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RF4D Glide Polar printer friendly version
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jb92563
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Posted Friday, October 23, 2009 @ 12:15 PM  

Does anyone have a glide performance polar for the RF4D?

I need 3 points on a polar for my GPS Soaring program XCSoar so that it
can display what airports are within glide range based on the speed and corresponding sink rate.

I need three points for the polar.

1) Minimum Sink from the Manual is 54mph with 1.2m/s (260fpm) sink rate

2) Maximum L/D according to the manual is 20:1 at 62mph corresponds to a 1.38m/s (272 fpm) sink rate if my calculations are correct

3) At glide of say 80mph what might the sink rate be?

Anyone have any engine off sink rate figures beyond 62 mph?

Ray

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Bob Grimstead
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Posted Saturday, October 24, 2009 @ 10:30 AM  

Hi Ray,

The best way to get this information is to fly a couple of flights yourself at a representative weight.

I say this because, if you go back to the original French manual it says those figures were obtained 'with minimum fuel and no equipment'. Both Rene and his test pilot, Bernard Chauvreau are tiny guys, and I would reckon they did this in a brand-new airframe with minimal instruemnts, no radio or battery, no upholstery or interior trim, etc etc. There is no mention of what propeller they used either. A feathering single-blade propeller was once available, so they might have used that to get the best possible figures, or a very coarse-pitched one to create minimal drag when it's stopped. Your prop is probably different, and it may not stop exactly horizontal, which is the mimimum drag position. All these things will affect your glide performance.

Exaggerating the performance figures was very common among all manufacturers in the late sixties. You cannot believe a word they said, and particluarly in this case, since Rene was trying to get American certification for single-ignition on the basis of the airplane having a good glide (as he suceeded in doing in Europe).

When I tried it (very carefully, high up, on a calm day with no thermals, wave or ridge lift) the best I got was a little over 1:16 and about 500 fpm sink. I only flew at the book airspeeds rounded up by a few knots, but of course if those original figures were attained at such a light weight, then you should be flying faster if your airplane weighs more.

And I'll bet your ASI is no longer dead accurate.

This would be a good target to go for when you fly your RF4. Time and measure the height loss in some glides at 50, 55, 60 and 65 mph, plot them on a graph and you'll find out precisely how your own personal airplane flies when you are at the controls.

If you use any other numbers, you will merely have a computer program very accurately reproducing utter rubbish.

Go for it. Good luck, Bob

jb92563
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Posted Monday, October 26, 2009 @ 11:50 AM  

Since my first flying day is also going to be the day I fly the 350 miles to ferry it home, any info like that will help.

I'll use 15:1 for the glide computer to be on the safe side and derate those sink figures to be much more conservative.

It just nice to have the "Nearest Airport" function and the glide/sink figures updates the moving map, highlighting all the fields I can make
based on altitude and wind.

Real handy on a cross country in an unfamiliar aircraft.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

D. Porter
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Posted Wednesday, May 29, 2013 @ 02:24 PM  

Ray,

I know this is an old thread, but I found climb and glide polars for an RF3 which should be similar to an RF4.

Don


Scan20001 by d3324p, on Flickr

jb92563
Second Lieutenant

Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583

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Posted Thursday, May 30, 2013 @ 03:55 PM  

Thats great, thanks.

I can use those numbers as a starting point for the Glide computer in XC Soar
so it can generate glide range amoeba that will show how far you can glide with the terrain
and safety height factored in.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

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