Thrustline centered in cowl?
 

The plane has a built-in 2 degree firewall offset/angle to the right. If I center the engine on the firewall the engines thrust plate will not be centered at the front of the cowl. Theoretically it should be 2 degrees off center.

My question; is it ok to off-set the engine on the firewall to make the thrust plate centered in the cowl? This would slightly change the balance along the longitudinal axis but probably not very much.

Any opinions? Thanks.

PS; plane is a 26% CA Extra 330 with a DA 50.

RE: Thrustline centered in cowl?
 

Surf...I center my engine on my planes in the following manner. I take a "Step Ladder," and I place my airplane in a vertical position with the landing gear resting on the top of the ladder. I then place my engine on the firewall, and slip the cowl in the position, and move the engine around until I have the engine centered with the cowl. When it's centered I gently remove the cowl, without disturbing the position of the engine. Mark you holes for the bolts, and there you have it. Remember......when you shift the engine a little off center, The engine is still mostly centered because the crankshaft is in the proper alignment with the firewall and cowl. Your plane will never know the difference.

RE: Thrustline centered in cowl?
 

Bob,
Thanks. I just kinda did something similar. I can't put the cowl on because I need to cut it out for the cylinder head. What I did was tape a ruler down the center line and set the fus. vertically. Then I set the engine on the firewall and eyeballed the position laterally. I'm ok side to side, and the horizontal plane shouldn't change.

So it doesn't really matter the minor sideways offset. Thanks, Dan

RE: Thrustline centered in cowl?
 

using a drafting triangle and a ruler - this all gets easy---
measure distance of spinner backplate to engine mounting plate (sometimes called firewall)
say it is 6"-
make a little 3" square plate of wood with a 6" long pointer exactly centered centered in it and perfectly vertical to the plate.
tape this to the firewall - add the cowl --then - using the ruler to check cowl lip-- get the pointer centered .
move the plate around and tape it as needed.
remove the cowl n mark the engine mounting plate to match the wood plate .
OR
You can use a sheetmetal layout protractor - and draw in various thrust angles to see how much mounting offset is needed -
When I am laying out a new design - I use the protractor . this gives firewall angle - engine offset etc..
for most jobs -- the little wood block works fine .

RE: Thrustline centered in cowl?
 

What Bob Laine said only I mount the engine before I put the rudder on that way I can set the plane on its tail tape it to my bench and do what you said. :D
Larry

I am watching you

RE: Thrustline centered in cowl?
 

I use this offset calculator: http://www.lcrcc.net/offset_calc.htm

RE: Thrustline centered in cowl?
 

Tail Strike....I do it the same way. Don't get any easier that that.

RE: Thrustline centered in cowl?
 

forget the offset its an old wives tale. or just offset the rudder if you think its necessary.
geez

RE: Thrustline centered in cowl?
 

I hope your kidding. Engine thrust is not a wives tale.

I do it like this:
Figure out how long the engine will be from the firewall too the drive hub. Let's say 6.5"

Now, draw 2 parrallel lines on a sheet of paper 6.5" apart. One line on top of paper--one line on bottom.

Now draw a CL mark 90 degrees to the parrallel lines. You basically got an I-beam shape now.

Use a protractor on the 90 degree mark. Put the protractor on the bottom line and line it up with the 90 degree mark.

Now find the 2 or 3 degree mark on the protractor and put a mark on the top line.

The distance between the 90 degree mark and your 3 degree mark is how much you need to offset your engine.

Crude paint image attached:

RE: Thrustline centered in cowl?
 

Rcpilet, I know what you are saying but I was to lazy to figure out the trig. involved. I used a method similar to what Dick mentioned and it worked good.

I agree that offset is not a wives tale! Thanks all.

RE: Thrustline centered in cowl?
 

$12 calculator, 2nd function, tan, enter thrust angle X distance from spinner face to firewall = offset distance. Thought you would never need that 8th grade math huh?

RE: Thrustline centered in cowl?
 

A sheetmetal layout protractor is cheaper than a decent calculator --and a lot more accurate --in that you see the angle - rather than input (and get output) of incorrect numbers
Basically-it is a protractor with a long arm and the sheetmetal guys use em to layout and scribe lines for bending metal ' excellent model tool as it lets you accurately look at any angle .

RE: Thrustline centered in cowl?
 

Dick,

I am mentally challanged when it comes to using the sheet metal protracter, the one I have the square portion extends below the protractor. This for some reason causes a lack of visualation of how to properly lay out dimensions. It is much simpler for me to take the tangent of the desired angle times the distance from the prop hub to the fire wall. take this dimension and transfer it using dial calipers to the fire wall. If needed I can draw this out on paper. I guess each to his (her) own.

RE: Thrustline centered in cowl?
 

I think what excaliber meant was that you can use a throttle to rudder mix instead.

Chip Hyde, is the most renowned advocate of this methode instead of offsetting the engine.

RE: Thrustline centered in cowl?
 

I use mine -- sometimes by simply drawing a squared T on my table top (glass)- then noting prop to mount distance on the vertical leg of the T.
The layout tool -set to degrees noted as offset- (pointing to spinner c/l)--will then easily show what the offset mounting distance is from C/L .

RE: Thrustline centered in cowl?
 

I still contend that there is no simpler way to center the engine thrust line with the cowl, than by doing it the manner described in "post # 1. Nothing to measure anywhere......just use your eyeball.

RE: Thrustline centered in cowl?
 

RCpilot, don't confuse THRUST with TORQUE or P-FACTOR
I still set my planes up, (aerobatic) at Zero degrees on the engine aas well as the wings, horizontal and rudder.
And some of the hotshot pilots that flown my planes have not noticed the difference.
I'm not trying to convert anyonebut it works for me, in patern or IMAC