Constant Speed Prop vs. Controllable Pitch

[rv6ejguy]

I think several people have posted that max speed was not achieved at 2700rpm with their prop combos and I know this to be a fact from other friends with RVs and C/S Hartzells. Prop efficiency is almost certainly lower at higher rpm. The question is, is prop efficiency at the lower rpm and likely lower hp, overall faster or slower? Only a dyno comparison, exact flight testing and some math could prove this for a given engine, airframe, prop configuration.

Although apples to oranges, I can vary blade twist but not full blade pitch with my IVO. You can certainly get outside the two ends of the efficiency ranges. Low twist and you make lots of noise and go slow with lots of rpm, too much and you go slow and can hear the cavitation and vibration that goes with it.

The sweet spot for best cruise is at 2045-2090 prop rpm for my combo. IVO had originally told me to gear for 2000-2200 in cruise. The MTs on alternate engines seem to be quite good in the 1900-2250 rpm range. Obviously this varies with speed but I agree with Bob that the Hartzell may not be best for cleaned up RVs. It is designed for standard airframes and engines.

More flight testing please. We already have lots of conjecture here.

[Bryan Wood]

Originally Posted by Bob Axsom

. I would secretly like to ease the throttle and prop full forward and out run every RV in the sky - period. When I fly, I want to be going somewhere, fast!

Bob Axsom

Bob,

These could be the best two sentences that have ever been posted on these groups! Surely there are a lot of others that have those same kinds of daydreams who will likely get a kick out of your post too.

As for the friend I told you about originally... His prop just happened to be set up for his Lancair 320, hence a Lyc 0-320 under the cowl. My 9a, 0-320 under the hood also. He offered to let me come to his hanger and install his prop to try on my plane about a year ago. He suggested that we go up and collect some data with my prop and then do the same with his. Since I didn't have the intestinal fortitude to let Sullivan bend on my brand new Hartzell I didn't waste his time. Now I kind of wish that I had just to have some real info to share. At this point George is sounding like the little voice in the back of my mind that kept me from doing it, only George is giving reasons. My little voice was ignorant but pushy.

Giving this a little more thought I came up with another idea that you might look into. There is a man named Earl Hibler who races a Glassair fixed gear taildragger and he is sponsored by Sullivan. I met and flew with Earl many years ago while we were trying to figure out a couple of problems with autopilots in airplanes he was working with. He is an A&P, and an AI who is current and active in the field. He is good at what he does and he is very much like you. Simply, he likes to go fast. Why don't you call Sullivan again and ask for Earls number at his place of business. Tell him what you want and see if his experience with the prop mods are for you. He certainly has the resume to lead you in the right direction. Keep us posted on what you find.

Best,

[Bob Axsom]

Today was the EAA Chapter 732 meeting and I had the opportunity to ask Cris Ferguson about Sulivan Propeller at Hayward and his reported Reno Biplane class work. He confirmed the fact and the quality of the work. He said that Brian Sullivan and his wife run the company but they have an expert that works the magic on the props. He also told me that they got Jeff Lo's biplane over 300 MPH at Reno this year with a Catto prop on one of the straight aways. They are seriously considering an attack on the world speed record for biplanes (in the 330 range) that has stood for approximately 70 years.

Bob Axsom

[neily]

constant speeding propellers keep the engine at pre set speed,which determines the power used according to the power curve of the engine. set at the speed of maximum horsepower,the prop will keep the engine under maxload at that horsepower thus maximising performance.set at another speed it will keep it at that particular horsepower at that rev speed.this could be 75 % cruise/75% power which could be 5% different in revs. why ever be without one ,a human could never duplicate the accuracy,hence performance of a constant speeding prop using a manual pitch change prop

[neily]

Originally Posted by gmcjetpilot

I don't think he was asking if FP or C/S is better, however I think you are wrong on two points.


Rob I have to disagree, fwd CG is often a good thing. First some RV's with FP props are tail heavy, like the RV-7, which is designed for metal C/S prop. With my Hartzell and O360 I am still a little heavy in the tail. If I had a wood prop I could not carry any bags. Of course more prop weight means fwd CG, but that is a good thing in some cases.

My RV-4, I flew over 1000 hours, had a C/S extended hub Hartzell on a O320. It put me right near the fwd CG solo, which was fine. I just needed full nose up trim on approach. However when I traveled with my girlfriend (120 lbs) and all kinds of bags and camping gear (all aft CG), I was glad to have the nose weight. With a light prop I would be way aft CG.

Aerobatics with a C/S is a dream. To say a FP is better for aerobatics is not correct IMHO. When have you seen any Prop acro pilot or serious acro plane with a FP? Set the C/S prop and loop and forget engine controls, as you roll and loop without the RPM's going overspeed and throttle jockeying.

As far as the props you mention they cost way more, cost more to repair and are less efficent than a metal Hartzell or Sensenich. That is just the way I see it. Cheers

airmaster cp332 constant speeding propeller weighs 29 lbs. there is better technology every day being introduced. 29 lb is not that heavy!