Doppler me Don! - Page 17 - RC Groups
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Nov 23, 2011, 09:43 PM
Fly it like you stole it..
Tram's Avatar
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Nov 23, 2011, 10:29 PM
Indoor Free Flight Modeler
you had a lot of passes!!!

Here is some of what I took:

RCSPeedo : My reading

102.7 105
85.3 86
108.8 110
84.2 87 (curve was not nice choppy, my speed is a guestimate, I would throw this pass out actually)

109.6 107 (voltage sag, I would normally throw a pass like this out as it inflates speed)

85.3 87.8
87.4 91.1
100.4 102.7
113 (the one you said "whatever" = erroneous reading because you chopped throttle so RCspeedo thought it was the doppler shift so the speed was inflated.

I had some discussion about lipo sag here:

My comparison (The one bad reading was due to my cell phone not getting the correct temp from my "location" that is why I mow manually set the local air temp.)

I have found that the app is generally very close to manual doppler but manual dopper does let you see things like throttle drop and voltage sag, depending on how severe these are RCSpeedo may or may not throw the pass out. Typically I see people get high speeds at the end of a flight, well think about that, how will a model go faster on an nearly depleted lipo? The answer is the rpm is slowly dropping during the pass from lipo sag so that shift gets added to the speed shift. So what I do is use the app for ballpark speeds but I also record the audio and then go over my fastest passes to see if they validate as sometime you get an erroneous reading. You had some perfect passes the app gave no reading on (not sure why but have had that happen to me as well) and some passes I would have tossed out that is gave a reading on. I like the app, I just get irritated when a guy does 10 passes at say 95 mph then suddenly gets a 110 mph and says his model is 110 mph because the app said so. Well how does a model suddenly gain 15 mph?

Nov 23, 2011, 10:36 PM
Fly it like you stole it..
Tram's Avatar

Thanks man. I really appreciate you taking the time to check it out.

Sounds like the plane is at least doing better than my estimate of around 75mph.. Looks like it's a solid 95mph bird and maybe 100mph on the right pass..

You're lipo sag analysis seems to actually make sense, as I switched batteries in roughly the middle of the video.

Thanks again.
Nov 23, 2011, 10:41 PM
cmala's Avatar
Thats cool. I never thought about voltage sag adding to the shift but it makes perfect sense.
Nov 23, 2011, 10:47 PM
Fly it like you stole it..
Tram's Avatar
Yep, the 109.6mph pass was the last pass before a battery switch.
Nov 23, 2011, 11:04 PM
Indoor Free Flight Modeler
Yeah you look to be right at the 95ish range. That is going pretty good I had a small 22" wing I bought from the Sylair guys called the X22 and used a 4.75 x 4.75 apc cut down to 4" diameter and got like 100-103 mph on a 3200 KV motor on 3S.
Nov 23, 2011, 11:09 PM
Fly it like you stole it..
Tram's Avatar

Now I need to get my Balsa Shark up and running..
Apr 22, 2012, 07:30 PM
Indoor Free Flight Modeler

Here is what I got on your youtube video of your Habu.
Habu @ 179mph passes and average 159mph both directions! (2 min 57 sec)

These were the two consecutive passes around 2 minutes into the flight. The passes before that I could not see anything in the spectrogram as the wind I guess was drowning it out or maybe this fan has a lot of blades? (I was going to try looking at higher frequencies on the other passes) anyhow, I was about to give up until I heard these two passes go by and they left nice traces at the lower base frequency range for me to doppler.

The first pass I got 171mph and the second I got 136mph for an average of the two of 153.5 mph. Winds appears to be about 17 mph based on the upwind/downwind speed differential.

Joe all I can say is you sure like your EDFs fast!

Apr 22, 2012, 07:51 PM
Ginger or MaryAnn ??
fh64_lucky's Avatar
Yes,I am using the 9 blade Mach Alloy fan so it is quiet!Thank you sir....I know you prolly cant tell, but I am wearing a Wicked T-shirt in the video....
Apr 22, 2012, 07:56 PM
Indoor Free Flight Modeler
I did not notice so had to go back and take a look. Awesome!

Apr 28, 2012, 11:47 AM
Ginger or MaryAnn ??
fh64_lucky's Avatar
Nother crappy windy day,and my camera man had a hard time with this one...I doubt you can a reading but if you can.... Mach alloy 70mm in a spear.
Spear.MOV (2 min 50 sec)
Apr 28, 2012, 12:27 PM
Indoor Free Flight Modeler
Cameraman makes no difference or doppler as I only need the sound, but the wind is rally killing the sound so makes hard to get a doppler, best I can tell you is is the 160-170 mph range on 3 of the passes.

If you have a smart phone or an MP3 player, place it on the ground on the flying field and set it to record the audio (voice recording mode on MP3 or use a voice recording app on a smart phone). It might not pick the wind up so badly. I do that for doppler speeds.

Apr 29, 2012, 02:17 PM
Ginger or MaryAnn ??
fh64_lucky's Avatar
Great idea Don...never thought of that.....This is why I luv ya so much!
May 20, 2012, 09:09 PM
Ginger or MaryAnn ??
fh64_lucky's Avatar
Well,at least I didnt destroy it!Right servo stripped,I caught this on last pass,it was acting funny so I tried and got it down in 1 piece.
Spear 2nd test.MOV (1 min 40 sec)
May 20, 2012, 11:43 PM
Indoor Free Flight Modeler
Last two passes were 168mph and 174mph! Nice!


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