Distance from firewall to prop flange

[whee]

Anyone know what the distance from the firewall to the prop flange is? I'm getting read to build my engine mount but I do not have the wings mounted yet so I don't have my exact datum location.

[Battson]

Is it always constant, no matter what engine and mount you are using?

[whee]

Yes, at least for the O540 and O360.

[Gavin Chester]

Prop flange to firewall on the trust line is 42"

[whee]

Thanks Gavin.

[S Lathrop]

Gavin;

I just blocked the engine up in front of my fuselage. I have not done anything like final measurements to locate the engine or fuselage, yet.

How did you arrive at 42" forward the firewall? I came up with something close to 34" but I have not checked that number as carefully as I want.

I did not get anything close to 42" forward of the firewall. Also where are you measuring that distance from. The firewall is at an angle to the thrust line of the engine, 6 degrees.

In the Beartracks , April 2000, Bob mentions that he placed the O 540 back 2" or 56.5 inches forward of the leading edge of the wing. 58.5 is the standard distance for 4 cylinder engines.

[whee]

In a later bear tracks Bob recommends going back to 58.5" for both the O540 and O360.

I scaled it on the drawing and came up with ~40" from the firewall but that's not accurate enough. Also, the O540 is like 37" long so 42" would seem about right.

[Gavin Chester]

42" is correct and it is measured on the trust line which happens to be the under line under Lycoming on the angle valve covers. I have the factory engine mount and it worked out to 58.75" from leading edge to engine prop flange on-my plane. I have a IO-540 here and it is 40" from flange to oil filter

[Battson]

I scaled it on the drawing and came up with ~40" from the firewall but that's not accurate enough. Also, the O540 is like 37" long so 42" would seem about right.

I would have guessed there was more room than 5" between the -540 and the firewall? Just off-hand guessing.

As you say, there was once a suggested change to move the -540's aft 2", but completed aircraft proved that to be unnecessary and in fact I would say detrimental to the useful CG range. The observant BH-spotters would have noticed the nose on Bob's -540 machine is noticeably shorter than most of the kitset builds which use the longer mount.

Does the firewall sit exactly parallel to the prop flange, or does it matter where on the firewall you measure from?

[S Lathrop]

I did make a mistake on my first calculation. But below is how I calculate the location of the prop flange:

First, I am using station A as the reference point on the fuselage. The wing mounts at station O which is 33" from station A. That is a horizontal distance. My wing, is 13.273" from the leading edge to the center of the mounting. That gives 19.73" from station A to the leading edge of the wing. The tube at station A is 3/4 dia. so the that tube to the prop flange is 38.395 using 58.5 for the distance from prop flange to the leading edge of the wing. The thrust line is 16.5 inches above station A and laid back at a 6 degree angle thus the firewall to the prop flange will be 40.1" inches.

So my number agrees with whee's calculations.