Vertical Descents

[asra]

This article has been offered for the Spring 2005 GyroNews which is currently being prepared. I feel it is a very important subject so on behalf of the author, I have posted the topic on the forum for further discussion.I was looking through some old paperwork lately, and came across this AD:Vertical descents:ASRA WebmasterPh (07)5464-4993Int +61 7 5464-4993

[NiqueNaque]

Barry,My thanks for posting this..Nick.

[birdy]

One other thing that I think is over looked in this decending thingo is the possability of 'reversed' airflow.Lets assume a newby, or anyone who dosn't have a good understanding of do'n a vertical decent, is cruis'n along and wants to drop down a few hunderd feet for wot ever reason.He eases the power to idle and holds the stick in the cruise position or back a bit to stop it from noseing down.Dose he know that when the AS drops to 0, the stick MUST be held forward,or else he will start to slide backwards, in very short time. Control inputs with the stick and or rudder are only going to confuse the poor bastered now.IF he hits the throttle now, depending on the power avalable, he could be behind the curve, with the nose high,prop cavitating, fly'n backwards and the insufficiant thrust avalable isn't enough to stop the reversed airflow over the controls.IF the machine dosn't have sufficiant forward stick movement[ I'v seen a couple], the nose can't be lowered enough for the thrust to arrest the reversed airflow.Not that I'v tested it, but I'd reckon the rudder would be pretty inaffective, if not stalled, in reversed, tightly spiraling airflow.Now I got a headache.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[NiqueNaque]

Birdy,That puts a damper on my idea.. being to rake the hinge on the rudder forward at about 15 to 30 degrees to compensate for the loss of forward velocity.Any suggestions?Chers,Nick.

[birdy]

Any suggestions?Be sure you have a compleat understanding of the machine before you try anything outa the usual.[]Most adverse reactions/ habits of any machine can be engineered out of it, but sumone will still find some way of geting into trouble[].If you are confident and understand wots going on and why, you'll get out of most sticky situations....................till you find another you never considered before.[it may also be of benifit to get into the habit of fly'n with your brains, and not your balls[}]]. Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[birdy]

One other thing that I think is over looked in this decending thingo is the possability of 'reversed' airflow.Gess this means it hasn't been overlooked, either that or I'm just dribbl'n s%$^ again.[V]woda you reckon Tim??Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[Tim]

Howdy Birdy. I recon that you touched on one of the main reasons that some modern gyroplanes are hard to get out of a flat spin, especially if a bit of power is left on and the stick is held so as to keep the nose high. They tend almost as though they are backing around the spin, making recovery impossible until the nose is lowered and forward motion is once again established. A big H/S will aid in lowering the nose, but will further blanket the rudder. We need someone who is confident in varying flat spin attitudes to tape wool tufts all over thier rudder and cam-cord it during a flat spin. For those that wish to flat spin safely, I am sure that they could alter their tail design to accomodate. I have noticed a couple of designs in the US where the H/S is behind the rudder, maybe something like that may be an answer. Another problem may be that in a tight spin, it is conceivable that the inner portion of the propeller is stalled, making the spin faster and further compounding the rudder airflow problem.Tim McClure

[birdy]

Thanx Tim.Depending on the steepness of the backward diveing spin, a big HS could also hold the tail down if there is negative airflow.Most people wouldn't know if they where in negative airflow, especialy at alt, and the string won't tell them either coz from where they'er sit'n, it'd look like its pointing up, and back'n off the power wouldn't immeadiatly cross their mind.A HS behind the rudder would shelter the rudder from the airflow more in negative airflow, but if it was in the prop blast, it would be better. Trouble is, you need the throttle open to get prop blast, but you need to close it to get the nose down, especialy in one of them LTL things. Of corse, no HS means there isn't this problem.Of all the streight virtical decents and virtical spins I'v done, I'v only noticed once when I actialy flew backwards.It was by accident. I was fly down a fence line in thick scrub when I dropped on some cattle on both sides of the fence just in frount of me at bout 100'. Not wanting to 'pressure' the critters on either side of the fence to jump through it, I chopped power and pulled back so's I wouldn't get in frount of them, planing to decend virticaly just behind them and split um off both sides of the fence. Think'n more bout wot was happen'n on the ground and not on fly'n , I suddenly realised I was fly'n backwards and loose'n alt quickly. Push'n forward to drop the nose and eas'n on power, it took considerably longer to regain positive AS than it dose in a normal virtical. I did manage to clear the timber, but not by much. The only reason I knew I was fly'n backwards was coz of the close proximity to the ground , and maybe a couple o thousand hours of fly'n forwards.Also, think'n bout it afterwards, if I tryed to stick or rudder it in any direction while go'n backwards would'v been interesting, coz the controles have an opposite effect in negative airflow.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

O.K., I'll bite. As a part of my training I practiced recovery from rapid decents both with and without power in a CLT, Tall Tail AAI modified RAF. In all cases, I would slowly add back pressure until I dropped below minimum level flight speed. The gyro would, naturally, begin a rapid, vertical decent. In all case, simply releaseing the back pressure and allowing the nose to drop and the gyro to regain airspeed was all that was required. Rudder authority was always adequate, with or without power. The gyro was totally controlable throughout the maneuvers, but, of course, the controls did get 'mushy', and more rudder movement was required, as the minimum level flight speed was reached. There was no tendacy to enter a spin, no problem lowering the nose -- it would have lowered itself if I let it -- and I always had full, positive control in all three axis. Birdy,When you say your gyro was flying backwards, was that relative only to the ground or also to the air? I'm not sure a gyro can fly backwards relative to the air -- I'll have to think about it -- and what it does relative the ground is irrelevant from and aerodynamic point of view, but not from the mustering point of view, or course.

[Tim]

quote:Originally posted by pwendellI would slowly add back pressure until I dropped below minimum level flight speed. G'day Peter. Minimum level flight speed in the AAI modified RAF is probably in the region of 40 to 45 mph and below that the gyro would be sinking. It is still a long way short of 0 mph of a true vertical descent. If the nose is held high in a vertical descent, just about any gyro will "back up" (in relation to the air) and will tend to swing the nose around and enter a spin. I say 'tend to' because it can normally be controlled with rudder. It may well be harder to get into this situation in the AAI gyro because of the exceptionally large tail volume, both horizontal and vertical.Tim McClure

[birdy]

Also Pete, if you had rudder authority, you MUST have had some forward AS or throttle on, coz a rudder don't work in virtical airflow.Your rudder authority obviosly came from prop thrust.Wot I'm describing is a machine is stopped suddenly by chopping power and holding the stick back, no AS either way. It quickly starts to sink and the only airflow is virtical. IF, the stick isn't held forward as soon as AS reaches 0, the machine will slip backwards off the tilted disc. In most cases, the reversed airflow over the rudder will initiate a spin in either direction, lets say to the left. The pilot, sensing the start of an unwanted spin, attempts to stop it by applying right rudder, but coz of the reversed airflow, it only makes to spin tighter.His brain instantly explodes and he sh1ts his pants and will become another statistic if he dosn't realise he's actialy going backwards and must go against instinct to recover with unfamiliar control inputs.Powering on will only give the rudder more authority, especialy a tall tail, and make things even worse, [if it could possably get any worse.]Leaving the power off, applying full left rudder and holding the stick on the frount stopper and to the left is the only way to stop it.But who's going to apply left rudder and left stick to a machine that seems to be jammed in a hard left hand turn??????The backward spin BTW, will start quicker than you'd imagine.Oh , yes Pete, I mean reversed airflow, fly'n backwards. A gyro won't fly backwards for long, coz the rudder/fin will start a spin very quickly for the reason above.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

Tim and Birdy,I have been in a power off, full vertical, zero airspeed decent in a Sparrowhawk. I was in the left seat, but Steve McGowen was in the right seat demonstrating the technique. He had control of the aircraft, but I was following on the controls. He was able to initiate a yaw to the right and then back to the left with little problem. Of course the engine was at idle and still providing some airflow over the rudder. I didn't notice any reverse control.Since I am a low hour pilot, I'm not going to talk about what I don't know. I was never taught to fear a verical decent, quite the opposite, only to make sure I had enough altitude to recover my airspeed. When I get back in the air, it should be soon, I'll be sure to explore this area of gyroplane flight.Thanks for sharing your experiences.

[birdy]

Obviosly the SH's disc was flat Pete, coz , like I said at the start, if the stick isn't held in a position that has the disc perpendicular to the airflow but still back too far, then the machine has to slide backwards.If you do find that your sliding backwards, never hit power to stop it, coz the thrust will lift the nose and if your flying a negative pitched stab in the prop wash, it too will push the tail down.All you gota do is stick forward. Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[Brian]

Another thing to take in account re flat spins, is that its a diferent ballgame to spin an open framed gyro versus one with a canopy, same results but the open framed gyro is a delight to spin. The canopy seems to catch a bit more wind and needs more controll to keep it precise.Brian

[asra]

Hi Guy's I flew my Gyro vertically spinning into the ground a few weeks ago, as it occured I reacted with forward stick, right rudder, power off. The reason it happened I was looking up at the blades thinking how brilliantly they worked, how daft was I,the Gyro lurched back I actually lent forward into the harness, Then she started to spin slowly, the blades started to hammer the stops, I had to take off foreward stick, I banked to the right away from the spin nothing happened, banked left into the spin this was a concern I thought this could possibly make things worse, still nothing, I knew I had to stop the spin or wreck the Gyro and probably get hurt I needed airflow over the rudder so I powered up,that was my second main mistake of the day the spin rate picked up alarmingly and I was not in control. I did not know what to do,I could not judge decent rate I thought the impact was going to be fatal, when your thinking like that things are not good .The impact was hard and painless the 60Lt seat and mounts collapsed along with everything else, and we fell over I let the harness go and stood up, A nearly nine foot high machine reduced to two foot .I spoke to my instructer the next day He said my best chance for recovery would have been to bank into the spin and hold it there, slide the gyro sideways presenting a lowered blade to the airflow creating some airspeed over the blades and unstalling the disc, also stop the prop, who stops a perfectly good engine, it probably would have helped, Torque is what coused the problem and then made it worse when I powered up, As my instructer said you can not teach this manoeuvre it could take hundreds or thousands of feet to recover, I don't know if I could have recovered probably not, it would have been nice to have known what to do, to have felt in control. There is a bit of a myth in Gyro cicles that these machines are a lot safer than fixed wings you can't stall or spin, Sorry but you can.You are most likely to walk away but one day one of us won'tThere is enough knowledge in ASRA for all these little things that are likely to bite us to be written down for full discussion, No one needs to go out and test fly for a spin they seem to be fully understood by some but not by most. One possible reason given me for the spin was the size of the prop 76 inches produces a lot of leverage. Small propped Gyro's Don't spin readily.Keep your eye on the speed, Behind the power curve is not a sinkRegards Frank Close Window