Question about pitot tube placement

[Jeremy]

I am in the process of setting up a new airframe and I have a question about the placement and length of the tubing. Since the active is not suppose to be put in the prop wash area, can I put these in my wings and run longer tubing to them and still get accurate results? Or can they only be so long? I have only set up in an easy star before and I am in the process of building a great plane PT-60 and a 6' Telemaster. Thanks for any info on this

[Chris Anderson]

Yes, you can run them out on the wings. A rule of thumb is to put them at least two prop radius (and ideally three) away from the fuselage, to keep them out of prop wash. The silicon tube can be as long as you want, I think.

[Alex]

The length of the tube should not make much differance, as long as there are no kinks in it and it does not become hugely long. Try to make it as short as you need it though, ie just outside of prop wash, not on wingtip.

Correct me if i am wrong but I think that the ardupilot code preforms a ground startup calibration, and then only measures the difference in pressure between the pitot, and inside the cockpit to get airspeed, so if there was a difference because of a long tube, it will be constant so you should not get any huge errors compared to a shorter tube and the calibration at startup would cancel out the error

[Chris Anderson]

Alex, actually the DIY Drones pitot tube is two tubes (active and static), both of which should be outside the cockpit. That's because cockpits are often pressurized by airflow ducted in to cool batteries and electronics.

[Mike Bakula]

Straight pitot setups are fairly forgiving, but a few notes;

You already know you want to avoid the prop wash.

When putting your pitot out on the wing, the end of the tube needs to be 1/3 chord or so forward of the wing, to avoid the circulation flow due to wing lift.

Unless you have coils of it in there somewhere, the tubing length can be neglected.

On the other hand, leaks will mess up your reading, as will kinks or blockages in the line.

[Jeremy]

Thanks for all the info and help so far guys. I appreciate your time. I am not to great with airplane terms so I just want to make sure I get your statement properly. So say if my chord or chord length is 12" I should have it sticking out 4" from the chord in the front of the wing? This is what I referenced to come up with what I just said. Or did I totally mess up what you meant? Do you happen to know of a pic I can see for reference? If not its OK, I just do better with pictures.

[Mark Whitehorn]

My 6' Telemaster has the pitot tube about 23" out on the wing (tubing routed through aileron servo bay) and projecting only 1 3/4" beyond the leading edge. Airspeed readings seem to be fairly accurate. My prop radius is 6.5" so I meet Chris's propwash rule. I didn't know Mike's 1/3 chord rule (which I read the same as you), but 4" projection seems excessive to me (and difficult to protect during transport).

[Jeremy]

Awesome thanks Mark. Helps a bunch. I agree though 4" sounds like a bunch thats why I did not think I was reading that correctly.

[YureZzZ]

I have related question, so I'll ask here.

Can I place both tubes on the side of fuselage, facing towards on a pusher plane?