Glide Ratio

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Pat Weeden
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Glide Ratio

Post by Pat Weeden »

Received at BPA headquarters via e-mail:
Hello,
at first, thank you for your nice homepage.

My name is thomas, 25, privatpilot from germany and a big fan of the pietenpol.
I think to me buying a pietenpol in future.

There are a lot of questions.
But for one question i'll find no answere, so i hope you can help me.
My question: How is the glide ratio of the aircamper? Or, how wide a piet will glide when the engine is off.

Thank you for your answere!
Regards from hannover, germany,

thomas
Pat Weeden, Site Admin
Brodhead Pietenpol Association
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taildrags
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Re: Glide Ratio

Post by taildrags »

It would seem that there are enough Piet pilots out there that someone must have flown timed descent tests at best glide speed to have some data points on this. I haven't flown such tests myself, but it sounds like a fun and interesting thing to do on a nice day. Popular lore has it that Piets glide like a brick, but I've never seen any numbers to quantify that. A quick internet search quotes 8:1 as a typical glide ratio for light planes but there are numerous variables... how loaded is the airplane, where is the wind coming from relative to the airplane's track, things like that.

Pat, this might make an interesting one-page writeup for the Newsletter!

Oscar Zuniga
Medford, OR
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Richard Roller
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Re: Glide Ratio

Post by Richard Roller »

When the crank breaks at 500ft, poor.
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KenBickers
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Re: Glide Ratio

Post by KenBickers »

I used Lowry's Bootstrap Approach to Aircraft Performance when doing my Phase One testing of NX313KB. I highly recommend this resource.

I found the best glide (Vbg) to be 57 mph. The glide ratio at that speed is 7.8 to 1.

You can find documentation of these flight tests under the "Files" tab of the Pietenpol FB page.

Cheers, Ken
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taildrags
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Re: Glide Ratio

Post by taildrags »

Ken: excellent information! Seems to solidify the 8:1 rule of thumb ratio for light planes. So (as an example), my home field here at Medford has a pattern altitude of 969 ft. If I respond promptly and correctly to an engine-out and set up best glide at 57 MPH, and my airplane can glide in a 7.8:1 ratio at that speed, in no-wind conditions I might be able to glide 7,752 feet horizontally.

-Oscar
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KenBickers
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Re: Glide Ratio

Post by KenBickers »

Oscar,

I suspect the V speeds may vary a bit across Piets. Recall mine has an extra 18" of wingspan (9" per side).

I found glide and climb tests to be lots of fun. They also helped sharpen my flying skills. For each test, I set up the glide a couple hundred feet above 7000' and would glide at pre-determined speeds through 6500'. Climb tests were conducted the same way, just in reverse.

To make the measuring part easy, I wore a Go-Pro on my chest aimed at the instrument panel. I also temporarily mounted a thermometer on the panel. The video gave me precise measurements of elapsed time as I crossed through the two altitudes, the baro presssure on my altimeter, and the temperature. The rest is just simple math. In the airplane, my only task was to maintain a given speed through the altitude block.

Here's the interesting part. My designated Phase One test area was immediately east of the Continental Divide (in fact the western edge of my test area was on the shoulder of Longs Peak). I chose to stay to the eastern portions of my test area, typically under the northern reaches of the outer rings of the Denver Class B. This kept me over the sprawling plains and mostly clear of light planes. I discovered that even modest winds out of any westerly direction affected my glides and climbs. There is apparently a wave, albeit typically imperceptible, that is induced by the wind flowing over the Rockies. Sometimes this had fairly dramatic impacts on my measured times. I ended up making a lot more measurements over a lot more days than would be required in many other parts of the country.

For your own edification and fun, you might give this a try. I suspect that your terrain might play games with your measurements, too.

Cheers, Ken
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taildrags
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Re: Glide Ratio

Post by taildrags »

Ken; yes- and that's another thing your post prompted: re-familiarizing myself with the airplane's V speeds. I'm going to go out to the hangar and check them. They're clearly presented in the aircraft's operating restrictions, which are in a pocket behind the seat along with the W&B, but I forget what they are. I should probably make a little placard for the instrument panel.

-Oscar
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