Hydroplaning speed

[gearlever]

I was recently asked by a mate about Vp, the hydroplaning speed.
Yes, most of us know Horne's equation Vp = 9 x square root tire press (psi) = ... kts.
Let's say the tire pressure is 220 psi, so Vp is about 135 kts or less (tire tread).
How does it influence take off calcs?
How is it implied in modern performance data tools (wet/contaminated runway)?

Thx

[Tomaski]

I was recently asked by a mate about Vp, the hydroplaning speed.
Yes, most of us know Horne's equation Vp = 9 x square root tire press (psi) = ... kts.
Let's say the tire pressure is 220 psi, so Vp is about 135 kts or less (tire tread).
How does it influence take off calcs?
How is it implied in modern performance data tools (wet/contaminated runway)?

Thx

Hydroplaning is not much of an issue on modern grooved (or porous friction coated) runways as long as the surface is not completely saturated from extremely heavy rain like one might get in a tropical storm or such. We have performance manuals (sometimes paper, sometimes computerized) that take account for other types of runway contamination. The data is generally conservative as long as the contamination and/or braking action reports are accurately reflect the current conditions.

Occasionally one might operate to a runway that is either not grooved or has substantial rubber deposits. Those case should be handled with appropriate caution.

[gearlever]

Hydroplaning is not much of an issue on modern grooved (or porous friction coated) runways as long as the surface is not completely saturated from extremely heavy rain like one might get in a tropical storm or such. We have performance manuals (sometimes paper, sometimes computerized) that take account for other types of runway contamination. The data is generally conservative as long as the contamination and/or braking action reports are accurately reflect the current conditions.

Occasionally one might operate to a runway that is either not grooved or has substantial rubber deposits. Those case should be handled with appropriate caution.

Thx Tomaski.
So may I assume Vp is considered in up to date performance charts/computer programms for contaminated runways?

Kind regards

[Tomaski]

Thx Tomaski.
So may I assume Vp is considered in up to date performance charts/computer programms for contaminated runways?

Kind regards

IIRC, dry and wet performance data is based on actual flight tests whereas other contaminates are by engineering calculations with generous safety factors. Vp would be one of the considerations.

See: AC 25-31 (https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25-31.pdf) for more information and references.

[gearlever]

Thx Tomaski,

looking for this document looong time:D

[safetypee]

gearlever, A more detailed reference is at https://www.easa.europa.eu/sites/default/files/dfu/CS-25%20Amendment%2023.pdf
AMC 25.1591 starts at page 958

I doubt that aquaplaning is an issue during takeoff as the physical aspects tend to reduce tire drag.
Spray / impingement drag might be of greater concern.

Also note that 9 x root P may not apply to all types of tire ( radial ply ?); the critical speed could be as low as 7 x root P.
See https://babel.hathitrust.org/cgi/pt?id=uiug.30112106773275&view=1up&seq=44 via https://en.wikipedia.org/wiki/Aquaplaning for a range of speeds.

[john_tullamarine]

Horne's report might more conveniently be downloaded directly from the NASA site at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640000612.pdf

[gearlever]

Thx John,
thx safetypee,

I really appreciate.:ok:

[tcasblue]

Also note that 9 x root P may not apply to all types of tire ( radial ply ?); the critical speed could be as low as 7 x root P.
Doesn't the hydroplaning speed vary depending on whether or not the tires are spinning or not(takeoff versus landing)?