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Wheel pants

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cdewey6969(at)yahoo.com
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Posted: Sat Jan 20, 2007 8:43 pm Post subject: Wheel pants

"pressure recovery wheelpants" can you explain how

these differ from regular wheelpants?

--- Brian Whittingham <dashvii(at)hotmail.com> wrote:



 	  Quote: 	
		   

 Whittingham" <dashvii(at)hotmail.com>

 

 Charles,

   The parachute on the Lightning is behind the

 seats.  Mr. Davis whose 

 airplane just flew a day or two ago is going to add

 an autopilot after he 

 flies the time off and gets it back home.  So he

 should be able to tell you 

 how the install was.  Can't be too hard though if he

 decided to wait until 

 after the build and fly-off.  The best guess that I

 have about how the 

 Lightning can be faster without retracts than the

 WT-9 would be that it's 

 almost like comparing apples and oranges.  THe

 lightning paid attention to 

 lessons learned from experience building Esquals. 

 The section of the 

 fuselage aft of the wing remains wide continuing

 back from the fuselage 

 further.  This shape is better for lower drag.  The

 cowling on the Lightning 

 is probably a lot less draggy than the WT-9, but

 that's just a guess.  The 

 wings are a huge part of the total drag of the

 airplane.  I believe this 

 figure is around 75% if I remember correctly.  The

 Lightning wing is a 

 wonderful performer for manuevering flight, cruise,

 speed, and climb.  Have 

 no idea what airfoil the WT-9 uses, but probably a

 less exotic and copy of 

 the old Clark Y or something.

 

 Now there's been some interesting discussion about

 landing gear drag.  I can 

 tell you that wheels and gear legs unfaired create a

 lot more drag than 

 faired ones.  Buz had a huge speed increase just by

 putting on the fairings 

 and wheelpants.  We never got a chance to test an

 Esqual fairing against a 

 Lightning one though.  Cirrus and Diamond aircraft

 had considered making a 

 retract for their single engine planes, but found

 that with "pressure 

 recovery" wheelpants the drag was negligible.  The

 insurance, weight, and 

 complexity increases with retracts.  The Lightning

 has pressure recovery 

 wheelpants that are similar to the ones you'll find

 on the Van series of 

 aircraft.  They minimize drag moreso than just a

 normal faired wheelpant 

 because the airflow stays attached to the unit

 further aft.  I've not flown 

 the fixed gear or retractable WT-9, but I bet the

 speed difference isn't 

 over 2-5 knots total.  It is an interesting debate,

 but if I was going to 

 design a high speed single I think that I'd make it

 fixed gear to help with 

 insurance and as a pilot it's just less to go wrong

 and have to maintain.  

 (although I do kind of like the old Mooney's with

 the all manual Johnson Bar 

 gear, emergency and normal gear extension is the

 same procedure!)  Brian W.

 



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dashvii(at)hotmail.com
Guest

Posted: Sat Jan 20, 2007 8:59 pm Post subject: Wheel pants

Charles,

   I have some pics somewhere of the differences in the wheelpants.  I 

believe the idea originally came from a NACA report and was first used by 

the Cessna company.  If you look down from above it is very much a teardrop 

shape.  The design has been windtunel tested and proven to produce less drag 

than simply putting a minimal area fairing around the wheels.  The term 

pressure recovery comes from the shape producing a low pressure area in the 

spot where the boundary layer would normally seperate from the standard 

fairing.  This helps to "suck" the layer back down, reattaching it to the 

surface of the fairing and keeping it attached longer.  This helps to reduce 

the amount of drag.



The same idea is used on the wing section.  It is a highly laminar flow 

wing.  (I'd love to do some oilflow or tuft testing on this wing!)  It uses 

the same idea to help the boundary layer stay attached to the wing further 

back.  This helps to reduce the amount of parasite drag and therefore the 

total drag on the plane.  If you read my earlier pirep you'll see references 

to dive testing the Esqual as compared with a Lightning.  The Esqual wing is 

a dragier planform.



Buz's Esqual tested the Lightning wheelpants and gear leg fairings.  Between 

this and a Lightning cowling (modified because the noselengths are 

different) he saw almost 50mph over a stock Esqual.  So there's definately 

drag reduction there.  What we don't know is how much more speed he got than 

if he had a non-pressure recovery wheelpant, like on the Esqual.  I can't 

remember but I believe that Buz also has the same wheel that is found on the 

Lightning which is wider than the Esqual, but I can't confirm that.  Brian 

W.



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