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# Rotor Blade Tip Temperature

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## Rotor Blade Tip Temperature

(OP)
Does anyone here know if the blade tips on helicopters get hot due to aerodynamic heating? Alternately does anyone here know a good reference for how to estimate how hot they get? I understand aerodynamic heating starts to become significant at Mach .8 or so. Does anyone have a formula for the way to calculate this heating effect?

Thanks for any help

LloydofDSS

### RE: Rotor Blade Tip Temperature

You can look up the isentropic flow equations in any fluid mechanics or aerodynamics textbook.
At Mach=1, To/T1=1.2

Starting at 300 Kelvin, the temperature would rise to 360 K.

This effect is not very significant until much higher Mach numbers.

An interesting college exercise I remember was to start with the melting point of aluminum and feed that backward through the equation to find the aircraft's top speed, then to compare the result to the Concorde.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

### RE: Rotor Blade Tip Temperature

I have never read or heard anything about aerodynamic heating of blade tips.  Perhaps this is because the tip is only operating at a high airspeed during a small portion of its rotation; i.e. When it is on the advancing side.

### RE: Rotor Blade Tip Temperature

OT (sorry).

"An interesting college exercise I remember was to start with the melting point of aluminum and feed that backward through the equation to find the aircraft's top speed, then to compare the result to the Concorde."

That is an interesting excercise. What was the result? I gather the russians are sticking to Mach 1.8 for precisely that reason.

Mart

### RE: Rotor Blade Tip Temperature

(OP)
In a hover, the blade tips are at a constant speed and it is generally 150-200 kts below Mach 1 (Sea level). At max Vne the tips going forward come pretty close to Mach 1, but as they go aft they drop below their hover speed by the forward velocity of the aircraft. At least that is how I understand it.

Thanks for the info, that was very helpful.

### RE: Rotor Blade Tip Temperature

Lloyd,
Yes, I didn't state explicitly that I was using Mach 1 for a maximum tip speed, even though they are almost always less than that.

Graviman,
The exact resulting Mach number escapes me, but the point of the exercise demonstrated that above a certain speed, aluminum cannot be used for a leading edge, and titanium must be substituted (for extra cost).  For higher and higher speeds, increasingly resistant materials are required, until you reach the ludicrous point of gluing millions of brittle 12 inch thick tiles all over your shuttle.

Sorry Lloyd, I've totally sidetracked your thread now.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

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