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Old Feb 12, 2012, 03:10 PM
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Mark,


All In My Opinion let that be clear!!

So

I indeed read a study about using airspeed measurement to set speed records, but what is needed for that?

First a pitot and static tube of which accuracy is known in detail. When someone is copiing some kind of model a detailed construction check and calibrating is needed. Keep in mind it isn't dificult to generate a pressure difference, but before values are presented, calibrating and certification is needed otherwise it's all nonsense. The tubes I show are all for personal use and so don't have to be certified.

Second ,the transducer, same story,
Only a calibrated transducer will do. If not calibrated the values that are presented are useless. What about a transducer with a span fault?
Also the transducer has to be qualified for circumstances that are actual during the whole flight.

Third, how to check the combination in the plane? Who does guarantee the total airspeed measurement system is within needed specifications? Was the engineer qualified to mount the system? Does he knows all installation requirements?

When it's all true what I write you will understand that an airspeed measurement with not any kind of qualification (calibration, certification) is a "boy toy" and only interesting for observing, maybe to use for some research but useless for setting any record.


About your pitot (and static?) tube decription.

And in any case, the pitot-static tube is a small tube, say 1/8" diameter, with a rounded nose pointed straight into the flow. Nothing else sticks out. It will have a drag area of about 0.01 in^2. By comparison the whole glider's drag area is 5 in^2 to 10 in^2 (depending on the CL), or 500-1000 times bigger. So the drag of the pitot will cost you maybe 1-2 mph at most.

It looks like we are one step away of the moment anybody is plumbing a tube on his plane and starts airspeed measurement record attemps, the action is accelerated by the axample shown in the post 38 of Jason Liily,

http://www.rcgroups.com/forums/showp...7&postcount=38


Quote:
Originally Posted by Jason Lilly View Post
As far as pitot tube design goes, I have attached a link to a .pdf document on pitot and static tube design. Alan showed this to me. The configuration on page 649, page 8 of the .pdf, Fig. 9 is the one Alan used on his system. The tubes are pretty easy to make compared with the other variations. He uses a .125" diameter tube. http://www.spaceagecontrol.com/naca-report-1364.pdf
Because this is a static pressure tube, did he modify this himself to some kind of pitot (and static?) tube??




Why I write this?
I am an industrial engineer for instrumentation, and better write my comments before than after measured values are presented, for that read the topic of the thread!!

My advice,
Speed records normally are set in two directions to eliminate windspeed because ground (water) speed is interesting. Also for DS ground speed is accepted and measurable with high accuracy, so don't use airspeed to set records!
If you still do?
What will happen when someone sets an airspeed record on a extreme high value? What is it worth? On that moment, read this post again.

Mark, last note:

“Site”, of Site Acceptance Test, Google for that, because it is worldwide known!!

Let the FAT be interesting in our workshop, the SAT we can use on "site" so mountain or hill.
Your "dive" can be part of a SAT just as some other highly recommended actions.


So, black and white story, but very important for you to know how public/readers are looking at your activities.

Let me know what you are thinking about this post, maybe we can do business and write about technical requirements of your measurements, calibrating, FAT or SAT, or even a calibrated vario!


Cees,
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Last edited by Taurus Flyer; Feb 12, 2012 at 03:55 PM. Reason: Picture of staic tube added
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Old Feb 12, 2012, 08:51 PM
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Too many variables...

Quote:
Originally Posted by Taurus Flyer View Post

Speed records normally are set in two directions to eliminate windspeed because ground (water) speed is interesting. Also for DS ground speed is accepted and measurable with high accuracy, so don't use airspeed to set records!

Cees,
Thanks Cees!

Because of RCSpeeds I have an interest in this thread and have been reading it.

Most DS'rs I've spoken too believe as we do. I'm not saying its up to me or I can't or won't make a section to record estimated airspeeds but I believe for records there are too many variables, a lot of room for error and other issues. Temperature, ridge gusts, pressure differences, changes in cloud cover and other factors could fluctuate during a flight and add variance. Many of our records are within one or two mph, ie the sixty inch record is currently tied at 360mph...

On the other hand I'm interested in airspeed after all that's what the airframe is exposed to. I've flown a D60 with the airspeed indicator and complete enjoyed it!! It so enlightening and it added another completely new way to enjoy flying. I wish I had the the right TX/RX and all the other gear to put one on an F3F model for slower smooth conditions. I would learn so much but I don't think windspeed is consistent enough to use for records.

The Guinness Book of World Records requires a pilot to fly a model between two fixed points, in both directions to eliminate windspeed for their records. I think its great how radar eliminates windspeed and forces us to use a witness. I'm surprised nobody's wound up a DS plane to 400 mph or so and flown between two fixed points. Maybe worth a try?? Their top record is only 337mph. From their link ,There downwind and upwind speeds were taken to eliminate the influence of the wind amongst other factors.

I've spoken to Jason of the link you posted to see if had a problem with me not posting his fast wind speed measurement to RCSpeeds. He agreed with me and I didn't post the wind speed measurement.

For now, I hope everybody's okay with this...

Chris
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Old Feb 12, 2012, 10:17 PM
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Chris,

Thanks for response. Indeed, all clear.

Rest my offer.
I do fly my planes with airspeed measurement and control (cruise control) and do design all my equipment for that.
If I can help in any direction, design of tubes, advice about calibration or back up of controle for calibration data for any environmental circumstances please let me know.

Success Cees
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Old Feb 13, 2012, 01:36 PM
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I like the out-of-the-box thinking, keep the ideas coming.
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Old Feb 22, 2015, 04:12 PM
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Happy Anniversary, interesting thread
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Old Mar 10, 2015, 12:13 PM
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Kurt, still flying or did someone hack your account?
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Old Mar 20, 2015, 11:26 PM
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Now that we have had pitot tubes for a few years and countless laps comparing radar to pitot tubes, the discussion can be more meaningful.

I really like the pitot tube system. You can fly alone with instant feedback on your speed, which allows you to refine your flying skill in a way that is otherwise impossible. I still think we should compare handheld radar speeds for records, but like gyro speeds we should consider pitot only speeds for informational reasons.

The current crop of high-end radar guns all measure within 1mph of each other. This validates their accuracy. Pitot tubes rely on the user properly setting the air temperature and if improperly calibrated can give errors in the tens of mph. This is the reason why I think handheld radar is still the gold-standard for record keeping. But we should not ignore pitot speeds, since Alan has done the complete engineering of the hardware and software and thus it is of the highest precision.
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Old Mar 23, 2015, 01:49 PM
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Can you mount a temperature sensor on or in the TX, and use telemetry to update the pitot calculations?

How close are pitot and radar readings (coming up the back side) when the pitot is calibrated correctly?

-David
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Old Mar 30, 2015, 08:22 AM
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Cooll thread guys..

Has anyone considered the use of on board accelerometers ?

They would have to be calibrated at 0 and would be subject to some degree of drift, but it could be pretty small and have telemetry capability.

EDIT : Did some reading and apparently this type of method isn't feasible with low cost sensors. Too bad!
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Old Mar 30, 2015, 05:18 PM
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Quote:
Originally Posted by rothlisburger View Post
Can you mount a temperature sensor on or in the TX, and use telemetry to update the pitot calculations?

How close are pitot and radar readings (coming up the back side) when the pitot is calibrated correctly?

-David
When I would stand next to Alan with a radar gun, on sub 400 days, I would usually read off speeds 0-5MPH slower vs. the lady in the box.
I would guess that his max, even in 400mph+ wind, was rarely higher that 15mph.
But I could be remembering incorrectly.
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Old Apr 04, 2015, 02:21 AM
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Quote:
Originally Posted by 1000MPH View Post
Kurt, still flying or did someone hack your account?
Lol. Still got my hanger and Seth and I are heading to Weldon again real soon. With dyke 8 closed for upgrades and lack of wind in general it's been awhile since I've flown. Missing it and the good guys in the sport. Hope to fly with you and the boys soon.

Was at Torrey pines today and even the jellies were grounded. Good thing it was 83 degrees and the surf was up. Hoping for wind!

Peace
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