Dive screws up airspeed?

[sgibson]

Hi,

 

I noticed this issue a couple of times ... I was approaching the airfield and did way ahead a stronger dive (approx. 20-30), pulled back throttle, expanded airbreaks slightly and suddenly the airspeed went way down and stopped at ~50. Warnings go on and the gear handle flashes - similar warning pattern to if you fall below 150 and have not extended the gears.

 

Is this a bug?? I was definetly way over 200!!

 

Once I recovered from the dive the warning stops and the airspeed goes up to normal.

 

I had no damages...

 

Any idea?

[Kaiza]

Havent seen that one. Did you have your pitot heat on?

[shagrat]

I don't know the technical reason, but it is "normal". Seems to happen when you put the throttle too much/early into idle.

 

A guess may be the turbines cause this warning?

 

I'm also interested in the root cause of this warning. Until then I just push the throttle a bit, 'til the warning ends... :D

[ralfidude]

Its the heat pitot, you probably forgot to turn it on.

[mvsgas]

Hi,

 

I noticed this issue a couple of times ... I was approaching the airfield and did way ahead a stronger dive (approx. 20-30), pulled back throttle, expanded airbreaks slightly and suddenly the airspeed went way down and stopped at ~50. Warnings go on and the gear handle flashes - similar warning pattern to if you fall below 150 and have not extended the gears.

 

Is this a bug?? I was definetly way over 200!!

 

Once I recovered from the dive the warning stops and the airspeed goes up to normal.

 

I had no damages...

 

Any idea?

 

I'm not sure if I understand correctly, but, for the landing handle light, it sounds like landing configuration warning, many aircraft have it now. I your speed, altitude and throttle position is below a certain level, the landing gear handle flashes, to let you know, it looks like your are landing with gear up.

 

As for the speed, what the guys already posted

[sgibson]

yes .. Pitot Heat makes sense ... but why does it work again once I recover from a dive?

[Inseckt]

I would guess it's only a coincidence that you recovered from the dive at an altitude that was warm enough for the pitot to unfreeze...

[shagrat]

it sounds like landing configuration warning, many aircraft have it now. I your speed, altitude and throttle position is below a certain level, the landing gear handle flashes, to let you know, it looks like your are landing with gear up.

Yep, that makes sense. Explains the dependency to the throttle setting.

Pitot heat was on in my case.

So we should not rush the throttle to idle when on an approach :D

[159th_Falcon]

yes .. Pitot Heat makes sense ... but why does it work again once I recover from a dive?

No it doesn't make sense, cause what happens when your pitot freezes is that the current indication does not change anymore.

 

So your diving, speed increases, pitot freezes and would then stay at whatever the speed was at that moment, for example 250 kts.

That is until the pitot unfreezes again.

 

Your speed however went down while in a dive which at least to my knowledge does not correspond to a frozen pitot tube.

 

Now given the fact you extended the airbrakes while in the dive there might be a change they disturbed the airflow infront of the pitot tube bad enough to give false readings? (note the pitot tube is on the RH wing tip)

No idea if such a thing is even possible and/or simulated though.

[mvsgas]

Yep, that makes sense. Explains the dependency to the throttle setting.

Pitot heat was on in my case.

So we should not rush the throttle to idle when on an approach :D

Is not that you are "rushing" the throttle to idle, is that your throttle is at idle, your gear is up and your below altitude. This should not happen if your landing gear is down, the light in the handle anyway.

[BlueRidgeDx]

No it doesn't make sense, cause what happens when your pitot freezes is that the current indication does not change anymore.

 

That's not necessarily true. That's only true under very specific circumstances, and the actual behavior could be very different.

 

If the pitot tube becomes totally blocked, but the drain hole(s) and static ports remain clear then, yes, airspeed would read 0.

 

If the pitot tube and the drain hole(s) are totally blocked, but the static port remains clear, then the airspeed indicator will act like an altimeter; a decrease in altitude will cause a decrease in the displayed airspeed, and vice versa.

 

If everything becomes totally blocked, then the airspeed will continue to indicate the last value, and will not change with altitude or airspeed.

 

If there are partial blockages, then things get weird and all sorts of indications can result.

 

For the record, I have no idea what the cause of the OP's issue is. Sounds wacky to me.

[ralfidude]

Before the times when I started to use the heat pitot, my speed indicator would dip to like 50 and I got the stall sound for like an hour because I had no idea what was wrong. So now that I use the pitot, never happened to me again.

[NC_Cyborg]

That's not necessarily true. That's only true under very specific circumstances, and the actual behavior could be very different.

 

If the pitot tube becomes totally blocked, but the drain hole(s) and static ports remain clear then, yes, airspeed would read 0.

 

If the pitot tube and the drain hole(s) are totally blocked, but the static port remains clear, then the airspeed indicator will act like an altimeter; a decrease in altitude will cause a decrease in the displayed airspeed, and vice versa.

 

If everything becomes totally blocked, then the airspeed will continue to indicate the last value, and will not change with altitude or airspeed.

 

If there are partial blockages, then things get weird and all sorts of indications can result.

 

For the record, I have no idea what the cause of the OP's issue is. Sounds wacky to me.

 

What he said is right. Depending on the type of blockage on the pitot tube, the airspees indicator will drop to zero or act like an altimeter.

 

As for the horn, the only thing I can think of is the throttle is at idle and landing gear is not down.

 

I was asked this question for a checkride in the Beachcraft Duchess (I am not saying Fairchild Republic built the A-10 off the Duchess). The question was, "why would you here a warning horn with the throttle at idle?"

 

Answer - throttle setting will not provide enough power to sustain lift, lower landing gear.

[Frostiken]

Well, since high-AOA would result in uneven airflow into the pitot line, I can see how dive / climb maneuvers *could* cause a temporary false airspeed reading...

[BlueRidgeDx]

True, high AoA and sideslip can affect displayed IAS. But a high speed dive doesn't involve either.