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Old 09-22-2008, 05:29 AM
Look out for that tree!!!
Larry3215's Avatar
Join Date: Mar 2006
Location: Gig Harbor, Wa USA
Posts: 7,061

Originally Posted by BEC View Post
Larry, your setup is different than mine. And if I understand what you were going to test correctly, you'd reach the zero thrust point dk_aero spoke of much sooner (low-pitched prop).

I'm sure a dyno and a wind tunnel would be a more precise way to measure this and it would allow controlling the other variable Larry's worried about - battery voltage sag - but a bunch more of us have loggers than we have wind tunnels and dynos....

Yeah, a dyno and wind tunnel would be great, but as Bernard says... we will have to get by with what we have

Yeah, my plane is a good bit different - which is a good thing. The plane Im using for the first test is very draggy and relatively slow and under powered.

I want to see how much things vary - if any - from one setup type to another.

My flights today were of no value. Somehow I had messed up the calibration settings on my Eagle Tree by a huge factor. It was reading 2.1 amps max current on a setup that pulls closer to 15 amps peak. Voltages were off as well but not as much. On top of that I didnt have it set to record RPM

So.. I'll have to wait for another day to re-fly the routine.

In looking at the raw data another bit of a problem occurs to me - thats how to decide which exact data points to compare.

For example - on the initial static run up should we use the first highest peak value or the lowest value it drops down to or the average or pick a point 3 seconds or 10 seconds into the runup?

Then later, during the flight, the same questions apply - where on the curve during the run do you pull a data point to compare?

Im going to approach it this way - unless someone can suggest a better method.

Im going to do the static run for aprox 5 seconds.

Then, during the flight, each subsequent full power run will also be aprox 5 seconds long.

Then I'll take data values from a point about 3 seconds into each run to do the calculations.

Oh - as Dr Kiwi mentioned and I as I said before - Im flying a specific flight patern that will hopefully make it easier to see and calculate the differences and reduce any variations due to climb/dive and throttle changes.

1)static run up on the ground right befor takeoff
2)level flight full power run starting from as low a speed as possible
3)level flight full power run as in #2, then pulling to vertical
4)level flight run as in #2 going into a full power dive
5)land and do another static run up.

All of those will be run at full throttle all the way thru with zero throttle points thrown in between so its easier to see on the graphs.
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