ASI

[ArthurR]

ASI thread modified

Does anybody know of a mechanical (Pitot/Static) ASI Range 60 - 255 kts
resolution 1 kt, which could be used for flight testing.

The ASI being looked at is a Kollsman model 38105.
But what is needed is one a bit lighter but with the same resolution.
miss read the e-mail I got yesterday hence the modification
Many thanks for your help..

[WeekendFlyer]

You may get an ASI with that resolution, but what about its accuracy? In my experience even the best mechnical gauges have hysteresis of about +/- 1 kt over that sort of speed range.

If you need consistent accuracy, rsolution and repeatability to 1kt or less, I would suggest considering a digital pressure transducer and associated display.

[Genghis the Engineer]

Originally Posted by ArthurR

Does anybody know of a mechanical (Pitot/Static) ASI Range 60 - 255 kts
resolution 1 kt, which could be used for flight testing.

The ASI being looked at is a Kollsman model 38105.
But what is needed is one a bit lighter but with the same resolution.
miss read the e-mail I got yesterday hence the modification
Many thanks for your help..

I'm rather curious as to what aeroplane has that sort of speed range, but is so weight critical that you are worried about the weight of the ASI!

I do suspect that for very lightweight with a wide range and good resolution, you probably want something digital. Can you make use of something like a Garmin G500, G600, G900 or G1000 and combine the primary flight display and flight test ASI functions? Presumably with something like that, you can also record off it, which would safe you a lot of other mucking about.

G

[Windmill Wiz]

I am a colleague of Arthur

Weight is not exactly the right word and not an issue; cost & complexity of the Kollsman unit are potentially an issue.

In order to use the GPS method for establishing Position Error we need to fly at a constant airspeed to keep the calculus simple. Unfortunately the scale and pointer (too wide) of the original aircraft instruments do not allow this. Any deviation in the Indicated Air Speed flown will immediately translate into a pressure error. The 3-digit counter of the Kollsman unit would show any deviation from "target" IAS. The accuracy of the ASI is less important as the standard cockpit fit is not that accurate; hysteresis would be a problem.

As this is part of a simple flight test for STC certification we want to keep it as simple as possible. A pressure transducer is an option, but one we would like to avoid at this stage. Using a Garmin GPS would not get us any closer to establishing PEC.

[Fitter2]

It would seem to me that a Dynon D6 would give you what you describe (Digital airspeed plus analog ribbon with settable bug) at little cost and weight compared to the alternatives. (Plus a lot of other info which may or may not be useful)

Dynon D-6 : Dynon - Airplan Flight Equipment

[On-MarkBob]

Some types of Distance measuring equipment have accurate speed readings. I've used this method myself, in the past, especilly if you need to fly at accurate constant speeds. Don't fly too close to the transmitter though, the nearer you get the more inaccurate the speed readings become. Best is to fly up a radial to a VOR/DME about 30 miles away. If you want airspeed you have to fly in both directions and take a mean. Both GPS and DME gives the ground speed.