Van's Air Force
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Rad props
- Thread starter elippse
- Start date
Not an expert here, but from what I understand: (a) Paul's props are designed for what you want ... 'ordinary' included; (b) I know of at least one on a RV (RV6).
Give Jim Smith from Wichita, KS a shout at [email protected]
Here's another thread: http://www.vansairforce.com/community/showthread.php?t=52556
-Jim
40603
Give Jim Smith from Wichita, KS a shout at [email protected]
Here's another thread: http://www.vansairforce.com/community/showthread.php?t=52556
-Jim
40603
I'm wondering if Paul can give us some independent data on that RV with the prop on it. We've heard for a number of years about the remarkable efficiency of your props, and I thought the goal fo the RV installation was to see what sort of data would result....
Cheers,
Stein
Cheers,
Stein
pierre smith
Well Known Member
Absolutely...
...and if there was any way to do a CS prop for a -10, my hat would be in the ring quickly. Makes you wonder what the P-51 could have done with one instead of that paddle.
Best,
...and if there was any way to do a CS prop for a -10, my hat would be in the ring quickly. Makes you wonder what the P-51 could have done with one instead of that paddle.
Best,
Christopher Murphy
Well Known Member
tip flutter
What keeps that thin narrow tip section of the prop from fluttering or flexing? What is the max RPM? It looks like they are pretty small diameter.
Chris M
What keeps that thin narrow tip section of the prop from fluttering or flexing? What is the max RPM? It looks like they are pretty small diameter.
Chris M
rvmills
Well Known Member
Been trading e-mails with Paul about props and wingtips...gotta tell ya, he's been takin' me to school. Smartest guy I've met since my Aerodynamics 201 professor, and that guy was a Lockheed Skunkworks SR-71 aerodynamicist (toughest class I ever took!)
Stein, he's run a couple models based on my increased HP, modified wing area (drag profile) and operating regions (Reno home field, X-C up high, racing down low), and shot me some numbers on a 73" 3 blade design, and a 68" 4 blade design (both FP). Its all theorectical, so I won't put the numbers in, but on the Super Six, it was increased rate of climb and increased speed over my current 80" 2 blade CS.
I'm currently asking him about where the performance costs of that speed would be. Moving from a CS to a FP would decrease X-C cruise power setting flexibility (when you decrease RPM, you decrease MP with a FP, so no more WOT cruise at altitude, unless you want to zorch along at 2700+ RPM!). Also, initial TO thrust and go around thrust will go down due to lower static RPM of a FP (at least that's the way I think I undestand it).
I've also asked about engine wear considerations, as I'm not a high budget Reno Racer looking to get a 6 lap TBO on engines, etc., but an RVer that wants a fun X-C machine that I can hone to go fast for a few SARL races per year...all in fun!
Since this thread has kinda taken a turn towards mainstream application of rad props (ie, can we have a performance prop that fills our basic needs as well), I thought I'd jump in with what we've been talking about offline.
I've been mulling over a change to a Hatzell BA, as it is touted as faster than my D-twist, but nearly as smooth as a 3 bladed MT. Looking at Paul's designs, and seeing his thoughts on performance, this is very, very tempting, though I am taking a slow deliberate approach, and Paul is a very patient guy with a ton of knowledge.
Pierre, I think all the designs are FP, though Paul would be the guy to answer that one. I think he has a very good name in props making them for his design customers...not trying to play "I've got a secret" with this or the numbers...but I better not name names, just in case that would be stepping on toes. Like you, I'd be interested to hear if such an animal could be made in a CS design...though one comment Paul made was that his FP design disrupts the air at the inlet less than CS props and other FP props, so inlet size can be made more efficient as well. All really interesting stuff.
Chris, not sure on the flutter part, and Paul will probably expand on it, but one line of discussion we had was prop diameter. With more blades, he can decrease the diameter to keep tip speed down, yet still generate the same mass flow of air as a larger diameter prop with fewer blades. Diameter and tip speed versus blade design (rad shape) may be a key piece in the flutter avoidance part of the design. I think much of the rest of the blade design is based on Paul's studies in span increase versus area decrease, which results in that triangular or tapered shape (like those wingtips shown earlier).
Those are just some interpretations from a "student's" chair. Its really becoming an interesting education, and I'm keen to learn more.
Like Pierre alludes to, there may be a market for "rad props" on RVs, if they add performance while still allowing the multi-mission performance that RV's and Rockets are so very blessed with!
And (IMHO) if we put really cool 4 blade props on our mo-chines, we'll be singing, "I'm too sexy for my plane, too sexy for my plane!"
Cheers,
Bob
Stein, he's run a couple models based on my increased HP, modified wing area (drag profile) and operating regions (Reno home field, X-C up high, racing down low), and shot me some numbers on a 73" 3 blade design, and a 68" 4 blade design (both FP). Its all theorectical, so I won't put the numbers in, but on the Super Six, it was increased rate of climb and increased speed over my current 80" 2 blade CS.
I'm currently asking him about where the performance costs of that speed would be. Moving from a CS to a FP would decrease X-C cruise power setting flexibility (when you decrease RPM, you decrease MP with a FP, so no more WOT cruise at altitude, unless you want to zorch along at 2700+ RPM!). Also, initial TO thrust and go around thrust will go down due to lower static RPM of a FP (at least that's the way I think I undestand it).
I've also asked about engine wear considerations, as I'm not a high budget Reno Racer looking to get a 6 lap TBO on engines, etc., but an RVer that wants a fun X-C machine that I can hone to go fast for a few SARL races per year...all in fun!
Since this thread has kinda taken a turn towards mainstream application of rad props (ie, can we have a performance prop that fills our basic needs as well), I thought I'd jump in with what we've been talking about offline.
I've been mulling over a change to a Hatzell BA, as it is touted as faster than my D-twist, but nearly as smooth as a 3 bladed MT. Looking at Paul's designs, and seeing his thoughts on performance, this is very, very tempting, though I am taking a slow deliberate approach, and Paul is a very patient guy with a ton of knowledge.
Pierre, I think all the designs are FP, though Paul would be the guy to answer that one. I think he has a very good name in props making them for his design customers...not trying to play "I've got a secret" with this or the numbers...but I better not name names, just in case that would be stepping on toes. Like you, I'd be interested to hear if such an animal could be made in a CS design...though one comment Paul made was that his FP design disrupts the air at the inlet less than CS props and other FP props, so inlet size can be made more efficient as well. All really interesting stuff.
Chris, not sure on the flutter part, and Paul will probably expand on it, but one line of discussion we had was prop diameter. With more blades, he can decrease the diameter to keep tip speed down, yet still generate the same mass flow of air as a larger diameter prop with fewer blades. Diameter and tip speed versus blade design (rad shape) may be a key piece in the flutter avoidance part of the design. I think much of the rest of the blade design is based on Paul's studies in span increase versus area decrease, which results in that triangular or tapered shape (like those wingtips shown earlier).
Those are just some interpretations from a "student's" chair. Its really becoming an interesting education, and I'm keen to learn more.
Like Pierre alludes to, there may be a market for "rad props" on RVs, if they add performance while still allowing the multi-mission performance that RV's and Rockets are so very blessed with!
And (IMHO) if we put really cool 4 blade props on our mo-chines, we'll be singing, "I'm too sexy for my plane, too sexy for my plane!"
Cheers,
Bob
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pierre smith
Well Known Member
I'm not a diehard CS fan.,,,
.....necessarily, and I'd gladly give up takeoff distance and some climb for 10-15 MPH cruise gain. There may also be a net gain from smaller intake cooling area with smoother inlet flow with Paul's rad props.
Best,
.....necessarily, and I'd gladly give up takeoff distance and some climb for 10-15 MPH cruise gain. There may also be a net gain from smaller intake cooling area with smoother inlet flow with Paul's rad props.
Best,
I did recontouring of the tips on two T-6 race planes and they picked up 5 mph and really cut down on the noise, but a T-6 techie ruled they weren't T-6 enough and wouldn't let them use them. One of them looked very much like Tony Higa's prop that is in the photo that looks like a saber. I also recontoured the tips on Bob Bryson's Pitts and he and Leah Sommer got best improved racer from 201 in 2008 to 212 in 2009. The efficiency increased 10%!
My new three-blade is similar in planform to Tony's. Static thrust is lacking and so initial acceleration is lower but once it starts going and the inner part of the blade unstalls it really gets up and goes. 'Like 82% efficiency in a climb at 105 mph IAS, 1350 lb, 1500 fpm, 2400 rpm, with a 125 HP O-235, and at least 90% efficiency in cruise. Even Jack in his book admits that 90% or more is achievable, and he found that my elliptical lift distribution was even slightly better than his Betz, Goldstein, Theodorsen design.
The blades are 15% thick from the widest chord outboard and are very stiff with carbon fiber over a wood core. The Biplane props turn 3500-3700 rpm and the F1s turn 4500 rpm. By having more blades the diameter can be reduced to keep tip Mach below M0.85, but there is so little chord that even with dynamic pressures of 800-1100 psf the tip drag and noise is insignificant. If you viewed the video that I posted the link of my takeoff and low pass at Hanford video-ed by Pat Panzera you can hear that there is only engine exhaust noise and no prop noise. That was with a two-blade prop that I re-contoured the tip to bring it to a point as on Bob Bryson's Pitts.
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Hi Paul,
The obvious question is then....if that kind of performance can be had on such draggy airframes as listed above, then why on earth don't you do the same experiment on one of the 6,000+ RV's flying? Relative to those planes it's a clean airframe "ripe for the pickin". I've seen similar data from you over the past number of years here, so why not get someone like Bob or Mel or Randy to do a substantive and independent collection of data?
I'm not trying to flame you or anything because you've forgotten more about this stuff then I'll ever know, and I respect the heck out of your knowledge...but after reading similar posts from you for years, I'm itching to see the "proof in the puddin" on the airframes we all fly here in VAF - that bein an RV. If you are able to even come anywhere close to that kind of improvement on an RV, the response would be tremendous.
To get the process moving, I'm willing to do the following:
We find two RV drivers with well performing FP installations (pitched for cruise)- like a CATTO or Prince or twisted up Sensi. Give the same guy a complete prop/spinner setup and have them do a detailed and independent review of the prop. Same plane, fly it the same day under the same conditions with neutral persons there to record data under identical conditions all the way around; engine parameters, weight, etc...
If you can get 12 mph on the same airplanes at same RPM/MP's (ones that were relatively fast to begin with...no picking a dog to start out with) I'll donate $500 to a charity of your choice.
If you can get 12mph on a draggy Pitts airframe, an RV should be a walk in the park!
Again, this isn't meant as a flame...just perhaps some friendly pushing to get some real life numbers on the planes we are flying here. Someone like Bob Axsom should be able to find planes that are good neutral starting points.
So, what say you - are you up to the challenge??! Should be easy for you!
Cheers,
Stein
Added because I forgot....the challenge can't appreciably affect takeoff & climb performance, because obviously one can do the "twist the heck" out of any prop (to a certain point of diminishing returns I know) and gain on the top end at the expense of the bottom. As I understand it your design is able to still perform well on both ends, but I needed to write it down for my challenge anyway!
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PainterJohn
Well Known Member
Paul these are awesome props!! Cant wait to paint one or 20 of them ;-)
Kyle Boatright
Well Known Member
Hi Paul,
The obvious question is then....if that kind of performance can be had on such draggy airframes as listed above, then why on earth don't you do the same experiment on one of the 6,000+ RV's flying? Relative to those planes it's a clean airframe "ripe for the pickin". I've seen similar data from you over the past number of years here, so why not get someone like Bob or Mel or Randy to do a substantive and independent collection of data?
I'm not trying to flame you or anything because you've forgotten more about this stuff then I'll ever know, and I respect the heck out of your knowledge...but after reading similar posts from you for years, I'm itching to see the "proof in the puddin" on the airframes we all fly here in VAF - that bein an RV. If you are able to even come anywhere close to that kind of improvement on an RV, the response would be tremendous.
To get the process moving, I'm willing to do the following:
We find two RV drivers with well performing FP installations (pitched for cruise)- like a CATTO or Prince or twisted up Sensi. Give the same guy a complete prop/spinner setup and have them do a detailed and independent review of the prop. Same plane, fly it the same day under the same conditions with neutral persons there to record data under identical conditions all the way around; engine parameters, weight, etc...
If you can get 12 mph on the same airplanes at same RPM/MP's (ones that were relatively fast to begin with...no picking a dog to start out with) I'll donate $500 to a charity of your choice.
If you can get 12mph on a draggy Pitts airframe, an RV should be a walk in the park!
Again, this isn't meant as a flame...just perhaps some friendly pushing to get some real life numbers on the planes we are flying here. Someone like Bob Axsom should be able to find planes that are good neutral starting points.
So, what say you - are you up to the challenge??! Should be easy for you!
Cheers,
Stein
If you're lookin' for volunteers, count me in!
Prop speed boost
Hi, Stein and Kyle! You have to understand that a speed increase from one type of prop to another has to do with how much difference there is to begin with in the relative efficiencies of the two. Jim Smith has done comparison tests of his three-blade with two other two-blade props in speed at four different altitudes and average climb rate from his field to 10,000'. He has prepared a summary sheet of these tests, and he will send it to you at your request. One of the first problems we had with Jim in his original testing of his plane with my first two-blade prop is we had to get rid of his large IAS errors due to the rivet-style static port; he was seeing errors of about 11-12 mph, somewhat the same as I had seen with tests on two other RVs. He corrected this by adding tape behind the port until his IAS-derived TAS equalled his GPS-derived TAS. He finally took a washer of the same thickness as the tape, cut it in half, and mounted it behind the static port. Because my design generates a different swirl pattern on the fuselage which influences the flow past a fuselage-mounted static port, it is not possible to compare IAS derived TAS; only GPS derived TAS can be used. You should contact Jim and see if he would be willing to support impartial tests of his plane with other props installed. I'm pretty sure you will see quite a bit of difference in speeds and climb rates, with Craig's three-blade props being very close to Jim's, and other types showing more and more difference. I did a test on Bill Grimm's RV-9 with my two-blade vs his re-pitched Sensenich 70CM659-0-77. The runs were done at 9521' dalt with my prop and 9086' dalt with his prop. His averaged 181.7 mph TAS at 2540 rpm, and mine averaged 189.9 mph at 2620 rpm. The efficiency difference is (189.9/181.7)^3 X 2540/2620 = 10.7% and if the power due to density difference, 1.6%, is taken into account it comes out to 12.4%. These flights were flown by Bill, not me. His IAS-derived TAS was about 10 mph high on both tests.
Hi, Stein and Kyle! You have to understand that a speed increase from one type of prop to another has to do with how much difference there is to begin with in the relative efficiencies of the two. Jim Smith has done comparison tests of his three-blade with two other two-blade props in speed at four different altitudes and average climb rate from his field to 10,000'. He has prepared a summary sheet of these tests, and he will send it to you at your request. One of the first problems we had with Jim in his original testing of his plane with my first two-blade prop is we had to get rid of his large IAS errors due to the rivet-style static port; he was seeing errors of about 11-12 mph, somewhat the same as I had seen with tests on two other RVs. He corrected this by adding tape behind the port until his IAS-derived TAS equalled his GPS-derived TAS. He finally took a washer of the same thickness as the tape, cut it in half, and mounted it behind the static port. Because my design generates a different swirl pattern on the fuselage which influences the flow past a fuselage-mounted static port, it is not possible to compare IAS derived TAS; only GPS derived TAS can be used. You should contact Jim and see if he would be willing to support impartial tests of his plane with other props installed. I'm pretty sure you will see quite a bit of difference in speeds and climb rates, with Craig's three-blade props being very close to Jim's, and other types showing more and more difference. I did a test on Bill Grimm's RV-9 with my two-blade vs his re-pitched Sensenich 70CM659-0-77. The runs were done at 9521' dalt with my prop and 9086' dalt with his prop. His averaged 181.7 mph TAS at 2540 rpm, and mine averaged 189.9 mph at 2620 rpm. The efficiency difference is (189.9/181.7)^3 X 2540/2620 = 10.7% and if the power due to density difference, 1.6%, is taken into account it comes out to 12.4%. These flights were flown by Bill, not me. His IAS-derived TAS was about 10 mph high on both tests.
Ok then, we'll borrow/rent a CAFE probe to put on the outboard wing (it's been done many times on RV's) to eliminate things or better yet have CAFE themselves do the test. The above numbers are good to see, but somewhat anectodal given that we don't know the MAP settings, fuel flow, weights, etc.. Also, what would/did his airplane do at 2620 RPM? Was that wide open with both props? 181.7 mph is good, but there are a number of RV9's that are a good deal faster than that to begin with.
Again, there are ways around the induced errors. If you have two planes side by side flying the comparison (one remaining the same), it should be able to be used as a baseline beside the modified plane, regardless of what that planes shows for IAS derived anything. GPS when properly used with the correct computations is also a good tool to offset system erros. People like Kevin would be able to nail this down quite easily.
Again, no flames intended - just trying to get some solid data points....
Cheers,
Stein
Christopher Murphy
Well Known Member
I would consider testing one
If you have a prop for a 320 Rv-4 I would consider comparing it to my catto 2 blade. We could do it at one of the SARL races. Maybe a speed dash type of thing. My airplanes performance has been well documented over the last few years,,, not that that data would mean that much in a prop test.
Chris M RACE34
If you have a prop for a 320 Rv-4 I would consider comparing it to my catto 2 blade. We could do it at one of the SARL races. Maybe a speed dash type of thing. My airplanes performance has been well documented over the last few years,,, not that that data would mean that much in a prop test.
Chris M RACE34
Those two tests were done WOT, but there was no MAP or FF available, and used two-way GPS runs. Bill's engine is a Lycoming O-320 of 150 HP, and the weight was probably within 50 lb, so I don't think that would increase the induced drag all that much in un-accelerated flight. As you are probably aware, a well-flown two-way run is as good as, or maybe even better, than a well-flown three- or four-way test, since you can do two two-way runs in the same time it takes to do a four-way, and you have the results available in flight, so you can see if the runs are consistent on each ground track! A four-way leads you open to four errors, one per run, as an input to a single set of computations, and if the errors are not zero-mean, that will corrupt the results. You don't have to wait until you are back on the ground at your computer to open the spreadsheet, feed in the numbers, and find out how you did. The worst case in doing any two-way test is if you have a direct crosswind. If you are flying at a TAS of 200 mph and you have a 20 mph 90 deg crosswind, guess what your error will be? 1 mph! Figure it out for yourself. You will be flying on the hypotenuse of a right triangle in which the ground track is one leg and the wind is the other. (200^2 - 20^2)^1/2 is 199.
There is no need for the CAFE probe; what does it add? Engine horsepower on our engines is basically proportional to rpm because of their relatively flat torque curve at the rpm at which we operate. As you also know, the power required to increase speed goes up with the cube of the speed ratio. That's the first part of the equation. Since power is directly proportional to rpm, and his prop was at a lower rpm, that ratio deducted from the speed ratio. Since engine power with density is proportional to the density ratio raised to the 1.135 power, that is where the additional density term came from since he was at a slightly lower density altitude with his prop so he had a little more power available. What I didn't take into account was the increased power due to the stagnation pressure rise into the induction system, which, corrected for compressibility, would have been 0.993" at 189.9 mph and 0.920" at 181.7 mph but I thought that the 0.073" difference, which would have meant 0.225% power increase, was dwarfed by the other effects. I really can't think of anything else that might have been accounted for other than maybe the difference in stagnation temperature rise into the induction system, but again, the 5.98 F rise at 181.7 mph vs the 6.53F rise at 189.9 mph would have only given 0.055% less power at the higher speed.
Fair enough...but instead of getting into the bits/bytes of calculations, another easy seat of the pants test is to get 2 equivalent RV's (performance/hp wise), put your prop on one, fly them side by side, then switch props, go fly and switch back. It's a quick/dirty and easy way to see how they compare. Collect some data on takeoff, climb, cruise, speed, RPM, etc.. on each plane with each prop and there you have it. No complex math required!
Sounds like a fun day at worst and a good excuse to burn some avgas - a win/win for all involved!
Cheers,
Stein
'Totally agree! Someone please contact Jim and see if he wants to participate; I'm sure he will!
