I fly an Ultra Sport 40 with a stock OS 46FX in it.. My only mod to the engine is removing the baffle. She is a screamer (especially in a diving low level pass)............. Ok now for the question.....

How would it be possible to accurately determine airspeed without a radar gun or other form of on-board telemetry?

Doppler. Get a video or sound recording of a low pass.

[link=http://www.rcgroups.com/forums/showthread.php?t=553909]One RCU Doppler thread[/link]

Scroll to the bottom and similar threads are listed.

Great info!!! Thanks!!! I'll be reading tomorrow then... I do have several new videos of the plane. I put my camera on a tripod at the end of the runway and zoomed past it.... I actually nicked the prop on the "last" past.... The prop exploded and I pulled up and killed the engine and came around "Dead stick" and landed......How do I know it was a nick? Because I have the Muffler hanging off the bottom... and there isn't a scratch on it! It tipped the wing tip and stripped the tail wheel off the hub!!!! and the other half of the prop landed in front of the camera.... I'll work on posting that tomorrow.... ..... Thank you so much for the info!!!!!

The WaveOScope Doppler program is easy to use and works well with two stroke engines. Google can translate the page for you.
http://www.sprut.de/electronic/soft/scope.htm

http://www.rcuvideos.com/video/Lowes...#theater_title

This is part of the video I was shooting yesterday.... It's crazy how alive you feel when your plane is screaming across the filed at chest to knee hight and you know that your plane is only one split second from death if you think to much and don't fly the plane.

I'll use this video I got yesterday and run it through these analyzers later on when I get past most of my classes. Mid terms and then finals..... UGh... Almost done though!!!!

Hunster, I get a 118mph for 4 foot left to right first pass, at a guess of outside temperature of 75 dgrees.
Rpm 14k

At my field they would have yelled LOWER. I got 123 mph on the first pass. Where was the wind?

Hey, didnt he go lower and scrape his prop!

There was no wind and the air temp was dropping. it was the low 70s to high 60s. How does that change with the speed.

I understand the colder air has more air molecules deal... but does that increase the speed at which the sound travels?

Oh.... and they were taunting.... But not just lower.... Inverted... Inverted... My Grand mother could fly faster and LOWER inverted!!!!

This side of flying is truly exciting!!!!! I wonder how much more alive it will be with a PIPE!!!!!! [>:] Oh YEAH!!!!

The speed of sound is effected by density and temperature is one thing that does effect density. The Doppler program considers temperature/density to determine speed.

I say a prop strike is low enough. A tuned muffler or pipe should get you to around 130 mph.

Thanks mike.... I knew that air temp had something to do with how sound traveled through the air.

I guess something without a Fuselage would be faster!!!!!!!

I'll enjoy this for a season more....and then reevaluate a new airframe... Guess I better buy a bunch more props!!!! Hee Hee

One of my friends puts Garmon (GPS) in his jet ocasionally. Works well.

Bill