Hot rotors???

[GyroRon]

I have noticed a few times, after a flight I go to put on the rotor strap and when I grab the leading edge of the blade near the tip, the blade is warm.... much warmer than the rest of the metal on the airframe. I haven't had a HOT blade yet, but certainly warm. What is up with that? 23 foot rotors, turning 360-400 rpm

[Mark Sanders]

Hey Ron you must have a really good rotor brake if you can stop the blades get out and feel the blades and their still warm. Mine takes atlest 5 minutes to come to a full stop never felt for warmth though. I gess if your flyn on a warm day lots of sun thay could get warm I don't know if friction would be enough with out the sun to heat them alone.

[C. Beaty]

It’s heating from skin friction, Ron. Ernie has a test stand driven by an old Chevy engine that will take a 23’ set of rotors up to 600 RPM and really heat up the tips.

[StanFoster]

Ron: I remember commenting on that back with my RAF. I could definately feel the tips were warm...not hot and you could feel them get cooler a few feet from the tips.

My sportcopter blades made out of aluminum cool down much quicker than the composite blades on my RAF....but you can still feel the extra warmth on the tips.

Those tips are going 350-375 mph...thats a lot of molecules getting kicked out of the way....



Stan

[twistair]

Ron, rotor blades in flight do some physical exercise trying to keep your butt in the air - anybody doing physical exercise becomes warmer :) Kidding.
I would just slightly add to Chuck for those who care - friction is between air and blade. At high (subsonic and higher)speeds it becomes significant. 7075 alloy is usually used instead of 2024 in high-speed airplanes because 2024 loose his strengh at high temps and 7075 is more stable.
In our first winter when we started to think about icing and therefore looked more carefully at the blades we noted that after a flight snowflakes thawed on the blade surface while they didn't on the rest parts of the gyro and around.
I'm still curious what is the difference in temps but hadn't time to measure it carefully.

[Fl90]

You bet they're warm. After the first 2hr. flight with my DW's ,I was talking to a gyronut that walked up after my blades stopped, a short time into our conversation one blade "popped" loud enough for both of us to jump, a few seconds later the other did the same. Now, when I fly for a while you can look at the end of the blade and see a gap between the extrusion and the skin, and watch the gap close as the skin cools.

[Harry_S.]

I'm not a USAF veteran, but I recall stories of the SR-70. Wings leaking fuel like a really leaky water faucet. When fueled before a flight and after return from a flight. True or no...I don't know, but interesting.

During pre-flght fueling, the wings would be leaking like a sieve. After reaching altitude it would undergo IFR, to replenish the fuel load.

As I understand it...the terrific airspeed in flight would heat the skins and close the structural gaps and no more fuel leak to speak of. Upon landing, the skins would cool and the leaks would resume. Interesting.


Cheers :)

[birdy]

It’s heating from skin friction, Ron
If this is so, why do we get ice forming, and sticking to our rotors?

[Fl90]

Now that one I've not heard. I think that's one for the minus side of the "p's and m's" of flying for a living!

[MMorgan]

It is the friction heating up the leading edges as stated earlier.

At airline speeds the leading edge temps can increase up to 20 degrees C. At lower speeds....250 kts. or so the temp increase is 8 degrees C. At the tips our rotors are travelling at these higher speeds thus generating heat from the friction.

Icing reports from airliners will differ significantly from a slower aircraft at the same altitude.

Birdy.... I have never flown my gyro in icing conditions.....(even if I wanted to we only get a day or two a year where we have moisture and freezing temps near the surface)....but I would guess that you will not get ice near the tips but would the farther you go inboard where the rotor speed is less and the temps would be closer to ambient.

[birdy]

Fair points Mike.
geez, there must have been alota ice on me blades that day it near shook me outa the seat if it was, as you say, inbored!!! [ coz the closer it is to the center, the less 'out of mass balance' effect it will have.

dose anyone know where on the blade the ice forms?? Wot Mike says makes sence, so im figuring the section with the greatest amount of ' drive' would be the most/ earliest effected.

BTW Mike, the ambienrt temp dont have to be freezn, just very damp. ;)

i live ina desert too, and moisture isnt very common, in all my time iv only had it once definatly, and two more times i recon it was starting to form, so i dived to stop it buildn. :)

[Al_Hammer]

from PPrune rotorheads(helicopter site)
==================
The rotor tips are the last things to ice up because of kinetic heating (IIRC it is the square root of the airspeed that gives the number of degrees C increase) but the root and inboard section can ice up very quickly. It is the assymetric shedding of rotor ice that causes most problems due to the high levels of vibration this can cause.
============
Another thing is, that the inner area of the rotorblades, where the blades first building up ice, is essential in the case of autorotation. Especially after an Enginefailure, you may be unable to build up enough RRPM for a sucsessful landing
================
http://www.helicopterservice.com.au/photos/pprune/icing%207.jpg
"Front shot of a Wasp blade, showing the stagnation-point at the L/E, and ice growing out above/below the blade; very dangerous as the rise in drag/ torque is very rapid."

[Allantat]

I spent a year and a half on the SR-71 and yes inded...it leaked like a sieve! When you saw it sitting in the hangar there were white plastic buckets on the ground catching the fuel. The 1st thing the plane did after taking off was to catch a tanker and re-fuel. Once it was up to speed (Mach3) the surface would heat up and the leaks would stop. What a machine!

[birdy]

Thanx Al, your a collage o knowlage mate. :)
This makes my understanding of wot happened all those hours back so much more understandable.
[ ans yes, the buildup was very sudden.

[Chopper Reid]

I would imagine it would only take a handful of ice, probably not even that much to get the rotors shaking heavily.

[JEFF TIPTON]

The R22 helicopter has roughly 25 foot blade diameter. We use AN960-10L washers at the tip to dynamic balance the rotor. I am not sure of the exact weight, but you get the idea.

[birdy]

As i said, an imbalance at the tip of 3 Oz is go'n to make it shake alot more than 3 Oz at the root.
Tie a rock to a pice of string. Spin it round with 1' of string. Now give it 6' of string and spin it round AT THE SAME RPM. You'll feel soon enuff which diamiter the rock spins at needs the greater force to hold it from breaking out of the flight parth.
You could stick those washers to the root of the R22 blades with snot and they would still be there wen you land. ;)

[Chopper Reid]

The thing is with ice that it alters the shape of the airfoil further increasing the possibility of shake.

[brett s]

You can wrap a loop of tape around a blade tip & feel the difference in balance, that was the low-budget trial & error method of in flight balancing we'd use in the field on Bell 47's - if it felt better, add a bit more. If it felt worse, remove it & start on the other blade - when done, peel off & wad it up then stuff in the blade tip :)

Takes very little buildup of *anything* to affect a blade's performance - was a problem in the ag business on calm days with some products (fertilizers were the worst), even bug buildup is noticable. Ice is a lot worse than that, takes very little to screw up the airfoil enough to make autorotation a real problem.

[birdy]

Ice is a lot worse than that, takes very little to screw up the airfoil enough to make autorotation a real problem.
thats why id like sumone to tell where the ice usualy starts to build.
Coz as you say, at the tip itd only have to be a few ounces, but at the root, in the stalled region, itd have to be alot more but wouldnt effect performance much, only cuase abit of shakeing. If it built in the 'driveing' area first, then youd get rrpm drop first, then shakeing as the build up became uneven, or sum fell off. On the tips youd get alota shake but only loose lift, not rrpm. So i gess ill have to just assume its go'n to start at the stalled area, coz theres less heat from friction, and i cant remember any performces loss, just a horrendous shake.

[Master Roda]

It only takes GRAMS, not ounces. If you had ounces, it would shake out of your hand.

[Al_Hammer]

For a 24 ft diam rotor spinning at 350 rpm:

a US dollar bill placed at the tip would "weigh" over a pound.
A ballpoint pen would weigh roughly 30 lbs.
An object experiences about 500 g's at the tip at that rpm. Half that much at the midpoint of the blade.

[birdy]

You people simply refuse to read wot i rite. :(
Im not talkn bout the frign tips of the rotors, coz it appears the ice dont build on the tip, coz of friction heat. Im talkn bout nearer the root, where the ice DOSE build.

Maybe im the idiot :). [Surely Todd or Mike cant ban me from calln meself an idiot. ;) ]

[Fl90]

Birdy, it's not that they're not reading what you wrote. They're just having fun with the calculator. I'd rather have a pound of dollar bills at the root than a dollar bill that weighed a pound at the tip.

[Heron]

and besides . . .when you say maybe I am the idiot, you cast this freaking shadow of doubt and many people will shiver . . .
Ban him at once! I say! :D
Heron (50% idiot 50% genius)

[autorotate]

waxeing the rotors should decrese the friction

[birdy]

Wax um??? i dont even wash um.:lol: