snowy rotor blades

[Doug Riley]

Has anyone had a problem with snow building up on rotor blades during flight? I've flown in falling snow at various times and had no problem with it. It made me nervous, though.

I'm guessing that some combination of moisture and temperature might allow a build-up -- but then again, rotor blades may naturally tend to shed the stuff better than a fixed wing does, since they flex more.

[StanFoster]

Doug: The only experience I had with snow was in a Cherokee 180. I had to taxi to the south end of runway 36. As I was doing my checklist..I saw an occasional snow flake. I thought nothing of it. I took off and as I was climbing out and just at the end of the runway at about 300 feet...my ASI went to 0. I thought..what the? then I saw some ice building on the leading edge. I immediately went downwind for 36. The engine was vibrating bad...and I landed with extra speed. When I shut the engine off...my prop had about 3/8 of an inch ice buildup on it....so the reason for the vibration.

Anyway..I never will forget that...and I will never fly when I see a snowflake. I can only imagine had I been in my RAF and the rotor started building up.

I am just a good weather pilot.

[CLS447]

Stan, all you need is the Rotor Heat option. Did you say you have the cabin heat?

What is your prop pitch & max RPM ?

[Udi]

Don't forget that icing conditions may also exist when it rains, and when there is no visible precipitation (e.g. fog). An airfoil leading edge may become colder than the ambient temperature due to the lower pressure and evaporation, which may lead to condensation and freezing. Same principle as carb ice.

Udi

[PTKay]

Again, one of the Birdy's concerns and observaions on the Oz forum was "blade icing" on the gyro. He has been played down by his Oz blokes, but obviously this is nothing uncommon to be seen in US.

Can anybody say anything more on rotor ice ?

PTKay

[Doug Riley]

I never got around to installing carb heat on my old VW gyro. It would ice up on damp, cool days. I could look down the carb throat after idling it for awhile and see icy slush all over the venturi and throttle plate. I never encountered blade ice, though. That by NO means suggests that it can't happen. The curved surface of a blade or wing is essentially a section of the wall of a venturi tube.

[jolly467]

I know that on the HH-60G I used to fly in Alaska we had both main and tail rotor heat....used it often and can remember one particular flight in which the ice buildup was particularily nasty...had to pull close to 95% torque (normal cruise torque might have been 65%) just to keep going... when the ice would begin to shed, the whole bird would shake like a dog trying to dry off!!

I would certainly not trust that an unheated gyro blade wouldn't ice up just as badly, given wet / cold / snowy conditions..

Steve Wages

[ToddP]

Don't forget that icing conditions may also exist when it rains, and when there is no visible precipitation (e.g. fog). Udi


Udi, have you been doing some instrument work in your gyro? I'm a little reluctant to be flying the gyro around in the fog. ;)

[StanFoster]

Chris: My prop is pitched at 13 degrees. I did my static test tied to a tree and it was 40 degrees. It pulled 5090 rpm. This was close to what it should be. I have had it over 90 but it still had throttle left.

[Harry_S.]

Stan;

I'm surmising you use full throttle on takeoff and initial climbout. What's your engine rpm at that time?

[StanFoster]

Harry: Its about 5250 on cclimb out.

[scott heger]

I would think that since most gyros we all fly are pushers, that the engine/radiator (and exhaust on most) heat going by the prop would make the icing less likely. But what the hell do I know, the sun "always" shines here in Southern California. Flying in less than very good weather as a private pilot is foolish, especially icing conditions.

Scott Heger, Laguna Niguel, Ca N86SH

[twistair]

Since we have chance to get icing almost half a year we thought on this though we never got icing on gyro. I've got it once on Rotorway trying to turn over the Moscow-river in winter. This river never freezes in that place and at 70-80 metre altitude we've got icing. OAT was near zero Celsius (slightly below) and there was no icing around the river, but vapour played it's role. It was very unpleasant: rotor lost his lift capability in seconds and we were forced to land immediately into the machine station yard. I estimate that icing conditions weren't the ugliest that time but small chord of helicopter blade and high airflow speeds make the icing influence much faster than it would be for the fixed wing with comparatively big chord.
As for gyro rotor, I suppose that icing would affect it even worse than helicopter's one:
in case of helo rotor loses his lifting capability but it at least stays rotating by the powerplant.
In case of gyro the distortion of airfoil by icing causes loosing of autorotative capabilities first which seems to be much worse since rrpm drops, flapping increases etc - you know the consequence much better than me :)
When I ferried Domin 250 km from Moscow last winter there was snow some times and some of them were suspicious to be icing dangerous. One time I even made forced landing in a forest gap. The reason was that I've suddenly (soon after trespassing just another snow shell) heard strange sounds from the rotorhead, some like something stucks between parts of rotorhead and hub. Since I didn't know what was the origin of these sounds I dropped to land. It was nothing more than parts of ice which collected on rotorhead's parts during I passed through the snow. When they collect enough they become to part out from rotorhead falling between cheeks etc.
No traces of ice were found on blades.
I suppose that flying in icing-suspective conditions one should permanently watch on rotor tach - if in level flight in tends to change rrpm then it may mean that things become worse.
In anyway, I'm completely sure that since icing develops very fast on narrow chord one should avoid flying gyro in icing-suspicious conditions.

Ah, yes, answering Doug's question: we've flown in snow regularly when there was no danger of icing, and no affect on rotorshake, rrpm etc was noted at all. I believe that if snow is dry (low humidity air) then there is much less affect than if you fly in good rain - dry snowflakes are much lighter than raindrops and they stick to the blade much less to affect them.

Just my 2cs.



Fly safe,

[birdy]

After reading about your experiances with icing I thought you may be interested in something that happened to me a couple of years ago.
I'v posted a story from the oz forum I wrote a month back that started some interesting conservations.

Go to http://www.asra.org.au
Under FORUMS, go to FLYING TAILS AND EXPERIANCES.

Topic
birdy
Junior Member


Australia
225 Posts
Posted - 06/03/2004 : 12:50:29 PM
--------------------------------------------------------------------------------

Here's an educational.

We were all set to muster a large paddock[more like a fenced area realy,550squ km]the next day.When in the early hours of the morning I was woken by rain on my face."I need this like a hole in the head"I thought as I pulled the swag cover over my head.By day break it had set in with drizzling rain.I'd be wasting my time trying to find 500 cattle in that country in these conditions,so we huddled around around the fire,drank tea and talked sh.t,waiting to see if the clouds would lift.
The stories were getting harder and harder to belive and I was getting itchy.I thought I would go and have a look see whether the rain was wide spread,fired up the trusty rosco,got boged,got unboged and tookoff.
I was only about 20 minuits from camp,pinned to 150' by cloud,flying through light drizzle when I noticed a slight shake in the stick,and the seat.This shake rappidly became very violent.The hole machine was shaking,trying hard to throw me out,the straps were chaffing my collerbones[I'm a skinny barsted],and the stick was almost impossible to hang onto.[anyone who has ridden horses would have an idea of the feeling when they do a shake down.Much the same as a dog shaking himself,only the gyro was a rotary shake]Am I loosing a skin off a blade?,loosing the hole blade?sh.t!!,this is not good.I chopped the power and aimed the nose at a spot in the thick gidgee scrub,with only enough room for me,but not the blades.Thinking on the way down that it would be hard to retreive the machine from the dence scrub,I noticed,at about 50',the shaking had stopped.?????Made another judgment on the'spot' and decided to save the machine,and head for a bigger 'natural strip' about 400 yards further on.With a death grip on the stick[yes,I sh.t my self,not lituraly]it seemed to take an eternaty to reach the clearing,waiting for something to happen.It didn't,and I landed normaly,shut off,got out and pinched my self.Yes,I was still alive.
As I stopped the blades I noticed there were still two,the skins on the 26'goodwin's were still intact,the head was still on the mast ,infact,everything was normal.Scratching a bald spot in to my head I thought"what the hell was all that about???"
After a thorough inspection I wound the blades up,did a few hops,and everything seemed as normal,so I took off and flew back to camp.
The weather had set in properly now and there was going to be no action for a few days so we covered the machine and boged our way home in the ute.
I rang all the people I knew who might have an idea what happend.It took a while[and I got some funny sugestions]but I was given a phone no. to a bloke in Darwin who was the ozzy gooroo on rotor blades.I explained every detail and he answered,very matter of factly,"I'v never erd of it on a gyro before,but you 'ad rotor ice.
Derr d...head,of course,why didn't I think of that.I gess I was looking for phisical damage and didn't consider the conditions.
He said the only thing you can do to shedd the ice is UNLOAD THE BLADES.No Paul,not that much to go PPO[although that would definatly stop the shake].He reckons what i did,cut power and ease nose down,was enough to lessen the vacuume on the top leading edge and weaken the ice and it fell off.

I have had it start to build up on my rotors twice since then,and unloading worked both times.
The moral to this story?
Sorry,you'r reading from the wrong bloke if you whant to know about morals.

"

[twistair]

Very interesting, Birdy, thanks.

Can you estimate (approximately) in seconds how fast shaking came grew? And :) - were you brave enough to watch what happened to rrpm in these seconds?

Fly safe,

[PTKay]

So Birdy,

you become now a personality and expert even in Moscow, hay....

World is small....

PTKay

[birdy]

Alex,time?? not very long,maby 3-5 seconds.It didn't take long to realise something was seriosly wrong.
Rotor revs?? no idea,don't have a tack on that machine.[not that I would have been able to read it,the shacking was too violent to be able to read anything.]
I didn't mention the air temp in the story,it was around 15-20c,but very humid.

All I know is it is very scary,but knowing that unloading will change the enviroment on top of the blades and will sling the ice ,it's not scary enough to ground me just because it's wet.

Ptkay,hardly an expert[I hate that word],but my personality I can hide behind this keybord.
These computer things do make the world seem very small ay!!A month ago I didn't even talk to the bolkes on the ozzy coast,never mind the Pols,Russians,poms ,yanks,kiwis and even a Tasweagen.

[twistair]

Birdy!

I believe this may be important:
It was hard to believe for me that icing could happen at high temperatures so I described (translated) your story to Vic Shumeiko and another grey-haired airfoil guy in TsAGI. Their ultimate answer was that it wasn't icing!
After they (separately from each other) heard what were the conditions, what were your feelings on controls and how you've escaped from this, they both told me that it most likely was flutter.
They'd become more sure in this when I've told them that the blades were (is it correct?) extruded ones which should mean they have chordwise balance problems which I believe solved by swinging the blade in the rotational plane.
What do you guys think about this?

[birdy]

Alex,thanx for the followup.

They was fabricated aluminium blades,[solid LE and two skins trailing.]
From what I can understand,these type of blades can be made very 'chordwise stable',but you'll have to ask the manufacturer to conferm this.

Flutter???? what is that,what causes it,how do you stop it and would it make the machine shake that badly.????

I'v hered from other blokes that the air temp has little to do with icing,as with carb ice[I'v had carb ice at 45c air temp].They reckon it is a critical combination of humidity and wing load that creats the enviroment for icing.

[darrellwittke]

If I remember right, Chuck B. defined flutter as the aerodynamic center of the rotor blade moving aft of the center of gravity of the rotor blade causing the rotor to fly out of track, return as torsional resistance and aerodynamic forces take effect, overshoot proper rotor track again, and continue the blade weave or "flutter."
Practically speaking it can cause horrendous vibration and I believe relieving the blades of part of their drive can result in the rotor resuming its normal track. Blade reflex is the primary means of controlling flutter.

Chuck B. gave me an experiment to do to understand flutter which entailed taking a strip of thin aluminum appx. 2" wide and 18" long, chucking it in a hand drill via a bolt and stop nut and spinning it. Then repeating experiment with small bolts drilled 1/4 chord and bolted.

I was too lazy to actually do the experiment, especially since the results can be easily imagined. I might do it now that I've thought of it again and Chuck B. might see this. I question whether the results are from aerodynamic center in the right place or centripetal acceleration (centrifugal force.)

As usual though, I digress.
Two practical things of note though Birdy, one is that the russians may very well be right and it may behoove you to ask the experts here what flight envelope blade flutter most often occurs at and correlate to your flying experience. Second would be to find out what blade profile you have and it's tendencies for flutter.

I sure admire what you guys do with gyros and cows being from cow growing country myself. (Boy, will Ken J. have fun with that statement!)

[KenSandyEggo]

Wish I could think of that old story where the shepherds chase the sheep to the edge of a cliff and then stand behind them while the sheep back up....or something like that. Is it the same with cows?

[birdy]

Darrell,I'm no gyro expert either,I just fly them.
What irritates me is,you can ask 10 experts the same question and you'll get 10 different answers.I suppose one should ask as many experts as possible and then choose yourself who is right.[one thing for sure,if he gives you an immediate answer,without ensuring he understands the question/situation,he's the wrong expert.]

[PW_Plack]

If carbs and throttle-body injectors suffer icing, and port fuel injected setups don't, I would have assumed fuel evaporation was a major part of the icing. If blades can ice at temperatures significantly above freezing, why are the throttle bodies of port fuel injected engines immune?

[birdy]

Been pondering your point for a while Paul,and while I no buggerall about fuel injection systms,it would be interesting to find out why the difference.
The only thing I can think of is maybe the intencity/rate of the pressure/vacuum change.

[GyroRon]

I think it cause in a carb you need a venturi to draw fuel from the float camber into the airflow to make the engine run, this area of the carb is the area that freezes up. In fuel injection there is no venturi since the fuel is injected into the cylinder or in the manifold just behind the intake valve. The intake manifold is just a tube to let air in.

[PW_Plack]

Ron,

Thank you! (Sound of Paul slapping forehead.) The throttle-body injectors also need carb heaters, because they also use venturis...duh!

Sometimes I overthink things I read on this forum...this wasn't one of those!

[RHerron]

Birdy,

IF you did indeed have ice on the blades, it shed because you descended into warmer air, NOT because you pulled power and lowered the nose.

[birdy]

Herron,
While I can't say for sure if it was ice,it sounds the most feasable answer so far.I'v had as many people tell me it was ice as have said it was something else,and to me, it sounds like ice.
With respect to your temperature idea,I dout wether there would have been much difference,if any.I was only at around 150',with 100% cloud cover,drizzling rain and nill wind.I dout if there would have been any difference in the air temp from 150' to50'.[definately no thermal mixing of the air,which is caused by temp differences.]