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Feb 20, 2020, 11:28 PM
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kablake's Avatar
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Fuse center line equals Crankshaft center line..


Hello,,

I'm in the process of building an airplane right now and the engine mount I want to use will be a BIG pain the butt if I align the fuse center line on the plans with the crankshaft centerline. Mounting it with the crankshaft center line about 1/16 to 1/8 inch below will make life a bit easier..

Question is.. Of course.. Will this cause much of an issue?? This is just a sport plane, A Big Stik. So not really an issue that it has to fly perfectly on edge or make a tight straight 4 point spin ( I can't even do one right now regardless)… I just like to go out and have fun...

The mount I am using has the crankshaft centerline off center of the 4 firewall mounting holes top to bottom. The upper bolts are about 1/4 inch higher than the lower ones. So the top mounting holes are pretty close to the top of the firewall. I believe I will have to cut the blind nuts or use a smaller washer with a locknut and make some simple mods to the top of the fuse area, just a bit but would rather not. I am putting a 1.20 4 stroke on it and the mount is pretty large. Flipping the mount does not help, then it puts the issue at the bottom of the fuse. So the mount would have to move up...

SO, is it OK to drop the mount a bit??

Thanks..

PS: Should have thought about this before mounting the firewall so some mods could have been made to make life easier.. Live and learn...
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Feb 21, 2020, 12:07 AM
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Yes. Ive had a bunch of sticks, have two right now, they all flew fine. Just slap the engine on reasonably centered and you're good to go. I use them as beater planes for testing engines and radio gear.
Edwin

PS - I use a secondary firewall to mount engines. Keeps from honey combing the fuse firewall.
Feb 21, 2020, 12:27 AM
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kablake's Avatar
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Quote:
Originally Posted by edwin1
Yes. Ive had a bunch of sticks, have two right now, they all flew fine. Just slap the engine on reasonably centered and you're good to go. I use them as beater planes for testing engines and radio gear.
Edwin

PS - I use a secondary firewall to mount engines. Keeps from honey combing the fuse firewall.
Well I am not really in the process of building an airplane, More like I just replaced the firewall and where I put triangle stock and basswood reinforcement stock is where the blind nuts will end up on the top.. So.. If I move the mount a bit I can get around that relatively easy... If not it will be a bunch of making room on the inside (get the Dremel out) for blind nuts or even washers and lock nuts I could get away with...

As for a secondary firewall, I see your point, But this engine puts the prop already about 1/2 inch past the point shown on the plans as well as "adds" weight to the front. The further from the CG the more forward it moves the GC. So putting it out even further would make those issues worse.. Right now I have everything arranged for no extra weight..

Do you mind sharing a few photos of your "Secondary" firewall installs..
Feb 21, 2020, 08:50 AM
Registered User
Cutting flat spots in triangle stock for T-nuts is what I do too. The secondary firewall is pretty much 1/4 to 3/8 ply with T-nuts on both sides.
Edwin
Feb 21, 2020, 10:11 AM
Registered User
I forgot to comment on the prop hub position. I've had three .60 size sticks and the ones with glow engines needed tail weight to balance. I had one with a dle20 on it and it still needed a little bit of tail weight. It also didn't stand up to the power of the dle20 very well. The stab had to be removed and rebuilt with a ply center section. On. Board GPS telemetry showed the stick at 100mph flat and level over the runway. A diving pass was over 100, but I dont remember by how much.
Edwin
Feb 21, 2020, 10:51 AM
Still gassin' it.
If it is a beam mount type of motormount, I guess it would not be too much trouble to shim the engine back to the intended centreline?

Anyway, I don't think it makes much difference either way.
Feb 21, 2020, 11:38 AM
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earlwb's Avatar
For the Ugly stick planes, it is not critical. When you get into precision aerobatic planes then it is more critical though. But even then it depends on how good of a aerobatic competition flyer you are. Thus if the engine center line crankshaft isn't perfectly aligned with the fuselage center, it is not a big deal.
Latest blog entry: yes I still fly airplanes too
Feb 21, 2020, 12:49 PM
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Getting one of these perfect is like peeing in a dark suit. You're the only one that will notice....
Feb 21, 2020, 02:38 PM
Still gassin' it.
Quote:
Originally Posted by ahicks
Getting one of these perfect is like peeing in a dark suit. You're the only one that will notice....
gotta remember that one...
Feb 21, 2020, 04:34 PM
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turbonut's Avatar
Centering the crank shaft on the fuse centerline is not a issue on any aircraft..Just need to pay a attention to down and right thrust if needed
I can affect how the plane responds to throttle but its not a big deal
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Feb 22, 2020, 11:21 AM
Registered User
It's a good thing many designers didn't stick with that theory of keeping the crank in line with the 'centerline of the' fuse. (edit)
Last edited by JimboPilotFL; Feb 22, 2020 at 02:42 PM.
Feb 22, 2020, 01:48 PM
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SeismicCWave's Avatar
Quote:
Originally Posted by JimboPilotFL
It's a good thing many designers didn't stick with that theory of keeping the crank in line with the fuse.
Sorry, but I don't see the logic of your statement. Do you think those planes in your attached pictures NOT have the crank inline with the fuselage? My question is what makes you think that the crank is not inline with the fuselage in the pictures?

There is a thrust line that the center of the crank shaft will be aligned to in an airplane. It all depends on where the design put the thrust line.

One example is a float plane with an engine on top of the wing which is on top of the fuselage.

https://www.google.com/search?q=floa...=2002&bih=1329

Those planes will have an engine thrust line farther away from the fuselage. As such the designer will have to adjust the design of the plane for various power settings.

Putting the engine crank shaft thrust line at a specific location is simply a matter of the design compromise in any airplane. Unfortunately in your attached pictures those airplanes are some of the more "typical" airplanes with the thrust line closer to the fuselage.

The thrust line of the Cessna is somewhere between the wing and the horizontal stab through the fuselage. The Chipmunk and the Ryan both have the thrust lines pretty much through the fuselages.
Last edited by SeismicCWave; Feb 22, 2020 at 01:55 PM.
Feb 22, 2020, 02:15 PM
Registered User
The Cesnna engine thrust line would be a bit above, and the 2 others (Chipmunk and Ryan) both use inverted Ranger 6 cylinder engines, and those cranks will be within a foot or so of the top of the cowl so both of those would be above as well.
Feb 22, 2020, 02:39 PM
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Quote:
Originally Posted by SeismicCWave
Sorry, but I don't see the logic of your statement. Do you think those planes in your attached pictures NOT have the crank inline with the fuselage? My question is what makes you think that the crank is not inline with the fuselage in the pictures? .
The crankshafts of the engines in the pictures are much higher than the centerline of the fuselages.

The OP has been talking about moving the crank centerline about an 1/8" below the centerline of the fuselage on a Stick if I remember right.


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