hevansrv7a

hevansrv7a

Well Known Member
Does anyone know of a source for a remote airspeed sensor? I was just sitting around thinking about Bob Axom's work and that of others regarding cooling drag and I thought, gee, wouldn't it be nice to have a remote sensor that could easily be placed at various points inside the cowl to broadcast data that could be interpeted as airspeed? I don't know if BlueTooth would work through the skin, but perhaps there's a way to do this? Could a MAP sensor be tweaked to do something like this? Maybe this could be used, directionally, to look at airflow speed and direction inside wheel fairings.

This would be nice for IFR back-up, too, but I was really thinking about measuring air flow inside the cowling or even at the wing roots, etc.

If good corellations could be observed between external airspeeds and inside-cowling airspeeds, then we'd have an ice-proof emergency sensor without the high current draw of pitot heat.

Any experts want to chime in?
 
Safety over Speed

hevansrv7a said:
Does anyone know of a source for a remote airspeed sensor? I was just sitting around thinking about Bob Axom's work and that of others regarding cooling drag and I thought, gee, wouldn't it be nice to have a remote sensor that could easily be placed at various points inside the cowl to broadcast data that could be interpeted as airspeed? I don't know if BlueTooth would work through the skin, but perhaps there's a way to do this? Could a MAP sensor be tweaked to do something like this? Maybe this could be used, directionally, to look at airflow speed and direction inside wheel fairings.

This would be nice for IFR back-up, too, but I was really thinking about measuring air flow inside the cowling or even at the wing roots, etc.

If good corellations could be observed between external airspeeds and inside-cowling airspeeds, then we'd have an ice-proof emergency sensor without the high current draw of pitot heat.

Any experts want to chime in?
Click to expand...

How about using GPS groundspeed, corrected for winds aloft beamed via satellite, corrected for temperature and pressure by a microprocessor -controlled digital barometer powered by lithium poly batteries, charged by
wing mounted solar panels.

Seriously, pitot tubes are how we measure airspeed, and the quarter knot they cost are not worth one life lost due to a leaking cowl seal or a muddy wheel pant. Let's keep our perspective guys.
 
Yukon said:
How about using GPS groundspeed, corrected for winds aloft beamed via satellite, corrected for temperature and pressure by a microprocessor -controlled digital barometer powered by lithium poly batteries, charged by
wing mounted solar panels.

Seriously, pitot tubes are how we measure airspeed, and the quarter knot they cost are not worth one life lost due to a leaking cowl seal or a muddy wheel pant. Let's keep our perspective guys.
Click to expand...

I don't think he meant it as a replacement for a normal airspeed-sensing pitot tube, but rather as a data acquisition device for people doing cooling measurements. Not a bad idea, in the sense that running wires (let alone pressure lines) through the firewall is a PITA.

As a backup for a real airspeed indicator, though, I'd want something that is at least as reliable (i.e. has at least as few failure modes) as the gizmo it's backing up.
 
If you want to see real time cooling pressure the cheapest way would be using a water manometer. For a few $$ you could use a magnahelic pressure gauge.

I plan on using one to get differential pressure readings form various locations when I start flight test.
 
Let's try this again

RV8RIVETER said:
If you want to see real time cooling pressure the cheapest way would be using a water manometer. For a few $$ you could use a magnahelic pressure gauge.

I plan on using one to get differential pressure readings form various locations when I start flight test.
Click to expand...


I looked at the Dwyer line of magnahelic pressure guagues. (Thanks for the terminology) I don't see any real difference from an airspeed indicator in that they both seem to need air pressure supplied directly. I was trying to get a remote sensor to solve the problem of running wires or tubes through the firewall, for example. I already have a spare airspeed indicator.

This might be such a device. Those of us with GRT's could even use them to read the signal, since this sensor uses a 5v supply.

I think when we are trying to think about the air resistance of the stuff inside the cowl - SCAT tubes, exhaust pipes, engine mount tubes, etc, then we should want to know what the velocity of the air hitting them is. That's an analogue to the possible savings, isn't it?

And for Yukon, who always seems negative about my stuff - no, I was not trying to replace the pitot! Where did that come from?

My primary purpose is to find/suggest a way to break down the factors that ultimately matter in cooling drag and yet have the device be easy to relocate, realign, etc. to facilitate getting lots of readings with good acccuracy. The down-the-road possibility of a backup airspeed indicator was just a freeby.
 
Use one of our low cost FLIGHT-2 primary flight planels, use the "airdata" version. This gives you firstly a display of the airspeed that you are interested in and using the data stream provided you can log it to a laptop. Then use one of our other systems (or a second Flight-2 for that matter) to measure the real airspeed (and log that at the same time).
Then, post mortem, you can graph your relative airspeeds and make real informed decisions about your cowling at lowest possible cost.

The high sensitivity and good resolution of the airspeed system in the Flight-2 will be of value for this. Measurements from 16mph to 250mph in 1mph steps with very good linearity.

Rainier
CEO MGL Avionics

hevansrv7a said:
Does anyone know of a source for a remote airspeed sensor? I was just sitting around thinking about Bob Axom's work and that of others regarding cooling drag and I thought, gee, wouldn't it be nice to have a remote sensor that could easily be placed at various points inside the cowl to broadcast data that could be interpeted as airspeed? I don't know if BlueTooth would work through the skin, but perhaps there's a way to do this? Could a MAP sensor be tweaked to do something like this? Maybe this could be used, directionally, to look at airflow speed and direction inside wheel fairings.

This would be nice for IFR back-up, too, but I was really thinking about measuring air flow inside the cowling or even at the wing roots, etc.

If good corellations could be observed between external airspeeds and inside-cowling airspeeds, then we'd have an ice-proof emergency sensor without the high current draw of pitot heat.

Any experts want to chime in?
Click to expand...
 
Rainier Lamers said:
Use one of our low cost FLIGHT-2 primary flight planels, use the "airdata" version. This gives you firstly a display of the airspeed that you are interested in and using the data stream provided you can log it to a laptop. Then use one of our other systems (or a second Flight-2 for that matter) to measure the real airspeed (and log that at the same time).
Then, post mortem, you can graph your relative airspeeds and make real informed decisions about your cowling at lowest possible cost.

The high sensitivity and good resolution of the airspeed system in the Flight-2 will be of value for this. Measurements from 16mph to 250mph in 1mph steps with very good linearity.

Rainier
CEO MGL Avionics
Click to expand...

Ranier, are you suggesting mounting the whole thing inside the cowl? I looked at your website and cannot see any indication of a remote sensor, so I infer it works on air pressure like any airspeed indicator. Thus I deduce you mean that it will record the data for later analysis. If so, this is a clever solution. But it's not what I was trying for. Good idea, though, so THANKS.

However, if the sensor were truly remote or using only a thin wire rather than an air tube, then perhaps multiple readings could be obtained in one flight under identical circumstances. This would entail using multiple sensors and a dial-switch, of course.

You lead me to think that all the AHRS/EFIS makers have sensors like what I am looking for, but they don't offer them for remote mounting. What would that take, do you think?
 
I'm not an expert, but in the course of my work with the motor industry, I've come across hot-wire anemometers being used for flow velocity measurements in hard to reach places, or where pitot-static rigs are impractical.

In essence its quite a simple bit of kit. Maybe it has potential for your project.
 
Yes, but..

Mark Albery said:
I'm not an expert, but in the course of my work with the motor industry, I've come across hot-wire anemometers being used for flow velocity measurements in hard to reach places, or where pitot-static rigs are impractical.

In essence its quite a simple bit of kit. Maybe it has potential for your project.
Click to expand...

If I understood what I read, having found it on a Google search, I'd have to know the local air density and the local ambient air temperature and probably the local humidity in order to get a meaningful reading. By local, I mean within inches of the sensor. The reason for this is that the sensor is actually measuring heat loss indirectly. In an otherwise steady environment, it would be terrific, from what I saw. Thanks for trying!
 
No, the Flight-2 units are 3.5" instruments normally intended for panel mounting. They are in fact pretty complete primary flight panels popular for ultralights and I have seen a picture of at least one RV using one as EFIS !
They are really low cost.
Your sensor is part of the unit but since any opening of a tube (we care little about diameter etc) will be a pitot port, you could just get a roll of fish-tank air tubing and then proceed to place the end of the tube where you would like to know the airspeed. You would need an educated guess (perhaps some experimentation) to find out the direction of airflow so you can place the end of the tube at right angles to the airflow for most accurate measurements (but that you would need to do regardless of technology).
Using just a length of tubing makes moving the "measuring" end particulary quick and simple if you need to check different locations.

And when you're done, you'll have a spare EFIS that could make a nice backup instrument....

Rainier
CEO MGL Avionics


hevansrv7a said:

Ranier, are you suggesting mounting the whole thing inside the cowl? I looked at your website and cannot see any indication of a remote sensor, so I infer it works on air pressure like any airspeed indicator. Thus I deduce you mean that it will record the data for later analysis. If so, this is a clever solution. But it's not what I was trying for. Good idea, though, so THANKS.

However, if the sensor were truly remote or using only a thin wire rather than an air tube, then perhaps multiple readings could be obtained in one flight under identical circumstances. This would entail using multiple sensors and a dial-switch, of course.

You lead me to think that all the AHRS/EFIS makers have sensors like what I am looking for, but they don't offer them for remote mounting. What would that take, do you think?
Click to expand...
 
Actually, the magnahelic I was thinking about is something like this;
http://www.dwyer-inst.com/htdocs/pressure/SeriesDM-2000Spec.CFM

Has remote output, but in 4-20mA, which makes reading a little more difficult.

I recently found this;
http://www.omega.com/ppt/pptsc.asp?ref=PX160&Nav=preb05

Output in VDC so you could just plug in your mulitmeter to connector in panel.

Of course, as you already have to airspeed gauge, understand trying to make that work.

If you are looking at pressure, then delta P is probably the best value to look at. If you want actual velocity you are probably going to need a flowmeter of some sort, but that would seem very challenging to try and find a place to locate it and have good readings.

Good luck,


hevansrv7a said:


I looked at the Dwyer line of magnahelic pressure guagues. (Thanks for the terminology) I don't see any real difference from an airspeed indicator in that they both seem to need air pressure supplied directly. I was trying to get a remote sensor to solve the problem of running wires or tubes through the firewall, for example. I already have a spare airspeed indicator.

This might be such a device. Those of us with GRT's could even use them to read the signal, since this sensor uses a 5v supply.

I think when we are trying to think about the air resistance of the stuff inside the cowl - SCAT tubes, exhaust pipes, engine mount tubes, etc, then we should want to know what the velocity of the air hitting them is. That's an analogue to the possible savings, isn't it?

And for Yukon, who always seems negative about my stuff - no, I was not trying to replace the pitot! Where did that come from?

My primary purpose is to find/suggest a way to break down the factors that ultimately matter in cooling drag and yet have the device be easy to relocate, realign, etc. to facilitate getting lots of readings with good acccuracy. The down-the-road possibility of a backup airspeed indicator was just a freeby.
Click to expand...
 
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Motorola/Freescale makes a 1.45psi differential pressure sensor that is temperature compensated and puts out 4.5V full scale voltage linearly proportional to DP. The MPX5010DP is available from DigiKey for $14.94. Just connect a 5V supply, one port to your static source and the other to your pressure input, then connect the output to a DVM and convert the displayed voltage to the correct pressure/IAS. We've been using a similar absolute pressure unit for MAP on the Plasma systems and it's very reliable, as these units were made for the automotive world. You could mount this somewhere out of the way and just route the pressure tube to where you want to measure the pressure.
 
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