Loss Of Lift

[Chopper Reid]

Flying back to the station the other day I ran into some reasonably heavy rain and noticed I was descending and added power to maintain altitiude, I glanced at the rotor tacho and it read 290 [normally 310/315].

I use fiberglass rotors and I was wondering why a loss of rotor revs occured.
Is it just the extra drag of the rotors forcing their way around through the moisture??

[C. Beaty]

Probably, the water adhering to the blade surface disrupts the airflow and increases drag. Also, there would be a fair amount of centrifugal pumping which eats power. The water tends to be pumped toward the blade tips and flung off tangentially.

[Harry_S.]

Dumb old me would say you hit the nail on the head.

Increased drag caused by the water impacting the underside of the rotorblade. :confused:

I'm sure the guru's will 'splain it. :)


Cheers :)

[Chopper Reid]

Thanks for answering my question.
Would alloy blades react the same way??
There must be some guys out there flying around in the rain!

[ventana7]

I've flown thru light to moderate rain several times in my AAI modifed RAF with the latest generation RAF blades and noticed the same thing, which I diagnosed basically as what Chuck B described.

I suppose a super slick finish on the blades might cause the rain to have less effect.

[C. Beaty]

Draggy blades, those with blunt noses and the like, most likely are less affected than low drag blades. I don’t expect material would make any difference.

I recall reading that on early versions of the Rutan family of tandem wing airplanes (Varieze, etc), pitchdown was abrupt and violent upon encountering heavy rain. The front wing was heavily loaded and lost lift in rain. This was cured by a change of airfoil.

[Cobra Doc]

Rain-X on rotor blades? When I used Rain-X on my '96 Firebird I was never sure when to use the wipers. There was never any water on the windshield except in very heavy rain.

[Rehan K.Janjua]

Hello Brian.

Looks like you are having lots of fun. Thats Great.

Alloy or glass rotors have the same effect.
Just avoid heavy down pures and hale stromes.
Water travelling downwards pushes the air/wind downward. Called wind sheer.
Quantity of water reflects wind sheer speed/force.

Hope everything is water seal proof/waterproof.

Best Wishes.

Rehan Janjua
Air Command Pakistan.

[Chopper Reid]

Thanks Rehan, fortunately for me I had the protection of a pod and widscreen but the rain was heavy enough to wet my shirt pretty well.
Yes, hail is to be avoided at all costs as is lightning.

[Fleamer]

My ultralight (pteradactyl) has a canard wing and I remember (vaguely) a discussion about water disrupting the flow over it and creating a large loss of lift as well. ON an Ultralight wha they seemd to find was that a "rougher" surface helped. the water didn't bead up on it, but would spread evenly over it and move umore uniformly, which would not create the conditions to drastically change the airfoil.
I'm trying to imagine a gyro rotor made out of fabric...!!

Of course the forces forcing (and potentially concentrating?) the water out to the rotor tips may have other unintended consequences....

I live in an area that gets nine feet of rain per year, so this is a topic of great interest to me!

Gerry

[Doug Riley]

The early 1930's gyro rotors were "tube and rag" construction, doped fabric over wood ribs.