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Off the map here: Any aircraft technicians/mechanics here?


Science Abuse

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I'm looking at airspeed indicators on ebay (because, that's why!), andi'm seeing that the majority of the simpler ones have two threaded holes in the back, and that's it.

 

I can assume that one of those goes to the pitot tube to provide pressure... what is the other one for?

 

When plumbing the pitot tube to its approlpriate pressure measuring device, I would assume that I should stick with a tubing that won't flex or bulge?

 

That tubing should not pass by heat sources that would effect the pressure?

 

Yes, I'm looking into putting one on a car. :)

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UH-60A/L crew member. It all depends on what type of aircraft it came off of. For your application you should be able to cap it off. Use rigid tubing. Dirt/debris/water getting in the pitot tube will degrade performance considerably. In the 60's the airspeed indicator is tied into the HUD, afcs, stabilator control, and a few more. I have wanted to do this as well but ours are measured in knots not actual ground speed.
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UH-60A/L crew member. It all depends on what type of aircraft it came off of. For your application you should be able to cap it off. Use rigid tubing. Dirt/debris/water getting in the pitot tube will degrade performance considerably. In the 60's the airspeed indicator is tied into the HUD, afcs, stabilator control, and a few more. I have wanted to do this as well but ours are measured in knots not actual ground speed.

 

Since I'm playing with aero, I'm looking for an airspeed measurment so I can establish a control speed. From there I can more accurately quatify improvements (or detriments) to airflow over/around the car.

 

The ASI's I've been looking at are takeouts from Beechcrafts, Cessnas, Pipers etc, so doubtfull it goes to a HUD... but you are saying that it goes to an accessory and isn't neccesary for the ASI to function, right?

 

I'm kind of assuming that an ASI works like an oil pressure gauge: You just have a line in where pressure is measured, and it's a closed/dead-end system.

 

Maybe the extra line leaves the gauge and goes to a Stall alarm?

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have you looked into pressure transducer style indicators? Homebuilt and ultralight guys use them in favor of a pitot static system.

 

I've got access to transducers at work, and I've seen anemometers for sale online. Trouble is, I'm seeing units that cost $400 and don't support the speed that I'm shooting for.

 

The RC plane stuff is awesome, I've seen micro-pitot tube and transducers that go to 350mph for $50.... but, they don't spit data directly onto a to a display, they only transmit.... to your $2500 controller and its data display.

 

Why not just buy a speedo that uses Gps ?

 

I have a GPS, goes to some ungodly MPH and logs peaks and averages, but that's not the speed I'm trying to measure with the ASI. Airspeed is different that road speed and has a different value when setting up a top-end car. I'll be using both at the same time to accumulate data.

Edited by Science Abuse
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A tiny transducer is exactly what I'd like to put in the low pressure areas on the car. The testing goes as follows:

-Establish a control airspeed

-measure pressure in areas where the boundary layer separation is the worst.

-Tweak around with VGs and belly pans et al and see if the pressure in those areas goes up or down.

 

If it goes up, I know I've done something that works. :p

 

The nose mounted AIS can also be used in conjunction with a GPS to get a better idea of potential. Supposed you do something, but it doesn't translate into an increase in ground MPH? You can check the airspeed to see if you had a headwind slowing you down; "I still didn't break 180mph, but my airspeed was 190, instead of 180, so I did something right."

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Flex tubing would make some things easier, though I do have access to a bunch of 1/4" copper tube.

 

Follow up question, I've been puzzling on this one: does the diameter of the Pitot tube inlet matter? I'm wondering, it if it a larger ID than the fitting inlet into the back of the ASI, that it may artificially cause a rise in pressure.

 

On the other hand, the PSI under water at a depth of 8ft is the same, no matter what the volume of the pool... so I can see this going either way.

 

 

I think I can get away with mounting this on the drivers door, and sticking the pitot and SA tubes out past the rearview mirror. The air out there should be clean, and it gives me existing holes to run things thorugh.

 

Now I just need to source a 200mph ASI, for cheap... don't any of these come in digital? Edit; Yes http://www.aircraftspruce.com/menus/in/airspeedindicators.html

Edited by Science Abuse
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I would think the size of the tube would matter. When we do inspections on pitot tubes, we aren't allowed any kind of damage/deformation on the leading edge of the tube that reduces the diameter of the opening, and I assume this is the reason why. I could be wrong, though.
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