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
libertyman777
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Re: Glide Ratio

Post by libertyman777 »

KenBickers wrote: Mon May 04, 2020 2:06 pm 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 »

Well since some of us are stuck on the ground due to winter weather, I figured more would have time to read stuff than go fly so I pulled out the first logbook on my plane to review the test flights, which were made by Mr. Edwin Johnson down in Louisiana. Here are some verbatim extracts for your reading pleasure. As a point of reference, I have found that in still air and the usual conditions, coming down on short final at 54-55 is just about the best and most fun for me. Here's what Edwin found when doing his test flights. ~OZ
=======

10/16/02, Flight #7. "Speed tests comparing GPS speed with IAS at 1000 feet. All speeds 45-67 within 1 mph of IAS; at 40 mph GPS read 42.6. Two no-power glides to landing to simulate emergency. Glide at 50 mph with my weight [140 lbs] and 2/3 fuel [10 gal in the nose tank] results in sink rate of about 550 fpm. One landing with glide at 50 mph and one with glide at 55 mph. The 55 mph gives a little more cushion for flare. Preliminary climb rate at 55 mph with light weight gave 605 fpm, full throttle." [This is when the plane had the A65 on it. -oz]

11/02/02, Flight #9. "Vx & Vy tests. With pilot at 140 lbs and full fuel Vx = 45 and Vy = 55. Vy gives about 650 fpm and Vx is about 575 fpm, but remember this is not at gross. Two wheel landings. Hesitation when adding full power unless carb heat on, so perhaps carb ice?" [How right he was! Carb ice was what brought the plane down after I got it. -oz] [I have not found Vbg tests in the logbook yet. -oz]

11/10/02, Flight #10. "Stability tests done: positive stability in all three axes- longitudinal, lateral, and directional. Landing in somewhat gusty conditions at Mansfield with wind estimation of about 15 mph, gusting to about 18, about 10 deg R crosswind. Both stall and wheel landings. My findings are that the plane with its light weight is difficult to three-point land as gusts tend to pitch the plane around very easily. Wheel landing with an approach speed of about 50-55 mph are easily done (stall shows about 38 mph) and are highly recommended for gusting conditions. 6 landings."

12/28/02, Flight #15. "Static runup was 2300 RPM on ground (have been told should be around 2100-2150)."

1/1/03, Flight #16. "Beautiful first day of the year. Fuel consumption 3.2 gph with 2150-2200 rpm. Happy New Year. 3 lndgs."

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 prop
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