Oops! I got icing on rotor [Archive]

twistair

11-08-2004, 11:42 AM

Another piece of experience: rotor icing in fog

Yesterday morning we found that there is unpleasant direct cross-wind at our base airstrip and decided to fly to another uncontrolled strip 15 km east from our and which is perpendicular to our strip. The day was that same "shiny golden autumn", and we flew patterns in our SparrowHawk all the day at this reserve strip training another pilots who should be transitioned to SparrowHawk soon and giving introductory rides to other interested parties.
Half an hour before sunset I made a call to a guy who stayed at our airfield (it is completely uncontrolled - no radio, no meteo, etc) and he confirmed weather is same good as it was all the day. I took-off home but decided to do what I like best of all in gyro flying: driving the bird at 5-10 m altitude over fields and around forests. The last 2 kilometers to our base, I need only to climb over a small hill to see the strip, climbing it and... all the ground surface behind the hill was covered with white dense cover of fog up to 50 m altitude. This fog which speaded from a river has already covered all our strip spreading approx. 1 km around it and moving further. I climbed above the fog to see if I can see the strip from altitude - no chance, it's too dense. And I see also that it looks cold enough (OAT was +2-3 C that time) for possible icing. Since I didn't like the idea to return to that second strip and to stay overnight there without even any cabin on the strip (not to count the cabin of SH :), I turn back, landing light on, descend to 1-2 meter and dive under the fog. GPS showed direction and distance. I had to pass only 600-700 meters to see the strip but it was enough: 3-5 seconds after I entered the fog RRPM dropped from 305 to 290,..280,..275. They dropped as fast as you read these numbers. I added throttle keeping 120-130 kmh and decided that if they drop below 270 I will land where it comes - I know this field around our strip and it's good enough for such emergency. But same moment I saw 270 RRPM I saw also our airstrip border and landed - like in deep waters. One kilometer from this place it was sunny autumn afternoon and it was dark like 2 hours after sunset here. Guys who waited me at the airfield were happy - they cannot inform me about the fog and were in a hurry hearing my engine in the fog. One of them made a short video shot of SH appearing from a fog - it can be seen by the link.
To be true I simply forgotten to look at rotor blades right after landing but a couple minutes later (after all that buzz about such funny flying) I looked at the rotor and saw that it was completely covered with good water drops.

Landing in the fog (http://delta.wtr.ru/files/shfoggymid.WMV)

craigjackson

11-08-2004, 01:03 PM

:( Can't get video to play, even after saving to hard drive.

darrellwittke

11-09-2004, 07:19 AM

Literally, with pun intended. Thanks for posting your experience, twistair, did you notice any rotor shake or an increase in rotor shake? What do you prognosticate would happen if you had to keep flying another couple minutes?
Lower rotor RPM until blades stall and fold?

Again, thanks for posting about this little known or experienced weather phenonmen. darrellwittke

Vance

11-09-2004, 07:53 AM

Alex, please don't do that again. It is my opinion that it was not safe, and we like you. Thank You, Vance

jucie

11-09-2004, 07:54 AM

That appear to be an action movie! When I was half way reading your post I imagined the end of it would be like: "... so, I am posting this message from an internet terminal at heaven cyber cafe." :)

You managed the adverse situation very well, Alex. I am happy for you.

KenSandyEggo

11-09-2004, 09:04 AM

I couldn't play it either. Says that Windows Media Player doesn't support the file. Any chance of changing it Alex? Sure would like to see it. Or maybe someone that was able to open it can tell us how and what they used?

twistair

11-09-2004, 09:38 AM

Well, we discussed in our club earlier what may happen in such situation. It was agreed that the most dangerous is not the decreasing of lift but the loss of autorotation capability first. We had such experience in Rotorway Exec once and it lost lift in seconds too but we managed to descend ("to drop" is more perfect) from ca. 50-60 meters on full up collective and made controlled landing safely due to ground effect. In case of gyro we predicted that rotor RPM decrease would cause by airfoil change is much more dangerous since it causes chain reaction: RRPM drops-->flapping increases-->further RRPM decrease etc. Since blade chord is very small compared to, say, fixed wing chord even small amount of ice causes fast, very fast progress.
After this flight we discussed the results again and tried to reconstruct the situation. It appears that RRPM dropped from 305 to 270 in less than 10 seconds. When I saw 280 I felt that airspeed also became slightly less and slightly added throttle to keep it at 120-130 kmh. There were two goals: to add more load to rotor and to reach airstrip as soon as possible. I understood that situation may become worse but was ready to land if it goes worse than I feel controllable. Some of you know that I was a diver (well, I was an oceanologist specializing in diving) in my previous life (prior to fall into aviation and gyros) and this profession disposes to foresee upcoming dangers and possible recoveries so this flight wasn't an improvisation. Though, to be absolutely candid, some little worm of curiousity played it's role for sure ;) Anyway it would be a big stupidity to sink into this fog from the altitude. Having only 1-2 meters of altitude instantly gave a chance to land quick and safely anytime I felt things are bad.
There was no shake on rotor nor on controls. We estimate that it would begin from slightly less RRPM, but there was no sign of it at 270, I'm sure - I specially tried to feel it (curiousity...).
Since aircraft was straight and level all these seconds I couldn't estimate if it became more sluggish on controls, I suppose it didn't since it's response on controls on landing was usual.
Darrell, for sure this situation couldn't last for minutes - for seconds only. Next things as I can estimate should be fast flapping increase, blades stall increasing, blades strike rotor stops and period. But this is only my guesstimation and actually I'd be happy to hear what our gurus would tell us about this.
Chuck, Doug, tell us some words of wisdom!

twistair

11-09-2004, 09:39 AM

KenSandyEggo

11-09-2004, 10:06 AM

No Alex, my Windows Media Player comes up as if it's ready to go, but I get a message box that this file is not supported, and when I set it up originally, I clicked "Select All" so it would play every type of media file.

Doug Riley

11-09-2004, 10:11 AM

Alex, I've flown in falling snow and cold clouds a few times and feared blade ice. I never got any that I know of, however. Based on your experience, it sounds as if you might not even notice it in the early stages.

It could progress to a dangerous stage very quickly on our little airfoils, as you say.

twistair

11-09-2004, 10:27 AM

Doug, yes, I've flown in snowfalls a couple of times and didn't met any signs of icing though we use to monitor RRPM change more carefully these times and we here have a convention to escape dangerous area immediately if RRPM drops more than 10-15 rpm. Our local recommendation is a steep spiral descend (to add load to rotor) and landing in case one cannot leave the icing suspected area fast. We estimate that situation really will become fatal in seconds at altitude.
That day we have some visitors from one of two well-known Russian helicopter design bureaus who are now working on the professional gyroplane simulator. Sounds funny - guys made a good bit of this work before they saw a real gyroplane for the first time :) But the results seem to be interesting: they are building a math model which can be adjusted for different loads, geometry, aerodynamics etc. They have already made a mathematical model for 30' SportCopter rotor and I was surprised that it correlates very well with our practical results.
After this story I asked them to make a math estimation of developing icing situation on gyroplane rotor. I will publish results when they are ready - hope this may be interesting and much more safe and inexpensive than our natural tests :)

twistair

11-09-2004, 10:32 AM

KenSandyEggo

11-09-2004, 10:55 AM

Aaaaaah. No wonder. Now it says it can't find the "Source Filter." My list includes .wav format, but so far no luck.

twistair

11-09-2004, 11:01 AM

I'm sure it simply wants something more from you. Is your computer male or female?

Udi

11-09-2004, 11:21 AM

My brand new MS Media Player tells me: "The source filter for this file could not be loaded." :confused:

Maybe my computer doesn't speak Russian...

Udi

automan1223

11-09-2004, 11:34 AM

Alex,

We all loved your videos from Russia. Dans web site still has them up I think. I wondered if icing was a problem over there but I cannot believe that a rotor could ice up that fast and down you go. That freaks me out. I would expect it to come on slowly. But that is not what you wrote.

Other rotor events....
I did have a bird strike to my main rotor 2 weeks ago and the poor bird really caused my stick positions to change and shook hard, not to mention getting pelted with bird guts...

When I landed with rough stick shake and the machine was still all weird, there was only 2 long feathers and some guts stuck mid way down the length of the rotor. There was no damage to the blade or the surfaces ( I must have picked the little bird off on climb out) but I learned that even the smallest debris on the blades can wreak havoc !!!

I would also check rotor brake and bearings to make sure nothing is in trouble.

Jonathan Weis
Oriental NC USA.

twistair

11-09-2004, 11:46 AM

Jonathan,

That's very interesting too. Which part of rotor that poor bird hit? And what rotor do you have? I'm asking since different rotors response differently on airfoil distortion and even light distortion on some rotors can cause significant shake. Did you try to fly this rotor after this strike?

Udi and poor Ken: let's try one more:

slightly converted movie (http://delta.wtr.ru/files/shfoggy1.wmv)

Victor Duarte

11-09-2004, 11:59 AM

udi, try this :
right click on the link and choose "save target as.." then got to the folder where it is saved and just open it..

I learned that even the smallest debris on the blades can wreak havoc !!!

john : see the effects of sand dust on night landing on a beach...
the small quartz are so violently stiked that they produce light & sparkles due to piezo effect.

cheers

jucie

11-09-2004, 12:10 PM

OFFTOPIC: MPG works better than WMV. Whenever you have a choice, pick the first. It's the Internet "the facto standard".

automan1223

11-09-2004, 12:45 PM

The small bird, most likely a sparrow or a finch, small creature, not a crow or a dove or a hawk.....

got wrapped around the leading edge of the airfoil. at about the mid point of the length.

The blades are a raf 30' latest gen blade, they have a kevlar leading edge, and after I cleaned the remants off of the blade they came clean and flew just fine. (I have got more marks from dragon flies and bugs on them....)

There was no damage to the paint, the gel coat or anything. Now I am sure that if I chopped into a much larger animal it would have been a different story. but what debris amounted to the size of a silver dollar caused the stick to shake about 2x as hard as bug guts/dirty blades, and caused my stick position on climb out to be about 3-4 inches to the right for straight and level, as if the tubes were way out of adjustment.

That's very interesting too. Which part of rotor that poor bird hit? And what rotor do you have? I'm asking since different rotors response differently on airfoil distortion and even light distortion on some rotors can cause significant shake. Did you try to fly this rotor after this strike?

Udi and poor Ken: let's try one more:

slightly converted movie (http://delta.wtr.ru/files/shfoggy1.wmv)[/QUOTE]

Udi

11-09-2004, 02:23 PM

Still doesn't work :( When I save to my computer and run it from there I get the following message: "Windows Media Player cannot play the file. The Player does not support the format you are trying to play."

It also gave another message to the effect that file format is not consistent with the file extension :confused:

Udi

Vance

11-09-2004, 03:04 PM

I believe that I have had birds, especialy turkey buzzards, want to play and more than a few times I have had to doge the birds. Most of these birds have more than a 3 foot wing span and they seem to like things that fly at their speed. Do you think that they want to mate? Or they just trying to be friendly? So far I have mised them.

I have hit a sea gull and an owl on my motorcycle, both times around 100 mph. It was quite violent and messy.

I saw on an NTSB report where a kite brought down a Robinson helicopter. The guy who was flying the kite took off before anyone could ask him about it.

Thank you, Vance

automan1223

11-09-2004, 05:20 PM

The day I am writing about also had another thing happen to me, but I have never ever heard about since I have been flying my keyboard here and there since 99 or so.

At 500 ft agl I was attacked by a swarm of bugs. No I am not making this up. It was a very warm day, and the second run up I climbed to my target altitude at 700'. Then it was like I was getting shot with a bb gun. First 1 or 2 strikes then a whole bunch. I was really perturbed. I was like what the heck is at 500' ? This has to be only in the movies. There is nothing out here but me, or so I thought......

I smelled my first smoke at 450' and it got me concerned and then I saw the haze and it was from someones burn pile way down the other end of town. But you have to realize that its not just us gyros and other aircraft up there. Mother nature was there first.

Jonathan

Harry_S.

11-10-2004, 09:55 AM

A little off topic.

Any of you remember a Tom Cahill? He wrote a monthly blurb in Mechanix Illustrated. He's been dead many years now. He had a dry wit.

One monthly question asked of Tom was; I was driving down the hi-way and a duck hit my windshield. I looked in the rearview mirror and saw the duck landing on the pavement. I felt bad and shook up. Does this happen very often?

Tom's succinct answer: Not to the same duck.

Cheers :)

KenSandyEggo

11-10-2004, 11:00 AM

I got the source filter message too. Alex, I massaged my hard drive thoroughly after bringing it flowers and candy, but it still won't respond.

twistair

11-10-2004, 12:03 PM

Ken,

What's the reason you keep such a obstinate person(al computer) at home? Well, I'll convert this video in mpeg this weekend but, Ken, stay macho - throw it (your wilful comp) out if it wants something more!
Seriously: ask sir Google to find something for words "codec" and "*.wmv". It will return some websites which have freeware for detecting which filter you need to read this file. One I know is called GSpot and may be found at gspot.headband.com
It checks your video or audio file and tells you which exactly filter you need. But there are many other sources to check and find exact codec.
BTW today I made some tasty inflight cockpit videos and will publish them this weekend as well. Hope to add some more tomorrow.

Victor Duarte

11-10-2004, 01:06 PM

Hi alex, off topic, but mpeg can be viewed with mediaplayer after save it to disk.. if you have an error like "can't open media" , do an upgrade to WMP 10, for working a little with video : .avi codec divx (fast motion) is fine and worldwide, or .asf for streaming media, avoid realplayer
thanks

automan1223

11-10-2004, 02:39 PM

Just reencode it to wma player 9 nothing higher, stop all this upgrade nonsense.

or mpeg 2. works even better.

Jonathan

Victor Duarte

11-10-2004, 04:25 PM

john i agree for wm 9, enough, but not mpeg 2 , dvd format, you need a dvd or a decoder and an encoder to encode it, divx avi : correct, widespread.
if it was avi, everyone could read it.
IMHO

automan1223

11-10-2004, 06:13 PM

Divixx is mpeg 4 and here in the usa is not a free encoder/decoder codec. you need to spend 50 bucks for it ! if not you get the spyware encoded one and I will never use real player because of the spyware embedded and it crashed my old system.

Maybe its free by you but it is not here yet.

It has good quality and small footprint but then any stock .avi file should play fine. go to the windows web site and down load the windows media encoder, its free and has a lot of settings and so far works well with most codecs.

Jonathan

Ron Marlett

11-10-2004, 06:15 PM

I have seen this type icing many times on chilly foggy mornings while driving to work. It dosn't build up on the vehicle cause it isn't quite cold enough, but it does form extremly rapidly on the antennas. The lowering of the airpressure as the air flows around the antenna is just enough to push the surface below the freezing point. This ice forms Very quickly under the right conditions at highway speed. I could only imagine a aluminum rotorblade at a few hundred MPH. The ice buildup adds an asymetrical shape to the antennas and in a matter of minutes the antenna is waving at me(side to side in the airflow). When I used to live in eastern Wa. I recall On a few mornings, having to stop several times during my 30 mile drive to break the ice off the antennas(3/8" fiberglass CB antenna and 5/16" steel radio antenna). They would get to waving so bad I thought they would break or rip out of the fender. If I stopped and let them set for a few minutes, the ambient air temp, which is still above freezing, melted the ice all by itself.
I have never seen it that bad anywhere else, but I did notice it where I live now just the other morning as I had a little wave out of the steel antenna.

Ron

Victor Duarte

11-10-2004, 07:58 PM

Divix is mpeg 4 and here in the usa is not a free encoder/decoder codec. you need to spend 50 bucks for it !
Damn, i didnt know.. yes, in fact, i use "premiere" so it's built in..
off topic again but microsoft realeased "windows media encoder" for free (it as at least) allowing to encode ASF files that are also pretty light.
cheers

birdy

11-11-2004, 02:30 AM

Hmmmmm..................A Russan gets rotor ice and noone douts it.
But a while ago,an Ozzy said he got rotor ice and everybody said he was full of sh*t.
????????

Aussie_Paul

11-11-2004, 04:04 AM

Birdy, I can't believe you waited so long about the icing!!!!!!!!!!!!!

Aussie Paul. :)

twistair

11-11-2004, 07:17 AM

Damn, Birdy, I only told you that you experience should be more likely flutter caused by distortion of an airflow by rainfall drops than icing which is I believe impossible to catch at +25 C. Both these experiences seem to be very interesting and useful for all the gang.

birdy

11-11-2004, 07:39 PM

That wasn't aimed at you Alex,you were one of the few who didn't dout.

BTW,wot dose this "flutter" thing feel like??

mceagle

11-13-2004, 11:55 PM

I am one of those ones that didn't believe Birdy, neither do I believe this incident was ice. I am not calling you blokes liars, because I believe you really experienced what you thought was ice
I mentioned in Birdy's case that I had experienced exactly the same thing after taxiing through sticky mud. As the increased airflow dried the mud, it slowely detached itself and the blades became smooth again.

The incident in this thread could also have a simpler explaination. Flying through fog (or suspended water) would leave water streaming over the blades and as such would adversly affect the blade performance. It would also leave the drops of water witnessed on the blades later. You even get drops of water on the blades in foggy conditions without even flying.

The minus temps required to get ice on rotor blades would normally be so low that it would not be the conditions that gyronauts would fly in. Having said that there have been many that have flown in very sub zero conditions, without any problems. Another point worth mentioning would be the skin friction of a 400 mph rotor blade. Some smart blokes may be able to work that out - whether the heating effect of the skin friction is enough to overcome the chill effect of the air at airspeed. It is quite interesting to note that you can get burns on your feet while barefoot skiing.

This is my opinion only, and perhaps somebody else here will prove me wrong.

birdy

11-14-2004, 02:17 AM

Yeh Tim,and I also said on the Oz forum it couldn't have been mud coz it started bout 20 mins after I last touched the ground.IF there was mud on the blades after TO,it would have been slung/washed off shortly after TO coz of the light rain,remember.

I'v fowen in -11c a couple of times Tim,would that be cold enough???

twistair

11-14-2004, 02:29 AM

The minus temps required to get ice on rotor blades would normally be so low that it would not be the conditions that gyronauts would fly in.

Tim...
This is vulgar delusion which may become fatal once. Icing conditions depend not only on temperature but mostly on it's combination with relative humidity and dew point which at low altutudes is mostly met at near zero Celsius temps. Some years ago I've got ~5-7 mm of ice at Yak-52 wings in less than 2 minutes in foggy athmosphere at low altitude. OAT was -1 deg C.

I'm certainly not the best in explaining physics in English but it was done many times by pros.

Take a look for example: Kivi Aircraft Icing Handbook (http://www.caa.govt.nz/fulltext/Safety_booklets/Aircraft_Icing_Handbook.pdf)

twistair

11-14-2004, 02:33 AM

Dave,

(OK, I recall "damn" :)
I have no exact picture of flutter at gyro rotor but from known examples in helos it should appear as sharp increasing of rotor shake. Our aerodynamists told that your recovery from this situation was likely caused by unloading rotor when you decided to land as soon as possible.

quadrirotor

11-14-2004, 02:38 AM

Thanks Twistair. :)

gyronutt

11-20-2004, 09:37 AM

;) http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4504376933&ssPageName=STRK:MEWA:IT

darrellwittke

11-20-2004, 06:23 PM

You have a good point, McEagle. I remember a post or rotorcraft article of a Raf flying in rain experiencing loss of lift which promoted a harder than usual landing on the runway on the end. The premise (as I recall) of the article was that laminar flow rotor blades shouldn't be flown in rain. I don't believe the Raf blades, or any blades, are laminar flow airfoils though?

As Twistair says, the physics of icing is well known. I seem to recall icing can happen up to 59 degrees fahrenheit with close to 100 percent humidity and a venturi effect.

And Birdy, please don't be upset about Twistair's believability. After all, he's in the frozen taiga and you're in the desert outback, sort of like believing an aussie's opinion of the best :D vodka and a russian's opinion of best mustard for cows, eh? :D

birdy

11-20-2004, 10:59 PM

One thing you blokes fail to understand bout this desert is that it can git cold here,like -11 degrees c,with moisture.I'v spent hours fly'n round on cold mornings with ice on my knees and hands,and if that ain't cold enough,I don't know wot is.[not as cold as Taiga,but cold enough.]

bones

11-21-2004, 01:19 AM

Sh*t and i said i'd come over for a lap,, thinking i should rethink this........ICE on your knees and hands, :eek: hmmmm i'll get back to you on this Birdy :cool:

birdy

11-21-2004, 01:44 AM

You only feel the cold if you look at the ice Mark[and don't pick your nose,the hair will cum out with the ice].Same as the heat,you'll start to realise it's hot when you drink2 gallons of water before lunch and ya thongs melt when you walk out from under the [wilt'n] tree.

Hognose

12-11-2004, 12:58 PM

Birdy in a meltin' thong -- there's an image I didn't need.

On ice, guys, bear in mind that you can encounter ice even in pretty warm temps. As Alex says, its the temp/dew point spread that makes the stuff precipitate, and at this point I can't resist throwing the effects of Boyle's Law at you.

People are used to thinking of constant pressure, standard day, that kind of thing, they forget that our machines alter the air we live in. For example, a friend was alarmed to see the temp gage in my car indicating 232º F. "You're boiling over!" she said, alarmed. But of course, I wasn't. (Neither was the car). Because the pressure inside the cooling system is well over 1 ATM. (Over 2, in this particular car) so a temperature that would evaporate the coolant at sea level pressure does not in a higher pressure system.

Why can you get carb ice when it's 70º F? (20-something for all you foreign johnnies who follow that French Revolution way of counting stuff). Because a carb contains a venturi, which reduces the pressure, and therefore the temperature, of the air.

Same way Alex could get ice -- or Dave could -- by flying into moisture. Basic private pilot question guys, describe the pressure existing below and above an airfoil, relative to the pressure in the ambient air that is not affected by the airfoil.

I leave the solution as an exercise for the reader.

PS -- we know Alex's situation was ice, why? In which way did his emergency differ from Dave's?

cheers

-=K=-

PPS -- taking a gyro into IMC is not a very good idea. Even if you have the rating, is your gyro equipped for safe flight and navigation in that regime? Instrument pilots die every month attempting VFR flight into IMC. And for every pilot who crashes in bad weather there's funeral on a sunny day (unless he's a Muslim). -K