?????????

[birdy]

A simple question to those who have a thorough understanding of rotors.

The other day, while geting a bit hot under the coller at work, i found myself in a sticky spot.
At bout 40pmh and 5' off the ground, i was confounted by a tree, a big tree that was too close[ only 20' ahead] and too high [20' above me] to get over.
It was also a little too wide to duck around in the normal fashon without some serious trimming happening.
Instinctivly, i chopped power and [ quite volently] heaved the stick left and back. Much harder than i would normaly, coz normaly i'v got a bit more room to move.
The machine basicaly stoped instantly and with the aid of some rudder, was pointing away from the tree. With the reapplication of full throttle and holding the stick back, i staggered to safty, missing the tree and stayn off the ground. IOW, a right angle turn on the spot and without any alt loss. [ says sumthn for gyros ay]
The only thing that concerned me was a loud and distincet 'chopping' sound.
As i was 'staggering' away to safty, i looked back, expecting to see part or all of my rudder missing, coz thats wot it sounded like. It sounded like a rotor chopping at a plywood rudder.[ bout 5 or 6 chops]
Knowing now that it wasn't the rudder getn trimmed, and i know i missed the tree[ allbe it not by much], and theres no other evedence of anythn hitting the rudder or rotor, i'm wundern wot made the noise.?????
Was thinkn maybe sumthn to do with the blades airodynamicaly, like a partial stall [ huge cyclic demands]or maybe this new 912 don't like such abrupt full power changes and pinged or sumthn.?????

It don't realy matter, coz i'm still alive and i'm not plan'n on do'n that sorta move any time again soon, but if i knew wot made the noise, and it was nuthn detremental, then with a bit of practice, it could become a handy move in my line o work, if you get my drift.;)

[Victor Duarte]

Geez,
glad you still here to post birdy....

[Harry_S.]

Do you have composite rotors, Birdy?

If you do and they're painted...check the tops for very faint cracks in the paint?! You may have stressed the blades a bit.:eek: If you did stress 'em, the cracks may not show up for a few days.


CFWMDF
Cheers :)

[Rehan K.Janjua]

Hello Birdy.

It could just be the aerodynamical noise created by the load on the rotors which were at flying rpm. This does happen in hard manovers or an extreme one like you performed and well done.
A helicopter type rotor chopping noise.You heard it loud because you were close to it.
Did you feel any abnormal stick shake. Indicating stall.

Well lets wait and see what the wise guys have to say, besides (with all due respects) Geez from Victor and Harrys...Imagination is more important than knowledge.

Best Wishes.
Rehan

[C. Beaty]

What you heard was rotor stall, Birdy.

Sounds like slapping water with a canoe paddle. Or sometimes, like a 12 gauge shotgun going off.

[Passin' Thru]

That would be my diagnosis. Way back in the “olden days of yore” when I was young and foolish, I used to do a similar maneuver, but higher than 5”! I too think it is from severe cyclic demands. When properly executed under the right conditions, it would sound like a short burst from a .50 caliber machinegun!
Sheesh! Now I’ll probably be admonished for encouraging dangerous behavior, so I’ll add the following cravat, “Kiddies, don’t try this at home!”

Pete Johnson

[birdy]

Thanx Mr B., but im not sure i wanted to hear it.:rolleyes:
Which portion of the disc was stalling then???
Is it going to damage anythn if i start making a habit of it???
They were over rev'n abit too, coz i'd just leaveled from a short dive.
You got the sound right too, it was alot clearer/crisper than the normal 'wop' sound that they make when you unload loaded blades.
BTW, i have heard the 'shotgun' sound befor too, but it was in a different situation, but definatly attention grabing all the same.:p

Rehan, i couldn't say for sure bout the shake, coz it happened pretty quick, and my mind was on some other miner details.:D

[C. Beaty]

Hey, Pete, how’s it going? I had heard you were in Puerto Rico running a plastics factory.

For those who don’t know Pete Johnson, he’s originally from Swainsboro, Georgia and a genuine gyro pioneer. Taught me about stabilizing feedback from offset gimbal rotorheads.

Birdy, rotor blades stall when cyclic input is faster than the rotor disc can follow. The blades get turned flatwise in their plane of rotation and slap the air.

I don’t suppose there’s any harm as long as they aren’t slapping anything except air.

Whichever side stalls depends upon whichever way you’re moving the stick. If you’re pulling it back, the blade to your right stalls; if you’re pushing it forward, the blade to your left stalls. It’s whichever blade that receives noseup rotation.

[scott heger]

Blade slap is:
the high amplitude periodic noise plus highly modulated vortex noise caused by fluctuating forces on the blade due to the cutting of one blade's tip vortices by another blade and transonic shock. Blade slap is a distinctive, low frequency throbbing sound which increases during certain descent, maneuvering and high-speed cruise operations.



Birdy, do you think it was blade slap or a stall? What I mean did it sound more like the multiple "wop-wop" of a big two bladed helicopter (like a HUEY)turning sharply or decending, or the sharp report like a shotgun? Blade slap is also a possiblity considering the high RRPM your blades were subjected to in the turn. As well as the other possibility of a stall/disrupted airflow since I bet you flew into your rotorwash in the sharp turn you made .

Very glad to see you made it out safely, but how did you let the situation get so close?

Chuck B, to the flying pilot, what would be the feeling in flight one would expect in a blade stall, or are both related?

Scott Heger, Laguna Niguel, Ca N86SH

[C. Beaty]

I imagine Birdy is quite familiar with the normal wop-wop from tip vortices if his flying is half as aggressive as he claims.

Rotor stall makes a sharp noise similar to that of cracking a bullwhip or slapping water with a paddle. The stick can get pretty rough and bang around when this happens.

[birdy]

Scott, it definatly wasn't blade slap.[ wop]
Blade slap is just one of a multitude[ f^&%$, thats a big word] of noise maken tricks we use to move stubbern critters.
I think Chuck's on the money, coz the noise was much more distinctive and sharp, like a paddle slapn water. It was a crack, not a wop.

but how did you let the situation get so close?
Not mean'n to sound like a smart ass Scott, but if you had any idea of wot i do, you'd be supprised its taken over 3000 hours for me to experiance me first blade stall. Gess i'd have to have gotn close to blade stall hundreds of times till now, but not close enough to actualy stall them.
Generaly i do my best to never force high cyclic demands into the disc, coz its simply not good flyn, its not efficiant, and shows little respect for the machine. But on this occasion, it was either heave on the stick, or ware the tree.

I don't like to call it aggressive Chuck. If i was aggressive, i wouldn't live very long.
It sounds like it was blade stall, but i don't remember feeling the stick kickn.
Maybe i was too preoccupied with the tree.

Could you stall a disc without feeln any feedback????
The feedback your refern to isn't contact with the stoppers, and resistance to the high cyclic demands is sumthn i am familiar with and can recognise, so is it the actual stalled blade kicking the stick?
If so, then you couldn't stall it without it feedn back.

[scott heger]

Birdy, no offense taken, just trying to understand what to recognize if/when it would happen. Stay away from those trees, they tend to be real show stoppersl. Do you do most of your mustering at 5 feet AGL?

Scott Heger, Laguna Niguel, Ca N86SH

[C. Beaty]

Eyewitnesses to tumble out of the sky fatalities in stabless RAFs and early AirComands frequently report hearing a noise like an explosion. It is my speculation the sound results from rotor stall.

The sound of the rotor chopping off the tail and prop tips is more of a whump-whump than a sharp sound. Even when a gyro rolls over during a landing, the sound of blades whacking the pavement isn’t sharp.

If in fact you did stall your blades in flight, Birdy, you’re one of the very few survivors.

Another survivor was the late Lloyd “Depity Dawg” Poston.

Lloyd had a gyro with really long Hughes blades powered by a Lycoming 0-235 and was performing one of his typical show-off routines: a series of hammerhead turns where the gyro is stood on its tail until airspeed mostly bleeds off and the airframe is kicked 180º by prop blast over the rudder.

During his final turn, there was a loud bang that caused the spectators to look around to see who was firing a shotgun.

Lloyd was far from being the smartest guy in the World but like a cat, always managed to land on his feet.

He instantly chopped power and allowed the machine to sink until the rotor recovered. He claimed the stick beat his legs black and blue but his stories were often embellished to make them more interesting. They usually improved with the telling.

*******************

I think one of those truck horns powered by compressed air would do a better job of getting your cows attention than rotor noise.

[MattPearson]

I sure would love it if you get get us some bystander video of a normal days work for you!

[scott heger]

Chuck B said" I think one of those truck horns powered by compressed air would do a better job of getting your cows attention than rotor noise".

Chuck I agree, but not near as much fun to watch.


Scott Heger, Laguna Niguel, Ca N86SH

[birdy]

If in fact you did stall your blades in flight, Birdy, you’re one of the very few survivors.
Again, not sumthn i wanted t hear Chuck.:(
Tho i think my situation is far more survivable than Lloyd's coz i was still 'rotor up', and only had to decrease the pitch demand to stop the stalling.
So thats wot you blokes call hammerheads.
There is a fool proof way of do'n it safely and not stress the disc with big pitch demands, but i recon i'll keep it t meself.:p

Correct me if i'm off track please Chuck.:)
My understanding now of wot happened is as follows;
The sudden and relitavly big cyclic pitch i was ask'n of the blades had them stall like a plane wing that had too much aoa for the load/airspeed, in the section of the disc where the blades were riseing. As they rotated to a point of less aoa, they 'regrabed' the air.
So where was the noise generated? At the point of stall or when the blade regrabed?
Am also thinkn, the reason i don't remember any hammering from the stick is coz at the fraction of time the blades stalled, i had near 0 AS[ no teetering happening] and alota stored inertia, so the blades didn't have time to teeter from the stall far enough to allow stopper contact before they regrabed the air and evened out again. Pitch hammering from the lift/no lift pulses as each blade stalled wouldn't have been transfered through the offset either coz in that instant, i was light in the seat and the head had little load on the offset.
Mind you, i recon the hub bar would have been getn a pizzeling as each blade stalled.:o

Do you do most of your mustering at 5 feet AGL?
No Scott, usualy between 50 and 150', but on occasions, you have to get a little lower to get their attention.:D
And tell Chuck, rotor wop is alot lighter to carry round than a truck air horn.:rolleyes: :D

[C. Beaty]

The canoe paddle analogy works pretty well to explain the sharp sound that results from rotor stall.

Slap the water with the paddle flatwise and you get a sound resembling a gunshot; edgewise, you don’t.

As you well know, tilting the rotorhead only rotates the blades about their feathering or pitch axis because of the teeter bolt.

At normal tilt rate, the rotor disc follows the rotorhead quickly enough that you don’t get anywhere close to stall.

But if you bang the stick fast enough, you can rotate the blades faster than the rotor disc can keep up, causing momentary stall. Then you’re slapping the air flatwise.

Or, if the complete airframe is rotated fast enough, the same thing happens in the case of a bunt/tumble fatality.

If you were to plot the pressure you get from setting off a firecracker, canoe paddle water slap, blade stall slap, etc., the curves would all look pretty similar; a single impulse with a very steep rise.

The steep rise is what produces the sharpness. Such a waveshape contains harmonics that extend throughout the range of audibility.

Slower rising pressure waves make a thump or wop and don’t have so many harmonics.

[_MOL_]

Birdy,
I'm extremely happy to hear you made it out of that one m8.
I lost a friend a couple of years ago due to partial/blade stall.
When spectators were around he usually did some manoeuvres I can't even start to describe. I tolled him over and over again that it was lethal to do so, and tried to explain the aerodynamic consequences of what he was doing, but I guess he was not clever enough to understand it, or I didn't explain things good enough, or he just didn't care.
Anyway, he usually did these manoeuvres in reasonable calm air, but on that day the wind was about 20- gusting to 30 kts, and I think he forgot all about that in the heat of battle.
- I lost my best friend.
Somebody filmed the accident too.
Plz don't try to do that again.

[iconnary]

Brian, sorry to hear about the loss of your friend. Can you elaborate a bit on the accident? Did it involve excessive cyclic input leading to blade stall? Was there a blade strike on the tail or prop?

On a more general note, what (if any) are the indicators that you are approaching blade stall in a cyclic-intensive maneuver?

[mceagle]

Birdy, I have used a variation of this manouvere (without the tree) when I required the gyro to pull up quickly without gaining height (as you would heading off a beast). It seemed to work best for me from approx cruise speed if I first lowered the nose and then eased the stick back quickly enough to stand the gyro nose high and the rotor became more of a brake than a lifting device. I just called it a mid air flare. The initial movement of the stick had to be quick enough to change the attitude without increasing height.
This required considerable stick force and faith in the integrity of the control system. I didn't notice any excessive control hammering and full control was available at all times. During the brakeing, the rotor speed would increase considerably such that forward speed and climb could be regained immediately without loss of height.
Such aggressive manouvering of the airframe should not be tried by low hour pilots because of the possibility of running out of control range.
The noises coming from the rotors varied from an irregular slapping or cracking to a repetative high frequency tommy gun sound. The gyro did not appear to be slipping through the air as you would expect with blade stall so I assumed that it was only a small section of the blade stalling, causing the slapping sound, and tip speed causing the tommy gun sound.
It would be interesting to have a camera focused on a blade while doing this.

I have also heard this slapping sound when a pilot was "hovering" at 100ft over the camp with a light weight machine with 27ft slow turning blades. He sat very nose high and started to tail-slide, and as he lowered the nose to regain forward speed the blades let out three or four loud cracks. He repeated this several times and did not appear to get into any trouble. I really did not give it much thought at the time as to wether he was close to the limit or not.

[_MOL_]

Elaborating a bit on my friend’s accident would be threat steeling.
But . . . here goes.
He was flying a light gyro with a 27' rotor (maybe on minimum limit load)
Cruising around in about 50' alt doing some "gyro manoeuvres".
The one he specially liked to do was a kind of quick flat spin turnaround back to same direction with minimum loss of altitude, which is a quick turn without much bank attitude.
I didn’t see the accident myself (fortunately for me) but according to the film at least up to the point where it goes wrong he was doing exactly that, but with in high wind. At a point he does a low pass in 5' from a lower point, (runway slopes) where the wind was not so strong, pulled up, vent vertically up into the strong wind. When things started to go wrong the ground speed is zero and altitude was about 120'. Nose attitude was high and it seemed that he then tried to turn back downwind, not much with a bank but rather that flat turn. After that the video is pointed towards the ground. A few large slap sounds followed by something that folded together on the ground.
Witness says that he was almost vertically in attitude and seemed to be on the edge to go over the top backwards, but then turned on its side and went straight to the ground. Our NTSB equivalent here in Denmark found nothing wrong with gyro, and stated it was pilot error.
Though they didn’t describe what went wrong but IMHO and from what I can see and hear from the film I believe he realised he was in deep **** when he found himself vertically with no ground speed. I think he then tried to lower the nose and might have realised that he couldn’t regain control that way and turn around to gain flight speed again. But when he turned around the violent stick and rudder input lead to blade/partial stall, hence those loud slap sounds. He then lost lift on one side of the rotor for a split second and the gyro went into a 90 dg bank with no airspeed, and continued like this to the ground.
There was no bunt over, nor any rudder or prop strike.
End of story

[scott heger]

Brian ,sorry about the loss of your friend. Maybe I missed something here, which will be pointed out by others....

Climb to Zero airspeed, nose pointed up,some wind, seems like he first lost it by getting himself deep into a negative"G" maneuver if he fell out of the end of it. The blade stall may have been next. 120 foot altitude, pointed nose up with no airspeed is far into the height velocity curve, especially if your blades are not working/stalled. If no blade strike occurred,prior to impact, more altitude may have allowed time for a recovery and saved him. Pilots have fallen out of rolls and spins in gyros before, but you need the height , and lots of it, for the blades to recover lift.

Scott Heger, Laguna Niguel, Ca n86SH

[_MOL_]

I know, but the thing is that you can't really see what happened in the end. I do not believe he initially was doing negative G’s; he’s attitude was not that vertical. As I see it he vas climbing vertical but maybe with a 45dg attitude. At one point I believe I can see the nose wheel and instrument panel. The position of this is almost level but with a 90 angle to the wind, still no ground speed, so that will be no airspeed too. If he did a violent manoeuvre with the rudder pedals and maybe the stick too to get into downwind he would have experienced the partial stall witch ended up in loss of lift on one side of the rotor.
After the loud slabs the rotor sounded like it lost rpm fast, (on that point he would have been sliding sideways into the ground) and the engine then stopped. The engine stopped during the fall where no positive G’s feed the carb. Propeller was not damaged other than from the fall. At one point I had the impression that he chopped the throttle before the event.
Why he didn’t just level the thing and continued forward and just rode it out by making a forward decent to the ground beats me. Maybe the engine failed and he couldn’t and decided to do the turn into downwind rather than end up in a tail glide. Who knows, it’s hard to tell. Our NTSB didn’t find anything wrong with engine, but subsequent I found a broken outlet fitting on the fuel pump. When I examined the wreckage the fuel line was still attached to the pump but when I began to disassemble the wreak, it just fell off. Note to this: our NTSB didn’t disassemble the wreckage for some reason. The broken surface seemed dirty so I expect it had been cracked for some time and might have failed. Then again, the dirt could have snug in there during the year the NTSB had it laying on the floor in their hangar.
If I can get permission from the widow, I would like to have some of our more knowledgably friends on this forum to get a look at it and maybe they can come up with something else. That is if any of them is interested. Any suggestion to whom that should be?

[birdy]

Thanx for the explination Mr B.

Tim, i used to do that sorta thing too, when i used to fly the lighter Goodwin blades, but you gota be a little more respectful of these heavier ones.

Sorry bout your mate Brian.

I think the biggest trap regarding gyros is the ease of control, which tends to have some pilots gett'n a bit too tricky in them long before they have a good understanding and feeling of the phisics.
As far as i'm concerned, 120', hell, even 50' is plenty of alt to recover and land safly from a no AS no power situation.[ i do it regularly]
And if you don't have the confidence in YOUR OWN ability to do it, then NEVER get into that situation till you are.
In the right hands, a gyro is almost fool proof, in the wrong hands, they can be made to look dangerous.

[_MOL_]

I guess he was just not skilled enough to do the manoeuvres he did.
I will move this thread to "Accidents" and we can continue it there. Sorry for the thread steal birdy.

[scott heger]

Chuck, correct me if I am wrong, but to do a true stall, it would seem that at least some loss of lift would follow. Partial stall maybe? With Birdy only being 5 feet off the ground, a complete blade stall would have turned him into a dirt dart for sure.

Scott Heger, Laguna Niguel, Ca N86SH

[C. Beaty]

Sure, Scott, in a stall, the lift vanishes.

The path of the machine following a stall depends upon its inertia and momentum.

A cannonball is always stalled but keeps right on going until it runs out of momentum.

[david holmes]

A cannonball is always stalled but keeps right on going until it runs out of momentum.

what happens after it runs out of momentum? Does it quit going?

[C. Beaty]

Yup. Then it falls.

[birdy]

No wurrys Brian, as i said, i'm sorry bout your mate, but i stand by wot i said bout blokes getn too cocky before they know the machine proper.

Chuck, lets assume it was a partial rotor stall that made the sound.
Why then dosn't a prop make the same sound when it stalls???
Or is prop stall more like cavitation?

[C. Beaty]

Chuck, lets assume it was a partial rotor stall that made the sound.
Why then dosn't a prop make the same sound when it stalls???
Or is prop stall more like cavitation?
I think a prop would make the same sort of noise if you could abruptly snap the blades flatwise to the air.

[Ron Iaconis]

When I first got into gyros ( 1984 ) I watched the hot dog flying that the Cincinatti Chptr 40 did. I watched them like a very studious student. Some would fly the bath tub as I will refer to it. From say about 500 ft come down get air speed up and start into a climb and at the top of the climb do a 180, kick the tail around and point the nose down. The keel seemed that it was perpindicular to the ground. When I told Bill Parsons about this manuver he asked me if I was looking through the blades and I said yes. He said that I was very close to having the blades slow to a dangerous RPM by not having enough positive load on them and that I only had a few seconds to the point that they would not be spinning fast enough for a successful recovery. I stopped doing thta manuver that point in time, and haven't since. I truly know that if I continued to practice this type of flying I would not be here today. I was green and full of pure enthusiasm and some of the other flying techniques were as dangerous. I believe that some of us out there are just too enthusiastic, and too inexperienced and too stupid to know how dangerous some of the agressive flying can be , especially in the hands of a novice. Willard Myers was a long time experienced pilot and he would perform flying manuvers that just seemed that he should not survive another day. Nobody that I ever saw tried to fly like Willard. He seemed to know what he could get away with,,,and if you asked him , he would say that he completely knew what and that he was flying safely.

[Rotornut]

Ron Great Post. MJ :)

[birdy]

Ignorance is bliss, till you realise you were.!!!!!!!
I don't post it coz it sounds smart or inteligent.

[Chopper Reid]

Ron L, A climb to the point of zero airspeed followed by a rudder turn back down isnt a problem [even looking throught the rotors] with the bigger and heavier rotors as they keep their revs better. I have a rotor tacho and and have verified their revs at the point of zero airspeed.

I wouldnt advise anyone without a lot of experience to let their airspeed decay to zero in this attitude as you are in a 'delicate spot' !!!
Also, make sure you have suffiect altitude to recover as the ride down is quick !!

[Passin' Thru]

Ron L, A climb to the point of zero airspeed followed by a rudder turn back down isnt a problem [even looking throught the rotors] with the bigger and heavier rotors as they keep their revs better. I have a rotor tacho and and have verified their revs at the point of zero airspeed.

I wouldnt advise anyone without a lot of experience to let their airspeed decay to zero in this attitude as you are in a 'delicate spot' !!!
Also, make sure you have suffiect altitude to recover as the ride down is quick !!

I agree with the above points, although I'm not sure what Bill Parsons meant by "looking thru the rotor". I often "look thru the rotor" side ways at the horizon in high banked turns to maintain same altitude. :confused:
Although I advise against inexperienced fliers getting into these "unusual" manouvers, as Brian sez, a good rotor will hold its energy quite well. I particularly like weighted tip blades. Also, proper entry into the manouver will pull some extra "G" force and accelerate the rotor considerably above normal level rotational speed. This is stored energy that can be used to complete the manouver. In the "mid air flair" that McEagle discribed above, you can store enough energy in tip weighted blades to come to a complete stop and have enough "hang time" to level off and rudder pivot 180 degrees and commence foward flight in the opposite direction without any noticable loss of altitude. With proper understanding of your rotor system and good rotor management, a gyro can do some amazing things. But one thing to always remember, no matter how skilled you may be, there are always some unexpected variables that can get in the mix and really screw things up!
Ron; did you ever see Roger Wood do his "All American Scream Machine" routine? It would make you scratch your head and wonder! :D

[Ron Iaconis]

You Mean The Famous " Roger Loop " stunt ?
I was an avid " student" of Roger Wood. From 1984 to about 1988 I always watched and tried to emulate Roger,,,,,actually, Roger test flew my new gyro at 1984 Tullahoma, TN PRA Convention. I hadn't yet gotten off the ground and was just wheel balancing then,,,and when Roger lifted off the ground with my gyro,,,,I believe that I actually was jumping up and down for joy even higher than Roger was flying my machine! I attended almost every major fly-inn that the Chapter 40 Club had from 1985 to 1988. I knew all the gyro people,,like Roger, Frank Black, Ed Alderfer, Johnny Hay, Glen Bundy, Eugene Young, Bob and Betty Wahn, Rick Heaken, I used to list many more but time has allowed me to forget most of them,,,Bobby Green, Mike Weed, Flash Flannagan, There were two men who had grass strips that we mostly flew at,,,,I forgot their names,,,,but The Cincinatti Rotorcraft Club was a super strong club,,,,,many super nice people
PS: The times that I flew the " Hammer Head " Type Routeen I used Bensen blades,,,and I flew like that for many a times,,, and once I ,,,,,WAS too close to the ground and just as my blades developed the needed lift my main wheels settled on the ground,,,,,,,it was a big wake up call,,,on ensuring that I get enough altitude before attempting that again.....But" Looking Through The Blades " to me meant, that as my keel was almost perpindicular to the ground( it seemed like it was perpindicular) and the reference point that I was looking at( a point out to the direction I wanted to go) I would be looking throught my rotor disc, so basically my rotor disc was almost perpindicular to the ground,,,,( I know that it wasn't) but close to it,,,or close to not having any load on the blades allowing them to decay in RPM's.
PPS: But after seeing Carl Hinshaw's routeen on his true loop all else seemed not so great!