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  #1  
Old 06-26-2013, 07:09 PM
RFazio RFazio is offline
 
Join Date: Jan 2007
Location: LI, NY
Posts: 409
Default An interesting thing happened to me today.

I flew up to my country place in the Catskills from my home base, Long Island's 1N2. We landed at Freehold 1I5 and tied down. My buddy picked me and my other friend Steve up and we spent a few hours at my place. It started getting grey so we decided to head home. Steve and I got dropped off at freehold at around 1:00pm. Untied the plane and took off for home. My plane is an RV-6 with full dynon Skyview system. I also have a backup steam airspeed, altimeter and a compass. My thinking was that if the entire electronic system went poof, I could probably get home on steam. Anyway, when we were taking off on the grass I noticed that the stall warning was screeming like it never had before. I mean beeping way more than normal. I chalked it up to taking off on the grass, and once we were off it stopped and we started climbing out. As soon as we got to the end of the runway we started hitting light rain. Very light rain and I let it climb to around a 1000ft and throttled back. I have a wood prop. I didn't want to damage the prop in the rain. We were climbing slowly and I headed home. I could see the weather was clearing ahead so I kept it throttled back and continued on. I noticed that the airspeed seemed very low like 100 knots, but figured it was because I was throttled back. I usually don?t fly that way on a trip like this. I was climbing slowly and had the autopilot set. All was well but it seemed much slower than normal even though I was throttled back. It looked like a nice tail wind because we had a ground speed of around 135 even with an indicated of 100. The trip is about 109 nautical, around 45 minutes. Steve fell asleep, I was up to 5500 ft cruising along and all of a sudden I hear CAUTION in the headset and the plan dives. I look at the screen and it's saying speed too slow, or some such thing. Steve jumped up and the airspeed indicator went from 90 knots up to 145. What the heck? I hit the auto pilot cancel button when the plane dived and wasn't sure what was going on. What we think happened was something crawled up the pitot and partially blocked it. It must have either blown off or back into the tube further and cleared. The rest of the trip was uneventful. Luckily it cleared, I don?t know what I would have done had it still been blocking the pitot. I did hit the cancel button and level it off before I even looked at the screen. But had it been reading stall and I was really not? I thought I was so cool having backup steam airspeed and altimeter but guess what if both are fed from the same pitot you don?t really have backup. I looked at the log file and you can see where it dives and the pitot clears and the airspeed jumps from 90 to 150 knots while the ground speed goes from 138 to 150. I haven?t gotten to taking apart the pitot and lines, but I will before I fly again.
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LI, NY
N966RV
RV-6 Slider
O-360
FP Wood Prop
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  #2  
Old 06-26-2013, 07:16 PM
bkthomps bkthomps is offline
 
Join Date: Jan 2010
Location: Destin
Posts: 1,543
Default

Pitot blockage indeed of your altimeter was right, my static system does this due to water so I am familiar with the symptoms, I would recommend not flying IFR until all your gauges agree
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  #3  
Old 06-26-2013, 08:02 PM
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Jesse Jesse is offline
 
Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,679
Default

If the pitot becomes completely blocked (I'm no sure at which point this happens), the Dynon should revert to GPS Groundspeed for your airspeed. Definitely disconcerting when the AP dives on you. The mud dauber threads going around cause this. I've had them in my pitot before.
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  #4  
Old 06-27-2013, 06:04 AM
terrykohler terrykohler is offline
 
Join Date: Jan 2005
Posts: 1,009
Default Bugs in the Summer, Ice in the Winter

Fly enough and at some point, you're going to experience pitot blockage. You might want to think about some sort of backup for attitude. On my "classic" panel, if the AI (and heading) pukes, I can turn to my turn coordinator,altimeter, and whiskey compass. You might want to look into something similar that doesn't rely on pitot input. I believe all of the Garmin portables have a "panel" page that might serve your purpose as well. Good post.
Terry, CFI
RV9A N323TP
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  #5  
Old 06-27-2013, 07:47 AM
videobobk's Avatar
videobobk videobobk is offline
 
Join Date: Jan 2005
Location: Near Scipio, in Southern Indiana
Posts: 1,779
Default

In 1200 hours, this has happened to me--once--on take off on 36 at OSH, with planes everywhere. I noticed as I rotated (I was flying by feel because of the situation) that my airspeed was zero.

Only months before I had a lesson in flying without an ASI, and how to accurately gauge airspeed visually. It really works! I set out to land somewhere 50 miles from there, but it cleared after about half that distance. A bug, as I expected. With a little practice, you can establish your airspeed within 5 knots if you can see the horizon.

Bob
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  #6  
Old 06-27-2013, 08:56 AM
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DonFromTX DonFromTX is offline
 
Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
Default

I don't have much faith in my own ability to judge speed, so I have a Dynon D1 which only gives me ground speed, but that is close enough if you know the wind direction and approx velocity. Seems to be a great little backup system.
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  #7  
Old 06-27-2013, 10:42 AM
novipilot novipilot is offline
 
Join Date: Jul 2010
Location: Novi, MI & Venice, FL
Posts: 66
Default

I had a CFI that turned off or covered up everything, then had me gage power by using the index finger as a gage of where the throttle should be, altitude by experience, and descent attitude by where the horizon is in the front windshield. It works good enough to get you home safe.
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  #8  
Old 06-27-2013, 02:22 PM
Jim F Jim F is offline
 
Join Date: Dec 2008
Location: Canby OR
Posts: 119
Default AOA

My solution to this is to have an AOA system independent of the pitot-static system.
Mine is from AFS. The port holes in the system are #64 and thus too small for most bees, wasps and bugs.

I also use a pitot cover when parked, even if for a short time....
Jim F
RV-9A
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  #9  
Old 06-27-2013, 02:34 PM
NASA515 NASA515 is offline
 
Join Date: Nov 2011
Location: Hansville, Washington
Posts: 536
Default

Loss of pitot (or static) pressure caused the loss of a NWA 727 out of JFK, two 757s in S. America, and most recently the Air France A330 in the S. Atlantic (AF 447.) Nothing to be sneezed at - but something to be handled when fore-warned. Pitch and Power is the air carrier mantra. Fly the appropriate pitch attitude and regular power and the air data numbers will be where they should be.

Plus - as mentioned, the Skyview has this Gps assist, something the Airbus could have used - a real plus.

When I trained with Mike Seager, he made me fly circuits with everything turned off. It's an excellent bit of training.

Bob Bogash
RV-12
N737G
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  #10  
Old 06-27-2013, 02:50 PM
terrykohler terrykohler is offline
 
Join Date: Jan 2005
Posts: 1,009
Default Something Else to Think About

If you've lost pitot in the summer, better also keep a close eye on your fuel tanks. A mud wasp in the vent line can cause the tank to collapse if you're drawing fuel from it. A good friend with a 9A had to replace a tank -the ribs actually buckled. Of course, if you've got a good screen over the vent opening, this may not be an issue.
Terry, CFI
RV9A N323TP
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