The POH for my 1958 C-180A doesn't have a speed for Best Glide. There is sort of a Vx- 60 mph and sort of a Vy- 90 MPH. I've heard folks say that Vbg is between the two. That's just a shot in the dark. To me its kinda important to know what speed is best to fly.

At any rate a POH number would refer to a stock wing. My wing has a Sportsman Cuff, the WingX STOl extensions and MA Vgs. Plus you add the drag of those Desser 31's and you have a whole different kettle of fish. I've been wondering what would be the best way to figure all this out so I noodled with Aerodynamics for Naval Aviators and some stuff on the interweb. There is a way to do this by figuring out what the V endurance is, from that you can compute Vrange. My assertion is that AOA is AOA and Min Sink is equivalent to Vendurance.

I ran the test and my numbers were little different than the Sportsman numbers offered in another BCP thread. Probably due to my drag profile. But there were no tests done for Flaps 10. My intention was to do the test with 0,10,20,30 and 40 flap. In the end I only did a full test at 0, and 10 flap. At flaps 20-40 I ran into the stall and any descent rates were well above those achieved at 0 and 10 flap. Since I was interested in only finding min sink I stopped the test. After all, I'm not validating the STCs, just what my airplane does.

The bottom line is that the best Vms I found was at flaps 10 and 43MPH (fr a 290 fpm descent rate) and a Glide Ratio of 13.1:1. Best Glide, Vbg, was at Flaps 10 and 57 MPH (590 FPM) for a Glide Ratio of 14.8:1.

Not too bad for those big tires and struts and all that. It's a test that everyone can try out for your own airplane, the way you usually fly it. Figure out your Min Sink Speed and then multiply it by 1.316 for your Best Glide Speed.

Check out the video.

gunny

Are these shoes all drag or can I classify them as a "lifting body"

Very interesting question... I suggest you try the test out and see what your speeds actually are!

gunny

Gunny,
I have been eagerly awaiting this video.....Thank you my friend!
Gypsy

interesting post!
two remarks/corrections
a) there's a typo (or I don't get it..) 57mph and 590fpm would give you a L/D of 8.5
b) best L/D does not depend on weight (ie wing loading), but the speed at which it's achieved does - it changes with the square root of the weight difference.
Example: run out of gas alone in your super light 170 (1500lbs) vs engine failure at full gross (2200lbs) gives you a 21% difference in best glide speed. Playing with a hypothetical (or even better: measured) polar would tell you how much range you'd give up by flying too slowly or too fast.

140eagles wrote:interesting post!
two remarks/corrections
a) there's a typo (or I don't get it..) 57mph and 590fpm would give you a L/D of 8.5
b) best L/D does not depend on weight (ie wing loading), but the speed at which it's achieved does - it changes with the square root of the weight difference.
Example: run out of gas alone in your super light 170 (1500lbs) vs engine failure at full gross (2200lbs) gives you a 21% difference in best glide speed. Playing with a hypothetical (or even better: measured) polar would tell you how much range you'd give up by flying too slowly or too fast.

Maybe I mis-poke a little (I'll check) the 590 FPM was at 70 MPH, at 57 MPH and 10 flap the descent rate was 339. You get glide ratio from the distance traveled over a 1000' descent. I'll post the spreadsheet on my website flywire.online in a day or two so you can test it out for yourself.

The point of using Min Sink is to maximize time aloft. I used it in this flight test because it was the easiest to test for, rather than do a longer flight or two to find V range. Sounds like another video...

gunny

If you are interested in trying out the Min Sink and computing Best Glide for your airplane I uploaded the spreadsheet on my website on the Hangar Flying Page: https://www.flywire.online/hangar-flying

Keep us posted, let me know if you find any bugs. Have fun!

gunny

Thanks for more quality information Gunny. I've got the MASA cuff on my plane and am adding the Wing X very soon. It'll be fun to see how close I get to your numbers. I know the Sportsman cuff is big glide booster.