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        Yippee! Doppler me Don!

#1 The Don Feb 09, 2010 09:05 PM

Doppler me Don!
 
If you guys need a video dopplered I will gladly take a stab at what you have, post a link to the video and also post the air temperature and i will see what I can get.

Don

#2 The Don Feb 09, 2010 09:06 PM

4 Attachment(s)
How to make a good doppler pass:

To make a good doppler pass you need a few things, here are some pointers on how to make good doppler passes.

1) First you want to keep the background noises as low as possible. Flying with a loud gas engine in the background, or adding music to a soundtrack, or talking close to the recording camera can make it difficult to extract the audio needed for doppler.

2) You must fly at a constant throttle setting. For doppler to work, the "source" frequency must remain constant. This means your rpm must be constant during the doppler pass. If you rpm drops (due to voltage sag or moving the throttle stick) then your "source" frequency changes as well and you will not get a valid doppler reading.

3) You MUST fly in each direction at least 5 to 8 times the distance from the microphone to the plane. If your plane passes 100 feet from the microphone, then you must fly at least 500-800 feet towards the microphone and 500-800 feet past the microphone. So the closer you are the better. I shoot for 50 feet and I often place an MP3 player in the flying field, set it to record audio, then fly over it as low as I can. This way you are not flying too close to your camera man. If you do not fly the required distance ratios, then you do not get a complete doppler shift, and you will rob yourself of speed.

4) Fly in a straight line coming to and going from the microphone. Do not pull up or turn. Always fly in a straight line.

5) Do not gun the throttle, you need to be at full throttle as you enter your doppler pass, reach the microphone, then go past the microphone.

6) Use the "rule of 3". This means your approach should be about 3 seconds and your depart should be about 3 seconds. Count in your head each way.

7) Know the outside air temperature. The speed of you model depends on the frequency shift and the local speed of sound. The speed of sounds varies with air temperature so make sure you know the air temp within a few degrees.

When you follow these guidelines you will get fast and complete doppler shift and the reading will be very easy to do.

#3 vvV FANG Vvv Feb 10, 2010 05:12 AM

Hi Don, I tried another few speed runs with the Funjet, not sure if they are usable due to another plane making some noise in the background.

I wonder if the flight patterns look better.

Funjet Speed test 3s (2 min 21 sec)


And you say you had a similar wing to the windrider ele bee i had, what extra carbon did you put in it? Mine ended up folding~

#4 The Don Feb 11, 2010 10:54 PM

1 Attachment(s)
I am getting about 86 mph consistently. However I do believe it is going faster and am willing to bet if you had the camera a little closer the speeds would go up to about 90 mph.

I did have the same Elebee wing. I ran a carbon rod along the leading edge and then a carbon strip along the trailing edge. I also replaced the elevons with balsa wood elevons, I got rid of the canopy and made a recess in the front that helped the lipo so about half of the lipo was in the wing and the other was sticking out.

Don

#5 JIMBAKER Feb 19, 2010 03:40 PM

Try # 2, Orange Crush
 
Hi Don,

Here is another run at it with my racer, Orange Crush. The wind was blowing and I recorded a lot of wind noise, so I don't know if the sound quality is good enough. I think I have a couple of usable passes? If it is faster than the average of 88.3 mph I did before, I'll post it on your speed challenge and make it official. I think I know what is going on now, I believe the horizontal stabilizer is flexing at the higher speeds. It becomes overly sensitive, more so than just what the speed difference should make. I will retire this one and finish OC II; it has a full 5mm spar in the stabilizer. It is all a learning experience! :D

jb:)

#6 The Don Feb 19, 2010 03:56 PM

Where is the file????

#7 JIMBAKER Feb 20, 2010 02:40 AM

Quote:

Originally Posted by The Don (Post 14394771)
Where is the file????

Here it is, sorry about that:o

Orange Crush_Feb 19_2010 (2 min 27 sec)

#8 vvV FANG Vvv Feb 20, 2010 05:16 PM

Don i forgot to thank you for dopplering this for me. Im keen to try and crack the 100mph mark on 3s, and maybe 200kmh on 4s. I will post another video once i get used to the sped and a closer better video.
And thanks for the info on your wing, it looks like the cf spars are about an inch back from the leading edge? I did wonder what size tubes you used.

Cheers man~

#9 The Don Feb 20, 2010 06:37 PM

Quote:

Originally Posted by JIMBAKER (Post 14398624)
Here it is, sorry about that:o
http://www.youtube.com/watch?v=RC5zo0m2iHg

I need to work on the video as the background noise is messing it up a little. I will post what I get.

#10 JIMBAKER Feb 20, 2010 06:42 PM

Thanks Don, I am guessing the wind noise. :(

#11 JIMBAKER Feb 23, 2010 07:26 PM

Doppler Please
 
2 Attachment(s)
Hi Don,

I took my regular camera (Canon PowerShot) with me on this outing the 22nd setup the tripod and got these. This was the Orange Crush racer, to post on the 2010 challenge do I need the whole video? If so I can up load it to youtube.

Thanks, jb:)

#12 The Don Feb 23, 2010 07:46 PM

These doppler VERY well, can you post the whole thing on YT?

Don

#13 Joe 1320 Feb 23, 2010 07:49 PM

Hey Don,

Not sure if you can pull anything out of this but there is a fairly decent pass from 2:04 to about 2:09

temps were 68 F

Starmax A-4 55mm edf (3 min 3 sec)



Possible?

#14 The Don Feb 23, 2010 08:01 PM

Quote:

Originally Posted by JIMBAKER (Post 14398624)
Here it is, sorry about that:o

http://www.youtube.com/watch?v=RC5zo0m2iHg

Jim,

I have tried my best on this video and the background wind noise is just loud enough that it drounds out the sound of you coming and going.

Don

#15 The Don Feb 23, 2010 08:04 PM

Quote:

Originally Posted by Joe 1320 (Post 14429961)
Hey Don,
Not sure if you can pull anything out of this but there is a fairly decent pass from 2:04 to about 2:09

That pass was ~76 mph.

Don


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