Ag Flying - PT6 Operation
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From that I would say there isn't a whole lot we can do about our PT6's going into beta or reverse all by themselves. None of those guys were selecting beta/reverse in flight.
Get what you want out of it. Better yet, contact the mechanic who wrote it, if he's still there, and see what he thinks.
Takeoff always requires more distance than landing, assuming proper speeds are used. Certainly a loaded takeoff. If you can takeoff loaded from a runway, you can certainly land back on it. If you were able to get off that short one way strip, you can certainly land, reverse or not.
Never land on something that you can't stop on without the reverse. Use it if you need it, of course...but a basic principle of airmanship is always having a second plan, always leaving yourself an out. If you're flying in and out of a location that absolutely must have reverse to stop, one has to question how you took off there with a load, and what you're going to do if that reverse fails. And if a go-around is such a critical issue, and you're going to try it from beta...flight idle isn't helping your case at all.
You decide. I find the idea that the prime reason several posters cling to the need for flight idle is because the aviation authority in their area found fault with operators who used ground idle to be a very interesting counterpoint...to the fact that the same operators use beta in flight contrary to every publication, instruction, and wisdom from manufacturers, government, and any reliable source on turboprop operation information you're going to find. On the one had they do something because they don't want to displease the government and act contrary to official data (might get into trouble if there's an accident...), and on the other they completely ignore it anyway. This just doesn't make sense to me. Clearly it's a matter of "we're going to do whatever we're going to do, no matter what."
If the power is retarded to flight idle on approach with the fuel controller set to ground idle, far less residual thrust exists crossing the fence to land. Without consideration for reverse or braking, you're not going as far down the runway.
If the power is retarded to flight idle on approach with the fuel controller set to flight idle, more residual thrust exists crossing the fence to land. Without consideration for reverse or braking, you're going farther down the runway.
Add braking. If the power is retarded to flight idle on If the power is retarded to flight idle on approach with the fuel controller set to ground idle, far less residual thrust exists crossing the fence to land, and the brakes do less work slowing the airplane, you use less landing distance.
If the power is retarded to flight idle on approach with the fuel controller set to flight idle, more residual thrust exists crossing the fence to land, the brakes do more work, get hotter, and experience more wear.
You add reverse to the equation. With ground idle fuel control setting you get slower response to reverse, and generally less reverse. with the fuel control set to flight idle, you get faster response, and greater Ng, resulting in greater reverse thrust.
A case of use it where you need it, and certainly an operator option. In other words, your choice.
Beta range in flight is not your choice. You can do it, but then there's a lot of things you can do that are unwise...nobody will say a word until they sweep you up.
The question then arises...is max reverse necessary? Are you applying this with the tail still in the air, or getting it on the ground where you have some tailwheen authority before you bring in the reverse? My guess is that most who are using a lot of reverse are doing it as the airplane touches down and are doing so on the mains, only. That can work a hundred or a thousand times...but sooner or later a brake will grab, or a brake will fail, and then you're going for a ride. I watched a thrush get destroyed that way once. I lost my hydraulics this summer...had I tried reversing when that happened with the tail off the ground, I'd have gone for a ride, too.
Do what you feel is best, when you need it, of course. But never assume that because we do the same thing every day that it must be okay because it's never hurt us, or that we're immune from it biting us. We aren't. Complacency kills.
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After 30,000 Beta landings in well maintained aircraft with no problems I feel the technique I was taught was safe and effective.
I agree, constant vigilance is the key to a long, successful career in AG.
I agree, constant vigilance is the key to a long, successful career in AG.
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Hi,
I am flying a Cresco's and have had some similar questions, regarding PT6, below was the response from the Pratt Instructor, which proved a number of thing i was taught to be BS.
Here is another question, if you start the PT6 with the Power Level full forward ( max power ), will it be a normal temp start, i.e. is the FCU still able to schedule in such a way ?, from start to full flame. ( I can not see why )
Reply from P&W, enjoy:
Q: Why does the Compressor have Axial stages, then, one Centrifugal Stage prior to the combustion chamber ?, what is the purpose of the Centrifugal stage ( why not Axial ) ?.
A : To achieve the requested ration of 7:1 we would need too many axial stages which are less efficient at lower speed . The total ratio of the 3 axial stages is 1.80:1 and the centrifugal is 3.9:1 . The centrifugal is more efficient at higher speed . I guess the engineers in 1958 have found the best mix of axial/centrifugal .The purpose of the centrifugal stage is to accelerate the compressed air ( by the axial stages ) then the diffuser ducts reduces it to increase the pressure prior to combustion .
Q: Will a Centrifugal Compressor be able to tolerate smalll excursions of airflow in the Super-Sonic region ?, ( airflow then passes into divergent duct, and could become sub sonic prior to combustion ) ?.
A : Yes , it is designed for that . The air is travelling at 2000 ft/sec at the inlet of the diffuser ducts and at 200 ft/sec at the exit thus
increasing the pressure prior to combustion .
( note to self, speed of sounds is around 1,100ft/sec at sea level )
Q: Beta / Reverse Operation in Flight, my understanding is that this is forbidden, Why ? ( aircraft such as the Pilatus Porter are used in Parachute operations all over the world, Beta / Reverse is used very much common place in descent ).
A : I don't see anywhere that this is forbidden . You are right , parachute designed aircraft have to go back down fast after jumpers are out and they are using flat pitch to slow down the aircraft during descent or agricultural operators are also using a lot of beta /reverse . This info could be found in POH ( pilot handbook or Airframe manuals ) because the are airframe matters , not engine matters . You are not damaging the engine
at all if you go reverse in flight . It's a question of rigging which is
determined by the OEM ( depending on the mission of the aircraft) . Some people adjust the beta/reverse tighter than others . Of course charters are adjusted smoother .
I hope this answers your questions . Feel free to contact me if you have
any other concerns .
Regards
Bruno Bourdages
PT6 instructor
Pratt & Whitney Canada
phone : (450)468-7881
fax : (450)468-7834
e-mail : [email protected]
I am flying a Cresco's and have had some similar questions, regarding PT6, below was the response from the Pratt Instructor, which proved a number of thing i was taught to be BS.
Here is another question, if you start the PT6 with the Power Level full forward ( max power ), will it be a normal temp start, i.e. is the FCU still able to schedule in such a way ?, from start to full flame. ( I can not see why )
Reply from P&W, enjoy:
Q: Why does the Compressor have Axial stages, then, one Centrifugal Stage prior to the combustion chamber ?, what is the purpose of the Centrifugal stage ( why not Axial ) ?.
A : To achieve the requested ration of 7:1 we would need too many axial stages which are less efficient at lower speed . The total ratio of the 3 axial stages is 1.80:1 and the centrifugal is 3.9:1 . The centrifugal is more efficient at higher speed . I guess the engineers in 1958 have found the best mix of axial/centrifugal .The purpose of the centrifugal stage is to accelerate the compressed air ( by the axial stages ) then the diffuser ducts reduces it to increase the pressure prior to combustion .
Q: Will a Centrifugal Compressor be able to tolerate smalll excursions of airflow in the Super-Sonic region ?, ( airflow then passes into divergent duct, and could become sub sonic prior to combustion ) ?.
A : Yes , it is designed for that . The air is travelling at 2000 ft/sec at the inlet of the diffuser ducts and at 200 ft/sec at the exit thus
increasing the pressure prior to combustion .
( note to self, speed of sounds is around 1,100ft/sec at sea level )
Q: Beta / Reverse Operation in Flight, my understanding is that this is forbidden, Why ? ( aircraft such as the Pilatus Porter are used in Parachute operations all over the world, Beta / Reverse is used very much common place in descent ).
A : I don't see anywhere that this is forbidden . You are right , parachute designed aircraft have to go back down fast after jumpers are out and they are using flat pitch to slow down the aircraft during descent or agricultural operators are also using a lot of beta /reverse . This info could be found in POH ( pilot handbook or Airframe manuals ) because the are airframe matters , not engine matters . You are not damaging the engine
at all if you go reverse in flight . It's a question of rigging which is
determined by the OEM ( depending on the mission of the aircraft) . Some people adjust the beta/reverse tighter than others . Of course charters are adjusted smoother .
I hope this answers your questions . Feel free to contact me if you have
any other concerns .
Regards
Bruno Bourdages
PT6 instructor
Pratt & Whitney Canada
phone : (450)468-7881
fax : (450)468-7834
e-mail : [email protected]
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An interesting response Left Handed rock Thrower! A word from the horses mouth so to speak.
I've been thinking about SNS Guppys reasons for not using Flight Idle, Beta and reverse a fair bit during the last week and because I've been flying a 402 during that time have had plenty of opportunity to try the different techniques. (Except wheeler landings.)
If the big danger is that the prop won't come back out of beta I don't see that as a concern the way most of us use it. Beta is used to select a thrust setting that gives the required approach speed and rate of descent particularly on late finals and to eliminate float following the flare. Most of the time the power lever is just coming progressively back until we're landed and slowed to a normal taxi speed. In a controlled approach, once the power lever comes back through the gate there's no reason to let it forward. Used this way, you wouldn't even know you'd had a failure until you couldn't make power to taxi to the pad.
I will however rethink my practice of deep reverse descents from high altitude ferries in future.
I've been thinking about SNS Guppys reasons for not using Flight Idle, Beta and reverse a fair bit during the last week and because I've been flying a 402 during that time have had plenty of opportunity to try the different techniques. (Except wheeler landings.)
If the big danger is that the prop won't come back out of beta I don't see that as a concern the way most of us use it. Beta is used to select a thrust setting that gives the required approach speed and rate of descent particularly on late finals and to eliminate float following the flare. Most of the time the power lever is just coming progressively back until we're landed and slowed to a normal taxi speed. In a controlled approach, once the power lever comes back through the gate there's no reason to let it forward. Used this way, you wouldn't even know you'd had a failure until you couldn't make power to taxi to the pad.
I will however rethink my practice of deep reverse descents from high altitude ferries in future.
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Well Guppy this has all been very very interesting. NOT.
I suspect you know your PT6 machanics pretty well, but I also suspect that your PT6 ag time is relatively low or at least narrow.
Page after page of verbal dribble. Believe me if all these beautiful Aussie AG pilots were pulling fistfulls of reverse as the mains touch down, there wouldn't be a turbine ag aeroplane left down under. So I suspect that you suspect wrong.
Most of the guys down here would do more ag landings in a year than you guys up there would do in a decade. So maybe you should just tread softly softly and just listen, sssssshhh.
Pretty much everything you have said not to do we have been doing very well for a long long time old son.
Actually I was at a clearing sale the other day and I purchased an old pair of wire strainers pretty cheeply with you in mind. PM me with your mail details and I'll post them over. Your going to need them as soon as you get away from those big long flat strips you must work off.
Happy fencing AgwaGGon.
I suspect you know your PT6 machanics pretty well, but I also suspect that your PT6 ag time is relatively low or at least narrow.
Page after page of verbal dribble. Believe me if all these beautiful Aussie AG pilots were pulling fistfulls of reverse as the mains touch down, there wouldn't be a turbine ag aeroplane left down under. So I suspect that you suspect wrong.
Most of the guys down here would do more ag landings in a year than you guys up there would do in a decade. So maybe you should just tread softly softly and just listen, sssssshhh.
Pretty much everything you have said not to do we have been doing very well for a long long time old son.
Actually I was at a clearing sale the other day and I purchased an old pair of wire strainers pretty cheeply with you in mind. PM me with your mail details and I'll post them over. Your going to need them as soon as you get away from those big long flat strips you must work off.
Happy fencing AgwaGGon.
Grandpa Aerotart
Hmm...in PNG we were taught 'Beta approachs' during our Twotter endorsement...and then told 'don't play with it'...which of course we all heeded
They were done in the Porters too..which had identical -20 or -27 PT6s.
Not only were we descending in beta but full blown reverse...as far into the reverse range as we could get it...flaps 20, full reverse and descend it 80kts virtually straight down and all the way to touchdown...was a lot of fun...not sure I would do it nowadays
Interestingly the series 200 Twotters with the -20 PT6 and skinny props did a MUCH better beta approach than the more powerfull -27 or -34 powered 300s with the paddle bladed props...never worked that out.
It was never an issue of damaging the engine/gearboxes and control was still wonderfull (I used to delight in doing multiple aileron rolls going straight down) but they stopped teaching them when the CP scared himself rigid when he thought he had an engine that wouldn't come out...the big bang he heard was actually just the tailstand crashing around the rear baggage compartment and both engines reacted normally..when his shaking hands finally applied enough pressure on the thrust levers to move them forward out of reverse....and of course those of us already doing them from time to time for 'currency' stopped doing them immediately
Chuck.
They were done in the Porters too..which had identical -20 or -27 PT6s.Not only were we descending in beta but full blown reverse...as far into the reverse range as we could get it...flaps 20, full reverse and descend it 80kts virtually straight down and all the way to touchdown...was a lot of fun...not sure I would do it nowadays
Interestingly the series 200 Twotters with the -20 PT6 and skinny props did a MUCH better beta approach than the more powerfull -27 or -34 powered 300s with the paddle bladed props...never worked that out.
It was never an issue of damaging the engine/gearboxes and control was still wonderfull (I used to delight in doing multiple aileron rolls going straight down) but they stopped teaching them when the CP scared himself rigid when he thought he had an engine that wouldn't come out...the big bang he heard was actually just the tailstand crashing around the rear baggage compartment and both engines reacted normally..when his shaking hands finally applied enough pressure on the thrust levers to move them forward out of reverse....and of course those of us already doing them from time to time for 'currency' stopped doing them immediately
Chuck.
Grandpa Aerotart
I don't reckon ag pilots are crazy.....
Oh and standard landing technique at short strips in the Twotter included selecting reverse a foot or two above the ground...it became so ingrained that you would get mildly chipped for it on 6 mthly checks when you did it on 10000' of blacktop
Not once in many, MANY thousands of landings did I ever get even a hint of assymetry...she slid into reverse, already spooled up because you just cocked your wrist and went straight from 8 odd PSI in forward to something similar in reverse in one fluid motion...the high thrust lines of the Twotter gave you a gentle pitch up and the big low pressure tyres rumbled onto the grass effortlessly.
Just about as horny a feeling as three pointing a Tiger Moth on grass....you could even have the big window open clear down below your left elbow for the open cockpit feeling.
Genuinely better than sex!!!
Chuckles.
Oh and standard landing technique at short strips in the Twotter included selecting reverse a foot or two above the ground...it became so ingrained that you would get mildly chipped for it on 6 mthly checks when you did it on 10000' of blacktop
Not once in many, MANY thousands of landings did I ever get even a hint of assymetry...she slid into reverse, already spooled up because you just cocked your wrist and went straight from 8 odd PSI in forward to something similar in reverse in one fluid motion...the high thrust lines of the Twotter gave you a gentle pitch up and the big low pressure tyres rumbled onto the grass effortlessly.
Just about as horny a feeling as three pointing a Tiger Moth on grass....you could even have the big window open clear down below your left elbow for the open cockpit feeling.
Genuinely better than sex!!!
Chuckles.
Last edited by Chimbu chuckles; 1st Nov 2005 at 13:23.
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Cheeky is probably the right word for it agwagon, but up here we're not nearly so polite.
My PT6 time is fairly broad. It's not the in the air tractor, but it also extends to a lot of aircraft outside Ag as well as in, both single and multi engine. And to having been a Director of Maintenance twice, as well as an inspector and mechanic. As for long broad flat strips...almost all my flight experience has been in VERY mountainous terrain, and seldom on long strips...thanks for commenting, however.
Getting back to the question I asked before...what do the manufacturers say? Not verbal drivel...nothing thus far introduced has been less than fact, so lets stick to that basis, shall we?
We have someone introducing an informal comment by a pratt rep regarding the company....how about the prop manufacturer and the airframe manufacturer...how does Air Tractor feel about coming over the gate in flight?
My PT6 time is fairly broad. It's not the in the air tractor, but it also extends to a lot of aircraft outside Ag as well as in, both single and multi engine. And to having been a Director of Maintenance twice, as well as an inspector and mechanic. As for long broad flat strips...almost all my flight experience has been in VERY mountainous terrain, and seldom on long strips...thanks for commenting, however.
Getting back to the question I asked before...what do the manufacturers say? Not verbal drivel...nothing thus far introduced has been less than fact, so lets stick to that basis, shall we?
We have someone introducing an informal comment by a pratt rep regarding the company....how about the prop manufacturer and the airframe manufacturer...how does Air Tractor feel about coming over the gate in flight?
