The (ongoing) Saga of My Norris BGT Prop

[hevansrv7a]

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:

• Part 1
• Part 2 posted Sep 16
  
• Part 3 posted Sep 26
• Part 4 (coming soon)
  

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.

[pierre smith]

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

Sounds a lot like what he does,

Best of luck,

[hevansrv7a]

I just posted Part 2 and have begun working on Part 3.

[logansc]

This is really interesting stuff! Thanks for taking the time to post...


Lee...

[elippse]

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!

[hevansrv7a]

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.

[hevansrv7a]

I've updated the first posting to include Part 3 which I posted 9/26.

[Danny7]

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

[hevansrv7a]

Originally Posted by Danny7

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

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.

[Danny7]

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?