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Airspeed Indicator Off?

LevelWing
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LevelWing Rising Star

LevelWing

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What is the possibility that my airspeed indicator is not accurate? Whenever I'm on the takeoff roll the plane gets very squirrely and basically starts to skid around the runway until I lift off. This starts to occur around 60-70 MPH indicated on the airspeed indicator. Conversely, when I land, as soon as I touch down the plane starts to skid around the runway again. My approach speed is about 80 MPH until I'm over the runway and then about 75 MPH at touchdown.

 

The only thing I can think of is that the airspeed indicator is off. The plane went through annual in December and nothing was noted about the airspeed indicator and I don't think he even checked it.

Jeff_S Grand Master

Jeff_S

Posted
Posted

Yes, that sounds like a classic nose wheel bushing problem and one you definitely need to get checked out. I'm curious, though, why you even suspected that your airspeed would be off. I'm having a hard time figuring out why you would like that behavior to an airspeed issue.  What was your thought process there?

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Marauder Grand Master

Marauder

Posted
Posted

What is the possibility that my airspeed indicator is not accurate? Whenever I'm on the takeoff roll the plane gets very squirrely and basically starts to skid around the runway until I lift off. This starts to occur around 60-70 MPH indicated on the airspeed indicator. Conversely, when I land, as soon as I touch down the plane starts to skid around the runway again. My approach speed is about 80 MPH until I'm over the runway and then about 75 MPH at touchdown.

 

The only thing I can think of is that the airspeed indicator is off. The plane went through annual in December and nothing was noted about the airspeed indicator and I don't think he even checked it.

 

Since you are talking about this occuring both on take-off and landing, the gentlemen above are correct that the nose wheel may be the issue. If you notice it on take-off only, I know that my plane has a tendency to wheel barrow a bit if I'm not trimmed for take-off correctly (which in my plane is a slightly above the "take-off" mark on the trim indicator).

LevelWing Rising Star

LevelWing

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Thanks for the replies, everyone. I found the service bulletin on the Mooney website and will have my mechanic look into it. About how many hours does it take to make the correction?

 

 

Yes, that sounds like a classic nose wheel bushing problem and one you definitely need to get checked out. I'm curious, though, why you even suspected that your airspeed would be off. I'm having a hard time figuring out why you would like that behavior to an airspeed issue.  What was your thought process there?

I guess I figured maybe the airspeed indicator was reading lower than it actually was and as a result the plane was skidding because it was ready to come off the ground but I was forcing it to stay on the ground. 

Seanhoya Enthusiast

Seanhoya

Posted
Posted

Gents,

 

Well, I wouldn't disagree with all of the previous comments, but I might add that I actually have had an airspeed indicator which was indicating 10 knots slow.  And considering that the pitot-static check is only done on a 2-year basis, and isn't part of the annual, why would we rush to rule out this as a possibility?

 

LevelWing dude, the indications that I had were abnormally long landing rolls and screeching tires.  Considering that I was landing at Freeway Airport in Maryland, which has claimed many a Mooney during takeoff and landing, I was lucky that I had good airspeed control, even if it meant that I was landing fast.  Now, I didn't have the control problems that you were mentioning in terms of squirliness, which would add weight to the previous arguments regarding the nose gear.

 

For what its worth, I think that the nose gear probably is the culprit.  But you initial instinct regarding airspeed is reasonable, even if the nose-gear turns out to be the culprit. When was the last Pitot-Static done?

 

Sean

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Mooneymite Grand Master

Mooneymite

Posted
Posted

Gents,

 

Well, I wouldn't disagree with all of the previous comments, but I might add that I actually have had an airspeed indicator which was indicating 10 knots slow.  And considering that the pitot-static check is only done on a 2-year basis, and isn't part of the annual, why would we rush to rule out this as a possibility?

 

LevelWing dude, the indications that I had were abnormally long landing rolls and screeching tires.  Considering that I was landing at Freeway Airport in Maryland, which has claimed many a Mooney during takeoff and landing, I was lucky that I had good airspeed control, even if it meant that I was landing fast.  Now, I didn't have the control problems that you were mentioning in terms of squirliness, which would add weight to the previous arguments regarding the nose gear.

 

For what its worth, I think that the nose gear probably is the culprit.  But you initial instinct regarding airspeed is reasonable, even if the nose-gear turns out to be the culprit. When was the last Pitot-Static done?

 

Sean

 

Careful, or we're going to get into another "virtue of AOA" discussion"!   :o

bnicolette Veteran

bnicolette

Posted
Posted

I have seen airspeed indicators off also.  I borrowed a friends Mooney a couple of weeks ago and something just seemed "not right" about it.  Lower speeds seemed to make sense with the power settings and configuration but high speed was definitely wrong.  See attached pictures.  They were both taken at cruise flight at the same altitudes & cruise settings albeit not the same temperatures I'm sure.

post-7889-0-44877000-1394155591_thumb.pn

post-7889-0-94273900-1394155692_thumb.pn

Mooneymite Grand Master

Mooneymite

Posted
Posted

If your airspeed indicator reads about 20 kts high in cruise flight, you can sell it to a Mooney pilot for a lot of money!   :lol:

 

About $1000/knot is the going rate, I think.

Andy95W Grand Master

Andy95W

Posted
Posted

What is the possibility that my airspeed indicator is not accurate? Whenever I'm on the takeoff roll the plane gets very squirrely and basically starts to skid around the runway until I lift off. This starts to occur around 60-70 MPH indicated on the airspeed indicator. Conversely, when I land, as soon as I touch down the plane starts to skid around the runway again. My approach speed is about 80 MPH until I'm over the runway and then about 75 MPH at touchdown.

 

The only thing I can think of is that the airspeed indicator is off. The plane went through annual in December and nothing was noted about the airspeed indicator and I don't think he even checked it.

Squirrely at 60-70 mph? I'm not at all surprised- lightly loaded in my M20C I start giving back pressure on the yoke at about 55-60 and It flies off the ground around 60-63 MPH or so. On landing I'm at 70-75 on final (I fly out of a VERY short field) and I touch down about 60-65. Mine is squirrely too when I'm much faster than that. (I always blame the crosswind- my wife blames my landing technique.)

Check out Don Maxwell's website:

http://www.donmaxwell.com/publications/publications.htm

Scroll down to the article on The Eight Second Ride, SB M20-202. If yours acts like Don describes, then you have a tracking issue.

Doing a rough check of airspeed accuracy by doing flaps up/ full flap stalls is a great idea. With only the pilot and fuel, you can expect indicated stall speed to be 3-5 knots below the bottom of the green and white arcs, respectively.

LevelWing Rising Star

LevelWing

Posted
  • Author
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Squirrely at 60-70 mph? I'm not at all surprised- lightly loaded in my M20C I start giving back pressure on the yoke at about 55-60 and It flies off the ground around 60-63 MPH or so. On landing I'm at 70-75 on final (I fly out of a VERY short field) and I touch down about 60-65. Mine is squirrely too when I'm much faster than that. (I always blame the crosswind- my wife blames my landing technique.)

Check out Don Maxwell's website:

http://www.donmaxwell.com/publications/publications.htm

Scroll down to the article on The Eight Second Ride, SB M20-202. If yours acts like Don describes, then you have a tracking issue.

Doing a rough check of airspeed accuracy by doing flaps up/ full flap stalls is a great idea. With only the pilot and fuel, you can expect indicated stall speed to be 3-5 knots below the bottom of the green and white arcs, respectively.

This definitely sounds like the issue. I'll have my mechanic fix this quickly and hopefully this will solve the issue. About how many hours does it take to fix the issue?

Andy95W Grand Master

Andy95W

Posted
Posted

My suggestion is to print out the Service Bulletin for him (2 pages), M20-202, from the Mooney website:

http://www.mooney.com/servicepdf/index.php

Jacking, leveling, and checking the nose gear's alignment should be not more than 1 hour.

If the spacer needs to be installed, it should be about another hour. If you do need the spacer, and unless he works on lots of Mooneys, he should order it from LASAR, SWTA, Don Maxwell, or Dugosh and he can ask for hints or advice when he has them on the phone.

I've been working on Mooneys for years and I still ask those guys lots of questions. All of those places are top notch and very helpful.

Guest

Guest

Posted
Posted

Do a search on line for ways to calibrate your airspeed indicator. I found an instruction for building a water manometer which I have used to check accuracy.

Clarence

slowflyin Mentor

slowflyin

Posted
Posted

My F model will do the same with flaps at TO setting. She will wheel barrow if left to her own devices. I have to trim properly and use some back pressure.

Sent from my iPad using Tapatalk

Andy95W Grand Master

Andy95W

Posted
Posted

Last time I checked (probably 10 years ago) the spacer was pretty cheap. Good chance you'll pay more for shipping than the spacer.

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