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Feb 02, 2011, 07:28 PM
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sll914's Avatar
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Raven Data Logger Info -- Kinetic 468mph flight


Adrian who posted here recently sent me a Raven data logger

http://www.featherweightaltimeters.com/The_Raven.php

and I had it on the Kinetic for today's 468mph flight. Unfortunately, it only recorded about 3.5min of data but it still looks interesting. I just downloaded it and haven't really made any analysis or conclusions yet.

Lets hear your thoughts...

Spencer
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Feb 02, 2011, 07:47 PM
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daboz's Avatar
And I'll try and get some video up soon...

c
Feb 02, 2011, 07:51 PM
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daboz's Avatar
? almost 90g's
Feb 02, 2011, 11:01 PM
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rockbus's Avatar
How do you get speed out of these graphs?
Feb 03, 2011, 12:08 AM
Rocket geek
You can get a rough estimate of the speed if you assume a circular flight path, and use the average acceleration plus the lap time.

Centripetal acceleration = (Velocity squared) / Radius
Time for one circuit = (Radius * 2 * pi) / Velocity

If you solve the 2nd equation for Radius and put that in the first equation, you get Velocity = acceleration * (lap time) / (2 * pi)

I took a look at three laps that Spencer took between 167.5 and 177.9 seconds on the plot, and eyballing a 35 G average, that gives: (35 * 9.8 * 3.4)/(2*pi) = 189 m/s or 423 mph. This is only a rough estimate, because the flight path wasn't really circular, and I only eyeballed the average speed anyway, but I'll be curious to find out how that compares to radar around that time.

Spencer sent me the raw data, and I'll post some of my own interpretations a little later.

Update: Holy cow, I just noticed that the title of the thread is 468 mph flight. I'm assuming that was measured with a radar gun, and probably later in the flight than the points I picked off that were a little less than 3 minutes in. Now I really wish the recording had kept going through the faster part of the flight. The Raven altimeter that Spencer used is a stock unit that's optimized for rocketry applications, including an auto shut-off when the measured altitude stops moving. If other people are interested in using a Raven for DS recording, I'll make a version that keeps going until the memory gets full.
Last edited by Adrian A; Feb 03, 2011 at 01:24 AM.
Feb 03, 2011, 12:48 AM
Rocket geek
Starting with a zoomed-out view of the lift acceleration (red) and drag acceleration (purple) and temperature (green):



there is a lot of stuff going on, but we'll need to zoom in to see what's happening.
Replacing the accel data with the baro altimeter data:


A couple of interesting things to see here. I agree with Spencer that the temperature data is affected by sunlight. I don't know what he's using for a canopy, but my guess is that it lets in IR, which can affect a very sensitive temperature measurement real-time. The dips look like the correspond to the sun angle to the sensor, while the straight sections are likely in the shade. Considering how fast the sensor is responding, I think that these tiny dips (~ 0.2 degrees F) are an artifact of the light on the silicon, rather than real temperature changes. This is convenient, because it gives an indication of the plane's attitude, with one divot corresponding to each DS lap.

The temperature shoots up as Spencer's plane gets going. 400+ mph will result in noticeable aerodynamic heating. Also, notice how the apparent altitude goes up as the plane starts moving faster. The fuselage probably has an air leak to a low-pressure area such that the altitude shown is probably a combination of real altitude and airspeed.
Feb 03, 2011, 01:15 AM
Rocket geek
Now let's start zooming in on a high-speed portion of the flight. Note that the red plot trace labeled as "Axial Accel" is the measurement direction of the sensor that's spec'd to 70 Gs, which is normally aligned with the major axis of a rocket to measure the motor thrust. In this installation, Spencer aligned it with lift, since that's where the big Gs are for this flight. The "lateral accel" axis is aligned with the plane's velocity here to measure drag.

Above are 5 DS circuits. You can see the airspeed going up twice in each one, with a strong, clean maximum in the airspeed, followed by the sunny part, and then a lower, less-consistent peak in the airspeed. Spencer would have to explain what this means in terms of which transition through the shear layer is which.

Zooming in some more, now with 2 circuits:


You can begin to see that the noise in the lift accelerometer isn't just noise; there's some smoothness to it. But you can see it better when we zoom in to just one DS circuit. Note that the peak G reading here of 67 Gs. There are other higher Gs measured elsewhere in the data. The sensor is specified to have a range of 70 Gs in that axis, and the real measurement range is around 80-85 Gs, which was pinged a few times in this flight. That's a lot of wing loading.


Below I added the drag acceleration back in, and I set the scale to be the same as the lift acceleration. I was expecting to see more of a shift in drag acceleration following the airspeed, but mostly we just see noise in that axis. But check out what the 400 Hz sample rate data shows for the vibrations. What's shown here is just a single second of data, and there are 16 oscillations in the lift acceleration. I think this is the wings ringing at 16 Hz. This is a plane with a 100" span, so to get a 16 Hz natural frequency, the plane is impressively stiff.
Feb 03, 2011, 05:01 AM
Windburner Factory Pilot
swoop119's Avatar
Amazing data.....90g's

Are these data loggers comercially available?
Link?
Feb 03, 2011, 08:07 AM
Rocket geek
Quote:
Originally Posted by swoop119
Amazing data.....90g's

Are these data loggers comercially available?
Link?
Yes. They're available here:

http://www.featherweightaltimeters.com/The_Raven.php

The Raven has been on the market for a little over a year, and now it's probably the most popular full featured altimeter/flight computer for rocketry. If you need to automatically deploy several parachutes or ignite a solid rocket motor from your plane, or measure your plane's altitude on a flight to 70,000 feet, it's great for that. . I got a Parkzone Radian for Christmas, so now I'm hooked on RC sailplanes, and I'm working on some new products specifically designed for RC aircraft.
Feb 03, 2011, 09:25 AM
Registered User
daboz's Avatar

Adrian A+++


Fascinating!



Thank you for your analysis...

Can't wait to hear about the new products for RC!
Feb 03, 2011, 06:15 PM
Registered User
Thanks Spencer and Adrian for posting and analysing the onboard data. It would be interesting to see what the G loadings were at 468mph.
Its also amazing that the electronics can with stand these loadings as well.
The old software with discrete components may have had trouble surviving. Just another advantage of surface mounted stuff.
John
Feb 04, 2011, 12:23 AM
Is it DS'able?
wr_mizzard's Avatar
Very cool data... very cool flight.

-James
Feb 04, 2011, 12:40 AM
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sll914's Avatar
Thread OP
Thanks for your analysis Adrian and for the pointers in using the FIP software. I guess it didn't really sink in just how precise this logger is and how high the sample rate is... Really is an impressive tool.

If you could incorporate airpspeed option up to 600mph-700mph in the airplane version, that would be a great feature to have.

Looking forward to another flight with a larger data set. I also wanted to try a vertical punchout at a known speed to take a stab at measuring the drag and confirming fuselage/interference drag estimates...
Feb 04, 2011, 10:51 AM
Can you DS it??
spotterone's Avatar
that is awesome! I love a good data set, and it's even better when someone analyses it! Amazing to think of the loads on our planes when DSing. Impressive.
Feb 04, 2011, 11:08 AM
Is it DS'able?
wr_mizzard's Avatar
Am I reading the graph right... 44 seconds from powerup to the first dive in? No wasting time tootin' around on the frontside.

-James


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