More Cat "A"
Thread Starter
More Cat "A"
Yet more 76 chat.....
Quicky for all twin drivers.
Scenario: Cat A takeoff. Light weight, thus oddles of power.
Problem: Chart shows that you should apply takeoff power and 5 degrees nosedown.
Therefore; If you apply Max T/O pwr the required attitude may be 15 degrees nose down. To maintain the 5 degrees the only option is to reduce power and that, to my mind, extends the distance required for the proceedure.
Let the games begin and thanks in advance for your thoughts.
Steve
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Hi Steve,
I think the 5 degrees is a figure used to stop pilots from nosing over too far at the initial hover to transition part of the take off. Nosing over too far reduces your ability to get it back up again if you have to abort the takeoff prior to CDP.
"I thought I was wrong once....... but I was mistaken"
I think the 5 degrees is a figure used to stop pilots from nosing over too far at the initial hover to transition part of the take off. Nosing over too far reduces your ability to get it back up again if you have to abort the takeoff prior to CDP.
"I thought I was wrong once....... but I was mistaken"
If very light....the question is more like "Who is looking?". If the thing will hover on one engine....are you really concerned about "Cat A " performance? Also, generally, the profiles have a limitation clause....something along the line of hover power plus a fixed percentage of power not to exceed maximum power or not to exceed that artificial limit of power. That allows you to fly the prescribed Cat A profile irregardless of excess power available.
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I feel that at light weights a 10% Tq margin over hover tq seems to do the trick nicely. It helps when one flies from virtually the same runway everey time, though.
IMO there is little difference in a max AUM cat a and a lighter one as described above.
As long as you can abort within the distance available, why pull all the power and make the pax's life miserable?
IMO there is little difference in a max AUM cat a and a lighter one as described above.
As long as you can abort within the distance available, why pull all the power and make the pax's life miserable?
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flight manual proc's
One thing to remember is that the flight manual procedure(s) are advisory/ reference.
The limitations section are mandatory while other proc's are reference.
I agree, max power= >5 degrees nose down. Therefore I use what is req'd only. 15 degrees nose down( to exaggerate) followed by an engine failure.... that nose is going for the runway, as you know.
The limitations section are mandatory while other proc's are reference.
I agree, max power= >5 degrees nose down. Therefore I use what is req'd only. 15 degrees nose down( to exaggerate) followed by an engine failure.... that nose is going for the runway, as you know.
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It is an interesting question, especially for those types where the profile/procedures says "use max two engine take-off power".
I may well be wrong, but where the helicopter is very light and it is not a tight site I ease up on the power a bit.
I wonder whether certification for newer types has taken this into account. For example, for the EC 135 you are supposed to pull IGE hover power + 10%.
I may well be wrong, but where the helicopter is very light and it is not a tight site I ease up on the power a bit.
I wonder whether certification for newer types has taken this into account. For example, for the EC 135 you are supposed to pull IGE hover power + 10%.
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Steve,
That is a glitch in the procedures, and was created by yours truly. When light, it is actually quite alright to just use 10% increase in torque over hover power, since that is about the excess power you have under the conditions that the Cat A procedure was developed (10,300 pounds, hot day).
It works.
Nick
That is a glitch in the procedures, and was created by yours truly. When light, it is actually quite alright to just use 10% increase in torque over hover power, since that is about the excess power you have under the conditions that the Cat A procedure was developed (10,300 pounds, hot day).
It works.
Nick
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it's just a job!
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Hi Steve!
The principle of Cat A on the 76, is to stay at the 5-10' wheel height 35 KIAS on an A/A+ model and V2 (approx 55 KIAS) on an A++. If you allow the aircraft to climb higher, then fly away, land back is not guaranteed. On the A++, we use hover Q plus 6% and adjust as required to maintain the 5-10' until V2. In our operation assuming a standard 32C at MSL and at least a 2400' takeoff area our CDP is 45KIAS and our V2 is 55KIAS. Keep in mind that with the A++ there are three OEI scenarios instead of two with the A and A+. First we have OEI prior to 35 KIAS, OEI between 35 and 45 KIAS and OEI after CDP. Each scenario depends on the 5-10' wheel height.
In summary, although the procedure is well layed out on the A++, there is nothing wrong with applying the same procedure to the A and A+, that is to say, hover Q plus a margin that will maintain the 5-10' wheel height until rotation.
Hope that helps!
Cheers
OffshoreIgor
PS Craig says Hi.
The principle of Cat A on the 76, is to stay at the 5-10' wheel height 35 KIAS on an A/A+ model and V2 (approx 55 KIAS) on an A++. If you allow the aircraft to climb higher, then fly away, land back is not guaranteed. On the A++, we use hover Q plus 6% and adjust as required to maintain the 5-10' until V2. In our operation assuming a standard 32C at MSL and at least a 2400' takeoff area our CDP is 45KIAS and our V2 is 55KIAS. Keep in mind that with the A++ there are three OEI scenarios instead of two with the A and A+. First we have OEI prior to 35 KIAS, OEI between 35 and 45 KIAS and OEI after CDP. Each scenario depends on the 5-10' wheel height.
In summary, although the procedure is well layed out on the A++, there is nothing wrong with applying the same procedure to the A and A+, that is to say, hover Q plus a margin that will maintain the 5-10' wheel height until rotation.
Hope that helps!
Cheers
OffshoreIgor PS Craig says Hi.
Thread Starter
Thanks to ALL for your input...
The last operation I flew the 76 in used the hover +10% method.
No problems.
Here we have no set figure and is is always a discussion point when one of my trainees goes for a checkride and applies "Takeoff power" and the subsequent 15 degrees nose down. Our op's manual calls for 5 degrees nose down as a limit so it always raises the eyebrows.
Some guys have all been briefed to pull to max takeoff power (100% if available) by other training pilots.
Typically during the recurrent training I do with them, I limit the power to a TQ of 75% (eg..) to simulate a heavier power limited aircraft, so the excess power thing is not a factor. However, during the ride there is no limit imposed, so the guys pull until they reach the first engine limit.
Yesterday, I got into the Flight Safety manual after looking in Ops and aircraft books and looked for a definition of "takeoff power".
The flight safety manual refers to a chart in the performance(?) section which calcuates your max TQ for a Cat A departure based on the OAT, PA etc etc...
Typically if you are a 1000ft AMSL you can expect an 85 to 95% (roughly) TQ limit from temperatures of 20 to 30 degrees celsius.
That is your "Takeoff power".
Nowhere in the books is there an suggested limit for the aircrafts nose down attitude. An engine failure with 10 to 15 degrees nose down, before CDP is something I will try with another training pilot sometime. I think with a reasonable amount of inertia in the airframe, that transitioning into a nose up position should be achieveable considering you only have to get to level with the horizon and have 1200 odd feet of run on landing area ahead. Its a lot easier in practice than in actual thou....
Thanks again to all replies....
Steve76
The last operation I flew the 76 in used the hover +10% method.
No problems.
Here we have no set figure and is is always a discussion point when one of my trainees goes for a checkride and applies "Takeoff power" and the subsequent 15 degrees nose down. Our op's manual calls for 5 degrees nose down as a limit so it always raises the eyebrows.
Some guys have all been briefed to pull to max takeoff power (100% if available) by other training pilots.
Typically during the recurrent training I do with them, I limit the power to a TQ of 75% (eg..) to simulate a heavier power limited aircraft, so the excess power thing is not a factor. However, during the ride there is no limit imposed, so the guys pull until they reach the first engine limit.
Yesterday, I got into the Flight Safety manual after looking in Ops and aircraft books and looked for a definition of "takeoff power".
The flight safety manual refers to a chart in the performance(?) section which calcuates your max TQ for a Cat A departure based on the OAT, PA etc etc...
Typically if you are a 1000ft AMSL you can expect an 85 to 95% (roughly) TQ limit from temperatures of 20 to 30 degrees celsius.
That is your "Takeoff power".
Nowhere in the books is there an suggested limit for the aircrafts nose down attitude. An engine failure with 10 to 15 degrees nose down, before CDP is something I will try with another training pilot sometime. I think with a reasonable amount of inertia in the airframe, that transitioning into a nose up position should be achieveable considering you only have to get to level with the horizon and have 1200 odd feet of run on landing area ahead. Its a lot easier in practice than in actual thou....
Thanks again to all replies....
Steve76
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it's just a job!
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S76Heavy The scenario of an OEI between 35-45 KIAS would require a "quick stop" type manouver ie flair and climb to decrease airsspeed and get back on the normal OEI landing profile, this manouver results in the aircraft at about 30' and 30KIAS then the rest is as per normal 5-10 degrees nose up with a run on landing.
Have a look at the S76 RFM Emergency procedures in Supp 29B, OEI.
Cheers
OffshoreIgor
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OK, Thanks Offshoreigor.
30 degrees nose up, sounds interesting..
To get back to the original topic: how about starting the initial run with 6 to 10% over hover Tq and when the nose comes up for the initial climb, go to T/O power? Would that make a siginificant difference for anybody?
30 degrees nose up, sounds interesting..
To get back to the original topic: how about starting the initial run with 6 to 10% over hover Tq and when the nose comes up for the initial climb, go to T/O power? Would that make a siginificant difference for anybody?
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S76 Heavy,
I wrote the Cat A procedure for the A back in 1978. It was based on the sea level 90 degree F takeoff, where the excess power from hover (about 78% torque) to takeoff power (about 83%) was small. If the conditions allow 100% torque for takeoff, the acceleration and nose down you have to use are too sporty to be comfortable. The use of 5 to 10% above hover power for the early portion of the Cat A takeoff will work, and does not add distance to the procedure.
Nick
I wrote the Cat A procedure for the A back in 1978. It was based on the sea level 90 degree F takeoff, where the excess power from hover (about 78% torque) to takeoff power (about 83%) was small. If the conditions allow 100% torque for takeoff, the acceleration and nose down you have to use are too sporty to be comfortable. The use of 5 to 10% above hover power for the early portion of the Cat A takeoff will work, and does not add distance to the procedure.
Nick
Arent we all getting a bit carried away with numbers? We are beginning to sound like fixed wing dicks.
Surely you fly the cat A profile (speed/height/attitude/Rate of climb/descent) for your scenario rather than blindly pull a power figure and adjust attitude to cope. Flying the profile is what keeps you alive, and the publication of power numbers is to give you a starting point.
As above, the newer types tend to publish a power margin above OGE or IGE so that those anal enough still have a figure to argue over, those who use judgement to suit the given conditions are still permitted to, and finally those who cannot operate without everything spelled out can still fool everyone into believing they can fly.
But it is ALWAYS the profile that gives you the best chance of getting out of jail - so use it.
Surely you fly the cat A profile (speed/height/attitude/Rate of climb/descent) for your scenario rather than blindly pull a power figure and adjust attitude to cope. Flying the profile is what keeps you alive, and the publication of power numbers is to give you a starting point.
As above, the newer types tend to publish a power margin above OGE or IGE so that those anal enough still have a figure to argue over, those who use judgement to suit the given conditions are still permitted to, and finally those who cannot operate without everything spelled out can still fool everyone into believing they can fly.
But it is ALWAYS the profile that gives you the best chance of getting out of jail - so use it.
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I guess one has to ask why you would want to use 100%...??
Not only would you have a "Sporty" take off..........also a deck angle that the passengers would write about.
But from the pilots point of view........you would have to be very quick in the OEI situation, as that good engine is already way up there.......not to mention the nose wheel on the runway as you where trying to get the nose back up...
Not only would you have a "Sporty" take off..........also a deck angle that the passengers would write about.
But from the pilots point of view........you would have to be very quick in the OEI situation, as that good engine is already way up there.......not to mention the nose wheel on the runway as you where trying to get the nose back up...
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Mr Lappos, thanks for the reply. Only 5%Tq margin, I'm glad I never had to suffer the A..
Helmet Fire, sometimes it's just fun to discuss numbers with fellow aviators. Nothing FW about that.
And as you know, the profile is defined by other numbers as well, so whichever way you look at it, it will always be about numbers.
Red Wine, could not agree with you more. But still nice to know how other experienced pilots feel about the subject.
Helmet Fire, sometimes it's just fun to discuss numbers with fellow aviators. Nothing FW about that.
And as you know, the profile is defined by other numbers as well, so whichever way you look at it, it will always be about numbers.
Red Wine, could not agree with you more. But still nice to know how other experienced pilots feel about the subject.
Thread Starter
Xnr,
Only when they get a few homebrews in the belly and then start ringing other hardworking pilots to harass them and remind them that they are home, drinking, eating and watching hockey.
But even then not really a pain in the arse (more like the neck... )
Thanks again MATE.....eh!
Might have some more work for ya soon if ya ask nicely.
Make sure you use the ROTOR Brake!!
Only when they get a few homebrews in the belly and then start ringing other hardworking pilots to harass them and remind them that they are home, drinking, eating and watching hockey.
But even then not really a pain in the arse (more like the neck...
)Thanks again MATE.....eh!
Might have some more work for ya soon if ya ask nicely.
Make sure you use the ROTOR Brake!!
Interesting topic, but it is a bit too late to write much. One point to make is that the accelerate stop distance depicted in the profile is a function of speed at TDP, and not weight ( for all intents and puposes). This means that it is (as said elsewhere) the profile that remains constant, not the absolute power applied. If you are light then you simply apply less power than if heavy. With the same attitudes you should end up at TDP more or less in the same point in space as you would at MTOW using MTOP (or what ever you need for that circumstance).
The weight penalties imposed by lower TDPs (CDPs) on a/c such as the 76 A++ are not a function of the rejected take off space being lower, per se, but of the lower Vtoss that the lower TDP dictates. Obviously lower TDP means lower Vtoss as you have to attain Vtoss within the Cat A requirements, and so (eg) with a 35 kts TDP you can't expect to reach 65 Kts Vtoss before hitting the ground (let alone clearing 35 ft obstacles). You might reach 45 kts though, and this speed with its attendent climb rate dicates the weight, not the distance required to stop.
As an example of the distance vs speed rule, the EC-155 reject distances for varying TDP are the same as the AS332 L-2 for the same speeds, despite the weights being 4,800 kg vs 11,200 kg respectively.
I also agree with the remark about fixating numbers to the extent that the pilot should be able to feel and visualise the procedure by external reference, but only if that is accurate enough to produce the desired figures and therefore meet the required result.
The weight penalties imposed by lower TDPs (CDPs) on a/c such as the 76 A++ are not a function of the rejected take off space being lower, per se, but of the lower Vtoss that the lower TDP dictates. Obviously lower TDP means lower Vtoss as you have to attain Vtoss within the Cat A requirements, and so (eg) with a 35 kts TDP you can't expect to reach 65 Kts Vtoss before hitting the ground (let alone clearing 35 ft obstacles). You might reach 45 kts though, and this speed with its attendent climb rate dicates the weight, not the distance required to stop.
As an example of the distance vs speed rule, the EC-155 reject distances for varying TDP are the same as the AS332 L-2 for the same speeds, despite the weights being 4,800 kg vs 11,200 kg respectively.
I also agree with the remark about fixating numbers to the extent that the pilot should be able to feel and visualise the procedure by external reference, but only if that is accurate enough to produce the desired figures and therefore meet the required result.
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Most fixed wind operators reduce take off thrust to match the aircraft's performance to the field length/ WAT conditions. This is
to achieve longer TBOs for the engines. Works a treat and is an accepted SOP with known thrust decrements applied for each field and set of conditions. Wonder why the helicopter world hasn't come up with a simple reduced thrust reduction for given weights below max CAT A?
to achieve longer TBOs for the engines. Works a treat and is an accepted SOP with known thrust decrements applied for each field and set of conditions. Wonder why the helicopter world hasn't come up with a simple reduced thrust reduction for given weights below max CAT A?