Wood Prop question

jtppalmer050390 · #1 10-06-2016, 12:13 PM

Hey wood prop guys,

I have an RV7A with a wood prop. Did all my weight and balance numbers and I am within weight and balance with one pilot, 3 gallons of fuel and 100 pounds of luggage in the back. With that being said, when I have less than 10 gallons of fuel and two people flying, I can tell I am aft heavy. It may fall within W&B limits but I know I am way aft heavy. As a matter of a fact, when the passenger steps on the step, many times the front wheel will lift off the ground. Anyway, I just ordered a 20 pound crush plate to install. I anticipate this is going to improve many characteristics of the plane especially the aft heavy issue. Anybody else done this? Any comments? Also I have noticed that in straight and level flight, the elevator is ever so slightly down deflected and I anticipate this correcting that too.

Beancounter · #2 10-06-2016, 02:21 PM

Tommy
An option to losing 20lbs of useful load could be to add spacers between your engine mount and the firewall.Try re running your weight and balance with this shift in your engine position, it may not take much. There may be side effects of this repositioning like changes to the baffles and a custom length prop spacer. Alternatively, I believe the RV9 uses a longer engine mount to adjust the W&B for typically lighter engine/prop combinations.

lr172 · #3 10-07-2016, 08:13 AM

I have a 320 with a catto and struggle with aft CG issues. I have a 19# crush plate and it helps a lot. They can be finicky to get installed with good balance. It just takes trial and error attempts. In addition to the WB help, it also smooths out the engine and allows lower idle RPM due to the extra rotating mass.

Larry

jtppalmer050390 · #4 10-10-2016, 08:51 AM

Quote:

Originally Posted by lr172

I have a 320 with a catto and struggle with aft CG issues. I have a 19# crush plate and it helps a lot. They can be finicky to get installed with good balance. It just takes trial and error attempts. In addition to the WB help, it also smooths out the engine and allows lower idle RPM due to the extra rotating mass.

Larry

Larry,

I got the 20# plate and installed it. Really changes the flying characteristics of the plane. I mean really changes it!!! Also, I did have to loosen and retighten the plate due to it being out of balance. Amazing that a mm can make a huge difference. Trial and error was the only way I got it balanced.

Raymo · #5 10-10-2016, 09:24 AM

I will be installing a Catto 3 blade w NLE and planning to install either a 15 or 20 lb plate for the same reason. You'll find that many others have done the same if you search the forum for Saber.

jtppalmer050390 · #6 11-14-2016, 11:03 AM

Follow up after 20# crush plate installation. After the extra weight up front, I am climbing out faster and my cruising speed in straight and level flight has increased by 10 MPH. The plane also seems to be much smoother in flight. I guess the increased speed is due to the angle of attack of the wings, horizontal stabilizer and elevator position in straight and level flight. Plane also flies much much different. Very glad I added the weight even though balancing it is difficult.

judoka5051 · #7 11-14-2016, 12:12 PM

I was going to recommend moving things forward to avoid adding weight. The easiest thing is the ELT with a remote 'shorty' antenna on the back of the seat. You can move it way up front, almost to the firewall.

lr172 · #8 11-14-2016, 10:12 PM

Quote:

Originally Posted by jtppalmer050390

Follow up after 20# crush plate installation. After the extra weight up front, I am climbing out faster and my cruising speed in straight and level flight has increased by 10 MPH. The plane also seems to be much smoother in flight. I guess the increased speed is due to the angle of attack of the wings, horizontal stabilizer and elevator position in straight and level flight. Plane also flies much much different. Very glad I added the weight even though balancing it is difficult.

That seems like a lot of speed increase. Maybe you had an issues with the incidence angle on the tail. Unless you found a hidden speed mod

Larry

Neal@F14 · #9 11-15-2016, 06:22 AM

Quote:

Originally Posted by lr172

That seems like a lot of speed increase. Maybe you had an issues with the incidence angle on the tail. Unless you found a hidden speed mod

Larry

I found the opposite effect on my RV6. With all my camping gear loaded in the back and the cg hitting the aft limits when the fuel tanks get close to empty, it gains almost 5 MPH. I'd always surmised that the tail was having to do less work to hold level flight and the lower induced drag from that was responsible for the extra speed.

rv7charlie · #10 11-15-2016, 08:53 AM

I'd have to agree with Larry. If a plane is set up correctly, as cg moves aft the tail has to use less down force, and speed goes up due to less drag. Only way a speed increase with cg moving forward makes sense, is if the cg was so far aft the tail was *lifting* prior to the cg move. That would be *very* unstable.