Manuvers in HTL/CLT/LTL gyros

[Greg Mitchell]

G'Day Tim,You can tell I'm bored. [][]OK suggest a few manuvers for HTL that CLT or LTL cannot do.Again I agree, a good pilot ( many are astounded at what Larry Neal does in a gyro, whatever gyro he flys) can make a box look good.Let's take it off of Michael's Magni thread and put it in Pilot Techniques. Let's explore the real differences and what experienced pilots would and would not do in a HTL as opposed to CLT and LTL. Might make for some interesting debate. No low blows Boys...not pushing a brand....I loved the Magni and if I had a spare $90,000 there'd be one in the workshop or out at the hangar as we speak.[][]Say no more.Cheers,Mitch.www.thebutterflyllc.com

[Tim]

quote:suggest a few manuvers for HTL that CLT or LTL cannot do.Real CLT, and to a worse extent LTL gyros drop the nose very quickly and to quite a steep attitude on cutting the throttle. This is not necessarily a bad thing but certainly could catch out a new chum if he is not ready and trained for it. the higher the G force, the more pronounced this would be. I would not like to be in a CLT or LTL machine during a high G tight turn and have a sudden engine failure. I am not speaking from experience here and neither do I ever want to. I might be wrong but I would imagine that the nose may drop further than the considerably used up back stick can recover (a sort of horizontal tuck under). Apart from a slight torque reaction, there is no problem cutting the throttle in a HTL machine during a tight turn. This is not intended to praise one or rubbish the other but rather point out different handleing traits.Another difference would be the torque reaction. Rather than call gyroplanes HTL and LTL I would prefer to call them High C of G and Low C of G. The thrust line dosen't actually change but the C of G is higher or lower. A HTL or low C of G should have higher moment of inertia (because the prop torque is further from the C of G). This should make a more gentle and managable torque reaction on power surges (eg. fuel starvation). Another interesting point that I have read on the US forum is that of different Dominator pilots talking about flying so fast that the joystick was nearly at, or at, its full forward stop. Given that the rotors fly nominally at 9 degrees, and the angle gets flatter with speed to approx 3 or 4 degrees, what has happened to the rest of the forward stick movement? Surely it hasen't all been used up in the "blow back" angle of the blades. I can only assume that they fly nose high at higher speeds. Either way it dosen't matter, it is just not good to run out of joystick movement at any stage of flight. Of course a very low C of G machine can run out of back stick at high speed which is more dangerous, but experience has shown that a 2" to 5" low C of G will maintain a comparatively neutral stick. This is all conjecture though because there are often many more factors involved than a few test samples will allow.I think that there is no doubt that it is easier to make a 'close to CLT' machine more pitch stable than a low C of G one, especially if the low C of G has a large differential like the 12 or so inches of the RAF. I doubt wether you could fit a large enough stabilizer to a RAF to pass Greg G's published stability tests, whereas a CLT may be able to get away with a very small stabilizer, depending on drag factors. Getting carried away here. Will finish it tomorrow.I dare say someone will help me out if I am wrong.Tim McClure

[Greg Mitchell]

Mornin Tim,I appreciate your comments.I'm not sure that CLT and LTL craft drop their noses as dramatically as you say, certainly I have read that very low thrustline craft do have this propensity.Could you explain the high G turn senario in more detail for me. I'm not quite following. lets say a tight high G turn 180 degree with a 60 plus degree bank. I would have assumed the inertia of the fuselage would be enough to complete the manuver with out due concern. And at 60 plus, or lets call it 90 degrees to the ground, how is it then going to hirizontally tuck under???I have read also that early AirCommands for example low C of G or HTL craft would also be fanging along with little forward stick movement left and be flying dangerously nose down. Some of this nose down 'pucker value' was reduced by use of a HS, so isn't configuration starting to take its rightfull place here? Why has just about everyone upgraded their old AC's...I've the greatest respect for Greg Grimminger and all the work he has /is doing with respect to gyroplane safety ect but I'm not convinced by all his arguements.If the the thrustline is within 2 1/2 inches high or low..then you have CLT... OK....I'd rather be flying a craft that has that thrust on the C of G or just below and certainly not in the other direction. Say 4 to 5 inches high thrustline, then I'm a lot more conscious about zero G type manuvers and that was my initial point about Magni.Convince me Tim.Cheers,Mitch.www.thebutterflyllc.com

[Tim]

quote:Originally posted by Greg MitchellI'm not sure that CLT and LTL craft drop their noses as dramatically as you say, certainly I have read that very low thrustline craft do have this propensity.I have not tried this myself Mitch but a typical CLT machine test flown by Dave Jackson did exactly that. He was told, and believed, that this gyro would be the most pitch stable that he had ever flown, so he decided to give it a throttle cut to test it. The pitch down was so sudden that he thought that it would have tucked under had it not been for the quickness of his ingrained response in getting the stick back. A further test showed that he could stop the pitch down if he moved the stick back in unision with the throttle. I would be concerned about the beginner who does not have this instant response.A query to Chuck B resulted in a test by Chuck and Ernie B in Ernie's tandem Dominator, and the test showed a pitch down of approx 45 degrees, which levelled out at about 30 degrees nose down. I would imagine that the tandem would be more gentle than a single seater. quote:Could you explain the high G turn senario in more detail for me. I'm not quite following. lets say a tight high G turn 180 degree with a 60 plus degree bank. I would have assumed the inertia of the fuselage would be enough to complete the manuver with out due concern. And at 60 plus, or lets call it 90 degrees to the ground, how is it then going to hirizontally tuck under???In normal straight and level, the stick would be neutral or forward of neutral in a LTL machine. Generally the higher the g force, the more back stick required. To arrest a sudden pitch down in a high G manouver, a fair slice of back movement is required, and it may not be available if the stick is already a fair way aft. There would certainly be enough inertia to complete the manouver but maybe not enough stick movement.quote:I have read also that early AirCommands for example low C of G or HTL craft would also be fanging along with little forward stick movement left and be flying dangerously nose down. Some of this nose down 'pucker value' was reduced by use of a HS, so isn't configuration starting to take its rightfull place here? Why has just about everyone upgraded their old AC's... Actually, this one is back to front. The early A/C's were more inclined to run out of back stick at higher speeds. This is of course the most dangerous situation of all. The aftermarket H/S improved the situation in that the gyro flew more level with the stick closer to center, but it did not do enough to improve the pitch sensitivity of the Air Command.quote:If the the thrustline is within 2 1/2 inches high or low..then you have CLT... OK....I'd rather be flying a craft that has that thrust on the C of G or just below and certainly not in the other direction.It does not matter which way the thrust line is offset, the same amount of offset applies the same amount of ft/lbs of torque to the airframe, the difference being that one is nose up and the other is nose down. In a zero "G" situation, both ways have approx 9 degrees of pitch before the control limits are reached. From then on the result would be a snap loop or tuck under, both with the same outcome. Zero thrustline offset gives zero airframe torque, which is undoudtly the safest in true zero "G" flight. Personally, I would prefer slightly HTL for other handling preferences, and the small offset would not be enough to to torque over the airframe before a normal time frame response can be made. This is just my preference.quote:Say 4 to 5 inches high thrustline, then I'm a lot more conscious about zero G type manuvers and that was my initial point about Magni.Your initial point about Magni was valid but in their favor they do have good stabilizer volume. I suppose that they would have a weight limit for their "useful load".Gyronauts have become a bit overlectured about the dangers of zero "G", and rightly so, to reinforce the point. However it is much harder to get into zero G than most realise, and almost impossible for an experienced pilot. I think the odds of finding that air pocket of perfect zero "G" would be like the odds of winning a lotto. It is mostly pilot induced through panic or PIO, which can only be corrected through proper training and more stable gyros.Tim McClure

[Greg Mitchell]

Mornin Tim,Thanks for your responses. Going out to lay up some stone and think about it all before I respond with more questions. Cheers,Mitchwww.thebutterflyllc.com

[birdy]

Another thing ya can't do ina LTL gyro, throw a leg over the keel n sit.[ without hav'n t climb.][][]Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[Greg Mitchell]

G'Day Birdy,I think that's only considered a 'manuver' by really short people.[:I][][]Hi Tim,Mate, I'm not sure what a typical type clt ship is. And without seeing what Jacko was flying at the time. Many CLT and even 4-5" LTL craft from what I have read and enquired about, do indeed drop their noses upon sudden power loss. But those that are set-up correctly do not drop dramatically or as suddenly as some report. I can only speak for Butterfly from personal experience and it is not sudden and dramatic at all.The Chuck B and Ernie B test does not indicate sudden and dramatic nose pitch, only degrees of same.I'm not real quick with this high g manuver stuff and still cant see the danger for me in Butterfly with 1.5" LTL (CLT by defn) in a tight 180 degree turn with power loss half way through the turn.???My apologies on the AC scenario, you are right of course, the faster they went, the lower the nose would get because of the high thrust line pushing over the top and back stick was required. Quite right. OK lets take this old AC ship.....addition of a stab available stick travel and lifted the nose some BUT was still pitch unstable. What sort of manuvers would you do in an Old AC ship, that you couldn't do in a CLT or LTL?????I think it does matter which way you take the offset!!! Because the CLT and LTL are more likely to assist in restoring G forces and not take the ship in the other direction and further exascerbate the neg g situation?????I'm with you on proper training and more stable gyros. I reckon I got a stable gyro...now to just get me some more of that proper training.Keep it comming Tim, you are helping me get my head around this issue. Appreciated.Mitch.www.thebutterflyllc.com

[Tim]

G'day again Mitch. A bit short of time tonight but I will try a couple from my point of view.quote:What sort of manuvers would you do in an Old AC ship, that you couldn't do in a CLT or LTL?????Actually the Aircommand is a bad example. Their unstability problems were equated more with a combination of short coupling, high power to weight ratio and heavy unstable blades, as well as the lack of stabilizer. Adding the stabilizer only fixed part of the problem. The thrustline really wasn't that bad (as lomg as they had those heavy rotors on top). They were capable of speeds that most gyronauts had not seen before and this coupled with the unstable blades made them very sensitive at speed, something that good pilots learnt to manage but was deadly for a brave beginner.quote:I think it does matter which way you take the offset!!! Because the CLT and LTL are more likely to assist in restoring G forces and not take the ship in the other direction and further exascerbate the neg g situation?????As long as the C of M is ahead of the RTV then all gyros should respond in the correct way to ensure positive pitch stability. The main problem would be in zero G, in which case neither high nor low thrustline has a restoring factor. This is where an effective stabilizer comes into its own, as long as you still have some forward speed.quote:I reckon I got a stable gyro I reckon your right.Tim McClure

[Greg Mitchell]

G'Day Tim,Mate I read and re-read that first para on the AC and there is a good deal of info in there relating to 'taking into account' the whole configuration of the design. Good post!OK so if the AC is too hot to handle...lets look at the Raf 2000. Same question applies with respect to manuvers. I'm still looking for examples. My example would be:-BUTTERFLY with small..60" prop and free flying tail of good size, more or less easily recoverable from a vertical desent spin Vs Raf 2000.Any other examples of manuvers HTL Vs CLT Vs LTL. Please Gents jump in.Tim, flying along S & L in slightly low TL, experience a momentary downward wind shear. Neg G for a second. Ok the HS will respond in the correct direction sure but so too does the thrust which will help to raise the nose in the correct direction. A high thrustline eg early AC or Raf2000 will be in the wrong direction True or false???Obviously, I agree with Posted "As long as the C of M is ahead of the RTV then all gyros should respond in the correct way to ensure positive pitch stability."And that the HS will be advantageous tool in restoring G loads.I think I'm still missing the point somewhere.???Cheers,Mitch.www.thebutterflyllc.com

[Tim]

quote:Tim, flying along S & L in slightly low TL, experience a momentary downward wind shear. Neg G for a second. Ok the HS will respond in the correct direction sure but so too does the thrust which will help to raise the nose in the correct direction. A high thrustline eg early AC or Raf2000 will be in the wrong direction True or false???Very true Mitch. But these two are two extremes of the problem. The A/C, though having a small offset compared to the RAF, had a lesser moment of inertia due to its close coupling and light weight. Hence it was just as deadly as the RAF, with its higher moment of inertia but far greater thrust. The "wrong" response from these two gyros led to extra pilot workload to keep them straight and level. A good experienced pilot got used to this and found it no more tiresome than keeping a car straight on the road. That actually makes an interesting analogy. I clearly remember the '56 Holden that I had - It had to be driven by constantly moving the steering wheel a couple of inches each way to keep the wheels in the middle of the spongy free play. If held still, the car would fairly soon decide that it had to head off one side of the road or the other and it was a toss up which side (unstable). My current VT Holden will stay dead straight if the wheel is held still, and seems to be that way even over undulating surfaces(stable).Back to the gyro, the rougher the air became, the greater the pilot workload became in a very high thrustline gyro.My personal preference for a slightly high thrustline comes from two charastics. Firstly, abrupt power changes do not cause strong pitching moments, making the gyro easier to control doing demos or chasing stock, and secondly, air acceleration does not cause abrupt pitch changes, making it easier to control through rougher air. Both these considerations lead me to believe that there is some some other force outside the C of G that is not being taken into account, because if the thrustline was exactly through the C of G then power changes should not cause a pitch reaction, (and it definately does). Perhaps the accel/decel-eration of the mass of the rotor causes a delay in the head movement, which is free to pivot on its pitch axis, causing a slight up or down pitch moment in the airframe. A slightly high thrustline would counteract this tendency. In my opinion, this was the reason why some of the earlier pioneers used so much downthrust on the engine. This would also counteract the tendency to nose up under power or nose down off power. It is often suggested that the down thrust on the engine is to get the thrustline through the C of G, but in some cases it is so pronounced that a line drawn through the thrustline would come out above the C of G making them a HTL machine. Perhaps the reason was a combination of the two above.Tim McClure

[asra]

Guys. I know nothing about this so bear with me. The other day Mitchposted some pics of a new Gyro that had the engine turned aroundwith the prop at the front closer to the mast and vetical centre line. I cant help thinking that this must have some relevance tosomething somewhere ? Do you think it does or doesn't it matter ?Tar.Robert DunnMackay. Qld.Growing old is good while it lasts.

[asra]

PS: What I mean is, would its position influence the horizontal thrust line ?Robert DunnMackay. Qld.Growing old is good while it lasts.

[Greg Mitchell]

Robert,That was probably the red tandem craft which had a tail boom concentric propulsion system. Be interesting to see how prototype flight testing of that craft comes along. The distance between the prop and vertical C of G, I dont know Mate. I'm not sure it influences the horizontal thrust line.Tim,I appreciate your comments.As you know Tim, I dont have enough experience or time in various types to make emphatic statements. However, my gyro does not pitch with Power or Air Acceleration. It is 1 1/2" LTL and has a Horizontal Stab which is in line with the keel.What I'm getting here is a slightly high thrust line...the gyro will be easier to control doing demos or chasing stock, and it is easier to control through rougher air. Tim are you then saying a slightly HTL gyro is easier to control doing manuvers? (demos)Are you saying a CLT or slightly LTL would be harder to control when chasing stock?And that CLT and slightly LTL are more difficult to control in rough air?Tim I thought the down thrust angle of 3 degrees or there abouts, was in an effort to get the thrustline closer to the C of G but not on it and they were HTL anyway were they not? I had a great rave with Terry Boatswain many moons ago about this engine down/thrust angle.Do you have any thoughts or theories as to 'the other force' you believe is playing a role in what you describe as pitch changes in a CLT gyro with power change? You might be on to something Tim.Thanks again. Mitchwww.thebutterflyllc.com

[birdy]

Sumthn I'v wundered with these stable machines, with big stabs is ,wots the likelyhood of the machines stablity actualy put'n the machine into a powered sink, behind the curve?Example; Your putt'n along in rough air, and because your fly'n a stable machine, you don't[supposedly] need to work the stick [ I'm talk'n rough air here]. You fly into a very strong down draft, the machine reacts as designed and the nose is up , look'n at the heavens, the power is still on, and coz of the strength of the downer, most of the machines effort is countering the draft, and theres buggerall forward speed.[ yes, theres still forward AS, but your nose is high, so your horisontal speed has almost ceased.Now, apply an updraft of the same magnitude!!! Wouldn't the machine now be behind the curve??? Needing pilot input to get out???At worst, you could end up in the dreaded "reversed airflow" coz the machine suddenly lost its forward air speed, the disc is tilted back, the stab has either stalled or isn't effective coz of the limited positive airflow.............. and the pilots still asleep coz he's been told repeatedly," you don't need to fly these stable gyros, they fly um selves".Either that or the stab is effective enough, and rips the rear of the machine up so fast it out runs the rotors, and gets chopped off.No, I'm not try'n to be a smartass, just through'n in sum scinarios.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[Brian]

Thats a great scenario Birdy, I know that my old HTL gyro is as safe as houses in that situation as I've been there many times and am looking forward to trying a near CLT gyro out and finding out what all the fuss is all about !Reading the US forum, one would think that anything but CLT is impossible to fly or certain to kill you which I know isnt the caseBrian