Sep 17, 2006, 09:13 PM
Wonderfully Wicked
Willoughby, Ohio
Joined Jan 2002
13,668 Posts
Cool
Doppler airspeed measurements

I was disappointed today that I was unable to get a radar gun speed on my little pylon model. I did some research and found out that unless I am loooking to spend \$700-\$1000 on a radar gun it will be VERY difficult to radar gun a small model like this which has such small frontal area. By the time you get a reading the plane is at too much of an angle and you the error is quite high. The Bushnell gun I got seems to be more suited for models in the 36" span or greater and smaller than that is a real hit or miss and depends on the intestinal fortitude of the guy willing to stand as a model swoops by 5ft above their head. Instead I dug into alternate methods and found the doppler shift method. The premise is quite simple, make an audio recording of your model flying by, then the frequency shift tells can tell you the airspeed.

I found this website which give you the idea behind it:

http://www.sprut.de/electronic/soft/scope.htm
It is free and it is in German, but that will not stop me!

Then I took my daughters MP3 player to the park (it has a audio record feature). Then started recording. You want to get a nice recording of you standing still and the model flying overhead. The nice thing is that you can be a little higher on the speed passes. I then took the recordings and made small WAV files about 4 seconds long, two seconds coming to you and 2 seconds going away from you. Then you open that in the Oscope software. You will see S shaped lines, then just left click on the left side and right click on the right side. You speed on km/hr will be displayed. To convert to MPH just multiply by .6217.

Here are the results I came up with:
My Minispeedwing = 136km/hr = 84.55mph
Bill's Scrambler = 141km/hr = 87.66 mph
My Pylon Model = 193km/hr = 119.98mph
Matt's Overloard = 137km/hr = 85.17 mph
Now the other day Bill clocked me at 83 and I clocked him at 84 with the radar gun. The winds today seemed about the same as the other day when we radar gunned them, so it seesm to corrolate pretty well.

Here is a screenshot showing Matts file and how you do the analysis.

# Images

Last edited by The Don; Sep 17, 2006 at 09:21 PM.
 Sep 17, 2006, 09:17 PM Road-Runnerus Digestus willoughby Joined Oct 2005 597 Posts Awesome Don! 119 mph! do not look us in the eyes....we are not worthy! here is the website translated in english.... english bill Last edited by wile_e_coyote; Sep 17, 2006 at 09:24 PM.
 Sep 17, 2006, 09:18 PM Suspended Account Mentor, OH Joined Dec 2004 8,426 Posts you didn't mention the "HOLY @%**!!! that almost ended all testing. that little pylon racer was SCREAMING!!!!
 Sep 17, 2006, 09:25 PM Wonderfully Wicked Willoughby, Ohio Joined Jan 2002 13,668 Posts The audio files are hysterical. I have kept them in full length format. Too funny to delete. Don Latest blog entry: Indoor Free Flight columnist for Model...
 Sep 17, 2006, 09:31 PM Road-Runnerus Digestus willoughby Joined Oct 2005 597 Posts hey don can you send me mine so i can try the program? thanks! bill
 Sep 17, 2006, 09:32 PM one game away... Willoughby, Ohio Joined Apr 2004 3,891 Posts I have to say I'm shocked. I thought that your and Bill's wings were at least +50% faster than mine. Maybe the size difference accounts for my misperception. I only wish we had a video of the pylon racer''s near terra firma incident.
 Sep 17, 2006, 09:37 PM Road-Runnerus Digestus willoughby Joined Oct 2005 597 Posts heres the video.... bill Last edited by wile_e_coyote; Nov 01, 2006 at 10:24 PM.
 Sep 17, 2006, 09:38 PM Wonderfully Wicked Willoughby, Ohio Joined Jan 2002 13,668 Posts Matt, I think the size is tricking you. That other day we were flying down by the lake and you and me were both up at the same time we were just about dead even. Yes that would have been something to see, I am just glad it did not pancake in the ground! Don Latest blog entry: Indoor Free Flight columnist for Model...
 Sep 19, 2006, 08:29 PM ukiMig29 Joined Sep 2006 3 Posts Cool Anton
 Sep 21, 2006, 07:30 AM How high will it go? Greenwood Lake NY Joined Oct 2003 3,351 Posts I downloaded waveosscope but I am not sure if I am doing all right I got 2 readings, 84kmh and 137kmh Both much less than I expected, but this is my first speed plane. I am adding the video, maybe someone else can do it, and tell me if I am doing anything wrong. It's a projeti running a mega 16/15/3 (I think, can't see label) just bought the plane, and a 5.5x4.3 graupner prop. I would love to get over 100mph with this plane. http://www.rcgroups.com/forums/show...565#post6099545 Latest blog entry: Plastic prop repair
 Sep 21, 2006, 08:02 AM one game away... Willoughby, Ohio Joined Apr 2004 3,891 Posts I forgot to say 'Thanks' Don. I didn't know that you were analyzing mine at all that day since it seemed slow compared to the mini wings (in my eyes anyways). It's nice to have an idea of how fast it's really going. Matt
Sep 21, 2006, 02:25 PM
willoughby
Joined Oct 2005
597 Posts
Quote:
 Originally Posted by antslake I downloaded waveosscope but I am not sure if I am doing all right I got 2 readings, 84kmh and 137kmh Both much less than I expected, but this is my first speed plane. I am adding the video, maybe someone else can do it, and tell me if I am doing anything wrong. It's a projeti running a mega 16/15/3 (I think, can't see label) just bought the plane, and a 5.5x4.3 graupner prop. I would love to get over 100mph with this plane. http://www.rcgroups.com/forums/show...565#post6099545
 Sep 21, 2006, 04:34 PM How high will it go? Greenwood Lake NY Joined Oct 2003 3,351 Posts http://www.rcgroups.com/forums/showthread.php?t=572565 I don't know why that link stopped working, it was fine last night. This one should be good. Latest blog entry: Plastic prop repair
 Sep 22, 2006, 12:02 AM Wonderfully Wicked Willoughby, Ohio Joined Jan 2002 13,668 Posts I am getting about 140km/hr which is about 87 mph and looks about right on the video. How many amps you pulling on that motor? Maybe a 5x5 prop would be better, that is 16% more pitch which would get you in the 100mph range. Don Latest blog entry: Indoor Free Flight columnist for Model...
 Sep 22, 2006, 05:21 AM How high will it go? Greenwood Lake NY Joined Oct 2003 3,351 Posts I wonder what you are doing different than me, to get that result. I used sound recorder to record the sound from the video, is that correct? Not sure the amps, I think it's over 30. I hooked up my power analizer very quickly at NEAT, and saw 40 amps for a brief second. LAter today, I will be running a better test. But 87 is way more encouraging than the number I had. I will also be making a better video as soon as I can. Latest blog entry: Plastic prop repair