Prop question

[rwarre]

I have a sensenich prop on my RV7a which has a redline of 2600 rpm. Since my Lycoming o320 is rated at 2750 for maximum horsepower, could I use the carbon fiber prop and get the horsepower?

[dan carley]

I've been using a catto 3 bladed prop on my rv4 red line 2700 rpm. very happy with it.

dan carley

[SMRacer]

So your peak HP is at 2750.

Are you guys really running your Lycoming 320 (360) at peak HP RPM for a typical cruise? And therefore is it really advantageous to have a prop pitched to make peak HP RPM?

Jim
N444JT

[rwarre]

Since I live at a higher elevation I would like to have the climb power.

[rvbuilder2002]

Originally Posted by rwarre

Since I live at a higher elevation I would like to have the climb power.

Not a lot of specific replys to your post so far... might be because people are unsure what you are after... I am a bit.

First off, standard red line RPM for non-helicopter O-320's is 2700 RPM (not 2750)

You say you want good climb power because of operation at higher elevations.

With a fixed pitch prop, if you choose a pitch that will allow you to get anywhere near rated RPM in climb, you will be reducing your cruise performance a lot (you will have to throttle back a lot to keep from exceeding RPM red-line).

What it sounds like you are asking for, is the main reason that constant speed propellers exist.

You do have a little bit of adjustment range with a fixed pitch prop. You can select a slightly lower pitch to get a bit more RPM for climb. This prop will suffer slightly at lower altitudes (1000 - 6000 ft), but would be a good cruise prop at higher altitudes (above 6000) because it would allow you to turn high RPM's even though the manifold pressure is low (but you need to be willing to turn 2600-2700 RPM in cruise.... not everyone is).
The O-320 Sensenich prop is at a bit of a disadvantage compared to most fixed pitch props because the 2600 RPM limit prevents you from cruising between 2600-2700) but for general operation it is not an issue (in the context of your question anyway) because you would never want to have it pitched so that you could get close to that RPM in climb anyway.

[Neal@F14]

Originally Posted by rwarre

I have a sensenich prop on my RV7a which has a redline of 2600 rpm. Since my Lycoming o320 is rated at 2750 for maximum horsepower, could I use the carbon fiber prop and get the horsepower?

The Sensenich carbon fiber ground adjustable prop for the 320 Lyc can be happily run at its 2700 rpm redline all day long, but not faster than 2700. You'll be burning a fair amount of fuel doing that, though. The install manual for it is downloadable from the Sensenich website and has good info in it.

[rwarre]

Thanks for the good information, that answers a lot of my questions. I would still like to get feedback on the advantage of going with the catto prop. I have read a couple of posts of guys that have catto props, but not sure that I want to switch just to be able to get 2700 rpm.

[rv7charlie]

Something that a lot of pilots don't seem to realize is that if you're flying up at '75% altitude' (7500-8500 feet msl, depending on who you ask and the phase of the moon), you don't get 75% power unless you're turning at the rated full power rpm and full throttle.

Yes, this is a rough number (and only applies to normally aspirated engines), but it's pretty close to reality. Most (including me) are happy to fly at less than 2700 rpm, but we shouldn't kid ourselves that we're getting 75% power while doing it (unless we're at a significantly lower, less efficient altitude).

Charlie

[jrs14855]

Originally Posted by Neal@F14

The Sensenich carbon fiber ground adjustable prop for the 320 Lyc can be happily run at its 2700 rpm redline all day long, but not faster than 2700. You'll be burning a fair amount of fuel doing that, though. The install manual for it is downloadable from the Sensenich website and has good info in it.

O 360 Parallel valve in Pitts, 2700 rpm above 10k, 6.5 gallons hour. Its all about manifold pressure, r/m is only part of the equation. 3500 r/m above 10k altitude would still be less than 75%.
The parallel valve 360 in aerobatics has an impeccable track record of surviving at very high r/m.(up to 3500) The later 320's are similar and will survive just as well.

[PerfTech]

Originally Posted by rv7charlie

Something that a lot of pilots don't seem to realize is that if you're flying up at '75% altitude' (7500-8500 feet msl, depending on who you ask and the phase of the moon), you don't get 75% power unless you're turning at the rated full power rpm and full throttle.

Yes, this is a rough number (and only applies to normally aspirated engines), but it's pretty close to reality. Most (including me) are happy to fly at less than 2700 rpm, but we shouldn't kid ourselves that we're getting 75% power while doing it (unless we're at a significantly lower, less efficient altitude).

Charlie

... This is correct and very important to your overall performance. Catto is without a doubt one of the worlds foremost authorities on propeller design. I think the best advise would be to give him a call and see what he has to say. I don't think he has any unhappy customers, with the possible exception of some that think he needs to work 28 hour days. He will steer you right. Thanks, Allan...