I have a hangar 9 super cub, and when it tells me to mark on the fuselage where its supposed to for my g26, the engine is more on the right hand side if I were to face the fuselage, and when I arrange my zenoah, its more on one side of the firewall, Should I follow by what the book says? or center the engine right in middle of the firewall and ignore that offset?

common a quick reply would be nice..... im sure other 1/4 --> guys know what it means to have an engine offset.


When I do per manual, the g26 is more to one side of the firewall, is this correct? I dont want to mount it yet till someone assures me its okay.

Since the firewall is offset with a bias to the right side (not sure of the number of degrees) if you mount the engine centered it will not stick out thru the center of the cowl.

Ed M.

Oh, BTW, when using right and left do it from the viewpoint that you would have if you were setting in the pilots seat.

Ed M.

hey bent, your the best thanks bud, ima go drill them holes

Follow what the book says!!!... the offset is to compensate for the usual right thrust so that the Propeller shaft ends up in the middle of the cowel... In other words the engine is angled 2 or 3 degrees to the right (right thrust) and so you move the engine mount slightly to the left to keep the prop shaft centered?
Hope I did not confuse you. ( Right and left refer to the airplanes right and left as you face the same direction as the airplane.)

You do understand why right engine thrust is built into the engine mounting??

Let's speak in terms as if you are sitting in the cockpit looking forward.....to help keep right and left correct.

The firewall of most planes will have a little bit of RIGHT thrust built in. What this means is that the firewall is angled to the right. We do this because of the forces that the engine creates causes the airplane to want to pull to the left if mounted to a firewall with no right thrust.

Now, because of the thrust angle built into the firewall, if you mount the engine in the center it will not exit the cowl (in reallity, you want to be centered to the centerline of the fuse) in the center. The angle of the firewall tilts the engine to the right and therfore has to be moved to the left to get the prop washer back to center.

Look at the picture... In the drawings of the planes, the one on the left is incorrect because the engine is centered on the firewall, the one on the right is correct because it is offset to the left which centers the prop shaft on the centerline where it exits the cowl.


Hope this helps

yeah i know why its there because of torque, i think. Now im having a dilemma to where to get it centered horizontally.... yikes!

I tried to be the first to answer, but I was busy drawing the CRUDE picture

Captain232, it may be crude, but it sure does make the point.

crashergs, if you don't have the rudder mounted yet, stand it on its tail end and get somebody to hold it steady while vertical. Place the engine & mount on the firewall. Slide the cowl over the engine and move the engine around till the prop shaft is centered in the cowl opening. Now slide the cowl off and make some marks so you can drill the holes you need in the firewall.

Ed M.

I highly appreciate everyones replies... if it wasnt for you id still be bummed in my room not working on my plane, you guys are good

If you're into trig... the amount of engine offset from the vertical centerline of the firewall is ....

offset = distance from the firewall to the back of the prop x tan (degrees of firewall right offset)

example:

with 3 degrees of firewall right offset and the distance from firewall to back of the prop being 6 inches

0.314 inches = 6 inches x tan(3 degrees) or (0.0525077)

5/16 " is very close to 0.314 inches ... so offset the engine 5/16 of an inch to the right of vertical centerline looking at firewall from the nose of the plane.

Hope this helps...

Larry

I have the same question, because they(hanger 9) only want the offset on on the g26 motor not on the glow motor???? Same thing on the taylorcraft I asked the tech line ,because I put a rcs 140 in the taylorcraft unable to get a anwser from them I set it up like the g 26 motor,because it was inverted,where the glow was on the side????????

John

If the firewall has a right offset... the engine must be offset to the right side (looking from the front) irrespective of engine mounting position or type of engine ... or the cowl won't line up perfectly...

However, the cowl can usually be moved around a little to accomodate a non offset engine... although lots of larger scale planes 25% and upwards have the offset built into the cowl... so the engine MUST be offset.

Larry