running symmetry when cylinder is tilted down somewhere near 45 degrees. But you'll have to move the fuel tank down accordingly, to keep tank centreline near spraybar. L

That is simply not true. There are literally hundreds of side mounted OS Fp's out there that run perfectly equal on inside and outside turns after adjusting the tank height with a properly built uniflo tank. It usually requires the center of the fuel pick up and uniflo tube to be 3/16" to 5/16" above the center of the venturi. Sometimes if it's not feasible to raise the entire tank you can raise the uniflo exit height inside the tank and achieve similar results. A change in height of as little as 1/32" will make a difference
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       Don
       AMA # 3882

Offline Shorts,David

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Re: Rotating engine adjustments
« Reply #4 on: May 13, 2022, 09:53:52 PM »
Thanks for the ideas. I hadn't considered running pressure. Very easy possible solution. I'll give that a try. Then I'll probably rotate the engine since everything is very easy to access right now. And yes, my problem is tank height.

Offline Lauri Malila

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Re: Rotating engine adjustments
« Reply #5 on: May 13, 2022, 11:04:46 PM »
Ok, let's put it this way:
If you plan to fix this so called tank problem (I assume that the tank in question is correctly and well made, with no leaks and with correct, symmetric plumbing.) with such a massive tank height change, what will happen to lap times, level vs. inverted?
The first thing to do is to get the engine running parameters such that it has the best stability. With OS Schnuerle it usually means running it as it was meant to run at the factory.
If you still get a rich burp in outsides, I'd strongly recommend tilting the engine 45 degrees, especially as you seem to have an excellent opportunity to do so. You might be surprised. L

Offline Shorts,David

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Re: Rotating engine adjustments
« Reply #6 on: May 13, 2022, 11:20:12 PM »
Thanks Lauri, it's a good running OS. Tanks is in good condition. I did the 45 degree on a plane a while back and I did like it. So, maybe I'll give that a try. I liked the muffler at the very bottom of the plane too.

Offline Lauri Malila

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Re: Rotating engine adjustments
« Reply #7 on: May 13, 2022, 11:45:26 PM »
It will be interesting to hear how it works out, David. L

Offline Tim Wescott

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Re: Rotating engine adjustments
« Reply #8 on: May 14, 2022, 09:30:48 AM »
Thanks Lauri, it's a good running OS. Tanks is in good condition. ...

Here's the thing, though -- if it's a normal tank, and a normal OS 40FP, and a normal profile, then you shouldn't have to turn the engine to lower the carburetor.  If the opening of the vent tube is over 1/2" above the centerline of the engine, then chances are there's something wrong with the engine or the tank. 

If you can't raise the tank that high, and you really want to mess with starting the engine inverted, then you can give it a try.  Note that you'll be lowering the center of gravity of the airplane; if the airplane currently hangs off of the leadouts correctly this lower center of gravity will cause it to roll in a bit in level flight and out a bit in inverted.

Personaly, unless I've checked the vertical location of the CG and found it a bit high, I'd take the back of the tank off and move the uniflow vent (not the pickup).  You ought to be able to nail it to the outside wall of the tank, about 1/4" above the fuel pickup, without affecting the end run very much.  This will have the effect of moving the tank up by 1/4".  If that doesn't work, you could contemplate making another tank then yes -- think about moving the engine (taking CG into account) or think about fabricating a tank with the wedge moved up, so you can move the vent up even more.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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