How's it going guys? I've got another little dilemma that I am hoping someone can shed some light on. I took off the other day after picking my plane up from a new voltage regulator install and my airspeed indicator was not working on take off. as a climbed, the airspeed indicator climbed. (seems like blocked pitot). As a leveled at 3500, the airspeed was indicating 160 mph then slowly backed off until it indicated 0 mph at level flight. As I descended it again begin to climb up a but then went back to 0 mph when on the ground.

Sooo, I tried sucking out the pitot tube with my lips (my gf refused to help me out working on the plane today) and didn't get anything. I then disconnected the pitot line to the airspeed indicator and blew a good amount of compressed air back out the tube to try to clear it out. Nothing to my knowledge came out of the tube but there was a good amount of air being successfully passed backwards through the line. I hooked the tube back up to the airspeed indicator and had someone watch as a tested the tube. I, stupidly, blew compressed air in the end of the pitot when I probably should not have used that much pressure. The person watching said the airspeed indicator did over a full rotation and I obviously messed up by blowing such high pressure in the pitot. now the airspeed indicator is zeroed a few mph off if 0. When I took off I thought that it would still work but it didn't not. It is reading very very slow and only showing about 70 mph when it should be showing 120 mph, however, it is not bei affected like altitude like it was before. I take off, climb and it will show 70 mph consistently on cruise, then gradually go down as a get into landing configuration. Any ideas? Do you think I just got the bug out of the line when i cleared it then completely screwed up my indicator by stupidly blowing that much air in the pitot while testing?

Thanks for all the help guys. Sorry for the long post.


On a quick other note And unrelated to the pitot tube, I am getting an insane amount of static in my radio. It is like I have one keyed mic in the sitting in the cowling. I can hear the engine very loudly in my headphones, probably a bad ground somewhere?

Sounds like you may have munched the inner workings of your AI. It operates off of air pressure, and very little air pressure at that. Blowing compressed air into the AI, or even blowing hard into the pitot tube isn't good for your AI.

Yeah figured. No bueno.

Blow hard in it, you bust it. Time for O/H or new one.

Gump

Had something similar in a 180 once. Took apart the Pitot head assembly and found several small dead and dried bug parts in the "lower" portion. Those bug parts could resist getting blown out like the ball in an old fashioned whistle, and then block drift back in the way. Separate the hose from the back side of the Pitot head. With your trouble shooting "luck" I think I would continue to "research" the problem until the AI reads consistently.
Best to ya.

That AI is toast now. Anything more than a gentle puff against the pitot tube wrecks it.

Gump

And, don't even blow into the end of the pitot tube with your breath. Send the instrument in. As Gump says, it's junk.

MTV

For lack of better words you blew it. New ASI is in order.

Think an overhaul is the route? Or just try to snag a salvage from dawsons?

Too late but for future refrence to test the airspeed indicator.

a. Airspeed check: Slip a long rubber hose
over the pitot mast (surgical tubing is recommended).
As one person reads the airspeed, the other should
very slowly roll up the other end of the tubing. This
will apply pressure to the instrument. When the airspeed
indicator needle reaches the aircraft’s approximate
recommended cruise speed, pinch the hose shut,
and hold that reading. The airspeed needle should
remain steady for a minute if the system is sound.
A fast drop off will indicate a leak in the instrument,
fittings, lines, or the test hose attachment. NEVER
force air in the pitot tube or orally apply suction
on a static vent. This will cause damage to the
instruments.

For more see page 12 http://www.google.com/url?sa=t&source=w ... 6Q&cad=rja

tcj wrote:Too late but for future refrence to test the airspeed indicator.

a. Airspeed check: Slip a long rubber hose
over the pitot mast (surgical tubing is recommended).
As one person reads the airspeed, the other should
very slowly roll up the other end of the tubing. This
will apply pressure to the instrument. When the airspeed
indicator needle reaches the aircraft’s approximate
recommended cruise speed, pinch the hose shut,
and hold that reading. The airspeed needle should
remain steady for a minute if the system is sound.
A fast drop off will indicate a leak in the instrument,
fittings, lines, or the test hose attachment. NEVER
force air in the pitot tube or orally apply suction
on a static vent. This will cause damage to the
instruments.

Excellent information, thanks tcj.

Mud dawbers often get into my AI. The first time this happened I didn't notice until after I was airborn. Now I check for it on every preflight and usually remember to put the pitot cover on after each flight. The only way to clear the pitot tube on the 180 is to disassemble the exposed part and blow the junk out from the back end.

I would take a close look at your VSI & altimeter also after you get the AI fixed. Since all 3 are tied to the static side, applying that much pressure to the pitot inlet & possibly rupturing the diaphragm in there may have a also affected them by suddenly pressurizing the static system. Did your helper notice the VSI or Alt show a rapid decent? I'm not sure if that could really happen, but it would be good to keep an eye on.

Kelly Instruments can rebuild/overhaul. Good outfit.

MTV

Be for you blow air in to the pitot tube, disconnect the air line in the wing and then gently blow air in the pitot air port. If it is clear then disconnect the line from the back of the airspeed indicator. Then clear the line by blowing lightly in to the line to clear it. If you do not disconnect the line be for you do you will run the air speed indicator. I just did one on a cub and the line was pluged.

Bought a salvage asi from we wentworth and sent it to Kelly for a certification. Not an overhaul but a little cheaper and doesn't require me to fly the plane to another island for the mechanic to pull the asi, ect. No mechanics on Nantucket.