Helicopter blade deicing ideas

[Higgler]

Wondering if anyone has experience with helo blade icing problems and some of the deicing sytems used?

Not allowed in the deicing solution;
1) heated wires on the blades, too much power and it can damage carbon fiber.
2) liquid deicing techniques stored on board, too much extra weight.

I've seen and read some ultrasonic solutions, seems like a direction to go. Or maybe plungers built into the forward edges.

Some thoughts my novice brain has;
1) Is the primary problem at initial starting, whereby ice has formed overnight or is it in flight ice buildup?
2) I realize that blades must be balanced, but do they start up an iced helo blade at low rev's to knock off ice, or do they need to be perfectly ice free to intialize the blades?
3) Are two different deicing systems needed,
a) inflight front edge of blades
b) preflight deicing of entire blade (once snow has been cleared)
4) If one was to modify and add a deicing system to the front of the blade, what's involved with modifying the blade? i.e. mechanical drilling, sealing, etc. I'd expect an entirely new blade design, test, etc....costly..

any thoughts would be appreciated, plus sources of info.
Thanks,


kch

 

[MikeHalloran]

-
2. Starting with an unbalanced rotor sounds like a bad idea.
-

Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

It's both. You need to get the ice off to take off, but you'll also need to keep ice off during flight.

SAE AIR 1168-4 is part of an entire series of environmental design requirements, of which -4 is specific to icing, rain, fog, and frost.

There is an FAA Aircraft Icing Handbook that's downloadable from DTIC. ADA238039, ...40, ...41 are the accession numbers for the 3 volumes.

ADA406321 is the Army Aircraft Icing tome by the Corps of Engineers' CRREL.

There are a few Army MIL specs regarding icing and deicing as well.

TTFN

FAQ731-376

 

[Higgler]

Thanks IRStuff,
I'll take a look at the spec's.

I've read about heater wires, acoustical vibration and surface heaters.
One heating technique uses a thin sheet of ?resistive film probably insulated on mylar to require the smallest amount of heating power to make a full sheet of ice come off. This was developed by a professor Dartmouth College engineering professor Victor Petrenko. He has some interesting video's. I think it takes a bit of power for his heating though.

kch

 

[IRstuff]

If you can get the SAE 1168-4 volume, there's lots of detail on the amount of heat required, dictated by the air temperature, water content, and the airspeed.

I'm more familiar with windshield deicing requirements, which for a 500 kt airspeed, requires about 4.26 W/in^2 to maintain anti-icing.

TTFN

FAQ731-376

 

[KENAT]

1. Both although I'd suspect on the ground could be mitigated by use of antifreeze spray.
2. Agree with Mike, as I said on the ground it may be possible to spray with antifreeze from an external source.
3. Due to mass considerations I'd expect only one onboard system.
4. Many systems would probably require a new blade though applying a film that can be heated might be retrofittable I suppose.

Unless it's what you mean by plungers I don't see you mention the pneumatic rubber boot, not sure if this is used on rotor blades though.

 

[berkshire]

Higgler
Have you looked at this?

Electro-impulse deicing
Kodet, A.C.
Southern Tier Technical Conference, 1988., Proceedings of the 1988 IEEE
Volume , Issue , 19 Oct 1988 Page(s):193 - 200
Digital Object Identifier 10.1109/STIER.1988.95479
Summary:Electro-impulse deicing (EIDI) which uses EM field induced eddy currents has been demonstrated to be an effective ice protection technology in various applications. The applications that EIDI has been demonstrated on by flight tests or icing wind-tunnel tests are the large transport aircraft, engine inlet, general aviation, business jets and commuter jets, and helicopter rotor blades. Various computer codes have been written for analyzing the pulse circuit, the electrodynamics, and structural response. It is concluded that EIDI is the only ice protection technology that has demonstrated potential in all market segments and does not impose the energy consumption penalties of present ice protection technologies


B.E.

 

[Higgler]

Haven't looked at EIDI, I'll read up.
Since that technology is 1988, one might guess it works but has drawbacks that stopped it from being widespread.

This requirement is for minimum power requirements.
Seems like impulse shock waves to fracture the ice is talked about using Piezoelectric shakers.

I was wondering if a laser mounted on the helo body would be able to cut slices in the ice on the bottom and edges, then with a small slot in the ice, the wind would to the rest. It may put a small slot in the blade too, which wouldn't be good.
On a similar thought, anything added to the body pointed upward would probably be attractive. Possibly focused sound waves to produce the shock remotely? Maybe a bank of high frequency acoustic transducers.

To minimize power use, the need is similar to switching power supplies, one blip of power, not continuous power.

KENAT, I think you're probably correct that on the ground a different system would be needed offboard. Thick ice is tough.

I'm on travel till the end of week in case I seem unresponsive.

Thanks for the thoughts.

kch

 

[IRstuff]

Any laser that could melt ice is probably non-eyesafe and therefore a hazard to other aviators.

A possibility might be to heaterstrip only the leading edge of the blade

TTFN

FAQ731-376

 

[WKTaylor]

Higgler...

Icing [blade, engine, airframe, controls, LDG, etc] is not a simple subject. In-fact the complexity confounds experts.

Suggest going to the following websites and entering terms such as "icing", "aircraft and icing", "helicopter and icing", "engine and icing", etc.

http://stinet.dtic.mil/

http://www.airweb.faa.gov/Regulator...rgAdvisoryCircular.nsf/MainFrame?OpenFrameSet

Special coatings, inflatable boots, electric heat, etc have been tried with varying success. The problem appears to revolve around the nature of the ice accumulation... and not only affects blades but aslo windows, airframes, stabilizers, stub wings, stores, landing gear, etc... have fun in Your research.

Regards, Wil Taylor

 

[FredGarvin]

I don't know if anyone has ever tried running compressor bleed to the blades. Granted, I can think of 5 or so technical difficulties involved, especially the sealing and routing of some kind of distribution manifold, but the big benefit is that you will always have CDP as long as you have operational engines. No extra power source required.

When I was on CH-47s, we didn't have any deicing capabilities once in flight. We deiced completely on the ground and then started up.

 

[Higgler]

Interesting thought, so if I interpret correctly, you'd be perforating the blades (maybe drilling some small holes) and adding an air pressure lines inside the blade. Air will break off the ice. Maybe have to have valves to control the air distribution.
I'd think the ice would seal the blade well. May take alot of air pressure to pop the ice. It'd be an interesting and easy experiment.
I could picture making the first crack in the ice, then maybe the air from other holes leaking out the original crack, unless that first crack sealed itself again. Short powerful bursts from many locations may work.
Thanks Fred,

kch

 

[IRstuff]

Unless you've got doors on these puppies, the ice will go INTO the bleed channels and you've still not get any deicing. And If you DO have doors, you won't be able to get the open once the blades ice over.

TTFN

FAQ731-376

 

[Higgler]

A good bit of realism added IRStuff. Water does like to plug up holes.
Thanks.
I guess that's why they use air to inflate rubber pieces to crack the ice. No holes.

Maybe the available air pressure can be used, have the air move a small door that's slightly flexible. Maybe a plunger that's oring sealed can be moved using the air pressure.

kch

 

[berkshire]

Higgler.
Compressor bleed air is usually warm, all you would have to do is run it up the D tube of the rotor and out the tip.
The major question is whether or not you could get enough warm air up the blade to de- ice from root to tip.
B.E.

 

[IRstuff]

If the outlets are plugged, and there's no flow, there's no heat transferred, or at least not much, since you'll be counting strictly on thermal conductivity of air through a skinny channel from the compressor ALL the way up the rotor mast.

Note also, the rotor mast will likewise be cold and the amount of actual heat that makes it up to the top strictly by conduction would be pretty miniscule.

TTFN

FAQ731-376

 

[Higgler]

How warm is compressor bleed air? Do you mean hot?

Discussions I've read hint two solutions, in-flight vs. on ground solutions. In-flight ice is primarily on the front of the blades I believe. If warm air is circulated on the front edge of the blade, that may be enought to melt ice, especially if the air is hot and under alot of pressure. To Thermally isolate the front edge enough to heat it, there is probably a need to change the front edge. I've read that blades front edges get beaten up and the military would like some better designs. I wouldn't want to presume that redesigning a forward edge of the carbon fiber blade that is nicely insulated (for hot air injection) is an easy task. I read that the hot wires added for melting ice does some damage to the blade.


kch

 

[FredGarvin]

CDP temperature and pressure varies from engine to engine. It is extremely warm and pressure is usually pretty high (800°F and 400 psi perhaps). I was actually thinking more along the lines of a radiant system that would not have external hole features. It would simply have an internal circuit that the flow would heat the entire blade surface via conduction.

However, thinking of electrical pitot heating, in many flights that is turned on and left on. If you did perforate the surface with holes, once the flow is started on the ground, I can not see them getting plugged as long as flow is maintained.

 

[berkshire]

Higgler (Electrical)
I had forgotten that you are using a carbon fiber rotor blade. I was thinking in terms of an aluminum blade where the metal would conduct heat.
B.E.

 

[WKTaylor]

Higgler...

IF You are truly serious regarding helo blade icing issues, then You need to "mix and learn with the big-boys".

There is a MAJOR SAE conference coming up in Seville Spain Sept 24--27 2007: "SAE 2007 Aircraft & Engine Icing International Conference".

The technical sessions appear to be very indepth... and it is likely that every major "player" in the fixed and rotary wing world with have attendees. These are THE folks worth knowing!

The notice and detailed info is available at the following website:

http://www.sae.org/icing

Regards, Wil Taylor