hevansrv7a

hevansrv7a

Well Known Member
This will be an ongoing story until the project is either done or has made enough progress. I'd like to keep this thread for discussion, so the (lengthy) story will be here:


I will modify the narrative in response to your questions and comments as the project moves forward. I will also, of course, participate in this thread.
 
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Hmmmmm?...

....I'm expecting to hear from Paul Lippse (sp?) shortly.

Sounds a lot like what he does,

Best of luck,
 
Last June I flew to Reno-Stead to oversee a modification to the propeller on Bob Bryson's Son of Galloping Goat, now Ghost, biplane. This modification consisted of cutting the leading edge in a smooth, calculated curve from 27" radius to a point at the tip trailing-edge at 37" radius. This sweep decreased the flow velocity over the airfoil in this section to M0.775, substantially decreasing the drag. As a result, the speed of this modified Pitts had the qualifying speed increase over 10 mph from 2008 to 2009. This was a 5% increase in speed, meaning a 15% increase in thrust, 10% of which was from increased efficiency and 5% from the increased HP due to the additional speed. Bob then did the modification to a similar prop he has on his RV-6 and he said he got a very good increase in ROC and speed.
George Andre did a similar mod to a prop on his Zipper biplane and saw a 5 mph qualifying speed increase from 2009 to this year. I designed this mod for his normal race prop, but some last-minute considerations caused him to do a somewhat similar mod on a different planform prop he had, but it still did the job. I previously modified a spare old two-blade Great American prop for my plane which increased its performance, and Bob Rowan modified the prop on his Q-200 and also got a speed and climb increase.
If your prop has any chord at the tip, the wider it is, the less efficient it is!
 
Drift

Looks like Pierre was right. I'd prefer, though, to keep this thread about its original subject. Jack's work speaks for itself. Pauls' work is useful and often impressive, but it's not the subject of this thread.
 
it looks like the posts you link to so far are all theory. is there a timeline of when the prince prototype "Norris BGT" for your airplane is going to be finished? how will you test the results? I think you've done some cafe instrumentation testing on your current prop? will the new one be comparatively tested against that?

i'm interested you are experimenting with different prop ideas. in the end though its "show me the speed!" i've seen the posts you and paul go back and forth in other threads. his props have shown some very amazing speed increases with minor drawbacks. It will be interesting to compare how this prop compares in actual use
 
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Responding

Danny7 said:
it looks like the posts you link to so far are all theory. is there a timeline of when the prince prototype "Norris BGT" for your airplane is going to be finished? how will you test the results? I think you've done some cafe instrumentation testing on your current prop? will the new one be comparatively tested against that?

i'm interested you are experimenting with different prop ideas. in the end though its "show me the speed!" i've seen the posts you and paul go back and forth in other threads. his props have shown some very amazing speed increases with minor drawbacks. It will be interesting to compare how this prop compares in actual use
Click to expand...


Danny7, I appreciate your interest..

Nope, not theory and especially not mine. There's a difference between an explanation and a theory. There's a difference between a concept and an implementation. Jack's book explains that. I'm just a helper. Betz, Goldstein and Theodorsen were the engineers and Jack is their "explainer".

Jack's design (using Andy's programs) is already out there at Reno and in the Whirlwind prop designed for the RV-8 which 70+ readers of this forum purchased as a group. The Prince version will just be the first fixed-pitch version for an RV.

I'm not about trying to "top" Paul or anyone else. I'm trying to tell a story and perhaps educate myself and some of the other VAFers. That story's timeline depends on Lonnie Prince, of course. The design is already on paper. It could be a few months. If winter WX closes in, then testing may not be until spring.

I will, of course, test the new prop. However, rather than comparing to "bad" props, I'll be comparing to my excellent 3-blade Catto. I will also be testing at or below 2700 RPM for the obvious reasons. Therefore don't expect huge and hard-to-believe percentage gains. I've pointed out before that prop efficiency is hard to measure. Andy's program says my new prop will be about 90% efficient. I know others claim to have higher percentages. I am not calling anyone names, but I find it hard to believe in a 95% prop for reasons I have already explained elsewhere.

At 8 to 10 thousand feet and full speed, my Catto prop is probably 80% or better. Craig suggested that I used 82% when I first started experimenting. Let's use 82% vs. 89% for an illustration. That would mean a HP increase of 7/82=8.54%. At 200 mph, my parasite drag is about 90% of total drag and the induced drag is nearly flat. So if 90% of my HP is 8.54% higher and 10% is flat, then the net HP would be 1.07686. The cube root of 1.07686 is 2.5% so at 200 mph my speed gain would be about 5 mph. My math may be off a bit because it's late and I'm tired, but you get the idea. My design is for 205~206 mph at 10,000 DA. There are faster -7A's, but this will be a direct comparison on the same airplane and with the same BHP (same RPM).

Not all prop design is about top speed. For a FP prop it is also about takeoff and climb performance and, of course, fuel efficiency. Jack's design is "6-way optimized". Read the book; it's only $15 plus shipping.

Just to clarify, my experiments with "Power and Drag" (see links below) are not using CAFE instrumentation, but that would be nice. My work has been about CAFE style testing for the rest of us, using what is already in our planes. My stuff is just basic GRT EFIS's and a Garmin 496 GPS. The EFIS and EIS are IFR accurate. Most of my methods can be used with six-pack instrumentation, too.
 
i was going to try and follow along again, it looks like the links are down. Who is the andy you mention that has done some of the computer work?
 
Thanks. My Bad. Fixed

I goofed, but it's fixed now. Thanks for the heads up!

Andy is Dr. Andy Bauer, a college friend of Jack Norris who, with Jack, spent 10 years developing the body of work described in Jack's book and embodied in those programs. Andy did all the important computer work. All I'm doing is resurrecting them from 8-bit limbo and separating code from data for safety.

He is the co-author of the articles on the propless C-152, also.
 
If the whirlwind was a NBGT designed prop, how will the prince manufactured one be different? It will be specifically made for your planes exact numbers?

you mention you will compare this new prince to the catto you have, will it be compared to the old prince one as well? Its a shame you don't have a "standard" prince model to compare it to that is properly pitched for your airplane/ engine.

this prince nbgt model will be a three blade also, right?
 
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Answers

Danny7 said:
If the whirlwind was a NBGT designed prop, how will the prince manufactured one be different? It will be specifically made for your planes exact numbers?

you mention you will compare this new prince to the catto you have, will it be compared to the old prince one as well? Its a shame you don't have a "standard" prince model to compare it to that is properly pitched for your airplane/ engine.

this prince nbgt model will be a three blade also, right?
Click to expand...

Thanks for asking:

The biggest differences between the WW prop and the one I will have is that the WW is a C/S prop and mine will be fixed pitch. In addition. as you point out, the input numbers are different. My best info is that the WW was optimized for 8000', 150 HP (at that altitude) and 220 mph. Mine was designed for 10,000', 137 HP and 206 mph, approximately. In addition, my "slowdown" numbers are different because the WW is for an RV8 with standard cowl and mine is for a 7/7A with SJ cowl.

It will be a two-blade.

The old Prince prop did not climb as well as the Catto even though it was able to turn about 150-200 rpm more during the climb. I don't have good numbers on this, but maybe 100'/min. I could not properly evaluate top-end because of the pitch issue. It was a very nice prop and very smooth, never needed balancing. I don't recall ever going faster than I can now, but I have no really solid data and I did not fly for extended periods above 2700 RPM, so could not measure top speed. Lonnie's newer designs are what he calls "elliptical" and they do as well for him as the old P-tip designs. Sorry I can't come up with more info on that.
 
won't it be a little difficult to properly evaluate the differences between prop shapes if you will compare your new prop (which will be a 2 blade) to a prop that is a 3 blade?
 
Not the right question, but a good one

Danny7 said:
won't it be a little difficult to properly evaluate the differences between prop shapes if you will compare your new prop (which will be a 2 blade) to a prop that is a 3 blade?
Click to expand...

Well, I am not trying to compare "prop shapes" as such. I'm trying to get the best prop I can. Jack's programs can design a 3-blade, but it's a more expensive prop and the numbers are saying it's not needed here. It is also a PITA to get the lower cowl off with a 3-blade on the A model.

The things you can physically control in a prop's design are pretty limited:
1. planform (the shape of one blade)
2. area (the area of one blade)
3. pitch at each station (twist, but twist is not necessarily uniform).
4. airfoil (sticking with 4412)
5. number of blades (affects total area).

So you can see that you must look at planform and area at the same time as the number of blades. If you see the efficiency fall off because the area is too big (same, here, as too low an aspect ratio) then it would be time to look at a 3-blade. The program predicts efficiency, so this can be done digitally before physically.

You may be interested in knowing that Craig Catto is following this, too, and is toying with the idea of having me test his newer design against the Norris BGT prop, once the data are known. It's all good! I hope we all benefit.
 
New, Simplified Spreadsheet

For those who are interested in details, I've posted the new, simplified version of my power & drag spreadsheet. The one item has the CAFE RV-6A numbers in it for a starter. You can download the file and use any numbers you like. It's a lot easier to see everything at a glance in this one.

It's here, where the others are.

I'm using it to help with prop design. You must know the power requirement of the airplane to get the prop design right. Different speeds and altitudes with different propulsive efficiencies are the targets for any given design.

It does not replace the previous version because it does not go into HOW to develop your initial parameters (as the earlier one does) but it is easier to use when exploring different speeds and altitudes once you have the numbers for the "Key Point".

If you are interested, use Van's numbers for the 6A and compare them to the CAFE numbers.
 
Update: Installment 3 major revision

I have done something that is, I think, new with respect to computing slowdown. Part 3 has been revised and I even added pictures.

Lonnie Prince has the new spec's and is working on creating a CAD image for review.
 
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