Rigid Nylon tube.

[Deskpilot]

I'm wanting to make a new pitot head for my Thruster and for that I need a length of rigid nylon or similar tube. About 12.5mm O.D. with a 5mm I.D. and about 700mm long. Alternately I could use a really thick walled Alloy tube if such a thing exists. Anybody got a idea where I can find some. I've searched the local web and been to manufacturers, plus tubing repair companies. No Go.

 

The design I'm after will be that it is mounted below the pod nose and can swing through 180 degrees to face backwards so that it is safe for storage and when on static show. Will be held in place by simple spring clips.

 

 

[Doug Evans]

I'm wanting to make a new pitot head for my Thruster and for that I need a length of rigid nylon or similar tube. About 12.5mm O.D. with a 5mm I.D. and about 700mm long. Alternately I could use a really thick walled Alloy tube if such a thing exists. Anybody got a idea where I can find some. I've searched the local web and been to manufacturers, plus tubing repair companies. No Go.The design I'm after will be that it is mounted below the pod nose and can swing through 180 degrees to face backwards so that it is safe for storage and when on static show. Will be held in place by simple spring clips.

What about a sprinker tube may do the job from bunning ?

 

 

[Deskpilot]

Hmm, hadn't thought about that. I assume you're referring to a riser tube. I'll have a look next time I'm there.

 

 

[geoffreywh]

rigid and nylon? a contradiction. very thick walled alloy? why not get 4130 steel? available from our local shop, could be the same weight as the alloy tubing for the size you require?

 

 

[Yenn]

I used 1/4" copper for my corby starlet and 3/8" aluminium for the RV. Both those work well. The aluminium has the advantage of light weight and can be joined with standard AN fitings. There is no advantage to having thick walls, it only adds weight.

 

 

[Deskpilot]

Thanks for your suggestion and advice guys. Here's a quickie image of what I'm aiming for. How far forward from the pod-nose should I end the tube? Tube can swing vertical or horizontal though vert locking will be easier to achieve. I'm not sure just how long the unsupported length will be.

 

 

I personally don't like the idea of a thin needle sticking out in front but that's just my idea of aesthetics coming into play.

 

 

[pluessy]

Look at the arrows from re-curve or compound bows, they are available in carbon fibre and aluminium, most are 7-8mm OD and 5-6mm ID and come in length up to 750-800mm. I have a few broken ones from my son and use them for all sorts of things. If you know anyone who is shooting with bow & arrow, they will have some damaged ones.

 

TP

 

 

[Deskpilot]

Thanks pluessy, I never thought of that. As an ex archer (shot for RAF Singapore way back when) and having a large archery club in a local park, I'll see what I can find.

 

 

[Soleair]

You could just use small bore 6mm dia copper tube, and clad the outside with a balsawood fairing to achieve whatever shape looks best. My main strut fairings are of balsa (from Bunnings' Aviation Dept), coated in epoxy & painted. Very light, tough, & durable.

 

 

[Doug Evans]

Thanks pluessy, I never thought of that. As an ex archer (shot for RAF Singapore way back when) and having a large archery club in a local park, I'll see what I can find.

How ya go have u design your tube yet ?

 

 

[Yenn]

The title of this thread was thick walled. Don't forget that a thick walled pitot will not be accurate. You need to fair the wall thickness down to nearly a knife edge.

 

 

[Deskpilot]

I think I have it sorted. Was clearing up my wife's half of the garage (she's the gardener) and came across some remains of a garden lighting set. The risers are rigid. Also found the part of the handle from a collapsible duster (or something similar) which is a nice fit over the riser tube. Using a bit of the original copper pitot tune I taped it all in position and, with the ASI on the other end, I fitted it to my car for a test run. Unfortunately, it was too close the the bodywork and suffered from turbulence. I'll make up some stand off sup[ports and refix it to the bonnet later today.

 

BTW, the first rial did move the needle but erratically. Also, the ASI doesn't go down to zero but stop at 10 knots. Can this be zeroed?

 

 

[Deskpilot]

Up-date. remounted my 'pitot tube' on the car and took it for another test run. At first I was horrified to see it reading way high and then the penny dropped. I'd made a list of Kilometers to Knots readings and woke up to remember that my ASI reads in MPH. Still, continued with the run out on the motorway where I knew 100kph was 62mph. I got a reading of up to 80mph so compared that with the return trip of about 40mph. Surprising what difference a head wind/tail wind can do.Very erratic needle movement so I'll stiffen my mount a bit and try again when there's no wind.

 

 

 

 

[Soleair]

Great idea on the testing. But. I think you'll find you are in dirty air from the flow over the bonnet where you have your probe. you need to position it further forward and/or upward to get less disturbed airflow. Quite a long way upward.

 

Attached pic of Snoopy that I used to fly in. Note how far forward the airspeed probe is - just to get into clean air.

 

 

 

[Yenn]

I thought that was an airborne barbers shop.

 

You can test using a manometer to see if you are getting the correct speed for pitot pressure. Then it is just a case of getting clean air.

 

 

[Blueadventures]

I'm wanting to make a new pitot head for my Thruster and for that I need a length of rigid nylon or similar tube. About 12.5mm O.D. with a 5mm I.D. and about 700mm long. Alternately I could use a really thick walled Alloy tube if such a thing exists. Anybody got a idea where I can find some. I've searched the local web and been to manufacturers, plus tubing repair companies. No Go.The design I'm after will be that it is mounted below the pod nose and can swing through 180 degrees to face backwards so that it is safe for storage and when on static show. Will be held in place by simple spring clips.

Could you mount the pitot under the leading edge of the wing like xair's Skyrangers etc?

 

 

[Deskpilot]

Could you mount the pitot under the leading edge of the wing like xair's Skyrangers etc?

Originally it was mounted on the port wing strut and had to be disconnected at the base to remove the wings. I'm modifying mine to have a folding wing so that trailing/wing folding becomes a one man operation. To that end, I don't want to disconnect every time so have made to decision to place the pitot under the pod nose.

 

Re clearance from the airframe, I did ask the question but no-one has given me a definitive answer....yet.

 

Soleair, 'Snoopy' is far from being normal. A test-bed for something or other. The E.E. Lightning had a very 'springy' pitot, far enough forward (approx 6ft) not to be effected by the intake airspeed which is higher than the aircraft's air-speed.

 

 

[Soleair]

'Snoopy' is far from being normal. A test-bed for something or other

True, it's far from normal. It was a flying laboratory for weather measuring instruments. The extended probe was for measuring very accurate gust speeds.

 

I posted the pic to show how far away from the nose you need to be to get clean air. I suspect the fluctuations you noted on your test setup were as much to do with the turbulent airflow around the bonnet as the tailwind component.

 

Re your proposed mounting point on the underside, beware bits of grass & low flying insects potentially clogging the pitot inlet. Though less of a problem if you fly exclusively off a hard runway.

 

 

[Blueadventures]

Originally it was mounted on the port wing strut and had to be disconnected at the base to remove the wings. I'm modifying mine to have a folding wing so that trailing/wing folding becomes a one man operation. To that end, I don't want to disconnect every time so have made to decision to place the pitot under the pod nose.Re clearance from the airframe, I did ask the question but no-one has given me a definitive answer....yet.

Soleair, 'Snoopy' is far from being normal. A test-bed for something or other. The E.E. Lightning had a very 'springy' pitot, far enough forward (approx 6ft) not to be effected by the intake airspeed which is higher than the aircraft's air-speed.

Why not replace the tube with a longer route? Say up from behind the seat and onto the wing via the trailing Wing edge attachment pivot area and onto the pitot tube. Ensure ok when folding and refitting wing. Cheers Mike

 

 

[Deskpilot]

Thanks Mike, that is an alternative I hadn't thought of.