Best prop for aerobatics

[Whirl Wind Propellers]

Originally Posted by David Z

MT makes some aerobatic props. The prop is counterweighted, so works in reverse fashion to normal props. Oil pressure pushes the blades fine, so in a small/short oil pressure interruption to the governor results in the blade angle going coarse. This prevents overspeeds.

Whirlwind also makes some aerobatic props, but they're 77" diameter and probably too long for most 2 seat RVs. Unless I missed something.

I'm not well versed at all regarding the aerobatic competition levels. Maybe there isn't enough negative or 0 "g" operation to make this worth while.

Whirl Wind has 2 constant speed aerobatic propeller options for RV's--The HRT74 is not currently available:

2 Blade HRT 72" for up to 220 hp counter-weighted engines. This weighs about 45 lb with counterweights and costs $13,100.

3 Blade HRT 73" for non-counter weighted engines (although it says minimum hp is 220, it can be used just fine with 190+ hp with only small losses in top speed traded for improved climb.) This weighs about 60 lb with counterweights and costs $15,400.

The ground adjustable GA-200L 72" is also ok for aerobatics on the counterweighted engines and weighs about 22 lb with the RV 2.25" spacer and spinner (kit cost is $3,910). Obvious concerns for ground adjustable propellers doing aerobatics is that it's easy to over speed the propeller (do NOT overspeed the propeller!)

For anyone doing only “gentleman's aerobatics” (NOT using an inverted oil system and only doing positive-g maneuvers), the 300 series 72" can be used on the counter-weighted engines. This propeller does not have a counter weighted aerobatic configuration. (Cost $12,500)

[Maxrate]

WW, thanks for taking the time to weigh in. Great info!

[Maxrate]

Another bit of valuable information. I called the Hartzell tech support line and spoke with their rep who said they did extensive testing on the blended airfoil prop with the non counterweighted crank engine combo and didn’t like the harmonics on the “pumped up” parallel valve motors, 370/375, and didn’t recommend mating anything more than the 360 unless counterweighted. He basically said just too much banging around in there without any dampening effect.

I think I’m going to explore the cost of having an engine built with the counterweighted crank before going with more horsepower. Thanks for all the great input!

[agent4573]

I think Whirlwind hinted at a big point that I overlooked when I first started looking at props. You have to define what you mean personally by "aerobatics". The entry level IAC maneuvers don't require negative g, the most you'll have is near zero g if you mess something up. Its up to you to decide your personal level of risk tolerance if you want a counter-weighted aerobatic prop when you really aren't planning to subject the engine to oil pressure transients. Our initial plan was for a full inverted oil system and a counter-weighted prop because we want to do IAC competitions. We've now settled on a half-raven system and an oil accumulator to help control those zero g screw up and a standard prop CS prop.

[ronschreck]

Originally Posted by agent4573

I think Whirlwind hinted at a big point that I overlooked when I first started looking at props. You have to define what you mean personally by "aerobatics". The entry level IAC maneuvers don't require negative g, the most you'll have is near zero g if you mess something up. Its up to you to decide your personal level of risk tolerance if you want a counter-weighted aerobatic prop when you really aren't planning to subject the engine to oil pressure transients. Our initial plan was for a full inverted oil system and a counter-weighted prop because we want to do IAC competitions. We've now settled on a half-raven system and an oil accumulator to help control those zero g screw up and a standard prop CS prop.

FWIW, I ditched my oil accumulator after installing a full inverted oil system because the accumulator caused RPM surges, particularly during takeoff roll. If you are serious about IAC competition I recommend going for a full Christen or Raven system. If you stay with a fixed pitch prop the accumulator is an inexpensive alternative to a full inverted oil system.

[Maxrate]

Ron,
When I built my tanks acro was not in the picture so I just put in the standard pickup tube. I plan on installing the 1/2 Raven and was wondering what sequences can I expect to be able to perform with that set up? I assume the primary and sportsman. What about the intermediate? RV7, IO 360/180 HP, CS prop.
Thanks for the input.

[ronschreck]

Originally Posted by Maxrate

Ron,
When I built my tanks acro was not in the picture so I just put in the standard pickup tube. I plan on installing the 1/2 Raven and was wondering what sequences can I expect to be able to perform with that set up? I assume the primary and sportsman. What about the intermediate? RV7, IO 360/180 HP, CS prop.
Thanks for the input.

Hi Mark. Hi doubt you will notice any fuel starvation events. The duration of negative G during typical IAC sequences, even through Intermediate are probably not long enough to cause a power interruption. If it does it's likely to be very short and not significant enough to worry about. Of course you should run the boost pump at all times while doing aerobatics. Having said that, installing a flop tube is not a really hard job. I have done it in one day.

[Maxrate]

Thanks Ron. What are your thoughts on the 1/2 Raven being sufficient through the intermediate sequence?

[David Z]

When does the aerobatic operation style prop become necessary or required?

I'm planning mild aerobatics. I don't know anything about the IAC levels, so can't draw a comparison. Loops, rolls, spins, some sustained inverted flight, that's about it. The occasional clean switch from positive to negative G, and no 0g. I've got the flop tube and planning inverted oil for the engine, just not sure how to handle the prop dilemma.

I didn't know the HRT 72" was available as a counterweighted aerobatic operation. That's great to know and might just sell me a prop once I get to that stage.

[smithflys23]

Originally Posted by ronschreck

Of course you should run the boost pump at all times while doing aerobatics.

FWIW, I don’t run my boost pump during aerobatics. I have fuel injection, and I’ve never had even a hint of a hiccup. That being said, I respect Ron’s expertise, and opinion on the matter.