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  #21  
Old 01-02-2012, 10:15 AM
hydroguy2's Avatar
hydroguy2 hydroguy2 is offline
 
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Location: Townsend, Montana
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thanks guys, Didn't know it was available from EAA....or anywhere for that matter
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  #22  
Old 01-02-2012, 06:21 PM
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David Shelton David Shelton is offline
 
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Location: Belvidere, IL
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Another good book is "Performance Enhancement of Modern Sailplanes" by Peter Masak. Although it's sailplane oriented, most of it is applicable to powered aircraft.

Trim drag is easily reduced by balancing the aircraft near the aft CG. In cruise, trim drag can be responsible for more than 5% of the total drag. For this reason, modern sailplanes have a ballast box in the tail.
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  #23  
Old 01-02-2012, 07:36 PM
jrs14855 jrs14855 is offline
 
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Location: Lake Havasu City AZ
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Default books

Another book which I have not seen but comes highly recommended is "the collected aircraft performance improvement articles and lectures of Bruce Carmichael". It is self published and I think Bruce sells it direct.
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  #24  
Old 01-02-2012, 07:42 PM
jrs14855 jrs14855 is offline
 
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Default Carmichael book

Aircraft Spruce pn 13-05022, $29.95. It covers among other things, Mike Arnolds AR5, a current world record holder. The AR5 is in the Hiller Museum in San Carlos CA
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  #25  
Old 01-02-2012, 10:44 PM
Bob Axsom Bob Axsom is offline
 
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Default I read Speed With Economy, and others

I read Speed With Economy and other articles and they are great. However, I believe their best value is the experimental insight and "can do" motivation. I gained 14 kts TAS since my wife and I built our RV-6A but none of the modifications were copied from a "How To" instruction book. You have to look at your airplane and recognize drag and eliminate it methodically and experimentally. You will come to realize if you chose to follow this path that some logical speed mods will not provide more speed in real life. When they work the improvements are sometimes so small that the gain is lost in the test method error margin. To date my best speed mod is the current lower cowl baffling which yielded 4 kts when that exact combination was put together. I have tried modifying it several times based on thoughts and comments from people I trust like Scott McDaniels but every one has reduced the speed until I backed out the mod. It is a wonderful pursuit Brian I look forward to your future race speeds.

Bob Axsom

Last edited by Bob Axsom : 01-03-2012 at 03:45 AM. Reason: typo
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  #26  
Old 01-02-2012, 11:12 PM
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hydroguy2 hydroguy2 is offline
 
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Hey Bob, I figured reading can't hurt. I know so little about drag reduction, I'm hopeful a little background reading will help move in the correct direction. You posts on mods and testing has been a great insight. I wish I was organized enough to document everything as methodical as you.

I have some other life stuff going on, but still am trying to make the mods, do the testing and get to 4 or 5 races in 2012.
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  #27  
Old 01-02-2012, 11:43 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Wow Bob.... Thanks for the nice compliment... Here on VAF I am much more accustomed to being criticized or yelled at...

When it comes to drag reduction, there are many others in the RV building community that have spent much more time experimenting, and who have learned much more than I have (your self included). It is one of the things I most enjoy reading about and learning from here on VAF (as long as it is obvious the person writing is using some testing procedures that are likely to give some valid data).

One thing that might be worth re-emphasizing (I know Bob has many times), is that speed gains with aerodynamic clean up on RV's is not easy, and purchasing Kent Paser?s book is not going to give you an RV-4 with performance equal to Dave Anders (a lot of his speed gain was also HP related BTW).

Don't get me wrong, I have owned Kent's book for many years and have read through it at least once, but the fact is, if you do drag reduction modifications to an airplane that results in a 60+ MPH top speed increase, you started with a horribly draggy airplane (in fact that is exactly where the origin of RV's comes from... a very draggy airplane... a Stits Playboy, and Vans willingness to invest some effort into making it better)

The basic RV airframe is refined enough that if you build a straight, well built airplane with properly aligned fairings, and you do a reasonably good job on some of the other well known finishing details, gaining speed performance over and above what the published specs are is going to take more than simple effort.

Slightly related rabbit trail....
One thing that always gives me a bit of a chuckle is when someone reports how great the propellers are from XXX propeller company are because when he removed his old prop and installed the new one he just got, he gained 14 MPH in top speed. He never mentions anything about the change in climb performance, engine RPM, or any other details related to the old propeller.
More often than not, his new propeller is probably not much different than most of the other prop brands available (if they would be properly matched to the airplane, most prop makers props would probably all be within a few MPH of the same speed). If his original prop brand had been properly matched to his airplane, the overall performance probably would have been quite close.

Now I know of a few people who have tried a bunch of different propellers on the same airplane, and done detailed testing during the process. When they write something about their experience, I move closer to my computer monitor so that I can be sure to not miss anything.

I now return you to your regularly scheduled mishmash of RV factoids.
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  #28  
Old 01-03-2012, 07:00 AM
sheepdog sheepdog is offline
 
Join Date: Jul 2009
Location: Clear Lake, IA
Posts: 56
Talking Speed

Years ago two friends had a friendly competiton with their RV-6s one a
taildragger and the other nose wheel, they changed the induction system, fairings ect. both were 160 hp fixed pitch and both were able to to cruise at 200 mph This was in an old Rvator that I loaned out. I was wondering if someone out there may have a copy that we could link to

Flying RV-6 and accumulating parts for a rocket
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  #29  
Old 01-03-2012, 07:08 AM
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GLPalinkas GLPalinkas is offline
 
Join Date: Jan 2005
Location: Venice, Fl
Posts: 1,020
Default Go To Guy

Quote:
Originally Posted by rvbuilder2002 View Post
Wow Bob.... Thanks for the nice compliment... Here on VAF I am much more accustomed to being criticized or yelled at...

When it comes to drag reduction, there are many others in the RV building community that have spent much more time experimenting, and who have learned much more than I have (your self included). It is one of the things I most enjoy reading about and learning from here on VAF (as long as it is obvious the person writing is using some testing procedures that are likely to give some valid data).

One thing that might be worth re-emphasizing (I know Bob has many times), is that speed gains with aerodynamic clean up on RV's is not easy, and purchasing Kent Paser?s book is not going to give you an RV-4 with performance equal to Dave Anders (a lot of his speed gain was also HP related BTW).

Don't get me wrong, I have owned Kent's book for many years and have read through it at least once, but the fact is, if you do drag reduction modifications to an airplane that results in a 60+ MPH top speed increase, you started with a horribly draggy airplane (in fact that is exactly where the origin of RV's comes from... a very draggy airplane... a Stits Playboy, and Vans willingness to invest some effort into making it better)

The basic RV airframe is refined enough that if you build a straight, well built airplane with properly aligned fairings, and you do a reasonably good job on some of the other well known finishing details, gaining speed performance over and above what the published specs are is going to take more than simple effort.

Slightly related rabbit trail....
One thing that always gives me a bit of a chuckle is when someone reports how great the propellers are from XXX propeller company are because when he removed his old prop and installed the new one he just got, he gained 14 MPH in top speed. He never mentions anything about the change in climb performance, engine RPM, or any other details related to the old propeller.
More often than not, his new propeller is probably not much different than most of the other prop brands available (if they would be properly matched to the airplane, most prop makers props would probably all be within a few MPH of the same speed). If his original prop brand had been properly matched to his airplane, the overall performance probably would have been quite close.

Now I know of a few people who have tried a bunch of different propellers on the same airplane, and done detailed testing during the process. When they write something about their experience, I move closer to my computer monitor so that I can be sure to not miss anything.

I now return you to your regularly scheduled mishmash of RV factoids.
Scott, just wanted to let you know that for a lot of us you are one of the "Go To Guys" for words of wisdom. We may not make the noise that the others do but we are "listening" just the same. Thank you for helping me build my -6 even though you probably didn't know it I can't count how many times I used the VAF advance search feature and your handle.... rvbuilder2002.

Thanks again for all your help.

Gary
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  #30  
Old 01-03-2012, 10:30 AM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default It was anexcellent article

Quote:
Originally Posted by sheepdog View Post
Years ago two friends had a friendly competiton with their RV-6s one a
taildragger and the other nose wheel, they changed the induction system, fairings ect. both were 160 hp fixed pitch and both were able to to cruise at 200 mph This was in an old Rvator that I loaned out. I was wondering if someone out there may have a copy that we could link to

Flying RV-6 and accumulating parts for a rocket
I was an excellent article that I remember well and one I was thinking about earlier. It ranks right up there with the prop comparrison test article in RVator. If you can't get what you need, though I don't want to part with it, I will send you my copy. You deserve it.

Bob Axsom
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