Aquaplaning speed
 

Does anybody out there fly any type of a/c that has a real time read out of the current tyre pressures?

I approached Ronaldsway recently in heavy rain, "runway wet, wet, wet" (the radar man said) - and the phrase "nine times square root of tyre pressure" sprang to mind.

Now if only I had taken a pressure gauge to the tyres on my walk round....

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Moved to Tech Log.

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Cub, you are absolutely correct re. the 9x sqaure root of tyre pressure etc., but I know of no a/c with the readout you mention. I would imagine that if such an animal exists, it would be some brand new all singing all dancing job that most of us have never seen. I know that the Airbus doesn't have it, and I don't think the Boeing does either.
I would imagine that you best policy (as I'm sure has already occurred) is to use the tyre pressure that the book says your tyres should be inflated to - I'm sure they won't be that far off. Personally, I would work it out for whichever set of tyres (mains or nose) has the lowest pressure and use that speed - thereby ensuring you maintain directional control.
I hear the rain in the IOM has been quite something - no change there then!!

Hope this Helps

SLT

[This message has been edited by SLT (edited 04 October 2000).]

Dont forget the nose wheel..... square root of the pressure by 7

The A340 has this option and it shows the tire press. For practical purposes you should have in mind the aquaplaning speed ,and it is calculated as follows;
7.7x squqre root of the main tire pressure. when you depart your tire pressure is correct hopefully because it is part of the checks done by maintenance and the pilot just has to satisfy himself during walkaround that it is o.k otherwise he can have it checked . So for example the aquaplaning speed for the L1011 is 112 knots. I hope this will be an answer to the inquiry , the tire press you can get from your Manual .

As far as I know it's also an option for the B744(Tirepressure indication).

Moonbeam

[This message has been edited by Moonbeam Purple (edited 04 October 2000).]

Don't have the books here, but i thought that tire pressure was displayed for both the B744 and B777.

Mutt

Wonder if we could get Boeing to talk to Piper - the snag was that I was in a Piper Seneca V...it just made me wonder, that's all.

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TPIS - Tire Pressure Indicating System.

It's an option on the 744 and I think standard on the 777 as CX chooses to have the bare minimum on their 400's, (No Auto-start, No taxi light just turn-offs, No PVD, No Headrests, No Full face Oxy, No Therapeutic Oxy, No lower Weather radar they have a torch, No Elec Driven Hyd pumps on 2 & 3, No TPIS, No Doors Auto/Man Indication even though the system is fitted when the A/C is built the wires just aren't hooked up, Plus the bare minimum on the PFD, ND and EICAS).


[This message has been edited by CCA (edited 05 October 2000).]

We've had 7.7 and 9 times sqrt tyre pressure... one of them is dynamic and one is static (i.e. wheel not turning) but which is which??

Oz....I believe the Americans use 8 and a bit.

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We use 9sqrt P, so, for the 47-400 the speed comes out at 127.27922061357855439215198517887 kts - approximately :): :):

It's 9 times for dynamic aquaplaning for all you Romans (or hydroplaning if you are of Greek descent)...
To be strictly correct you should also multiply the result by the specific gravity of the contaminant, so if someone salts the runway....

OK...so how about adding the runway specific gravity to the ATIS?

This could be the start of a job creation scheme - get some person to go out and take three readings every 30 minutes (they won't block the runways for long).

....but it still comes back to knowing what the tyre pressures are - and are they affected by regional QNH?

How about more job creations...as well as waiting on stand for the refueller, you could all wait for the tyre pressure man to come along with his pocket pressure gauge from Halfords and take the readings.

Another little placard to put on the pedestal with the "cabin secure" card - just for tyre pressures.

Wonder how long it would take on a 747 with..what, is it 18 or 20 wheels?

P.S. .... yes, I'm teasing.

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Could someone explain why aquaplaning speed is related to tyre pressure only?

The mass of the A/C must go into the equotation aswell - right?

Tor

As weight increases, the tyre bulges thereby increasing surface area touching the runway/water, and thus maintaining the same lb/sq in. irrespective of weight.

Sounds a bit sus to me, but that's what I was told by someone who should know.

Ok - sounds reasonable.

So this speed, if you are above it the A/C will aquaplane and if below not? Or how does it work?

Tor

I think you've got it. I read an accident report/inquiry, and this NASA guy was spouting them (the formulae) in the courtroom, he had spent all his life investigating this sort of stuff, and used them as if they were the law.

tyre pressures are required to be checked as part of the daily. this is in the tech log on our company aircraft and can be referred to. question is , how does the temperature exposure at cold and high altitudes affect tyre pressure on a long flight (cold soak). so without a gauge indication, tpis, the calculations are all out the window. if you are not happy, maybe use a low pass and afterburners to dry out the runway. :) or find a dry place that has a good pub.

Where does tread/water depth come into all this?Can 1mm of water 4 mm tread depth have the same Vp as 3mm and bald tyres?