Prop/Engine harmonics

[Darin Watson]

I am new to the "RV club", as well as the experimental aircraft world, however, i have been enjoying every minute in the RV7. My plane has an O-320 and the recommended Hartzell C/S prop.

I have one nagging concern with the engine/prop combination; that being that the engine has 9:1 pistons in it. As most of my flying was either behind Lycomings with fixed props or Continentals with six cylinders, I was not aware that some certified aircraft with 4 cyl Lyc and C/S props had operating limits in the 2100-2350rpm range, and as such caused me to research in much greater detail the specifics of my setup.

Sorry for the long post but my question is this...has anyone out there run a similar combination? If so, how long and what have you found?

Both ECi and Hartzell tell me this is not a certified installation. And that torsional stresses are mostly related to CR and not displacement.

Thanks, Darin

[Geico266]

Welcome to VAF!

A knowledgeable person will be along shortly.

[Finley Atherton]

Hi Darin,

I don't think you will be able to get the definitive answer to your question. The only way you would know for sure is if Hartzell tests your specific prop/engine combination including compression ratio, ignition type, ignition timing, exhaust system and fuel system type.

I also have a 0-320 with 9:1 pistons and a Hartzell prop and have had no problems over 340 hrs and never give the issue a second thought.

I purchased my engine from Aerosport Power who have an excellent reputation and are considered very knowledgeable regarding standard and modified engines. In response to my questions regarding 9:1 pistons with the Hartzell prop they replied; "They are not approved but it is our experience that they have been used successfully on many O-320's with the Hartzell Propeller" and "We do not know of any restrictions with the Hartzell Prop".

If you are still concerned and want to keep the Hartzell then you could always consider replacing with standard 8.5:1 pistons. If I was starting again I think i would have gone with the 8.5:1 pistons. I think there is likely to be little benefit from the higher compression pistons as any power increase is likely to be cancelled out by the required retarding of the timing by 5 degrees from standard.

Fin
9A

[Darin Watson]

Thanks Fin...I really don't want to change pistons as previous owner just finished cylinder replacements to deal with the ECi AD and rings/cyl are nicely run in with about 40hrs on them.

[Ifly1,2]

Darin,

I have a 6A with an o-360 and a constant speed prop. I have the restriction that you are referring to. I can't say that I have heard of this with the 320 engine.
Also, I think the idea is to avoid continuous ops in this range.

Regards,

John Thach
___________________

RV-6A Flying
180 h/p constant speed

[Darin Watson]

Any further insight out there?