[kentb]

I have searched the forum, but was unable to find the information or maybe it was there but I didn't understand it.

I have a RV9A with an IO-320-D1A, CS.

I understand how to compute the percentage power and my engine monitor (AFS 2500) computes it and shows it.
The Lycoming Key Reprints says that you can operate over-square, but you need to follow the plane manufactures approved settings to do this.

I am the manufacture and I don't know what to approve!

The Key Reprints also show and example for a C 177/IO-360-C with over-square example.

How do I determine what is safe and acceptable operation. The engine runs quieter at lower RPM settings, but if I want a certain power setting I will need to increase MAP to get it.

Any help figuring this out would be appreciated.

Kent

 

[RV6_flyer]

Over square operation O-320

Kent:

I sent you an old 1961 Lycoming Curve No. 10156 in PDF format to your private email address. It is for the 150 HP 320 but is typical on what the limiting manifold pressure should be for continuous operation.

You should have graph's in the back of your Lycoming Owner's Manual.

If you do not have a Lycoming Owner's Manual, you should be able to purchase one form Lycoming for about $20.
http://www.lycoming.textron.com/sup...enancePublications/serviceLetters/SL114AM.pdf

I now have 1,977 hobbs hours on my RV-6, O-320, Hartzell. I like to run over square. See article that I sent to your private email. My personal limit is to avoid more than 3 inches over square for continous operation. I do not worry about a temporary over squre of 6 inches. My SOP is to push the prop in to HIGH RPM on short final. I do GUMP twice in the pattern. Once on downwind then again wings level on final.

I have an old 1961 11 X 17 copy of Curve No. 9541-C for the 150 HP 320 that has more info than the chart I emailed. I can scan / send it if you like.

Hope this helps.

 

[Bryan Wood]

oversquare

Kent,

Good question and I'm looking forward to the answer also on the oversquare issue. With no hard data to quote or forward to you I've been going off of information that I think came from Bart Lalonde. At one time I asked him at what altitude I could safely run full throttle without hurting the engine by leaning it to ambitiously. Also asked him at what altitude I could run full throttle and set the prop to 23 as an example. While not pinning this on Bart since it has been such a long time ago and I'm not positive that it came from him, I've been going with a 6" spread between manifold pressure and rpm/100 as being okay. Not wanting to run the engine with internal pressures this high I've cut it to a spread of 3 for my actual use. On the 0-320 you'll find that running 26" and 2300rpm is very close to 75% power. You can get this at 5500' which just happens to be what I'm thinking Bart suggested. You might get just over 26" which can be compensated by going down slightly on rpm if you want to be more regimented. Basically if you had a fixed pitch prop you would be running a differential of 7 on a sea level takeoff with 30" and around 2300rpm on climbout. The engine can take it, but doing this in the air continuous scares me, thus my own rule of 3. At 6500' and above I never even think about it anymore. The throttle is shoved forward and the prop is set to 2300. Unless flying with one of those big motored cheater RV's I never turn the prop fast any more except on takeoff. FWIT, when flying with one of those big cheater engines you can't run your prop fast enough to fix the problem anyway.

Anxiously awaiting offical data on this too,

 

[Bryan Wood]

Gary,

I appears that you and I were typing at the same time and we kind of said the same thing only yours was backed by data. Could you please send it to me also via e-mail?

Thanks,

 

[RV6_flyer]

Gary,

I appears that you and I were typing at the same time and we kind of said the same thing only yours was backed by data. Could you please send it to me also via e-mail?

Thanks,

Bryan:

I looked your email address up on SoCAL and sent it to you after I saw your post but before I saw your request. Since you have DSL, I saw no problem sending you all three documents.