Determing speed

[Schwemmer]

I have watched DSing and never have I tried it. (I crash enough on the front side as it is) I have read with interest how the radar guns you're using are limited in picking up the top speeds. I know that real planes have a pitot/static system which is accurate for them. With the new electronics available would it be possible to have this type of setup?

Sherpa

[Jantar2A]

The pitot static system is only good for air speed not ground speed

[THUREN]

I think at 300mph(ground speed) the "pitot" setup would probably blow up hitting the 50mph shear.. :)

Really though, if it was taking the reading on the backside maybe?

[nauga]

With the new electronics available would it be possible to have this type of setup?
The short answer is yes...but.
Jantar already pointed out it will tell you airspeed, not groundspeed like a ground-based measurement (i.e. radar) will give you. I guess you could use a telemetry system for pilot feedback. The pitot-static system would need to be calibrated for installation effects, that usually requires flying with a calibrated source (usually airspeed or just pressure altitude, not groundspeed) to get 'truth' data. That *can* be done with a GPS, but you'd need to fly a box pattern at test speeds to get cal data. Seems to me an onboard GPS with augmentation or better radar gun is likely to be the best option for the forseeable future.
Photo measurement is also good, but to get decent accuracy at soon-to-be seen speeds you need high resolution and possible high speed camera(s).

What with your job and all, do you know the operating range of LIDAR? Guess I could ask a Virginia Trooper ;)


Nauga,
who nearly hit the water on the AIMS range once :eek:

[D.S.]

That's incredible! I was just going to post the exact same thing that Naga just wrote but I used more technical terms and I threw in a bunch of equations to prove my points. I'll just save it for the next time this comes up. ;) ;) ;)

Dean

[Schwemmer]

[QUOTE=nauga]The short answer is yes...but.
Jantar already pointed out it will tell you airspeed, not groundspeed like a ground-based measurement (i.e. radar) will give you.

I thought that's what we wanted, the speed of the plane.

I guess you could use a telemetry system for pilot feedback. The pitot-static system would need to be calibrated for installation effects, that usually requires flying with a calibrated source (usually airspeed or just pressure altitude, not groundspeed) to get 'truth' data.

Pitot systems are calibrated on the ground by a black box which adjusts for altitude.

What with your job and all, do you know the operating range of LIDAR? Guess I could ask a Virginia Trooper ;)

I am scheduled for Lidar training in the next 90 days.

QUOTE]

Sherpa

who used to fly low and slow

[nauga]

I thought that's what we wanted, the speed of the plane.
Yes, but the standard so far has been to use groundspeed, not airspeed.


Pitot systems are calibrated on the ground by a black box which adjusts for altitude.
Airspeed and altitude systems are calibrated for *instrument errors* on the ground but calibration for source (static port and pitot tube) installations for precise measurements is done during flight test. In-flight calibration gives a correction for errors in static pressure sensed by the static port due to speed and AOA, and to a lesser extent the same type of error at the pitot head. That can't be done with a pressure test set.

Nauga,
who has done a few airspeed cals.

[Jantar2A]

the airspeed thing would be fine but the shear spikes would have to be averaged in along with the lows as well as the static ports would have to be very extensive to work in the shear,,,I don't think a flask would work as in full scale and there there is a 2 second lag on mechanical and still quite a lag on electrical..,,,I think I'm good with the gun untill I top it out at 309,,,,,,,,,,,,,,,,,,heck I'm still waiting to hit 200 on my gun lol,,,,Nick

[Schwemmer]

Nauga
Jantar2A,

Well guys, thank you for helping me understand more about DSing. I was just thinking (I know :eek: ) what systems might be helpful in obtaining a faster and more accurate speed. It's great to know we have many people like yourselves to answer these types of questions.

Sherpa

Who has done 200 mph in a H-53 E

[M Scherrer]

I have watched DSing and never have I tried it. (I crash enough on the front side as it is) I have read with interest how the radar guns you're using are limited in picking up the top speeds. I know that real planes have a pitot/static system which is accurate for them. With the new electronics available would it be possible to have this type of setup?

Sherpa
Yep it is possible using for example Eagle tree system
http://perso.orange.fr/scherrer/matthieu/aero/ds-session.pdf
this was very smooth DSing ( about 15kph wind)
location for DSing :
http://fabrice.estivals.free.fr/Bales%20DS%202006.wmv

as quoted, this is only about airspeed, but still it is interesting...
G's are interesting too...

matthieu

[D.S.]

I spent some time on the phone last week with one of the senior tech guys at Applied Concepts who make Stalker radar guns. He told me he has 50 years experience in the field and even though he is actually retired, he enjoys the work so much he just can't stay away.

Anyway, I told him about the problems we were having with the guns failing to pick up some of the faster passes with the more pointy planes like the Kinetic and the 300 mph limit on the guns. He told me he has already spoken to others about the same problems. His recommendation to me as it was to the others he has already talked to was to mold a small tetrahedron corner reflector into the front of the lead we put into the nose of our planes. He said it could be made of any conductive metal. As far as the 300 mph limit he told me that only a software change is needed to bump that up. No changes would have to be made to the guns at all.

Dean

[THUREN]

Wow that's cool dean!!!

Have all the floating around Stalkers programmed to work from 100-400mph, and build a refector in the nose.. Seems like the most reasonable solution..

All these other suggestions have to depend on individual calibration, which to me leaves margin of error. Having a few guns all saying +/-2 mph is much more dependable reading... :)

-Don

[Daemon]

As exciting as that news is though, the next logical question is,
what *exactly* will it take to get a software update to the Stalker Pro?
Software engineering isn't free, and I seem to recall other folks have talked
to Stalker on this subject before without any further progress.

ian

[D.S.]

Very true and I didn't get any further than the other people that have already asked the same thing. The very helpful tech I talked to doesn't get involved with the software himself. He told me that the software guys are beyond busy just trying to keep their police radar systems ahead of the competition. They will take on special software modification projects as time allows but he told me about one such project which has been waiting for more than a year and they just haven't been able to get to it yet. Police radar systems are their main business and that is where they put all of their resources.

Isn't there a website somewhere that has instructions for hacking radar gun software, how hard can it be ? :p

Dean