AirSpeed-RCU

I've got a few posts out there asking what method of air speed indication people want. What I mean by that is, is real time indication critical or would reading a display in the aircraft after the flight be adequate.

If your interested check out the Q&A and scale forums on this site for threads with airspeed in the subject line. I'm looking for ideas of what features people think would be best in a device like this.

I want to develop one of these gadgets thats more affordable than whats out there now.

ArthurR

I'd like to see a cheap and light device that would read and hold maximum airspeed onboard untill read and reset on the ground before for the next flight. Readout could be a direct LCD display, a voltage that could be read with a DVM and translated with a chart to give MPH, or digital that could be read with a reader.

Razor-RCU

My Feedback: (50)

After each flight would be fine- That way you could still fiddle with different props and fuel/plug combos-

Cactus.

My Feedback: (1)

if all you want is outright speed during the flight, whats wrong with a thingy in a clear plastic tube pointing into airflow that the air forces down, end of the flight read the scale and see where the thingy ended up. copyright phil 2003

ArthurR

Great idea, Philly. Would you be interested in showing us your creative abilities and produce a working model?

Cactus.

My Feedback: (1)

i don't have the ability to make a finely tapered tube or the wotsit accurate enough. i got the idea watching a program about airships and a machine used to test the ability of the material to hold the gas in. they force air through it, and a series of tubes give a reading, 10's 1's, .1's 01's ect
it would have to be damm accurate to measure 0 too 300 mph, and then find a way for the wotsit to stay put. either no gap around it, or a marker of some sort

sydclement

My Feedback: (1)

Hi Airspeed;
Go to page 9 of extreme speed prop planes
and take a look at the Garman 201 GPS installed
on my Whiplash.
It is light and and has a fast microprocessor to
make it usable on fast R/C planes.

Syd

AirSpeed-RCU

phillybaby

cool idea but sounds like it might be expensive to produce and would add drag.


sydclement

Super cool, although GPS will give you a lot more info ie alt, max speed, average speed and more I can do it cheaper and lighter.

ArthurR

I could do it with a display or with an LED. The LED version would be cheaper and lighter. A combination of flashes with long (2 or 3 sec) delays in between. 1st flashs= 100s 2nd flashs = 10s 3rd = 1s.

All the micro controllers I'm considering have some flash memory so you could capture a number of data points.

ArthurR

AirSpeed,
That would be a reasonable readout. Sounds similar to the way error storage is read on autos. It takes a little practice to learn but it's not too hard and would simplify and keep light the whole thing.

What price target would you be aiming for?
Will it require a pitot tube?
Would it be self-powered to facilitate easy locating and mounting?

I'd be willing to pay around $30 for an item like that. What do you think of an on-line survey to see what people would be willing to pay? That might dictate the design.

I hope you pursue the project. It would fill a gap which has no competitors. The whole area of instrumentation, i.e., acceleration, speed, altitude, etc. has not been exploited.

AirSpeed-RCU

As far as price goes I haven't got that far yet. The micros are reasonable, the pressure sensors I'm not sure on but I think there relatively expensive. The most expensive parts will probably be the hardware and PC board.

As per above (pressure sensors), yes you'll need a pitot.

Being self powered has its advantages but depending on the voltage required might be expensive. The question for me would be what would be an acceptable max size and weight? Could I use a std 9 volt battery?

Price is the key! If I know what people will spend then I can aim for that price point in my design. As far as I know $30 wouldn't cut it but it a bit early to say. If you think there's enough interest I'll definitely do a survey.

I agree, I think instrumentation has been almost ignored in this Hobie since the advent of digital. I quess what might have happened is the BIG guys haven't been successful with it in the past so now there all sleeping at the wheel.

Now that I have some direction I'll do some pricing and get back later with a more accurate Estimate (you never know the exact cost till your past the proto type phase.

Thank you very much for your input so far, hope to read more.

Charlie E

My Feedback: (1)

Hello AirSpeed,

I think a 9 volt Battery would be heavy for some of the small speed planes. Something powered by a large watch battery of some type would be great. Weight and size is critical. I'll be more than happy to beta test....

AirSpeed-RCU

I appreciate the offer to beta test but I live in Canada. The cost of watch type batteries are high but if size and wieght are critical thats the way it'll be done.

Thanks

ArthurR

AirSpeed,
Someone has a thermometer that is a strip of heat sensitive calibrated adhesive paper. You stick it on a thingie and it progressively darkens as the thingie warms to each temperature segment on the strip. You come back later and see the highest darkened segment. That's the highest temperature the thingie has been since you stuck the strip on.

It costs only a few cents each, and of course, is not reusable, not powered and can go almost anywhere.

Now, if you can figure out how to do that with air pressure.............

Assuming you can't and are stuck with an electronic (complicated/expensive/heavy/big/drag-inducing/hard-to-read) solution, you may do well to test the market with a price tolerance survey.

I may pay more than $30, but I would balk at adding anything even as large as a 9V battery if it's exposed or requires me to go inside the wing.

But, keep thinking! Just keep it small, cheap, simple.

Cactus.

My Feedback: (1)

gell in a clear plastic tube, gets pushed back by air pressure? maybe not precise enough depending on air temp, never mind, move on.

Holst

I thought of a potentially cheap way of making one, however it would take allot of tweaking to make it usefull..

The idea is to have a plunger inside a tube pushing onto a soft spring.

The air pressure pushes the plunger into the tube compressing the spring.

behind the plunger is something like an O ring, that will record the position of the plunger at maximum displacement.

Im not sure how accurate this would be, probably not very accurate unless you spent allot of time getting together the right bits. The spring would be the hardest part.

Obviously this wont take into account air speed, so running into the wind it will read high, and running with the wind it will read low...

Cheapest way I could think off.
plus you could poke this into a wing and it will be quite light.

I dont think you can build an electronic solution cheaply, and still keep low weight and small size. Id love for somebody to proove me wrong.

AirSpeed-RCU

Good idea, my son has asthma and there is a similar unit available to measure the max air flow he can produce. This helps determine what condition his lungs are in from day to day. The unit has no spring but relies on friction to limit the movement of the plunger/diaphragm. The problem with this design is contaminants reduce accuracy with this device.

As far as wieght and size are concerened there's no problem (I think), it's a matter of price. The reason I say "I think" is because I still haven't had anyone advise me of an acceptable weight and size. Bear in mind if you respond to this question I mean avg size and wieght.

Keep the great advice comming.

Thanks

AirSpeed-RCU

Forgot to mention that my unit will likely have an audible stall warning emmitted from the unit (in the aircraft) and enough memory to store some flight data.

Rudeboy

Why not power the unit from a spare receiver channel?

These modern microprocessors consume next to nothing.

AirSpeed-RCU

The sensor consumes a hefty 10 Vdc at 6mA. The processor on the other hand only consumes a max of 3 mA @ 5 Vdc. I need at least 10 volts.

That means about .08 watts consumption @ 10Vdc +2 -0. Can any of you battery gurus out there tell me what type of battery would be good for this application??

Rudeboy

I cannot believe there is no pressure sensor around that doesn't need at least a 10V power supply...

People that are developping turbine engine control units are using pressure sensors too (to determine engine power output via case pressure), and most turbine controllers run off a 5 or 6 cell nicad battery pack... that is 6 to 7.2 volts...

If you really need 10 volts+ you can put 4 litium cells in series... they would give you a 12 V supply...
Might be expensive though... I don't know how long they'd last at 0.08 Watts...

Mluvara

My Feedback: (10)

Interesting thoughts. However, I think it would be hard to keep it accurate. The PSI ratings that most models fly at are rather low. E.G., 150mph is approximately .4 psi. Therefore, friction would need to be low with tolerances right on. A spring would certainly be hard to find and probably delicate.

AirSpeed-RCU

Rudeboy

So far I've only been able to find this one that hit the bill.

Mluvara

Would you know how much the diameter of the pitot effects the sensed pressure? What is the minimum dia of tubing that can be used, after calibration if required? Is there a linear relationship with respect to dia and pressure?

Rudeboy

You need two tubes: one for static pressure and one for dynamic pressure. This way the unit is always adjusted for differences in air pressure and altitude. The static tube is placed perpendicular to the airstream, the dynamic one with the opening straight into the air stream. The electronics should determine speed by the relation between these two different pressures.

The turbine guys are already using this to have a sort of a cruise control or speed limiter on their jets.

You are reffering to the dynamic pressure tube. Diameter has no bearing on the pressure in the tube... 0.5 psi in a 0.01" diameter tube is also 0.5 psi in a 0.1" diameter tube... pressure is pressure...

Don't go too small in tube diameter though... the 0.01" was just an example... it might be too small to get correct readings (I'm not sure though)

Cactus.

My Feedback: (1)

damn, i thought of the spring one, but after embarrasing myself with the gel idea i thought, nahhhhhhh LOL

Rudeboy

Maybe... if you had a REALLY fast plane you could use a thermometer... you know, to measure the airframe heating caused by compression effect on the air... like a Concorde or an SR-71....



Yo Airspeed,

Take a look at the JetCat website... these guys have cruise control that works in a very similar way as to what you are trying to do... buy one of those units and take a look inside...