Engine thrust line

Beancounter · #1 11-01-2008, 11:19 AM

What is the better method of aligning the engine thrust line. Does one shim the dyna mounts or the firewall mounts.

David-aviator · #2 11-01-2008, 11:36 AM

Quote:

Originally Posted by Beancounter

What is the better method of aligning the engine thrust line. Does one shim the dyna mounts or the firewall mounts.

Not necessary to do either. The off set is designed into the engine and mount.

I just hung the Lycoming and noticed the mount bolts took 3 washers on the right side but just one on the left. The engine is off set to the right.

Beancounter · #3 11-01-2008, 12:02 PM

David I should have been more specific. My engine is pointed about a 4 degrees down on the vertical plane as compared to the longerons. I have read that for the plane to be most efficient they should be in the same vertical plane.

L.Adamson · #4 11-01-2008, 12:10 PM

Quote:

Originally Posted by Beancounter

David I should have been more specific. My engine is pointed about a 4 degrees down on the vertical plane as compared to the longerons. I have read that for the plane to be most efficient they should be in the same vertical plane.

I'd double check again, because my 6's engine has the downward offset, and so does the cowl to fit it. In fact, a whole lot of aircraft have the engines slanted downward, as well as many R/C models that I built. I'm sure that Van's engine mount is taking all this into account.

L.Adamson --- RV6A

pierre smith · #5 11-01-2008, 12:45 PM

.....as it comes from Van's. Don't shim it up or to the left. Just mount it. As has been said, it's supposed to have down and right thrust.

Regards,

Beancounter · #6 11-01-2008, 12:58 PM

Thanks for the suggestions guys. Does anybody shim their engines back up when they sag. Just being cautious before I make the final cut on fitting my cowling.

L.Adamson · #7 11-01-2008, 01:59 PM

Quote:

Originally Posted by Beancounter

Thanks for the suggestions guys. Does anybody shim their engines back up when they sag. Just being cautious before I make the final cut on fitting my cowling.

I adjusted my cowl, so that the spinner is towards the top for any eventual engine sag. The engine has been on the mount for four years, but only 25 hrs. of use (which is in the last 1 1/2 month). So far, it hasn't sagged at all. But lower firewall mount -- washers can also be installed to make up for sag, if required later.

L.Adamson --- RV6A

az_gila · #8 11-01-2008, 03:44 PM

Quote:

Originally Posted by Beancounter

Thanks for the suggestions guys. Does anybody shim their engines back up when they sag. Just being cautious before I make the final cut on fitting my cowling.

...and the correct washers to use are Lord part numbers J2218-6 (about 1/8 thick) and J2218-61 (about 1/16 thick). AN970's will also work, but their diameter is a little smaller.

However, build it now and worry about shimming later only if it sags....

Steve Sampson · #9 11-01-2008, 03:51 PM

I am pretty sure the thrust line is meant to be down, compared with the horizontal (canopy rails on the RV) on most aircraft.

The reason I understand, though I dont know where I got it from, is so that when you put power in it reduces the pitch up. In other words it stays close to trim over a wider power range that way.

Not 100% sure of that but close.

Andy_RR · #10 11-01-2008, 04:17 PM

I can kind of half buy the pitch trim theory for downthrust, but why do we need right-thrust too? I don't believe torque reaction makes any engineering sense either.

I'm guessing it's because the stagnation point of front of the aircraft is actually below the propellor axis and both angles are there to correct for the unequal angles of attack of the propellor blades caused by the consequent assymetric flow.