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  #391  
Old 07-13-2012, 02:34 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default Here are the table and chart

Next I have to convert this development patch work cover and outboard fins into a single piece and retain the center fin as is - hopefully in the next few days.





Bob Axsom
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  #392  
Old 07-13-2012, 10:11 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default Rough cut and fit

The development cover and outboard fences unrolled to pattern flatness.



I had some 0.040" 6061 O bare so that is the first (hopefully the last) single piece copy:



I fit well:

Bob Axsom
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  #393  
Old 07-13-2012, 11:03 PM
Dennis Fox's Avatar
Dennis Fox Dennis Fox is offline
 
Join Date: Sep 2007
Location: Oklahoma City, OK
Posts: 13
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Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.
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  #394  
Old 07-13-2012, 11:51 PM
jrovey jrovey is offline
 
Join Date: Aug 2011
Location: Wickenburg, Arizona
Posts: 26
Default Pitot/COM antenna

Quote:
Originally Posted by Dennis Fox View Post
Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.
I am currently working on eliminating the COM antenna. I don't want to put an Archer antenna in a wingtip. My idea is to create a COM antenna/Pitot tube combination. Every time I look at my simple 1/4" pipe pitot tube I think "why can't that also be my antenna"? I have searched on the internet about this idea for a GA airplane and have not come up with anything. Someone else must have thought of this idea before.

I have been reading about handheld tranciever antenna design from HAM radio sources since they are a shorter 1/4 wave antenna than a standard whip. The VSWR/field strength meter I ordered will show up next week and I will start experimenting. I expect the performance will be less than the bent whip currently on the belly of my RV8 and not sure what the result will be but looking forward to the learning process.
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  #395  
Old 07-14-2012, 01:14 AM
Bob Axsom Bob Axsom is offline
 
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Posts: 5,685
Default Yes I have thought about it but ...

Quote:
Originally Posted by Dennis Fox View Post
Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.
I think about EVERYTHING that touches the air - inside and out - I can't imagine a racer that doesn't. A long time ago I was a guy that worked on com equipment in the Air Force and I draw the line at compromising my com system for anything. During a race I have to make turn calls, finish calls and that's all - pretty trivial stuff - but the plane is my transportation, it's not just a racer.

I live in Arkansas but last Saturday I was in a race in Three Forks, Montana. When I was coming home I was very tired. I had only slept for about three hours because I had to prepare for the race, then I flew the race, waited for the disappointing results and finally it was time to head for home. Storms were over Colorado in the Denver area and I knew from talking to a briefer in Sheridan, Wyoming that they were moving north. Coming south from Muddy Mountain VOR I could see it and I'm flying VFR but on Victor airways. I left the airway to the east, flying to light and lowering terrain, looking for an out. I know it's on me to find the way out and I am too tired to play super pilot, drag out my IFR charts and try to work my way into the system while flying the plane avoiding the storm, etc. Regardless of what CFIs and other perfect pilots do, I Fly the plane and work my way through the options that I personally have control over first. At one point I saw the path to Cheyenne was VFR but a low ceiling. It was not night time but under the clouds it was pretty dark. I was in the 20-30 mile range from the airport and according to the ATIS it was still VFR there. I committed to flying there and I called the tower on the way in. I gave my location and all the usual stuff but I also emphasized that I was not familiar with the area. He said do you see the large tank painted red and white ? I confirmed that I did and he said the airport is not far behind that. As I got in closer at about 500 ft AGL getting squeezed between the land and the clouds I saw the airport and reported it. He cleared me to land on runway 31 and I told him that I had a runway insight to my right but I could not confirm that it was 31. He said no that is a different runway, whatever number it was. So I continued on until another one showed up on the right and we confirmed that it was 31 and I landed and taxied off. I had no Idea where the FBO was because I had not planned to land there but it was a port in a storm and I really didn't care if it was a little awkward. I called ground told the operator I need to taxi to the FBO, I would be staying the night and I was unfamiliar with the airport. He gave me taxi instructions and it was all over but tucking the Blue Bird away and getting a room for the night. Drag could not have been further from my mind. I do unscrew the nav antenna elements during a race but my previous testing of drag effect was not measurable - still if they are off it is less drag. I am sure the bent whips are even less draggy. It's a personal choice but so far I don't mess with my optimized VHF com antennas.

Bob Axsom

Last edited by Bob Axsom : 07-14-2012 at 01:28 AM.
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  #396  
Old 07-14-2012, 06:57 AM
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logansc logansc is offline
 
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Default

Bob: For what it's worth, the SL-40 you sold me works better (has more range and is clearer) on my Rocket transmitting and receiving through a cheap(er) Bob Archer antenna in my right wingtip than does my Garmin 530W transceiver operating through a more expensive exterior Comant whip antenna located on the belly of my airplane.

Based on that (admittedly only a single data point), I would say that you don't necessarily have to give up any communications performance to gain an improvement in drag by dropping your external antenna.

Just a thought...


Lee...
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  #397  
Old 07-14-2012, 08:44 AM
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Alan Carroll Alan Carroll is offline
 
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Location: Madison, Wisconsin
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Default internal antenna

Has anyone thought about mounting an antenna under the canopy, above the passenger's seat? You'd have to build a support structure of some sort and perhaps a ground plane. It would also have to be easily removable to return the airplane to non-racing configuration.

I agree about the drag being pretty low; I remove one of my two com antennas for racing but can't measure a difference in speed.
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  #398  
Old 07-14-2012, 11:24 AM
gereed75 gereed75 is offline
 
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Location: pittsburgh pa
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Bob, I've been following the whole thread. Glad you are finally beginning to see some good results.

The current configuration is looking a lot like the one I fashioned basically on intuition. I have always though that getting the outlet curves smooth is a benefit by minimizing sharp discontinuities that "trip" the airflow into something more turbulent than it needs to be.

Gettin' smooth now!

Have you seen any consistent effect on CHT's.

Continued good results!!
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Last edited by gereed75 : 07-14-2012 at 11:30 AM.
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  #399  
Old 07-14-2012, 12:36 PM
Bob Axsom Bob Axsom is offline
 
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Default The CHTs have increased a little

The CHTs range from around 350 for #1 to 373 for #2 now and before they were 320 to 350. It indicates to me that the air mass flowing through the system has been reduced some.

Bob Axsom
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  #400  
Old 07-15-2012, 11:01 AM
flyvans.com flyvans.com is offline
 
Join Date: Feb 2005
Location: Zurich, Switzerland
Posts: 487
Default

Quote:
Originally Posted by Alan Carroll View Post
Has anyone thought about mounting an antenna under the canopy, above the passenger's seat? You'd have to build a support structure of some sort and perhaps a ground plane. It would also have to be easily removable to return the airplane to non-racing configuration.

I agree about the drag being pretty low; I remove one of my two com antennas for racing but can't measure a difference in speed.
We mounted an ELT antenna inside of the tipup rollbar on the passenger side as COM2. Fine for short range stuff, ground or formation communication. Not useable for inflight/ATC, too limited in range / field of view.

Sounds like the Bob Archer used for COM as well would be a better way to go.... Still possible issues with field of view however.
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