Airspace variance at cruise and descent.

[Mac80]

Today while in cruise and descending I had a large variance in airspeed.

I noticed up to about 30 knot difference in air speed, mostly about 10 knots. 

Could strong crosswinds cause the Mooney pitot inlet to read erratic airspeeds, 155-110 max variance.

 

 

 

 

 

Edited May 22, 2022 by Mac80

[Mac80]

On 5/1/2022 at 5:34 PM, Mac80 said:

Today while in cruise and descending I had a large variance in airspeed.

I noticed up to about 30 knot difference in air speed, mostly about 10 knots. Had about 30 knot headwind that was due to high crosswind, projected to be 50 knots.

 

 

 

 

 

 

I just looked at my airspeeds on FlightAware. They look like some crazed jack in the box was flying?

https://flightaware.com/live/flight/N981SM/history/20220501/1606Z/KHEZ/KJEF/tracklog

Edited May 22, 2022 by Mac80

[EricJ]

Looks typical for turbulence, no?

 

[carusoam]

Hand flying or was the AP hiding the fact you were in vertical air currents?

Spring weather has interesting ways of moving air around…

APs have a way of trimming the plane without telling you.

First time…? Things can get pretty disconcerting…

Descending air can beat your ability to climb…

Note the weather at the end of the flightaware trip…

PP thoughts only, not a CFI…

Best regards,

-a-

[N201MKTurbo]

Looks bumpy alright.

[cferr59]

I had a case of this recently due to up/down drafts. I was surprised how much variance it caused in airspeed it caused. I was questioning the aircraft performance for a bit, but heard other aircraft complaining about it. There were reports of moderate turbulence, but I only experienced light. I was IFR and, for the first time, requested a block altitude. This helped a lot because I could let the airplane climb or descend (within the block) rather than fighting the winds. I wished I had done it sooner.

[Mac80]

1 hour ago, EricJ said:

Looks typical for turbulence, no?

 

It was very smooth except pushing the plane sideways. The zig zag is air speed it held altitude with no problem.

[EricJ]

14 minutes ago, Mac80 said:

It was very smooth except pushing the plane sideways. The zig zag is air speed it held altitude with no problem.

Changing airspeed on autopilot usually means it's compensating for up and down drafts.   It's not unusual.

[carusoam]

Strong winds + high terrain = orographic lifting and often smooth air…

Thermals can be similar, more likely to be bumpy…

 

In updrafts… the AP holds altitude, and speed increases…

In down drafts… the AP holds altitude, and speed decreases…

 

Kind of aviation 101 like the books say… but,  re-taught in real life via Mooney!  
 

Now… to find the source of the vertical winds…?

 

As PIC… you get to control things… so the airspeed doesn’t go to low, or too fast… or the ground doesn’t come up to smite thee… or you bust an altitude restriction…

Some APs can lose control if the vertical speed changes too quickly for them to react properly…

Be ready to hand fly…

Or click off the AP… and see how fast the vertical winds are actually going…

Ups can be in the order of 1k+fpm 

Downs can be 2X of what the ups can be…. It can be very possible to run out of climb rate…

There are strategies to flying in these situations…

PP thoughts only, not a CFI…

Might want to invite @Scott Dennstaedt, PhD Scott know a thing or two about weather and flying…

Best regards,

-a-

[Mac80]

Carusoam
“Hand flying or was the AP hiding the fact you were in vertical air currents?”

I believe this could be it I was using AP. I had pitch servos and computer boards recently replaced. They do a great job now. 
Could be up AP was compensation for clear air up and down drafts causing the change in air speed. 
There was no chop or turbulence and nothing like up and down drafts in the clouds.  
The altitude hold was rock solid but I did not put my hand on pitch control wheel it may have been working hard.I was heading north with strong winds from west. If it happens again I’ll switch off AP and see what happens. Might get really scary then.

I have over 1000 hours in this plane but have not done many multi state trips that have different weather.

[Ragsf15e]

13 minutes ago, Mac80 said:

Carusoam
“Hand flying or was the AP hiding the fact you were in vertical air currents?”

I believe this could be it I was using AP. I had pitch servos and computer boards recently replaced. They do a great job now. 
Could be up AP was compensation for clear air up and down drafts causing the change in air speed. 
There was no chop or turbulence and nothing like up and down drafts in the clouds.  
The altitude hold was rock solid but I did not put my hand on pitch control wheel it may have been working hard.I was heading north with strong winds from west. If it happens again I’ll switch off AP and see what happens. Might get really scary then.

I have over 1000 hours in this plane but have not done many multi state trips that have different weather.

Were you possibly downwind of a good size mtn range?  Like 50-100nm east of the Sierras, rockies, Smokies, etc?

[Mac80]

I was over Missouri Ozarks when I noticed it  6 to 7 thousand feet above any hills. My ground speed was only 110 130 knots while airspeed was 150 except when it dropped off closer to ground speed a couple of times.

It was a strong crosswind in air and on ground most people were not out on otherwise nice Sunday PM.

 

[PT20J]

The airplane will not "know" that there is a crosswind. Unless you are slipping or skidding, the relative wind is on the nose. The only affect of a crosswind aloft is drift over the ground. Changes in indicated airspeed would be caused by the autopilot compensating for up and down drafts or an instrument error such as water in the static lines (which would also affect the altimeter and VSI) or perhaps water in the pitot line. Mountain waves can be very smooth and occur several thousand feet above the ridge that triggers them. 

 

Skip

[takair]

If the aircraft has auto trim, it can be a good indicator of how hard the autopilot is working. In the conditions you describe, I might expect the trim wheel to be compensating. Just drop your hand on the wheel to see what it is doing. 

[KB4]

   

14 hours ago, Mac80 said:

Could strong crosswinds cause the Mooney pitot inlet to read erratic airspeeds

Yes.  Only once, was on final, gusts that made you feel like a rodeo bull rider, the AS needle looked like a mini windshield wiper.
 

You have good amount of time in your J, so if it isn’t performing as YOU have come to expect, something ain’t right. If flown by numbers and that remains constant, any deviation in performance is the first sign that further investigation is necessary.  Kudos to you for identifying potential issue  

 What FPM on climb out? Settings?  if you give settings and performance you see, u can compare to other J drivers and what they are seeing. 
 

Does 3 always burn hot? First to peak? pull #3 plugs throw 2 new in. Its cheap and if goes away u know was fouled plug and hopefully issue doesn’t reoccur

 

[Mac80]

Yes the Century 2000 has auto trim. 

I should have also looked at slip skid on turn coordinator.

May have had some water in pitot line as it set out in some heavy rain night before. The position lights had water under the lens.

I also forgot I had pitot heat on?

Does not sound like any engine or prop problems so thank you all for your suggestions and comments.

 

[Ragsf15e]

On many models there’s a tiny button under the forward, left wing root to drain the pitot lines.  Theres one under the ~battery area near the back to drain the static lines.  They are nondescript.

Pitot heat likely had nothing to do with your problem.  It’s designed to be left on.

[PT20J]

3 hours ago, KB4 said:

Yes.  Only once, was on final, gusts that made you feel like a rodeo bull rider, the AS needle looked like a mini windshield wiper.

Turbulence induced windshear. It’s not possible to fly a constant approach speed in these conditions. I just aim for an attitude that puts the lowest excursions at the desired speed. 

[rbp]

attitude, and power setting. 

And if in a gusty crosswind, you want to crab until over the runway, then slip for alignment and drift. I avoid cross-controlling except in the lightest / smallest xw

[Fly Boomer]

3 minutes ago, rbp said:

I avoid cross-controlling except in the lightest / smallest xw

Why?  I dislike the switch from crab to slip at the last second.  Is there a safety issue with slipping all the way down?

[rbp]

12 minutes ago, Fly Boomer said:

Why?  I dislike the switch from crab to slip at the last second.  Is there a safety issue with slipping all the way down?

the slip increases drag, so you'll need more nose down to maintain airspeed, and and you'll have more sink, so you'll need  more power to stay on the glide path. 

also, you can't cross-control stall if you're not cross controlled!  You also get pitot.static errors in a slip, no bueno.

https://www.boldmethod.com/learn-to-fly/maneuvers/how-to-fly-a-forward-slip-to-landing-if-you-are-high-on-final/

[PT20J]

I agree with @rbp. Most teach primarily the slip method in primary training for a couple of reasons. First, when first learning learning, pilots lack the skill to convert from a crab to a slip at low altitudes, and second, the slip allows you to better gauge how close you are to the the limits of your and the airplane's capability. But it is more comfortable to fly the final in a crab (that's how the autopilot flies an approach) and you can handle higher crosswinds with this technique.

You don't have to use the kickout method of aligning at the flare. You can crab to say 100' and then convert to a slip. As you get experience, you will find that you can do it at a lower altitude and stronger crosswind.

Skip

[Ragsf15e]

1 hour ago, PT20J said:

I agree with @rbp. Most teach primarily the slip method in primary training for a couple of reasons. First, when first learning learning, pilots lack the skill to convert from a crab to a slip at low altitudes, and second, the slip allows you to better gauge how close you are to the the limits of your and the airplane's capability. But it is more comfortable to fly the final in a crab (that's how the autopilot flies an approach) and you can handle higher crosswinds with this technique.

You don't have to use the kickout method of aligning at the flare. You can crab to say 100' and then convert to a slip. As you get experience, you will find that you can do it at a lower altitude and stronger crosswind.

Skip

Ha!  We all have our own technique on that one.  First to @rbp, you can’t stall cross controlled if you maintain appropriate airspeed.  Typically 1.3 vso plus half a gust factor.  I like to set up my cross control about 1 mile final.  RAP in that order.  Rudder to maintain pointed down the runway, Aileron to stop any lateral motion, then Power to maintain airspeed.  You are correct, more power is needed to maintain airspeed but not a lower nose down attitude.  I like this method to get stable and asses the xw longer.  Also, the USAF had us teach it this way in primary training in the T6 which is like a Meridian size airplane.  I find it works well for me, but nothing wrong with the other way.

[rbp]

24 minutes ago, Ragsf15e said:

Ha!  We all have our own technique on that one.  First to @rbp, you can’t stall cross controlled if you maintain appropriate airspeed.  Typically 1.3 vso plus half a gust factor.  I like to set up my cross control about 1 mile final.  RAP in that order.  Rudder to maintain pointed down the runway, Aileron to stop any lateral motion, then Power to maintain airspeed.  You are correct, more power is needed to maintain airspeed but not a lower nose down attitude.  I like this method to get stable and asses the xw longer.  Also, the USAF had us teach it this way in primary training in the T6 which is like a Meridian size airplane.  I find it works well for me, but nothing wrong with the other way.

you can stall at any airspeed and any attitude

did you read the part about inaccurate airspeed indications in a slip? its because of ram air pressure in the static port on one side of the plane and vacuum on the other. the ASI reads *higher* when in a slip, so you may not actually be flying at 1.3Vso, but something slower, which I suspect is true considering you said you didnt  lower the nose. 

[Ragsf15e]

10 minutes ago, rbp said:

you can stall at any airspeed and any attitude

did you read the part about inaccurate airspeed indications in a slip? its because of ram air pressure in the static port on one side of the plane and vacuum on the other. the ASI reads *higher* when in a slip, so you may not actually be flying at 1.3Vso, but something slower, which I suspect is true considering you said you didnt  lower the nose. 

Yes, I’m well aware that you can stall at any attitude or airspeed.  I’ve got a reasonable amount of time in all attitudes and from zero to 900+ kts.  Putting your nose down isn’t going to save you.  As I said, you’ll need to add power to maintain airspeed if you’re planning on maintaining a 3 degree glide path.  If you lower the nose, that’s another way to maintain airspeed (they are both ways to maintain airspeed), however you will be on a steeper glide path.

If you have static ports on both sides, they average out pretty close to actual static pressure.  If only on one side you may get slightly erroneous airspeed in a forward slip.  According to aopa, “Most modern airplanes have very little airspeed error associated with sideslip”. However, that’s why you have some safety margin.  

It’s exactly the same as slipping to a landing that we all did on our checkride, however, there you generally leave the power out and take the steeper descent, so in that case you will have a lower attitude to maintain the same speed.  However, that lower nose attitude doesn’t change your stall speed.

https://www.aopa.org/news-and-media/all-news/1999/january/flight-training-magazine/no-dumb-questions