Pitot system question

Hi all,

I was reading somewhere a while back, about placement of pitot tubes, distances under/above/behind/forward etc., etc. when one fella said he put his pitot tube right on the vertical leading edge of his vertical stabilizer, a couple inches down from the top, protruding out about 6 inches. 1/4" aluminum tube. I've never seen one in that location, and was wondering if you guys might consider this an option. My wings are going to have to be removeable after my flights anyway, and this would eliminate another disconnection, allbeit a single one, and small, it's still something I wouldn't have to disconnect.

My one concern was/is: the 12 or 14 feet of tubing from the tube its self on the tail, to the instrument hook up under the panel.....too much distance?

Your opinions/advice are appreciated as always.

John

I would guess there is close to 12 feet or more of pitot tubing in my glider wing.
It's only 1/4 " tube, but if the pressure loss is of concern, just use larger tube, but I don't think it matters.
That 's a good idea to avoid wing hookups if it's not in the prop blast.
BB

Since you're measuring static or stagnated pressure (rather than flow), the tube diameter is irrelevant. Putting the pitot into the vertical is a great idea - you'll probably get a more accurate readout than with a wing installation.

Thanks guys.

The prop blast was a concern too, but I think I'll give it a shot anyway, keeping it as high as possible on the vertical. And if it dont work, it wont be a big deal to change it, I dont spect. And if it does work, more accurate readings is a good thing!! Thanks again fellas.

John.

Depending on airplane, the prop blast should not be too much a concern for this installation. As you say, keep it as high as possible and the prop blast should be pretty negligible. You're most likely going to calibrate your indicated airspeeds as you do your flight tests so any induced error will be reflected in the markings for your green and white arcs.

Didnt I see the pitot on the verticals of some British planes circa WWII? Or am I dreaming?

Probably not dreaming. It's actually a not-uncommon place for a pitot tube.

Originally Posted by orion

Depending on airplane, the prop blast should not be too much a concern for this installation. As you say, keep it as high as possible and the prop blast should be pretty negligible. You're most likely going to calibrate your indicated airspeeds as you do your flight tests so any induced error will be reflected in the markings for your green and white arcs.

Orion,

Yea, thats the plan. I think it will be good. You guys cleared up the only real concerns I had.

It's one of Roger Manns....the Ragabond. (Piper Pacer clone). And just by looking, I think it will be plenty high enough to be out of the prop wash.

On your web site, that P-38....did someone scale down an original? And are there plans for it? That is my dream right there! A half or three quarter scale P-38, darting around the skies and strafing the beaches along the Great Salt Lake!! Keep dreaming huh...

John

The owner of the P-38 was approached by several individuals who were interested in making it a kit (I did the stability and control analysis and the first cut performance) but I don't think it ever happened. The one you see in the picture was built from glass, wood and foam and was really done as a one-off. It was powered by two beautifully done Geo Metro three cylinder engines with belt reductions. Performance was actually better than my initial calculations (later I discovered that my prop model was off) and handling was very benign.

Last I heard, the kit possibility was being discussed and they were looking at pulling molds off of the prototype but I think the task got a bit overwhelming and of course the owner did not want his baby damaged in the tooling process, so I think the project faded away before it even got a chance to start.

Orion,

Man, thats a bummer. I wish they'd have offered plans at least. They sure would have had an order for some coming from me. Cant blame the owner either though....were it mine, I wouldn't want it used for mold making neither. I bet he draws a big crowd where ever he lands too.

Personally, if I had your education and intelligence about anything and everything that has to do with aviation, that'd have to be where I put alot of my time.....getting a scale P-38 up and running!!! I've got a set of "plans" for a P-38 around here somewhere, and they're quite detailed, but they're for an RC model.....84 inch wing span, I think.....and I'd had hopes of just scaling them up a little and building one like that. A couple of 2100CC vw's....but that was a long time ago and I know now that, thats not all there is to it....another bummer! Oh well......who was it that was saying we should open a "dreamers" section here!!! Good idea!!

Thanks again bud...

John

I know its been a while but I just saw this thread. Some certified aircraft use a fin mounted pitot eg Ted Smith/Piper Aerostars. It's not exactly a short path for the plumbing to cover in an Aerostar. Bit of a bugger puting a pitot cover on though!