WWI Aircraft Glide Ratios

[hitech]

Rather then fly so far, just measure the time it takes do descend 500 or 1000 ft. Then do the math from your speed in TAS.

HiTech

[FLS]

Thanks. It occurred to me to do it that way, I even grabbed my stopwatch, but I went with the slower less accurate route for some reason. 

[FLS]

Clocked it for 1000 ft, 3k to 2k,  TAS 61-60, so I used the lower one.
Prop windmilling about 400 for F1, 380 for Dr1.
F1       9.1  Time was 1:44
Dr1      8.9  Time was 1:41

[Pyro]

An easy way to do it is to use your speed autopilot and the E6B.  Get in the condition you want (idled, engine stopped prop stopped, engine stopped prop windmilling) and engage the autopilot speed.  Use the .speed command to test at different speeds.  Pull up the E6B display and record TAS and descent rate once a steady state is reached. 

Convert your TAS and descent rate into the same unit, either FPM or MPH is fine.  Remember that your airspeed is traveling along the hypotenuse of a right triangle.  Your rate of descent forms one leg and you need to calculate out the last leg which is the distance traveled over the ground.  The ratio between the ground leg and the descent leg is the glide ratio.  So you need to calculate that leg using trig or geometry and divide the result by your rate of descent.

[FLS]

That's pretty much what I did the second time Pyro. I assume I'm getting higher numbers because I didn't stop the prop. I had expected that windmilling would increase drag. I'll have to try it again with the prop stopped.

[hitech]

FLS a STOP prop will glide better, but are you just throttling back or shutting the engine off.

HiTech

[FLS]

I shut the engine off then waited a bit for the rpm to stabilize before I measured.

Pyro mentioned converting the distance traveled on the hypotenuse to the ground distance traveled and that's what I left out. I used TAS as if it was ground speed. I misunderstood what he was saying initially but it's clear now. Thanks for the help.

[kvuo75]

I shut the engine off then waited a bit for the rpm to stabilize before I measured.

Pyro mentioned converting the distance traveled on the hypotenuse to the ground distance traveled and that's what I left out. I used TAS as if it was ground speed. I misunderstood what he was saying initially but it's clear now. Thanks for the help.

without wind, tas = gs

[FLS]

Kvou75 that's true if you fly straight and level. The point Pyro made here is that I was descending, so the distance I traveled in the air between my start and end point was greater than their distance on the ground. Since I didn't allow for that my glide ratio was high. The F1 actually tested at 5.27 instead of 9.1, which shows the drag from the prop windmilling.

[FLS]

Kvou75 that's true if you fly straight and level. The point Pyro made here is that I was descending, so the distance I traveled in the air between my start and end point was greater than their distance on the ground. Since I didn't allow for that my glide ratio was high. The F1 actually tested at 5.27 instead of 9.1, which shows the drag from the prop windmilling.

Oops, forgot time of flight. That should be 8.9 not 5.27. I still think I'm off though.

[Biggles]

I owned a Gere Sport Biplane for a couple of years, and that thing dropped like a rock after you cut power. A couple of pics:

In the cockpit:


Flying just south of the US/Canadian border (Orcas Island to KBLI):

[pervert]

I owned a Gere Sport Biplane for a couple of years, and that thing dropped like a rock after you cut power. A couple of pics:

If you got a skinhead you'd probably add another 5 minutes to your glide time 

Nice plane, must've been a blast tooling around in her 

[Wmaker]

Very cool plane Biggles!