Hazards of slow flight.

[birdy]

Theres been abit of talk about flyn slow lately, and noone has yet mentioned any of the hazards, just techniques of how they do it.
I spend most of my airtime behind the power curve, so i thought id put my SCG 2 bobs worth in.

Firstly, theres slow, then theres slow.

1; From wot i understand, the term ' behind the power curve'[ BPC] means any airspeed [ AS] slower than that which requires min power to hold a streight and level [S/L] flight parth. IOW, a slow, uneconomical cruise.
Not many people are go'n to get into trouble flyn slow, till they get too slow, but even then, if you have alt, you have room to recover.

2; Then theres the more hazardous AS, wot ill call ' hangn off the sink.'[ HOS]
This is wen the slightest drop in AS[ wether its from wind drop or late pilot correction] will have the machine start to sink, coz your already at full power with alot of backstick.
Most times a little more power will arrest the sink, but if you are already on full power, you need other alternitives.

3; Vertical decents are 0 AS decents, with or without power, and have similar hazards to HOSs but are generaly less dangerous coz your already sinkn.

4; Then there is reversed airflow, or flyn backwards, or tail sliden, wotever you want to call it, usualy caused by the pilot not knowing he's gon beyond 0 AS.

General ruel, keep away from max power and always have sum spare hight up your sleave wenever your slower than cruise.

BPC flyn is safe as a house, solong as you have alt to spare and or power in reserve to recover. Gyros can fly all day BPC in any conditions the pilot is comfortable with. Its not very economical, coz of the 'higher than criuse power' required.
Theres not alot to go rong coz even if the noise stops [ and you have alt] its no different to a regular unschedualed stop.
The key is knowing wen your getn TOO slow, and knowing that will depend on the machine/pilot/conditions combination.
[Like you said Thom, experiance here is everythn, so work into it steady.]

Flyn on the verge of sink [ HOS] at full power is abit more tricky coz you have virtualy no AS, sluggish cyclic responce, low RRPM and a thrust line that has alot more effect on the machine than normal, torque roll and where the effects of even the slightest change in wind speed AND direction, virtical and horisontaly, are greatly exadurated.
Power is on the limit, and if you stuff it up, any amount of alt wont help you. Itll just give you further to fall. [unless your only 2 inches off the ground. ;)]

The main thing to watch for wen do'n virtical decents is reversed airflow.
All machines will need a little backstick in a true VD coz the SH[ stabilizer] will be tryn to push the nose down, so you need the disc lean'n back sum to hold it up. Its wen you apply slightly too much backstick that you can get into reversed airflow. If your in a cab you wont feel it, and your yaw string wont tell you either. Iv flown backwards plenty of times in the open single and am only now getn to 'feel' reversed airflow.
Its the 'reversed control responce' that youll notice first, and it WILL be very unnverving.
The other is an uncommanded spin, started by either an assymetrical drag on the machine pulln it one way, or the effect of the 'down side' of the prop disc haven more thrust than the 'up side' from the virtical airflow causeing the machine to spin.
So wether its reversed airflow or a spin, your go'n to need plenty of alt and a cool head to get it sorted before you touch the ground, coz its comen up pretty quick.

Reversed airflow, or true backwards flight is definaly controlable. It can be deliberatly induced and held, if you know wot your do'n. I wouldnt recomend it to anyone who dont understand WHY the controls are reversed, coz its sumthn youll need to understand very deeply to be able to pull it off while your actualy flyn.

Because i spend alota time at low ASs close to the ground, iv developed reactions that will differ to the general ones youd have at alt, coz down low, youv little or no room to move and 'at alt' responces dont work down here.
Most instructers will tell you to drop the nose/add power if your AS is too low, or your sinkn.
Thats fine, if you have alt and or power to spare.
But the first thing that happens wen you drop the nose is, the rrpm will also drop from an already low state coz youv just unloaded them more.
Then, wen the nose drops, and the throttle is full open, the props thrust is now pointing down, accelerating the already fast decent. Not good if you dont have the room.



Bloodyell, now i gota blister on me pinky.:rolleyes:

[dragonflyerthom]

Thanks Birdy. I'm going to bookmark this one to study. Your a good mate and all. Good info to know.

[bones]

Well get a band aid and get on with it, i was just getting into it :)

[Fl90]

The desire to use rudder turn is greater at those speeds, with the stick back. If your hanging the sink and get agressive or anything ther than mild with the rudder, you stop hanging and start draining. It's the same with the tailslide into spin, your sink starts fast and continues fast. If you can get it to limp a little before your low enough for ground effect, you can use ground effect like a rough field take off. If you have to do that, you were too low and your but was kissing the seat. BTW, tre lines give good lift air but they don't have ground effect and they don't move out of the way.

Phil.

[Resasi]

Thanks birdy, always good to get the gen from someone who does it all the time and knows through experience what it feels like and what to look out for.

[ventana7]

Good Stuff mate-- Thanks.

Rob

[reelmule]

GREAT POST BIRDY--probably saved someone from themselves!! Just like a rainy day bank reserve for our home life we need a "rainy day gyro flight account" with adequate altitude and power reserve.

[EI-GYRO]

Just a note of caution.
A few years ago a gentleman named Bill Dass died exploring a particular
slow-flight high-power trick.
He was at minimum airspeed, max power, nose-high.
He did a rapid rudder turn in this attitude, and exceeded the
rotor discs ability to follow the machines turn.
Massive mast-bump followed by departed rotor blade.
Be careful.

[ferranrosello]

Very good post,Birdy. And one question. If you are sinking at very low speed and too close to the ground to recover by pitching down (that is being in the prohibited area of the height-speed curve), what would you do?

Obviously you are going to crash or to perform a very hard landing... But the question is what to do to minimize damages.

Thanks. Ferran.

[Gyropilot007]

Great post Birdy and good question Ferran. I was thinking the same thing myself!!!

Bob

[Harry_S.]

Spot on, Birdy.


Cheers :)

[birdy]

Excellent point Fergus.
He did a rapid rudder turn in this attitude, and exceeded the
rotor discs ability to follow the machines turn.
But without known the details, that could have been induced [ he stood on the rudder peddle] or it could have been uncommanded [ unaware of a tailslide, the machine suddenly wethercocks into the tailwind. Either way, the result is the same, the rotors cant keep up.
You can do zactly wot Bill did without leaven your rotors behind, but you need to know wot to do with the stick and wen to do it, and the timeing is critical, to save the rotors from such huge pitch demands.
As always, if you insist on exploring this sorta stuff, you need to have a very good picture in your mind of every reaction possable from the machine before you even attempt it. Things can get outa hand very quickly and you dont have time to think it out, And most correct reactions will seem, at the time, to be the rong ones.

Obviously you are going to crash or to perform a very hard landing... But the question is what to do to minimize damages.
Ferran, its a split second decision between two alternitives.
Depending on alota things [ hight, conditions, machines capabilities] Your either too low or your just high enuff.
If your decision is your too low, then you have no alternitave but to mush in under full power, hitn the ground harder than youd ever want to, tail first, and an instant before contact, youll need to chop power to stop anythn else getn outa hand once your down. Bit of luck youll only scare the crap outa yourself, but i think in most cases, depending on the machines configuration, you can expect to land rotor first,[ rotor strike] followed by a roll over and all sundery bends.
But, if you think you still have room, you can [ and i have countless times] simply apply a little side stick.
I know the forum isnt the right place to post this sorta stuff, but you asked, [ and humans be'n human, we will try it] and ill accept no responsability for any bungled attempts.
Obviosly, anyone who flys at HOS AS just off the ground will know their machines capabilities. [ we hope]
I have a 'dead mans zone, its roughly between 20' and 50'. Unless i realy must, ill avoid any HOS type stuff between these hights. At 20' or less, id opt for the mush in, sumthn BTW iv never had to do yet. :) [ seems my judgement is holdn up so far;)]
If im at 50' and the power is full on, the nose is high, rotors slow n sluggish, and the breeze[ if any] im hangn off stops, ill apply a little side stick. Either side, depending on the situation. The machines starts to crab sideways, and gains sum resemblance of AS. If this has arrested the sink, coz usualy if your in dead air, and fly outa it, youll be in better air, [ but not always, sumtimes it gets deader] Ill let the machine wethercock into the side wind and give a little forward stick and stagger out of trouble.
If however, im still sinkn, or the rate has only slowed, then ill apply opposite rudder, to keep the prop thrust pointed down and feed abit more side stick. This will accelerate the crabing and cost abit more alt, but at least ill have sum inertia to play with if im draged all the way down.
Again, iv never gon in like this yet, altho its been very close a few times, its got me out sticky spots countless times, times where a simple push forward would have ment hitn the ground from higher up with more virtical speed, and no rrpm to flair with.

Wether decending or holdn alt between 20 and 50', ill always have a little AS or power in reserve, coz from this range, your go'n to have more virtical speed up if you get caught and elect to mush in, or you dont have room to gain much side AS if you elect to crab outa trouble.

No matter wot results [ mum nature generaly has a big say in it], you gota chop power just before contact. [ and just means inches]
And use the rudder peddles as foot rests. A streight rudder wont cost the machine any energy and will only help if your in trouble.
Power failures in this zone will be handled basicaly the same, only itll be quieter and faster. ;)
Airtime, and heaps of it, is a huge bonus coz the longer you spend in the air, the more your subconsious tunes into it. I have no idea wot im feeln, or see'n, but theres gota be sum cues that tell me which way to go to get better air. After all this time, you wouldnt think i have fluked it every time.
Id like to know more bout wot it is that you tune into over time.

Stick pressure.

Wots your machine's HOS AS?
Its wen it starts to drop with full power on.
Trouble is, in high power to weight machines, its so slow, the ASI wont even register. And it takes alota practice and airtime to 'feel' such low ASs.
Stick pressure is the best indicater of AS/rotor load at min ASs.
As you start shedn AS from cruise, youll need sum backpressure. The machine slows and you gradualy add power and backpressure, to a point.
At a certain AS and power settn, youll notice you dont need to hold the stick back, and as you get slower still, youll need to apply forward pessure on the stick to hold att. This is coz of the machines attitude. The prop thrust is starting to point downwards and take sum of the weight off the rotor, so the trimm spring tension is now too high for the rotor load, and you have to push against it to stop the stick flopn back to the back stop and driven you into a sink, followed by a tailslide.
Iv never taken notice of wen it changes from backpressure to forward pressure, but ill know, without lookn at the ASI or feeln the wind, that wen iv got to push hard on the stick, im getn pretty damn slow.
The higher the power to weight the machine, the more your prop can unload the rotor, and the deeper you can push yourself into the sh1t, so its logical to say, if you want to play round at min ASs, start ina lower performace machine. At least wen you find yourself in the sh1t, it wont be so deep.

Iv found meself in a situation a few times, specialy with this new 100hp 912, that im so slow its hard to push against the spring. It feels like the stick is locked on the back stop.
Makes the adrenilen pump.

Geez, now i got blisters on 2 pinkys. :(

[ferranrosello]

Thanks, Birdy. Good points.

[Resasi]

"The higher the power to weight the machine, the more your prop can unload the rotor, and the deeper you can push yourself into the sh1t, so its logical to say, if you want to play round at min ASs, start ina lower performace machine. At least wen you find yourself in the sh1t, it wont be so deep."

Now there's food for thought. Inexperienced pilot in a powerful machine can get himself into worse trouble than when in a lower power one, when flying low and slow. Been thinking along the lines of going for higher power to weight due to the density alt's at home. Nairobi 5,500'+, factor in temp and the density alt starts getting up there. Some places up-country a lot higher. Good warning.

[EI-GYRO]

Resasi, you dont have to use all your available power.
You could use an arbitrary engine RPM setting instead, and work from
there. Carefully.

[EI-GYRO]

Birdy, In the Bill Dass accident, he was believed to have been attempting
a deliberate rapid pedal-turn. An article about this had appeared shortly before the event.

I guess if he had been backsliding and found rudder control reversal, it would
have to have been at a lower throttle setting and lower nose attitude, so he
would probably have gotten a big fright, but survived.

Is it likely to get rudder reversal at a high throttle setting given that the rudder is in the propwash.? I expect you could on a tractor but not on a
pusher.?

[birdy]

Resasi, you dont have to use all your available power.
Fergus, most of us are human, and the ones with more balls n brains wont wait till theyv got the feel to open the throttle. ;) And a low P/W machines CANT do wot high P/W ones can, ie; get you in power related strife.

An article about this had appeared shortly before the event.
Dont spose youd have a copy of this do you?

Is it likely to get rudder reversal at a high throttle setting given that the rudder is in the propwash.?
Yes, even in a high P/W machine.
Iv been slipn backwards with WOT and nose high. But there are so many variablse to consider. Regular rudder, tall tail, tri tail, theyll all respond differently, and power avalable and settn have different affects, rate of reversed airflow...... , its all go'n to complicate things, thats why its critical you understand wots happen'n, coz theres no blanket ruel. [ cept to avoid it] And no time to think it out while its happen'n.

Theres a certain point, on my ferel where im still puzzled as to wots happen'n.
At a certain power setn and rate of reversed flow, my rudder dose nuthn. ?????
It dosent respond positivly or neg, and the peddles feel like theres no rudder there at all, feels like im pulln cables with no rudder attached, coz the machine dont respond.
IOW, in those perticular spesific conditions, the rudder, no matter wot the deflection, has the same airodynamic pressure on both sides, so it dose nuthn, its in neutral air. Prop blast on one side and reversed flow on the other.

Iv never backslid a tall tail, but id imagine the effects of power off would be the same as regular, but power on, depending on power settn, could remain pos, or it could be neg, depending on how much of the rudder is see'n prop blast and how much is in free air.

As you can see, there can be alota variables on the same machine, in different situations. Then you have different configurations to add to that, and you can open a nasty can of worms if you try to instruct this stuff.

[TomCarlisle]

I went down to Buckeye, AZ a few years ago to get some instruction from Steve McGowan because I wanted to learn to do verticle descents and I didn't want to attempt it in my Dominator without instruction. We went up to 1000' in the Sparrowhawk and Steve showed me the manuver. I then did two or three and then when I did the last one I'll ever try, the machine started sliding backwards. There was no rudder control at all. Steve took over and recovered, but it cost at least 400' (and you would have to ask him how he did it). We then took a nice cross country for a couple of hours and he signed off my BFR. I no longer have the desire to do verticle descents.

[EI-GYRO]

Birdy, Thanks for all that. At the moment, straight and level is as much excitement as I want. But its nice to know the possibilities.

I dont have the article. I believe it was published in the PRA mag, written
by Bill Ortmayer, a gyro instructor.
He had done this maneouvre in his two-seat tandem trainer, which would have had a much slower yaw rate than Bill's single-seater.
I dont think there's much more to it than that.
At first it looked like a rotor failure, but Craig Wall came up
with the real reason.
Only reason I raised it was that if someone got in a nose-up backslide,
and got rudders reversal, they would most likely go to full rudder trying to
correct it, thereby making the yaw rate worse.

[EI-GYRO]

By the way, how about some more onboard videos?.

[Passin' Thru]

Birdy, Thanks for all that. At the moment, straight and level is as much excitement as I want. But its nice to know the possibilities.

I dont have the article. I believe it was published in the PRA mag, written
by Bill Ortmayer, a gyro instructor.
He had done this maneouvre in his two-seat tandem trainer, which would have had a much slower yaw rate than Bill's single-seater.
I dont think there's much more to it than that.
At first it looked like a rotor failure, but Craig Wall came up
with the real reason.
Only reason I raised it was that if someone got in a nose-up backslide,
and got rudders reversal, they would most likely go to full rudder trying to
correct it, thereby making the yaw rate worse.
Here's what Craig Wall had to say about it ... http://yarchive.net/air/helicopter_yaw_accident.html

[birdy]

Thanx for the link Pete.
I gota meet this Craig Wall bloke, he dont f%$# around, and nor he should.
He's spoton in everythn he said, [cept the 1G bit], and i hope sumthn positive came from his post.

Just proves wot i been sayn for ages, just coz youv thousands of hours up and all the rateings you could think of, nun of it means jacsh1t if you dont know the physics.

I dont think there's much more to it than that.
It wouldnt matter wot configuration machine your flyn Fergus, you can still outrun your rotor if your not careful. That clown who published that crap, i wunder how he's sleepn these days?

how about some more onboard videos?.
Soon's sumthn happens out ere worth lookn at. ;)

[EI-GYRO]

One thing about Craig, Birdy, was when he told you something, you knew
you'd been told something. A lot of folks couldnt take that.
I got lots of useful advice from him, which helped me 'calibrate' myself
better to approach self-training in a more analytical and structured way.
So far, so good.
He also succeeded in putting pitch stability top of the list of things
to be fixed. For that alone, we all owe him.

[EI-GYRO]

Bill Ortmayer's two-seat trainer shed a blade while taxying and the remaining
blade struck and killed his student, and mashed Bills hand up badly.
This accident had the positive result of establishing that there was a problem with the type of bolt used on RAF blades. The radius under the head of the
bolt disagreed with that of the hub bar/blade attachment, IIRC.
This might well have claimed many other lives had it not been caught then.
I think in the article he just didnt factor in the more rapid yaw rate of the
single-seater and the further implications of that.

Your mustering videos are probably of much more interest to us than you
may think. The power delivery and timing involved in low-down flight
is interesting and needs to be onboard footage or the sound is
t's out of synch due to distance. Also if the camera is helmet-mounted we can sort of see what you are thinking.

S'alright, I 'wont do this at home', as they say.

[C. Beaty]

Craig was even more loathed for his blasphemy by the RAF Faithful than I.

One year at Bensen Days, one or more of the RAF CFIs, with the assistance of some of their camp followers, decided to give Craig the thrashing he deserved. But cooler heads prevailed.

I think it was Bud and Terry Wells who broke it up. But I only heard it secondhanded; Charley Presnell and I had gone back to the motel by that time.