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  #11  
Old 01-12-2021, 04:35 PM
Whirl Wind Propellers Whirl Wind Propellers is offline
 
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Location: San Diego, CA
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Quote:
Originally Posted by David Z View Post
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 ďgentleman's aerobaticsĒ (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)
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  #12  
Old 01-12-2021, 08:14 PM
Maxrate Maxrate is offline
 
Join Date: Dec 2008
Location: League city, TX
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WW, thanks for taking the time to weigh in. Great info!
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  #13  
Old 01-13-2021, 07:34 AM
Maxrate Maxrate is offline
 
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Location: League city, TX
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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 didnít like the harmonics on the ďpumped upĒ parallel valve motors, 370/375, and didnít 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 Iím 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!
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  #14  
Old 01-13-2021, 10:31 AM
agent4573 agent4573 is offline
 
Join Date: Aug 2019
Location: Mountain view
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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.
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  #15  
Old 01-13-2021, 04:20 PM
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ronschreck ronschreck is offline
 
Join Date: Mar 2006
Location: Gilbert, AZ
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Quote:
Originally Posted by agent4573 View Post
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.
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  #16  
Old 01-13-2021, 06:31 PM
Maxrate Maxrate is offline
 
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Location: League city, TX
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Default 1/2 Raven

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.
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N442MM reserved
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  #17  
Old 01-13-2021, 06:40 PM
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ronschreck ronschreck is offline
 
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Location: Gilbert, AZ
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Quote:
Originally Posted by Maxrate View Post
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.
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  #18  
Old 01-13-2021, 07:11 PM
Maxrate Maxrate is offline
 
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Location: League city, TX
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Thanks Ron. What are your thoughts on the 1/2 Raven being sufficient through the intermediate sequence?
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N442MM reserved
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  #19  
Old 01-13-2021, 08:53 PM
David Z David Z is offline
 
Join Date: Aug 2010
Location: Thunder Bay Ontario
Posts: 481
Default Aerobatic Prop Operation

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.
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  #20  
Old 01-13-2021, 09:27 PM
smithflys23 smithflys23 is online now
 
Join Date: Feb 2017
Location: Jupiter
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Quote:
Originally Posted by ronschreck View Post
Of course you should run the boost pump at all times while doing aerobatics.
FWIW, I donít run my boost pump during aerobatics. I have fuel injection, and Iíve never had even a hint of a hiccup. That being said, I respect Ronís expertise, and opinion on the matter.
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