F1 EVO wing is it worth the extra cash? - Page 4

pierre smith · #31 11-22-2007, 06:16 AM

Hi Bill,
What I brought to the table was the best L/D speed...to go the furthest distance from a given altitude in an engine out scenario, not the final approach speed. During my gliding days, we used minimum sink speed during thermaling, and it was much slower than best L/D speed. I can't tell you if 65 MPH is minimum sink or not. I have on many occasions showed transition students the 105 MPH glide speed in my -6A. An 11:1 glide ratio is way better than the 7:1 you get from Skyhawks and 150's. This is the speed I'd use to go the furthest distance if I need the distance. CAFE's pretty darn good at figuring all this out.

BTW, I use around 75 MPH across the fence in my airplane.

Regards,

Bill Wightman · #32 11-22-2007, 08:54 AM

Pierre,

Interesting report on the 6A, I just read it. (Thks for the link Kevin) Yes, these guys were on the ball with their test methodology.

The flight test here was done at zero propeller thrust, just as you noted. 106 is reported as best L/D, but with propeller thrust/drag taken out of the equation. So, do we have apples/oranges when comparing the CAFE numbers to an actual engine-out windmilling glide? I think so, how about you?

With a windmilling prop up front, my experience has been the windmill drag at higher speeds degrades the glide pretty badly. In an engine-out situation, it would be the L/D for the airplane with windmilling prop up front that you're dealing with, right?

Anyway, nice exchange of ideas here! Wish I had the sailplane hours you've got: my best gliding experience was the time as a new private pilot I had the engine quit on a 172.

Had 8000 feet to play with that time.

Lastly, 70 was a nice number across the fence in my 4. Compares well with your 6.

Happy T-day!!!

Kevin Horton · #33 11-22-2007, 10:22 AM

Quote:

Originally Posted by Bill Wightman

The flight test here was done at zero propeller thrust, just as you noted. 106 is reported as best L/D, but with propeller thrust/drag taken out of the equation. So, do we have apples/oranges when comparing the CAFE numbers to an actual engine-out windmilling glide? I think so, how about you?

With a windmilling prop up front, my experience has been the windmill drag at higher speeds degrades the glide pretty badly. In an engine-out situation, it would be the L/D for the airplane with windmilling prop up front that you're dealing with, right?

The prop's windmilling drag would effectively raise the profile drag (The CAFE guys called this parasite drag) vs speed curve. The induced drag vs speed curve would still be in the same place it was. The speed for minimum drag (and best L/D) is found where those two curves cross (unless the addition of the prop windmilling drag has substantially changed the shape of the profile drag curve). If you raise the profile drag curve, the speed at which those two curves cross will decrease.

I expect that if the prop is windmilling following an engine failure, the speed for best L/D would be a few knots lower than it would be with zero thrust. Also, the CAFE best L/D speed is for 1650 lb weight. If the actual weight is lower, the speed for best L/D will be a bit lower.

If you have an engine failure, it is better to be gliding a bit too fast than a bit too slow. The glide performance decreases quite quickly if you get too slow.

Bill Wightman · #34 11-22-2007, 12:24 PM

Right on, Kevin. The windmilling prop can add gobs of drag. Just take the throttle at cruise speed and chop it to idle while running the prop RPM to full increase. That'll give you an idea of the "engine braking" a C/S prop can produce. Its great in formation, but you better have your shoulder harness tight!

By the way your RV8 site is freaking awesome!! Its in my favorites as of NOW.

Not to mention the airplane itself: Exquisite!

Exquisite = "... of rare excellence of production or execution, as works of art or workmanship" - Websters

Fly safe...

logansc · #35 11-25-2007, 08:39 PM

To all who have contributed to this discussion, this is one of the more interesting I've read on the VAF site. Thanks to all who participated; I always stop to read what Kevin Horton, Bill Wightman, George McQueen, Pierre Smith, and of course, Mark Fredericks have to say. I don't mean to leave anyone out, but you guys always seem to take the time to TRY to get things right and to make best-effort contributions. I, for one, appreciate the trouble you guys always to go to help shine a little light on some of the more esoteric issues associated with our sport.

By the way, wouldn?t it be accurate to say that the EVO wings lower stall speed has at least as much to do with its Fowler flaps as it does with its airfoil, aspect ratio, and span loading?

Now, if someone will just tell me where I can get one of those 210 mph cruise RV-4?s, I might be interested!

Regards,

Lee?

Linedog · #36 11-26-2007, 07:32 AM

Wow...Tom once again is a huge aid to all of us Rocketeers...nice sumation of the EVO/Sport differences. I guess I better not get in a knife fight with an EVO...hadn't thought about the turn rate advantage as applied to ACM...

I have only 100 hours in my Sport and have yet to fly an EVO, but do fly a lot of formation with one... I can't add much to Tom's great sumation, except just to point out a couple of quick things.

1) It amazes me to see how slowly the EVO lands...easily gets off a turn-off earlier than me.

2) We just had the SARL race down here, and the EVOs didn't show an speed advantage over the Sports. HOWEVER, that was a down low sprint race. We normally don't fly crosscountry at 500 ft. Due to the aerodynamics of the higher aspect wing, I am certain it has a big advantage at altitude. It would be interesting to get an EVO and a Sport wing side by side at-say-9,500'. I would be very surprised if the EVO didn't run away from the Sport. (matched airplanes, etc..) Tom could probably talk to this also, as he flies x/c regularly with Wayne, who has one of the fastest Sports around... So..don't take the SARL race numbers out of context!

Either airplane is about as good as it gets...can't go wrong wither way!

logansc · #37 11-28-2007, 05:42 PM

I wouldn't count a well flown Sport wing out in a dogfight...you won't just be fighting wing to wing...

If you get my drift!

Lee...

logansc · #38 11-28-2007, 05:46 PM

I wouldn't count a well flown Sport wing out in a dogfight...you won't just be fighting wing against wing...

If you get my drift!

Lee...

pierre smith · #39 11-29-2007, 07:10 AM

Quote:

Originally Posted by logansc

I wouldn't count a well flown Sport wing out in a dogfight...you won't just be fighting wing against wing...

If you get my drift!

Lee...

Hi Lee,
If you haven't read "Reach for the sky" by Brickhill, you really should. It's a story about the best pilot in the RAF during WW2, Doug Bader. He outflew 'em all, with no legs but prostheses!

Regards,

logansc · #40 11-29-2007, 07:10 PM

Thanks for the heads-up on the book, Pierre! I own and have quite a few biographies and autobiographies of WWII era pilots, Bader is mentioned often! My most recent was an astonishing account of the life of a German Messerschmidt pilot, Heinz Knoke. Holy smokes! 80 victories or something like that, shot down twice in the same day, shot down a P-47 once while on fire, engine out, just before crash landing in a field! Amazing!

You may not remember me, we met when you visited Ridgeland Airport several months ago. I'm building an F1 in my hangar there (dark blue, no engine yet!).

Best wishes,

Lee...