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F-16 pitot tube for RV

tonyjohnson

Well Known Member
I have acquired an F-16 pitot tube that I hope to use on my RV8A. I have two issues with it.

1. It has stamped on the side "aerodynamically compensated". I don't know what that means. I hope that it does not mean that it is not suitable for use on my RV.

2. The heating element is wired for 115 volts, at 400 hertz. I am trying to figure out how to adapt it to work with my 12 volt system.

Any insight or ideas would be appreciated. Perhaps some of you electronic whizzes out there could help me solve this problem.

Thanks,

Tony Johnson
RV8A N12TJ (reserved)
Orlando
 
Weeeelllllll,

I don't know about the first question, but the second one I can help with.

The 115volts and 400hertz is a complicated task and one which will likely end in you not using the pitot.

In order to change 12 (or 24) volts DC to 115 volts AC at 400 hz, you will need an inverter. I am not sure how common that is, as I have never seen one. Maybe the military has used them in certain applications, but I don't know what they would be.

The other thing would be to install a 115v, 400 hz alternator in your plane, just to run the pitot. Not likely.

Another possibility is to try it on a 12 (or 24) volt DC system. The pitot heating elements are usually resistive and I can't think of a reason why it won't work on DC, unless there is circutry or switching in it that prohibited it from being used on DC. Odds are, if it doesn't smoke and performs adequately... it may be ok!

Bear in mind, this is all experimental... hence the name for the category.

Hook it up to a battery and see if it smokes! If it does, try and cram the smoke back in before you lose it all and then sell it on ebay!

Lemme know if it heats up!

:D CJ
 
For the first question... that means that the pitot tube takes into consideration the slipstream disruptions off the F-16. I don't think that you'll notice a problem when your cruise is below F-16 stall speed. j/k

As far as the inverter goes, I know nearly every military aircraft has an inverter, or 2 or 3 or 4. (Even the mighty T-37 has an inverter.) I would venture to guess that most large airplanes do (guys with civilian heavy time could answer that). However, they are also 28V systems. I think your hurdle is going to be getting 12V to 24V. But you can do that with this: http://www.aircraftspruce.com/catalog/avpages/lonestarconverter.php

You can buy an inverter at Wal-Mart to plug into your cigarette lighter to power a TV, laptop, etc. Your car is 12VDC, your TV is 110VAC. The 115V most likely has a +/- of 7 or so, so that would fall in the range. Even "110V" is not really 110, that's just the convention.

Actually.. I just googled "aircraft inverter"... http://www.aircraftspruce.com/catalog/avpages/dcac_inverter.php

That's a 14V (14V generator/altenator, 12V battery) or 24V, 400Hz inverter.

http://www.edmo.com/s10/s10-45.asp - Model PC-17A 750VA Static Inverter is a 28VDC - 115VAC/400Hz inverter.

Good luck

By the way, everybody has seen an inverter. Anything you have that runs off batteries and has a AC power "adapter." It really is an inverter to convert the wall AC to the equivalent battery DC.
 
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Yes, it will take a fairly skookum inverter to operate your pitot head. Inverters are a fair draw on your system too, perhaps between 5 and ten amps, maybe more, to power that unit.

I'm not sure why you would want to use a supersonic aircraft pitot sytem on your RV. Why not get one designed for under 200 knots instead of the one you have, which is designed for over 200 knots.

Inverters that operate off 12 volts are common and can be purchased at any RV (as in Recreational vehicle) place. Lots of people like to run small TVs and radios that operate on 110volts@60 cycles. The inverter that you need is aircraft specific and could be expensive as most of these units would be certified. You might ask yourself if this venture is worth it? The inverter would not be used for anything else on your aircraft introducing uneeded weight and complexity.
Cheers, Pete
 
400Hz?

I'd be suprised if the 400Hz part is important, pitot heads are usually just resistive heaters, so the RV type inverter mentioned above would possibly (probably?) work. Try hooking it up to a wall socket and see? The major problem might be supplying the current required. How many watts does the pitot head take? It could easily be several hundred. At 115V the amperage is low, but at 12V its x10, plus the current to drive the inverter.

How badly do you want an F-16 pitot tube?

Pete
 
pitot tube

I told Doug that I would try to behave myself on this forum, so here goes...

If the pitot tube was mine, I think it would be mounted on the wall in my bar, or used in the backyard in a game (lawndarts, just ask Smokie). Either way, it would generate a lot more converstion.

My 1 cent.

Hwood
 
Tony, Why are you bound to using this pitot?

Put it on the wall of the bar room and hang your jacket on it.

;) CJ
 
Thanks for your responses

Thanks for the input regarding the pitot tube. Some of you have asked why I want to use it.

1. It is way cool looking.

2. I got it for 50 bucks. Even if I have to use an expensive inverter, I will be ahead of the game since heated pitot tubes are VERY expensive.

Even if the heating element cannot be made to work, the tube will probably be suitable for VFR use. I talked to some USAF maintenance guys who told me that it will work at low airspeeds, and even shows taxi speed.

I am not sure at this point if I will have an IFR panel, so the heating element issue may be moot. I might just use it for airspeed and switch it out later for a heated tube.

If I can arrange to have the heating element work, all the better. Please keep the suggestions coming.

Tony Johnson
RV8A Orlando
 
Like you and I'm sure many others, I am also watching my budget while building. My intent, however, is to get flying as soon as possible, and I am trying not to get held up with financial slowdowns (aka, "running short of money" along the way).

So what I'm doing and what you might consider is to install the cheap $15 pitot tube, but run the wires out to the pitot location and just tie them up out of the way there and under the panel. That way, installing a heated pitot later will be just a 1 hour job instead of having to go through all the trouble of running the wires later in a flying aircraft.

My .03 because I'm hoping it's worth more than .02
 
I, for one, like the idea

Although fabricating a bracket for it may be a PITA.

Highflight had a good idea. I just tied off a pull string at the pitot location and after it exited the wing in the event I ever install a heated pitot.

FYI Highflight, you might as well install a regular pitot tube bracket now why the wing is open rather than do it later. Cutting the hole in the wing skin and riveting the bracket in place is a real pain, I couldn't imagine doing it with the wing closed up.

Just my $.005 because that advice isn't worth a fully penny.
 
It did not smoke

For those of you who asked me to let you know what happened when I tested the pitot tube......I hooked it up to house current, using a dimmer switch set on the lowest setting. It heated up. I was afraid to turn up the power because the tube got too hot to hold with the lowest power setting available.

Next I will see how it responds to 12 volt input at a low setting.

Tony
 
Hmmm, very interesting!

One thing you will want to watch is amps!

Watts is a function of volts times amps. As your volts DECREASE your amps will INCREASE, so long as your resistance remains the same... and it will for the most part.

Too high a current (too many amps) has a possibility of toasting your pitot lead wires. Keep an eye out for that. Once the smoke leaves the unit, it is hard to get it all back in!

;) CJ
 
Incedentally, keep in mind that your ampacity will increase by approximately TENFOLD, as the difference in test voltages is 10 times (12vdc compared to 120vac).

Wattage is equal to volts times amps... or P=EI
Voltage is equal to amps times resistance... or E=IR

Hope this helps.



:cool: CJ
 
12 volt test

John,

Thanks for the info. My plan is to acquire an adjustable resistor, set it for the highest resistence, and run 12volt power through it into the tube. I will increase the resistence until I find the right amount to heat the tube up but not smoke it.

Do you have any suggestions about what resistance I should start with? Does that seem a workable plan?

Tony
 
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