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Cowling Fabrication For Lowered Engine Mount

PA18project

Registered User
Missoula MT
I have not fabricated the engine mount for my experimental project yet but in looking at other projects where people have lowered the engine mount it looks like everyone has built a custom fiberglass/Kevlar/carbon fiber cowling (Wayne Mackey and others). I am not a guy who has any idea how to do much in the way of fiberglass work beyond patching boats so I would like to avoid the pain of making a fiberglass cowling.

The question is whether one can use a standard piper nose bowl and still have a nice cowling constructed roughly the way piper did it while still using the lowered mount. I would like to have the visibility if at all possible but I really do not want to make a fiberglass cowling. Thanks for any input and ideas.
 
Just curious------- Why are you lowering the engine mount? Lowering the mount/engine will reduce prop ground clearance. That doesn't sound like a good idea for a group of pilots who like long props for a lot of good reasons. It also would increase the pitching moments when changing power settings. Which, in turn, would effect increased use of elevator trim. Do you think that the minimal increase in over the nose visibility is worth the negatives?
 
skywagon8a, Can you explain the increase in pitching moment? I know the engineers told Mark Englerth that his thrustline modification would do this. Two people with formal education have told me the same thing but in all the thrustline modified Super Cubs I have flown I have not noticed any pitching moment. Is it from actually lowering the thrustline or the angle of thrust? I am very curious since I have heard this a few times. I wish I could take some aerodynamic and structural classes so I understood a lot more about our airplanes than I do. Thanks.
 
Steve,
I am not an engineer either, however over time I have learned that the relationship of the thrust line to the vertical center of gravity effects the pitching moment. For an extreme example take the Lake amphibian, of which I have owned several and flown a fair amount of experimental flight tests in them, the engine is mounted way above the vertical center of gravity, when power is increased the nose tends to pitch down and when it is reduced the nose tends to pitch up. This is not a problem, just different and must be understood. Most high winged airplanes, such as a Cub, with the engine below the vertical CG will pitch up with the addition of power and visa versa. As for the zero thrustline mount, two things have been changed, the crankshaft/prop has been raised and the angle of the thrust in relation to the center line of the fuselage and stabilizer has changed. The net effect has been, according to what I have read on this site, a reduction in the need to adjust pitch trim with different power settings. If the engine, with a zero thrust engine mount, was mounted so that it's thrust centerline went directly through the vertical CG there theoretically would be no effect on pitch changes with power changes. Note that most serious acrobatic planes have a mid wing or biplane and center mounted engine so that it is able to fly in most any attitude with minimal stick pressure changes.
I have not flown a zero thrustline Cub, but as you have noted there isn't a noticeable pitching moment change. My guess is that Mark Englerth got the formula just right.
Perhaps some of the engineers here can improve upon my explanation?
 
Skywagon, nicely stated. The only change would be to include center of drag, (aerodynamic force, applicable to both steady state and accelerating flight) with center of gravity (inertial force, applicable only to accelerating flight).

As a practical matter though, I'd guess that the vertical locations of center of gravity and center of drag probably aren't very far apart.
 
Guys, Hi. Using the Lake amphib is an example at the extreme. Lowering a Cub firewall forward 2 or 3 inches isn't even close to a Lake.

skywagon, I'll give you that the prop tips are closer to the ground, but with long gear and big tires nowadays, that is a non-issue.

With these birds (any Cubs, some with VG's, some with slats, etc.) able to fly along with the nose so high, and with long gear and big tires,thus a higher angle of attack for slower landings than a stock Cub, a bit more over-the-nose visibility is a good thing.

Which brings us back to the question of using a stock Cub nosebowl. If you use it, consider how much of that stock nosebowl is sticking up above the ring-gear and the top of the cylinders and is in your field of view.

That's a good enough reason to shape a new nosebowl. I did it for that reason.

IMG_1861.JPG
 
Dave---- good answer. My purpose with using the Lake for an example was only to emphasize my answer to Steve's pitching moment question, knowing full well that it is an extreme. Also, PA18project did not say whether or not he was going to use the alterations which you mentioned.
 
skywagon8a,

Good point, I didn't mention the tires and gear. I will be using three inch extended gear and large tires. In fact, right now the thing sits on six inch extended gear but on further reflection, I am going to build up another set which is a little shorter.

I didn't even think about all the dead space with the stock nose bowl. Good point dave.
As for pitching moment, I think that is a good observation. I think in practical use most people are not seeing any real difference on these planes. Wayne Mackey reported no real difference with his Stolquest. Although, if anyone has lowered the mount and found a significant difference in how the plane flies, I would love to hear about it. I do plan on using a relatively long prop on this thing but expect to have more than enough clearance. If my prop ends up in the dirt it will more than likely have everything to do my handling of the airplane anyway :lol:
 
My engine is lowered 4" with built in zero thrust swinging a 90" prop. Absolutely no pitching at different throttle settings.

I can stay in the pattern doing touch and go's without trim change.
 
mount

I fly a stock 150 cub back to back with my SQ2 on a regular basis and Ican't see any difference in pitch when you hit the throttle. Palhal and Ihave the same mount. My plane has not had any adverse affects do toeng. angle or being lowered.  I have more clearance with the prop thana stock cub with 31s.  Useing  84 43 prop.  Wayne
 
Dave Calkins said:
........to shape a new nosebowl. I did it for that reason.

IMG_1861.JPG

you fixed one thing I noticed on the horizontally split(randy's) normal -18 nose bowl.... don't make the split at the center of ring gear, make it above or below so you have room and don't worry about the teeth hiting......
 
Mike, yes, I saw that I could make it much stronger and better fitting by splitting it there. This split nowebowl and top cowl weighs only 3.5 pounds. Carbon fiber.

DAVE
 
palhal

[My engine is lowered 4" with built in zero thrust swinging a 90" prop. Absolutely no pitching at different throttle settings.

I can stay in the pattern doing touch and go's without trim change.]

This is good information. It shows that, in a Cub at least, it is the zero thrust line that improves the pitch characteristics and that moving the engine up or down by as much as 4" makes little or no difference. I wonder if lowering the engine 4" effects any of the other flight characteristics?
 
Digging up an old post for a new project. Dave do you happen to still have the mold for the nose bowl on the 12?
DENNY
 
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