Pitot - sourcing / making

[Marty_d]

Hi all,

 

Interested in where to source a pitot head in Australia.  The CH701 plans just show the single (facing airflow) tube under the wing, but it seems common that people use the double tube where static is on the same probe either concentric or parallel.

Aircraft Spruce have them for about $40 US - https://www.aircraftspruce.com/catalog/inpages/pitot15144.php - but it's the postage that kills it!

 

If unavailable in Aus, has anyone built one?  I'm guessing the static tube has the forward end closed but small holes drilled into the side - how many, what size?  etc.

 

Do you use 1/4" nylon or plastic tube?

 

All advice welcome.

 

Cheers, Marty

[facthunter]

You are better with two static ports one on each side of the fuselage.  Water in any of the connections is an issue. If you want a heated pitot it's a different matter. Purchase  one, rather than make it. Cuts in the side will do for the static bit of the combined one. You need to provide for a cover to keep wasps from blocking it.  Nev

[spacesailor]

I bought a ' simple ' static , from A S ,and like you say $ 16 for very light ' bent alloy tube ' , with $ 32 for postage .

The post-packet weighed more than the ally tube .

Yes , I tried unsuccessfully a lot of times to make that tube bend to it's 90 deg shape .

I have seen a modified ' pito tube ' on 19- 1944 Hummel Bird .

spacesailor

Edited August 10, 2023 by spacesailor
A I

[facthunter]

It can be a very gradual bend and if it's on a strut, fairly straight.  Nev

[IBob]

Hi Marty. During my build I came across quite a few references to the ASI dropping out on high angle of attack approaches. And I came across either a reference or a pic of JG's VG where the pitot was cocked down a bit to help prevent this.

I think I may have contacted him to ask about it at the time. And I then put a small bend in my pitot to cock it downwards also.......I cannot now recall how much, something like 7 or 8deg would make sense.

I fly my approaches heads up but with constant momentary references to the ASI until just a bit short of flare, when I'm fully heads up.

I have never seen my ASI decay or drop out at high A of A.
In normal cruise etc my ASI still reads accurately.

I'm not promoting this, and I don't think JG was either. But it may be worth considering?
 

[skippydiesel]

If you don't need anything fancy, like a heated unit  - make your own!

The photo shows pitot & static. The static should have been nice and tight to the pitot - but sometimes art/aesthetics gets the better of the project (has increased vulnerability though).

They are both the same tube diameter (easy bend).

The static tip is blocked and 2 small, 1mm holes are drilled through, to give 4 holes.  Having the static out on/below the wing removes any concerns about picking a bad spot on the fuselage.

The auto pitot "lide" is a bit fancy - it works that the main thing - I still cover the exposed pipe tips, in a purpose made bag, with draw string & "Remove Before Flight) tag.

The "shaft" is just fiberglass wrapped around the two pipes.

Tubing inside wing is yellow "Tygon" but you could use any long life(don't want it going hard & cracking) push on - I secured with spring hose clamps (not easy to find these days).

Hose diameter is immaterial as both pitot & static are registering pressure not volume.

Don't have a photo at the moment but have since added a 45 degree pipe for angle of attack/reserve lift.

 

 

[Old Koreelah]

1 hour ago, IBob said:

Hi Marty. During my build I came across quite a few references to the ASI dropping out on high angle of attack approaches. And I came across either a reference or a pic of JG's VG where the pitot was cocked down a bit to help prevent this.

When I learned about this error, I built an extension to mine. 

Joined via a short length of flexible tube, the extension had a “tail” that always pointed it into the airflow, whether sideslipping or near stall. It eventually broke and I didn’t bother replacing it. Can’t say if it helped much.

[Blueadventures]

2 hours ago, IBob said:

Hi Marty. During my build I came across quite a few references to the ASI dropping out on high angle of attack approaches. And I came across either a reference or a pic of JG's VG where the pitot was cocked down a bit to help prevent this.

I think I may have contacted him to ask about it at the time. And I then put a small bend in my pitot to cock it downwards also.......I cannot now recall how much, something like 7 or 8deg would make sense.

I fly my approaches heads up but with constant momentary references to the ASI until just a bit short of flare, when I'm fully heads up.

I have never seen my ASI decay or drop out at high A of A.
In normal cruise etc my ASI still reads accurately.

I'm not promoting this, and I don't think JG was either. But it may be worth considering?
 

Hi IBob  I learnt about that in gliding.  When turning in the circuit the air speed on the ASI would drop a little.  Had to keep the screen view attitude; and don't stick the nose down to bring the ASI up as you would be over the desired speed when out of the turn.  The air flow at an angle across the pitot tube caused the situation.  

[IBob]

Blueadventures, similar effect by the sounds of it, and I would guess of more or less relevance depending upon the aircraft and the phase of flight.

In mine, for the full flaps landing that I use a lot, you have to hold the nose up and the speed down on finals if you want a reasonably short landing. And especially if lightly loaded, which I usually am.

It took me a while to transition to what the aircraft will do in this configuration, to the out of balance controls, to more rudder and less or no aileron.
What I read of high A of A in STOL machines was that the IAS could drop out entirely.
I think having reliable ASI helped me practise that phase of flight, at height initially, then in landings.

[Blueadventures]

4 minutes ago, IBob said:

Blueadventures, similar effect by the sounds of it, and I would guess of more or less relevance depending upon the aircraft and the phase of flight.

In mine, for the full flaps landing that I use a lot, you have to hold the nose up and the speed down on finals if you want a reasonably short landing. And especially if lightly loaded, which I usually am.

It took me a while to transition to what the aircraft will do in this configuration, to the out of balance controls, to more rudder and less or no aileron.
What I read of high A of A in STOL machines was that the IAS could drop out entirely.
I think having reliable ASI helped me practise that phase of flight, at height initially, then in landings.

Also, gliders can be slower in their circuit all the way at 40mor 45 knots so the drop is a little more noticeable and not able to add speed with an engine only by lowering the nose; which may not be good at times.

[facthunter]

The stall angle is about 14 degrees. That shouldn't kill the pitot working. When you are taught side-slipping properly you would be warned of a possible IAS low(er) reading and cover that by holding a safe speed.. Nev

[IBob]

I don't know, Nev. Quite possibly the airflow over a pitot head at 14 deg is less likely to be disrupted at, say, 60kts, than at 40kts or 30kts?
And I expect the head could be designed to reduce the breakdown or disruption of airflow: mine is a very crude open ended pipe, not the polished bullet heads you see on real aeroplanes...............)

[skippydiesel]

2 hours ago, IBob said:

............. mine is a very crude open ended pipe, not the polished bullet heads you see on real aeroplanes...............)

IBob - all pitot's are just a an open ended pipe  (positioned to be in relativly undisturbed air flow)- some are in fancier packaging than others, for which you will pay handsomely.

 

Oh! & if it flies , its a real aeroplane, subject to the same physical laws as any other

Edited August 10, 2023 by skippydiesel

[spacesailor]

Why do most pitot's have the bent piping ,

If you use a straight pitot with a bent plastic elbow , shouldn't it work the same ? .

Pipe- elbow , tubing , Instrument .

I just thought about Mr King's H bird modification. Straight piece of alloy, That screwed into receptacle. 

spacesailor

[pluessy]

Using a sharp pointed pitot or a very thin-wall tube will reduce the effects of AoA and sideslipping on the ASI. Most commercial pitot probes have a very pointy end (conical) to reduce the flow disturbance at angles.

[IBob]

My kit supplied pitot is simple aluminium tube, not sure of size, maybe 4mm ID. Cut off square, but with the inner edge of the cut bevelled, so the tip is a sort of little funnel.

[facthunter]

Where are the static ports.  ?   Nev

[IBob]

Either side of the rear fuselage, Nev.
And I only once washed her with a hose.......and after that I modified the static pipework to add a high spot before running it forward.

[facthunter]

Do you have an "alternate static"? Nev

[IBob]

19 minutes ago, facthunter said:

Do you have an "alternate static"? Nev

No......(

[facthunter]

Just the cabin interior would do.  Provided you know the errors.  Nev

[IBob]

True.

It was instructive flying without the gauges, not that we were up for long. And I spent the rest of the afternoon purging the static pipework, disconnected, with a hot air gun.