AirTalk.org

Nick · Guest

on helis?... and the static pressure point??...... rc or full
size....R22...or Jetranger any info appreciated..

Cheers

Nick

Maxwell · Guest

"Nick" <nick.costin1 (AT) btinternet (DOT) com> wrote in message
news:RrCdnRGjgZfMxFLYnZ2dnUVZ8vednZ2d (AT) bt (DOT) com...

Nick · Guest

Hahahahahahahahahaha.........You don't know what a pitot is do you?

sigh......anyone know where a piTot is situated? ..... when do they start to
work?...... Oh alright then......at what airspeed do they start to function
usefully / accurately.... or even .....when does the down wash have no
effect of the pitot.

"Maxwell" <luv2fly99 (AT) cox (DOT) net> wrote in message
news:KaJzh.103530$qy.43544 (AT) newsfe16 (DOT) lga...

Maxwell · Guest

Aaaaagh, that's what I get for trying to answer without my glasses. I
thought it said pilot, and was wondering why you were asking about the
static port too.

I recall two different locations in my limited experience. Seems like the
Huey's and larger birds often had a long pitot straight out the front in to
clean air, maybe as much as 18 to 24 inches long, and very much horizontal
with the air flow. But I also think I recall seeing at least a few Jet
Rangers that had a 90 degree mount, about 3 inches from the cabin, and
pointed down the center of the windshield, paralell with the windshield, and
about 45 degrees or so to the horizontal. Obviously placed to measure flow
up the windshield after deflection from the nose of the aircraft.

I don't recall the location of their static ports, but every one I have ever
seen has always been on the side of the cabin, 90 degrees to the slip
stream. But again my knowlege is somewhat limited. I'm just a fixed wing
pilot, that loves helos.

"Nick" <nick.costin1 (AT) btinternet (DOT) com> wrote in message
news:Kv-dnQXP79zdHFLYnZ2dnUVZ8vednZ2d (AT) bt (DOT) com...

Bill McMullen · Guest

On the R22 / R44, the pitot is a short tube mounted on the front of the mast
fairing perhaps about 3" above the cabin. The pitot on the R22 is just an
open tube located within the rear top fairing about a foot behind the
transmission. Anything below 20 knots is too hard to read with any accuracy
.... above that seems to be OK.

"Nick" <nick.costin1 (AT) btinternet (DOT) com> wrote in message
news:RrCdnRGjgZfMxFLYnZ2dnUVZ8vednZ2d (AT) bt (DOT) com...

Guest

Pitot locations vary depending on engineering convenience, but in
general somewhere near the front end of the helicopter, pointing
forward, matters not much where unless the bubble shape influences
airflow (vs, for instance, bernoulli).

Static can be on side of fuselage, but another good place is in some
wide-open space over the engine or behind the transmission.

Low-speed (less than 35 knots?) accuracy, however, is just plain
terrible for any pitot system mounted anywhere, the extremely low ram
pressures at those low speeds are woefully sensitive to minor changes
in angle of impact of the airflow, making it nigh impossible to get a
good reading.

The only remedy I've seen is at the engineering-test-pilot training
school at the Nat'l Test Pilot School in Mojave, CA, on a 206: a 24"
dish-shaped pod, non-rotating, above the main rotor (looking something
like the radar pods on the OH-58 for target aquisition), with a
rotating cuff (100 rpm?) containing multiple pitot tubes (or so it
appears), electronically instrumented with pressure transducers to
look at the DIFFERENTIAL between forward-moving side of disc and
rearward, the arithmetic sum (hey, at last something simple, 3-1=2)
being the airspeed. Quite accurately.

The quickie tour I got was brief on this, I may be misrepresenting
portions of the mechanism. Whatever. Certainly you won't find one on
ebay.

The total absence of real accurate IAS data throughout the rest of the
helicopter fleet is a flaming pain in the butte, there are so many
useful things we could teach and learn and do if we just knew
accurately, for instance, how much translational lift we were getting--
or even exactly when we achieve zero airspeed in OGE hover. But there
seems to be no way to get that info easily, so the entire industry has
gotten used to doing without it--even though a gyroscopic HSI costs
around $3000, nobody sees a NEED for 10 or 20-knot airspeed accuracy.

Not that it would free us from the grim realities of the h-v
curve . . .

B4RT · Guest

The pitot is useful at about any speed as long as youre going forward. It
might not be totally accurate at low speed, but its all relatve anyways.
Bart

"Nick" <nick.costin1 (AT) btinternet (DOT) com> wrote in message
news:Kv-dnQXP79zdHFLYnZ2dnUVZ8vednZ2d (AT) bt (DOT) com...

Nick · Guest

"Maxwell" <luv2fly99 (AT) cox (DOT) net> wrote in message
news:YRNzh.80727$5q6.66022 (AT) newsfe17 (DOT) lga...