# Thread: L/D Ratio of an RV 3 ?

1. ## Re: L/D Ratio of an RV 3 ?

Autoreply, Thanks again, I'm looking at that now. I will ask Jan what he uses for CDo to get his predicted L/D.
Fly2kads, So vey true about the program, however it is well worth the asking price, I've had all sorts of fun playing with this. At the very least it gives a guide even with a WAG on L/D. It's good to get feed-back as to the accuracy of the program, I'm very impressed with it overall.
Thanks for all the comments - it all helps.
George

2. ## Re: L/D Ratio of an RV 3 ?

X-Plane will give L/D in any speed or attitude. If you input correct numbers.

3. ## Re: L/D Ratio of an RV 3 ?

Autoreply, I looked up Sadraey for CDo and there are some guides there -'e' should be easy enough with his formula and there is a scale 'from/to' for CDo. I will do some comparisons within that scale and see what eventuates. The JC prop Program does it's own L/D estimates so that may be helpful as a comparison.
George

4. ## Re: L/D Ratio of an RV 3 ?

Autoreply, Well I did the maths and will have to check everything again, but at this stage all I got was 9.42 L/D Ratio -(Bugger!!). 'e' was a little low at 0.64, Sadraey Gave from 0.65 to 0.7, as a guide.
George

5. ## Re: L/D Ratio of an RV 3 ?

Originally Posted by Himat
The L/D ratio is related to the wing aspect ratio, but not a direct function of the wing aspect ratio. NACA/NASA published a long list of L/D and A/R for different planes.

Thank you !

8. ## Re: L/D Ratio of an RV 3 ?

Good planes have AR>>30
I am not quite sure a 50+ feet span wing would look right on the RV-3.
At least one of the great aeroplanes in history did have an A/R below 2.
That plane did have a best L/D above 12.

9. ## Re: L/D Ratio of an RV 3 ?

Originally Posted by Lendo
Autoreply, Well I did the maths and will have to check everything again, but at this stage all I got was 9.42 L/D Ratio -(Bugger!!). 'e' was a little low at 0.64, Sadraey Gave from 0.65 to 0.7, as a guide.
George
Sounds about right. Which CD0 did you use? CAFE tested a few RV's. EFPA was consistently between 1.8 and 2.2. I wouldn't expect the RV3 to be much lower, maybe a clean one at 1.65 or so. Should be straightforward to compare the used CD0 to that value.

10. ## Re: L/D Ratio of an RV 3 ?

If Van's Nr is correct they usually are, I make a wild guess and say L/D on a slippery RV-3 is 10.6-10.7 without propeller but with spinner, but never seen one like that.

11. ## Re: L/D Ratio of an RV 3 ?

I'm going purely on WAG. 6.5-7.8 L/D.

I know that's lower than most guesses here, but I'm going "Price Is Right" low ball. If you take the prop off and tape some curved cardboard over the nose & air intakes.... 8.5/1.

It's a fairly clean design, the RV guys say that landing gear intersection fairings make a big difference, ( a sign the big things are proper ) but it's a fairly low A/R and The Wing Is The Thing.

12. ## Re: L/D Ratio of an RV 3 ?

Originally Posted by Jan Carlsson
If Van's Nr is correct they usually are, I make a wild guess and say L/D on a slippery RV-3 is 10.6-10.7 without propeller but with spinner, but never seen one like that.
If you take away the propeller, you have to add in the tow hook.

CAFE developed a zero propeller-thrust sensor that used a proximity sensor to determine when the crank was floating between the front and back faces of the thrust bearing. Scroll down here to read about it http://cafe.foundation/v2/aboutcafe_orderfromchaos.php

I don't know if they used it when testing the RV's, but the greater-span -9A had an idle power glide ratio of 12 : 1. The -6A had a calculated Oswald span efficiency of 0.851 and a glide of 11.39 : 1.

BJC

13. ## Re: L/D Ratio of an RV 3 ?

The 10.6 - or so L/D I got from my propeller design software, is a result from the performance page, the L/D with propeller stopped isn't useful for propeller calculation, only important when it stop spinning.

14. ## Re: L/D Ratio of an RV 3 ?

Originally Posted by Jan Carlsson
The 10.6 - or so L/D I got from my propeller design software, is a result from the performance page, the L/D with propeller stopped isn't useful for propeller calculation, only important when it stop spinning.
Yup, lots of things suddenly get important when the propeller stops.

BJC

15. ## Re: L/D Ratio of an RV 3 ?

Is that 10.6 at best L/D speed or cruise speed?
I would think the prop is designed for cruise speed.

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