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08-04-2006, 06:13 AM
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Join Date: Aug 2005
Location: Mendon South Carolina
Posts: 1,391
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Quote:
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any issues with grass or unimproved strips?
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Yep,
Shattered one hitting a bump at Mallards Landing fltin last year and the othe retained enough dirt/grass to chew up a disc.
Cut more clearance in the next set and it cost a little speed.
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Milt Concannon
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08-06-2006, 06:38 AM
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Join Date: Mar 2005
Posts: 5,685
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More Info Please
I would like to get more information through this forum on the original question. DGlaeser's answer provides the best information so far but the name is so universally accepted that there must be someting special about the shape that relates directly to the words "pressure" and "recovery". I can imagine all sorts of "bar of soap squeezing" anologies and I can remember seeing what I think were pressure recovery wheel pants as early as the Formula 1 airplane Nemesis. I believe they are characterized by: a shape that expands uniformly in all directions from the front with a maximum cross section near the axle location except for the wheel cutout, then starts to reduce cross section in a non-uniform manner such that the sides actually curve in more quickly and have some reflex or concavity resulting in a trailing edge that is a vertical line instead of a point.
If I think of the the wing and lift explaination and apply it here I could generally rationalize some accelleration of the air relative to the surface and reduction of pressure then after passing the maximum crossection it recovers to ambient and effects a little push to the shape. I think there is more to it than that and there must be a lot of experimental development behind the shape that is now so familiar. I wonder which ones I see are actually optimized and which ones are just general copy-cat shapes that do not qualify as pressure recovery wheel fairings?
My plane has the destinction of being caught in the development phase at Van's. The mains are pressure recovery fairings but the nose gear is not. I question whether there is truely anything to be gained by switching the nose wheel fairing to the new design notwithstanding the cost, paint and other negative factors? I also wonder about the exact effect of the gap around the tire? Like others I had some early rub experience and trimmed them back a bit before painting.
Bob Axsom
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08-06-2006, 08:48 AM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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From what I understand, the point of pressure recovery wheel pants is to have the airflow on both sides moving as parallel as it can when it comes off the back. Cessna has been using this style on the 182 since 2001, I don't know how much gain it affected on the 182, but I'd like to find out  .
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Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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08-06-2006, 08:48 AM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Any Recent Aero Graduates?
Bob - I think that you and I both suffer from having been out of school too long! The textbooks I had (and still have on my shelf) were all first printed in the late 40's, when they were just discovering that supersonic flight was posible - but didn't even know about the area rule!
My guess is that the modern tesxtbooks might not even include the concepts of presure recovery pants, becasue in the real world of aero engineering these days, the experimenters are out ahead of the academics....
I just did a search of some of my favorite Aero web sites,and didn't find anything on the topic...but maybe we've got some young guys lurking that can educate us!
Paul
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Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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08-06-2006, 10:41 AM
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Join Date: Aug 2005
Location: McKinney, TX
Posts: 52
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Old Pant vs PR Pant
I have the older, non-PR wheel pants and have occasionally thought about doing the conversion. Anyone out there that did the conversion and has actual comparisons as to the performance impact they received? ie performance with old pant compared to performance with the PR pant?
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Dick Flunker
RV-6A, 2000 hours
North Texas
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08-06-2006, 11:03 AM
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Join Date: Jan 2005
Location: Elk Grove, CA
Posts: 411
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Speed difference of fairings
In Van's accessory catalog and online webstore the following is shown under Sensenich fixed pitch prop section:
"Cruise speeds for RVs with older wheel fairings (narrow cross-section w/ brake blisters) will be 5-6 mph slower and require a prop with approximately 2" less pitch."
Since I haven't got to the wheel fairings yet I am definitely going with the newer ones.
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Mike F
RV-6A wings/fuselage
RV-3 empennage (extra thanks to Mr. Zilik)
RV-4 Plans only S/N 2938
Cessna 152
Elk Grove, CA
VAF #744 Exempt but paid anyway
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08-06-2006, 02:32 PM
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Join Date: Jun 2005
Location: Sugar Land, Texas
Posts: 27
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Per Bob Axom's request here is what I know about the pressure recovery wheel pants. First let me clarify that I am the person that on another thread posted that...I don't fly or have built an RV...but would like to in the future...and that I have scratch built a one of a kind that sort of looks like a small RV4 (tubing fuselage, aluminum wings, C85 engine) One of the things that was scratch built was a set of pressure recovery wheel pants. I have the "regular" wheel pants on the plane now and will soon be testing the PR type. I will let you know, if you are interested, the difference between the two. The following is what I know about PR pants. First it helps to have an inventor buddy that did all the leg work. This inventor explained the theory PR in layman's terms this way to me.... 4 air molecules meet the PR pant at the tip one goes over...one goes under...one goes right ...one goes left. They all remain attached and meet at the back. They don't swirl or meet each other on the sides top or bottom....thus you have no turbulence or separation of flow and less drag (the flow remains attached). This inventor made different pants and flew them until he came up with a design. To make the pants a symmetrical air foil is used. The air foil does not have to have a good coefficient of lift but a good coefficient of drag. If one Looks DOWN at the wheel pants one can see the full air foil...looking from the side, the air foil has been split at the chord. The "Sam James" PR pants are designed the same way....why it's called "pressure recovery" I don't know....I hope this helps....Ivan/Sugar Land, Tx.
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08-06-2006, 02:34 PM
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Join Date: Jun 2005
Location: Sugar Land, Texas
Posts: 27
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Sorry Bob Axom...on the previous post I said per your request and I meant per Paul F. Dye's request...Ivan
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08-06-2006, 04:01 PM
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Join Date: Jan 2005
Location: Roanoke, VA
Posts: 306
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Pressure recovery
For streamline shapes, the air pressure changes as it flows around the body, initially decreasing as it is accelerated toward the point of maximum thickness, then increasing again toward its original pressure as the air is decelerated during its flow to the aft edge of the body. This increase in pressure along the aft portion of a body is referred to as "pressure recovery".
If this deceleration (and resulting pressure gradient) is not gentle enough, the flow can seperate from the body, leading to increased drag. If everything is done just right, the pressure can be fullly recovered, and the flow remain fully attached (and mostly laminar), all the way to the training edge of the body.
One characteristic of low drag laminar shapes is a reflex curve on the aft portion of the body, such as can be observed in the shape of Van's "pressure recovery" wheel pants.
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Dave Cole RV-7 N97DC reserved
dave.cole@cox.net
Started SB April 2004
Hope to fly in 2011
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08-06-2006, 04:58 PM
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Join Date: Aug 2005
Location: Williamsburg, IA
Posts: 366
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I'm just following this thread trying to learn a little about the theory. I found this page interesting also.
http://www.geocities.com/mgd3/flying/wheelpants.htm
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John Roberts
RV-7A - Fuselage
Williamsburg, Iowa
VAF 393
N624KJ reserved
Numbers 6:24 - The LORD bless thee, and keep thee
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