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Convert a 6A F/P to Constant Speed

Chet66CR

I'm New Here
after 15 years of flying Im thinking about installing an MT constant speed. Been flying an O360A1A and wood F/P. Im concerned about modifying my cowling. Seems that when I purchased my 6A kit years ago I had to specify a short cowl or long cowl to accommodate my F/P prop. I have the correct engine and the original plumbing that came with it. Any thoughts about the cowl modifications?
 
First thing to do would be confirm which cowl you have (unless you are already certain).

If you have the longer fixed pitch prop cowl, your prop spacer will be 4" thick. If you have the shorter constant speed cowl, your spacer will be 2 1/4" thick.
 
I just went the other way

Just to back up what Scott said, I have had two different Hartzell C/S props on the RV-6A (one blended airfoil and one not). I aligned the original cowl installation with the non-constant speed Hartzell and when I switched to the B/A Hartzell the alignment was perfect. When I just completed the switch to a Catto F/P prop, Sam Tillman shipped me a 2.25" Saber prop extension and again the alignment and spacing was perfect.

Bob Axsom
 
Out of curiosity Bob, why did you switch from the Blended Airfoil to a Cato FP prop, was it a weight or a speed difference?

Cheers
 
How about Phase I?

I will ask the question, because I have been asked the question. If a flying RV with a two-blade constant speed prop gets fitted with a two-blade or three-blade constant speed prop of a different manufacturer, is it necessary to reenter Phase I? Or, is it necessary when going from two-blade to three-blade constant speed, from the same manufacturer.

And to address the situation in this thread, does going from fixed pitch to CS require a new Phase I?
 
I will ask the question, because I have been asked the question. If a flying RV with a two-blade constant speed prop gets fitted with a two-blade or three-blade constant speed prop of a different manufacturer, is it necessary to reenter Phase I? Or, is it necessary when going from two-blade to three-blade constant speed, from the same manufacturer.

And to address the situation in this thread, does going from fixed pitch to CS require a new Phase I?

This is such a gray area, that it is difficult to comment on.

I checked with the Charlotte FSDO, when I lived up there, and said that as long as I stayed with the same type of prop from the same manufacture, I didn't need to put it back in to Phase 1. However, if I changed from FP to CS, then I need to go into Phase 1 for five hours.

Five hours isn't a long time and should you change from one type to another, then you probably want to test it and make sure you have no oil leaks.

Going from a two bladed CS prop to a three bladed CS prop will depend on your operating limitations and your FSDO.

A lot depends on your FSDO. Some of the FSDO's are going after people for hanging external cameras on their airplanes and not putting the aircraft back into Phase 1 to document that the camera does not create undue control issues.

Due to the new requirement to renew N-numbers, the FAA is finding out how few airplanes are actually flying and they must be struggling to justify their staffing levels.
 
Speed

Out of curiosity Bob, why did you switch from the Blended Airfoil to a Cato FP prop, was it a weight or a speed difference?

Cheers

I made the change in a desperate attempt to beat Jeff Barnes in SARL Cross Country Air Racing for the Experimental Gold National Championship. it was a completely wishful fast response attempt not supported by first hand performance data. It did not work - I lost by the largest margin that I have in years. After the race at Jasper, TX I flew my formal top speed test and found that the plane was 4.4 kts slower than the Hartzell with F7496 blended airfoil blades (faster than the F7497 blades being installed on RVs today). The fixed pitch prop is a beautiful piece of work specially designed and manufactured for my airplane. We now have a sound basis for systematic development but I am going out to the airport today to back convert to the Hartzell for the last three races of the season. Then, we will start the long and expensive process of future development. Nobody said it was going to be easy but I had high hopes.

Bob Axsom
 
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Prop

The only way the fixed pitch will work in a racing environment it for the pitch to be such that the r/m will be 3000/3100 rpm at full throttle.
The Formula One racers turn 4000 r/m plus which works for them because of the relatively small diameter props.
 
We were trying for something like that ...

The only way the fixed pitch will work in a racing environment it for the pitch to be such that the r/m will be 3000/3100 rpm at full throttle.
The Formula One racers turn 4000 r/m plus which works for them because of the relatively small diameter props.

I think that is right. I first coordinated with Hartzell and they said they could not go along with operating their prop over 2700 rpm and they felt a fixed pitch prop with a closed and well faired root operating at higher RPM was the way I would have to go. So, I think we are all in agreement but the first cut at a suitable racing prop was such that even at the low altitude of the race at Jasper last Saturday I could only gat a maximum of 2720 rpm at 700 ft MSL. When I did my standard speed test at 6000 Dalt the next day the RPM max was 2660-2670 rpm so it appears to be a little too much of a load on my particular engine with my airframe. We will pursue this further after the race season is over and I think we will be able to come up with a custom prop optimized for speed on my airplane. I am part way through the conversion back to the C/S prop for the time being.

Bob Acsom
 
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