Butterflies make RV-10's a whole lot faster!!! - Page 2

Whiskey Charlie · #11 05-13-2006, 06:17 AM

Quote:

Originally Posted by glenmthompson

"gills" added to side of cowling (read - tunnel MUCH, MUCH cooler since now TONS of hot air now leaves the sides instead of all out the bottom of the cowl Glen

Glen,

Is there a thread on the "gills" you have added?
This may be the modification that greatly reduced your drag.

Chuck Stuhrenberg
http://rvparachutes.com

glenmthompson · #12 05-13-2006, 12:01 PM

Jim ordered (his idea, I cannot claim this one, I just blended them in during painting) a set of the "gills" that are sold to be installed also on the bottom of the 10 cowl, and we added them on the sides of the cowl too, next to the heat muffs. Very similar on what is found on the Cardinal's ( I think) cowling. Cessna's gills are chevron shape though, not the slotted Van's style.
When taxiing, there is a very hot stream of air passing the side of the fuselage that can be felt if your hand is stuck out and fwd of the door opening. Can you imagine how much heat goes out that gill at 180 knots?
Drag reduction to a significant order of magnitude we have observed here??? HHHHMMMMM..What say my fellow engineers of the aeronautical type?
This might be a justification maybe...Of my comments in my RV6 speed reduction thread for the huge drag reductions/speed increases one can see with lowering cooling drag? Maybe????
PS,.... bottom line, we are now getting the 201 mph at 75% Van's advertises, and 8 MPH F A S T E R than the B***s to the wall advertised speed of 210! Just how loud can one say WOW!!!! Basically this whole situation is very S.H..
Glen

Whiskey Charlie · #13 05-13-2006, 01:21 PM

Does Vans sell them or where can I get them?

Do you have any pics of the cowl locations where you installed them?

Thanks,

Chuck

rvbuilder2002 · #14 05-13-2006, 10:15 PM

Quote:

Originally Posted by glenmthompson

Drag reduction to a significant order of magnitude we have observed here??? HHHHMMMMM..What say my fellow engineers of the aeronautical type?
This might be a justification maybe...Of my comments in my RV6 speed reduction thread for the huge drag reductions/speed increases one can see with lowering cooling drag? Maybe???? Glen

It likely added drag not reduced it (though it is probably a small enough amount that it would be difficult to measure).

Having an airflow spill out into the airstream disturbs the flow on the skin surface causing a turbulent flow which will produce more drag down stream of this point.

Speed is gained when you reduce drag in the path that the engine cooling air flow takes. This air can be considered the same as air that is flowing around the airplane on the outside.
Causing more air to flow through the cowl without doing anything to make it flow more freely (with less drag) will likely slow you down (though probably very slightly in this case).

This is one of the reasons some airplanes have cowl flaps. To get enough air through the cowl for engine cooling when flying slow at high power such as when climbing (needing lots of cooling) but then reduce the amount of flow at high speed to reduce the cooling drag (and avoid over cooling the engine).

Airplanes like the RV-10 (actually all RV models) are a compromise in cowl design. Avoiding the complexity (and associated maint., etc.) of cowl flaps, the cowl inlet and outlet sizes are designed to cool well in most conditions but still have the minimume flow possible for the best drag situation. I think the principle of the louvers is that at lower speeds the air can more easily exit into the airstream flowing past the openings. At higher airspeeds it is more difficult for the air to merge into the airstream which sort of automaticaly reduces the amount of air flow through the cowl. An automatic cowl flap in a way, though not as low in drag as actually closing up the size of the opening as a cowl flap does.

flyingdefinescontent · #15 05-13-2006, 11:11 PM

Your enthusiasm is addicting. Stop it! I can't afford it yet.

Maybe the hot air escaping provides MORE thrust, similar to a jet engine, and also similar to the belly cooler on a P51?

Than again, maybe not. But it sounds good doesn't it?

brenthg · #16 05-15-2006, 05:00 AM

Quote:

Originally Posted by Whiskey Charlie

Does Vans sell them or where can I get them?

Do you have any pics of the cowl locations where you installed them?

Thanks,

Chuck

Here's the best photo we have of the cowl vents added. N331JH is still in a hanger in Harper, KS and I'm down here 'neath the sun and the stars. Will have to wait until my Dad returns and get a better photo and post it FYI.

Would the paint job make it faster? Maybe it could be the butterfly effect, huh?

Brent

Whiskey Charlie · #17 05-15-2006, 06:11 AM

Thanks for the pic.

Looks like the side vents are creating less drag on the bottom by letting some
air through the sides instead of the bottom.
I bet there's alot of bottom drag created with all the air trying to exit
the bottom and going around the exhaust pipes.
Remember how much drag round pipe shapes make (like gear legs).

Chuck Stuhrenberg
http://rvparachutes.com

Mike S · #18 05-15-2006, 08:19 AM

Scott posted

"Having an airflow spill out into the airstream disturbs the flow on the skin surface causing a turbulent flow which will produce more drag down stream of this point."

This IMHO is not always correct, I remember expirements where air was purposly injected into the airstreem just aft of the wing high point in an effort to reduce drag-----worked. I think it was something the Air force did.

This is actually incroporated into some modern high perf gliders also.

The key here is WHERE the airflow is introduced, and how much.

Mike

glenmthompson · #19 05-15-2006, 09:34 AM

This is a good pic to show the cool LED nav lights I built for Jim as well....., Painted inside the lens red/green for an even cooler effect in the dark.
As far as the mention of the gills, I think too and have previously mentioned that the drag around mufflers, engine mounts, large sharp angles on exit....Are HUGE drag areas. Is this significant on this plane? Hmmmm, please lets maybe see others install "Headberg Gills' and do some comparing! BTW these gills, as I prev. said, are a Van's part, the gills are installed on the bottom of all 10's cowls in a pair, one on each side on the flat bottom near cooling air exit. I have seen similar, longer & skinnier ones on some 8's. When I get Jim back to Fl. this week from Kansas, I'll see if we can dig up the part number.
All I know is that we are getting faster speeds than Vans at power settings above 75%, and that REALLY intrigues me, lemme tell ya. Remember boys and girls, the faster ya go, the more significant the results from drag reductions.....HHHMMMM
Glen

glenmthompson · #20 05-15-2006, 10:01 AM

[quote=Whiskey Charlie]Glen,

Is there a thread on the "gills" you have added?
This may be the modification that greatly reduced your drag.

Chuck Stuhrenberg
http://rvparachutes.com[/QUOTE
IMH(experienced)O, these gills could very well be the solution to AT LEAST the tunnel heat problem, ( But lemme ask something here,... is a built in stove really a problem anyway? I mean, I love my eggs, and, did get to experience 2 engine failures when I boiled my fuel along with my eggs during testing) without significant changes to the tunnel area, ie. sub floor installed there to protect fuel pump, lines, legs, etc. What say 10 builders about another thread to discuss this?
I am interested in hooking back uo Jims' cabin heat to at least one heat muff ( Jim got cold on his trip last week flying to Kansas), and blocking the other one we have vented to the tunnel for better cyl. cooling. Then I am curious to see if we can still fry eggs on the tunnel now that we have the gills installed.
Glen