- May 3, 2009
- Reaction score
I had a rocket weather cock, turn horizontal, fly for 1000 feet sideways, never getting much above tree level and reported back an altitude of 416 ft.
Altimeter sampling holes blocked / too small / too close to air turbulence? Coulda been a lot of things. Have you ever flown the altimeter and it reported a reasonable altitude? Have you downloaded the data to look at the curve?
Previous flight because it never saw enough pressure change for the launch detect algorithm to trigger.Well it flew across an open field landing between two trees, but seriously, it couldn't have reached more than 100 ft. and I dont have the computer interface yet to download the flight data. I'm thinking turbulance was the best answer here. thanks
OK, but you didn't answer the question: "Have you ever flown the altimeter and it reported a reasonable altitude?"Well it flew across an open field landing between two trees, but seriously, it couldn't have reached more than 100 ft. and I dont have the computer interface yet to download the flight data. I'm thinking turbulance was the best answer here. thanks
No problem on being away - Moms get priority! Here's a repost from the folks that make Perfectflite altimeters, in response to a question posed by a TARC Team sponsor last year. He noted that the altitude spikes were only on one sample (the Alt15K Vers 2 samples 10 times/second) and did not usually affect the beeping altitude readout post-flight, but was clearly visible when they downloaded the data into the viewer that Perfectflite has available for the altimeter. Perhaps it will help explain what everyone is talking about, though I don't think that is what happened on your aberrant flight.Sorry ,I was away on a busy mother's day.
Yes ,I have One Flight that appeared to be the altitude it reported.
I better get the USB software. I was unaware of ejection spikes
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All barometric altimeters sense the pressure around them to determine
altitude. *Any spurious increases and decreases in the pressure
sensed will be reported as decreases and increases in altitude. *For
this reason it is important that the pressure in the altimeter bay be
kept as close as possible to the true outside pressure, with minimal
When the ejection charge separates the airframe, and also when the
shock cord abruptly stops the separation, the payload section is
subjected to sudden changes in velocity and attitude. *This can cause
pressure fluctuations to be introduced through the static sampling
ports in the altimeter bay.
The Alt15K/WD will reject momentary spikes from being reported in the
beeped-out altitude reading, but all data are faithfully logged to
memory. *As a result, brief spikes can appear in the downloaded
flight curve, but will not be reported as an erroneous apogee
altitude. *Longer duration spikes, which are very rare and are caused
by gross error in the placement and sizing of sampling hole(s), will
not be rejected and could cause errors in the beeped-out altitude
Using 4 static pressure sampling holes spaced at 90 degree intervals
around the airframe helps to minimize the presence of pressure
spikes, as the pressure changes are equalized by diametrically
Using the proper sized static pressure sampling holes is even more
important. *As depicted in the table in the altimeter manual, the
proper size for a single static hole in a typical TARC rocket (1.6" x
6" altimeter bay) is about .050". *If four holes are used spaced at
90 degree intervals, each hole should have 1/4 the area, or 1/2 the
diameter, of this single hole. *So with four holes, the proper hole
size would be .025". *It sounds like they are using holes that are 5
times too large in diameter, or 25 times too large in area.
The possibility of a spike (even of longer duration) affecting the
beeped-out reading can be minimized further by insuring that
deployment occurs shortly after apogee, after the rocket has fallen
20 or 30 feet. *That way a spike would have to be greater in
magnitude than the 20 or 30 foot drop before it would alter the true
Conversely, rockets that separate before apogee while still
travelling upwards at high velocities will be subjected to more
turbulence, increased probability of spikes, and the certainty that
any spikes will add to the true apogee of the rocket.