We need another Prop fly off
rv6ejguy said:
While some would like to believe that the Hartzell is the fastest prop, there is mounting evidence from new flight test data that this may not be true. I'll take the flight test data offered up by Darwin and Jim that the Whirlwind and some MT models are equal to or better than the Hartzell.
Darwin's evidence is compelling. The only way to settle this scientifically is to switch props on the same airframe or better still a side by side with 2 RVs and then switch props. Times and products change.
Do you have the data you reference, I don't recall seeing it. Here are my sources:
Randy Lervold's excellent test. RV-8 flown with several props Hartzell (older C2YK/F7666), WW 150, WW 200C and WW 200RV. Some of this data dove-tailed off of Vans test (below). Van used some of Randy's data. From Randy's data for the old Hartzell HC-C2YK/F7666-2, it was as fast or faster +/- 1 mph and about 5 mph faster than the WW150 (three blades). This was consistent over cruise and top speed test. The new BA prop is about 3.5 mph faster than the old Hartzell so we can make the assumption that the new BA is faster. Van found the the New BA was faster than the WW 200 RV by +1 mph. I freely admit this is within the tolerance of error.
http://www.romeolima.com/RV8/Prop.htm#Test results
Van's data: Hartzell BA + 2mph faster > WW 200 RV
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Lazy8: High performance RV-8 flown with the older Hartzell F7666 bladed prop, MT and Aerocomposite. (note there was no doubt that the MT was slower and the Aerocomposite was not faster than the older Hartzell.)
http://www.lazy8.net/proptest.htm
RV-10 Side By Side MT v Hartzell BA (Note: The MT prop plane had a more powerful engine and was at a higher power setting and was just as fast as the stock engined RV-10 with BA prop. Van estimated the power advantage of the MT prop plane (all things being equal and equal I mean prop) than it should have been up 11 mph faster, accounting for the power the hot engined RV-10 was making.
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All we can go on is what we have. Time and again the MT is much slower. Granted we could use more data on the Aerocomposite and WW150, WW200RV and Aerocomposite.
Ross we need more flight test data, two planes, seven props (two hartzell, two WW, two MT, Aerocomp and what ever else), side by side flying. Switch props and fly again. Prop test are not promoted by prop manufactures, especially if they are not as fast. There's nothing in it for them. The reason prop data is shrouded in mystery, hearsay and hard to come-by is the time consuming nature to test them, on planes under controlled conditions.
The most unbiased results we have as I posted above, Randy and Van; Their test are well documented and seem to be unbiased. Granted Van's test used "normalized" data (with Randy's data) based on a common prop, so there may be some error there. However the MT has consistently been shown to be much slower by other sources. Props tend to vary by 1% or fractions of percent, usually, but the MT is full 2 points to 4% slower in some cases, so a MT being faster than a BA, I am skeptical.
The 200RV was only 2 MPH slower than the BA Hartzell (Van's test), so I can see with a +/- error tolerance they may be comparable. Lets do a fly off. Side by side with two RV's, switch props and side by side again. Or even one RV with the switch made. That would settle it. When it comes to speed the 200RV, in my opinion as I have not tested it my self, is probably close or equivalent to the BA.
The more I learn about prop theory as I have studied it, the more I realize its the interaction of the prop with airframe/engine that's the critical factor separating men from the boys. In other words one prop might show a distinct advantage on one airframe from another airframe. One prop may be technically better, advanced composites for example but it's up to the prop designer to tweak that 1% out of it, by tuning it to that engine/airframe and mission. It's analogise to a fixed prop with the proper pitch.
For Example: If you fly with out wheel pants and your fixed pitch prop is pitched properly, than put wheel pants on, your pitch will be wrong. Airframe drag and prop design are intimately related. Same with power. You add more power you need a new prop, IF you want to be most efficient or optimal. Clearly this has to do pitch and not as much an issue with a constant speed prop, but it illustrates that one prop is not good for every airplane. Many props are generic.
There is no doubt Hartzell tuned the BA just for the RV power, airframe and mission by doing not only theoretical calcs but they test flew it on RV's during development. I am sure WW200RV designer (who wrote and article in the RVator about how he designed it) did consider the RV in his design, but not sure he did extensive flight test? I don't know.
There is no getting around the interaction of the prop and the POWER and DRAG of the airplane its mounted to in actual flight. That is why the BA is good, best in my opinion in performance' not only the thin metal blade has advantage, which is theoretically better for high speed, but it's matched to the airframe.
Granted not all RV airframes are the same. So prop test should be done on average RV's with stock engines to super clean high powered RV's. Bottom line what is a few MPH? That is up to the individual and some care some don't.