More Cat "A"
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S76Heavy,
I think the point wasn't clear enough earlier in this thread. The S76 Cat A procedure in the flight manual is based on takeoff at sea level 90 degrees F, where the takeoff power is only about 5 to 10% more than the power to hover at 5 feet. When you fly the procedure as written at that condition, you must pull takeoff power.
The difficulty that sparked this thread is that when you pull takeoff power at standard temperature (59 degrees F) you have about 25% power above hover power. This makes the acceleration to 35 knots very fast if you pull all that power, and the procedure is abrupt and uncomfortable.
If the power used in such conditions is about 10% above hover power, the procedure is easier to fly, yet still meets the flight manual distances.
Nick
I think the point wasn't clear enough earlier in this thread. The S76 Cat A procedure in the flight manual is based on takeoff at sea level 90 degrees F, where the takeoff power is only about 5 to 10% more than the power to hover at 5 feet. When you fly the procedure as written at that condition, you must pull takeoff power.
The difficulty that sparked this thread is that when you pull takeoff power at standard temperature (59 degrees F) you have about 25% power above hover power. This makes the acceleration to 35 knots very fast if you pull all that power, and the procedure is abrupt and uncomfortable.
If the power used in such conditions is about 10% above hover power, the procedure is easier to fly, yet still meets the flight manual distances.
Nick
Thread Starter
Continuing the thread on another tack....
Nick, you said the excess power makes the profile fast and abrupt. How would you train someone to fly the Cat A profile?
My description is to pitch up to 15 degrees nose up at 35kts in a positive and authoritive manner. The intention being to transfer the aircraft into the next phase of flight. Post CDP it is the same thought pattern. Move into the next transition with positive and authoritive action and make your intentions to fly away.
Some pilots consider the technique a tad aggressive but generally acceptable. Through experience I have found dithering, slowness or lack of positive action through the Cat A prevents the proceedure from working correctly to give the desired resultant during the engine failure. The aircraft often balloons or labours to fly away if required.
The query here is how would you describe the pilots actions during the profile.
This is a tough question as I have to display it to guys to get them to understand.
Good luck
Nick, you said the excess power makes the profile fast and abrupt. How would you train someone to fly the Cat A profile?
My description is to pitch up to 15 degrees nose up at 35kts in a positive and authoritive manner. The intention being to transfer the aircraft into the next phase of flight. Post CDP it is the same thought pattern. Move into the next transition with positive and authoritive action and make your intentions to fly away.
Some pilots consider the technique a tad aggressive but generally acceptable. Through experience I have found dithering, slowness or lack of positive action through the Cat A prevents the proceedure from working correctly to give the desired resultant during the engine failure. The aircraft often balloons or labours to fly away if required.
The query here is how would you describe the pilots actions during the profile.
This is a tough question as I have to display it to guys to get them to understand.
Good luck
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Nick,
perhaps I should have been a bit more elaborate in my previous post. I meant to say that applying a set margin over hover tq (as in 10% in the A+) is our equivalent to downrated thrust in an airliner. But it's also infinately more comfortable when the A/C is light.
But I do believe that the flight manual specifies T/O power for Cat A and the graph shows that that is quite often (in our met. conditions anyway) at or close to 100%
So is it safer to fly Hover tq + x% or pull the lot?
And indeed, how do you train a pilot to fly the profile, like Steve76 asks?
Personally, I like 10% margin and swift rotation, but is there a better way?
perhaps I should have been a bit more elaborate in my previous post. I meant to say that applying a set margin over hover tq (as in 10% in the A+) is our equivalent to downrated thrust in an airliner. But it's also infinately more comfortable when the A/C is light.
But I do believe that the flight manual specifies T/O power for Cat A and the graph shows that that is quite often (in our met. conditions anyway) at or close to 100%
So is it safer to fly Hover tq + x% or pull the lot?
And indeed, how do you train a pilot to fly the profile, like Steve76 asks?
Personally, I like 10% margin and swift rotation, but is there a better way?
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Wow! This thread is a testament to the fact that language is not communication! For both S76Heavy and Steve76:
1) On a cold day, the Cat A takeoff works most easily by using about 10% more torque than hover power.
2) Under the limiting (Hot Day) conditions, when the engine power is least, there is only about 5 to 10% excess power (above hover) whilst doing the takeoff. That is where the procedure was designed, and why it is somewhat uncomfortable at colder days where the power is greater.
3) If you pull full takeoff power in cooler conditions, you have to really exercise the machine to follow the written porcedures, because those procedures were written for hot day.
4) If you pull only 10% torque above hover power on a cool day, the procedure works quite well, is comfortable and will meet the flight manual charts for takeoff dostance and rejected takeoff distance
5) You don't need to pull 100% torque for the procedure to work, try a few during the next training flight, just exercise a land back at CDP while having pulled about 10% more than hover power. You should be able to reject and meet your reject distance anyway. You can just reject on two engines, and land with two, to make the practice safer and easier. Just try to observe your torque on touchdown as being in the ball park for OEI power (about 100% single torque at 826 degrees OEI is like 50% twin torque during practice).
6) If you pull only about 10% torque more than hover power, you don't have to horse the aircraft around and pull 15 degrees nose up just to follow the words in the flight manual. At the slower acceleration, you will more easily capture the 35 knot CDP speed without over shooting.
This is a good thread!!
1) On a cold day, the Cat A takeoff works most easily by using about 10% more torque than hover power.
2) Under the limiting (Hot Day) conditions, when the engine power is least, there is only about 5 to 10% excess power (above hover) whilst doing the takeoff. That is where the procedure was designed, and why it is somewhat uncomfortable at colder days where the power is greater.
3) If you pull full takeoff power in cooler conditions, you have to really exercise the machine to follow the written porcedures, because those procedures were written for hot day.
4) If you pull only 10% torque above hover power on a cool day, the procedure works quite well, is comfortable and will meet the flight manual charts for takeoff dostance and rejected takeoff distance
5) You don't need to pull 100% torque for the procedure to work, try a few during the next training flight, just exercise a land back at CDP while having pulled about 10% more than hover power. You should be able to reject and meet your reject distance anyway. You can just reject on two engines, and land with two, to make the practice safer and easier. Just try to observe your torque on touchdown as being in the ball park for OEI power (about 100% single torque at 826 degrees OEI is like 50% twin torque during practice).
6) If you pull only about 10% torque more than hover power, you don't have to horse the aircraft around and pull 15 degrees nose up just to follow the words in the flight manual. At the slower acceleration, you will more easily capture the 35 knot CDP speed without over shooting.
This is a good thread!!
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"Language is not communication"; I agree
But now all the parameters have been explained at length, I think the procedure has become clearer to everybody.
But reading back one of your earlier posts you mention "10% for the early portion of the Cat A procedure".
Can you confirm that once past CDP pulling all available tq is a good idea or do you mean even after rotating nose-up at 35KIAS to reduce the time before CDP?
Pardon me for being dense, it's the shiftwork..
But now all the parameters have been explained at length, I think the procedure has become clearer to everybody.
But reading back one of your earlier posts you mention "10% for the early portion of the Cat A procedure".
Can you confirm that once past CDP pulling all available tq is a good idea or do you mean even after rotating nose-up at 35KIAS to reduce the time before CDP?
Pardon me for being dense, it's the shiftwork..
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S76Heavy,
Yep, pull the moderate power before CDP (when cool conditions make the full takeoff power impractical) then increase to full takeoff power afterward, to climb away from the ground and obstructions quickly.
Try this method on your next training hop, reject at CDP with twin engines and then land back. Note the distance and compare to the charts in the flight manual. Should be quite similar.
Nick
Yep, pull the moderate power before CDP (when cool conditions make the full takeoff power impractical) then increase to full takeoff power afterward, to climb away from the ground and obstructions quickly.
Try this method on your next training hop, reject at CDP with twin engines and then land back. Note the distance and compare to the charts in the flight manual. Should be quite similar.
Nick
It's not just an adventure....
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S76 Heavy
I guess I was not clear in my previous post either. I didn't say 30 degrees nose up, I said a quick stop resulting in about 30 feet altitude and 30 KIAS. A quick stop is defined as any deceleration requiring a nose up attitude in excess of the normal procedures. In the case of the S76 this would be greater than 10 degrees. As Nick pointed out, this will also depend on OAT and A/C weight.
As for the Cat A power required, the S76 RFM Supp 29 B states for Cat A, Hover Q + 6% and Cat B, Hover Q + 10%. As most S76's will require somewhere in the neighborhood of 70-80% Q to Hover IGE, there is no need to adjust power after V2 as you will already be stabilized above 70% which is the accepted minimum climb power for most operators of the S76 or 212.
Just one comment about the A model CAT A profile. Although it may seem a bit agressive to some, it is the the most reasonable trade off of distance available for land back and continued take off. This profile alows a safe land back prior to CDP and in the case of after CDP, (35 KIAS + 55 feet rad alt) a safe continued take off if the Nr is drooped to 96% and VToss (52 KIAS) is maintained. My hat is off to Nick for designing that profile.
I think the bottom line here is to give yourself a loaded deck ie extra power available in the bank incase the preverbial **** hits the rotor.
Cheers
OffshoreIgor
I guess I was not clear in my previous post either. I didn't say 30 degrees nose up, I said a quick stop resulting in about 30 feet altitude and 30 KIAS. A quick stop is defined as any deceleration requiring a nose up attitude in excess of the normal procedures. In the case of the S76 this would be greater than 10 degrees. As Nick pointed out, this will also depend on OAT and A/C weight.
As for the Cat A power required, the S76 RFM Supp 29 B states for Cat A, Hover Q + 6% and Cat B, Hover Q + 10%. As most S76's will require somewhere in the neighborhood of 70-80% Q to Hover IGE, there is no need to adjust power after V2 as you will already be stabilized above 70% which is the accepted minimum climb power for most operators of the S76 or 212.
Just one comment about the A model CAT A profile. Although it may seem a bit agressive to some, it is the the most reasonable trade off of distance available for land back and continued take off. This profile alows a safe land back prior to CDP and in the case of after CDP, (35 KIAS + 55 feet rad alt) a safe continued take off if the Nr is drooped to 96% and VToss (52 KIAS) is maintained. My hat is off to Nick for designing that profile.
I think the bottom line here is to give yourself a loaded deck ie extra power available in the bank incase the preverbial **** hits the rotor.
Cheers
OffshoreIgor
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Offshoreigor, you're absolutely right, I got carried away by my wild imagination.
I suppose the reject is similar to our (A+) group B reject, i.e. bleed off the speed by climbing, then land back on.
As far as the profile is concerned, it's certainly safe but not very comfy for the self loading freight..
I suppose the reject is similar to our (A+) group B reject, i.e. bleed off the speed by climbing, then land back on.
As far as the profile is concerned, it's certainly safe but not very comfy for the self loading freight..
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Seem to remember going along as ballast on a training flight moons ago in an A model 76. Cat A clear area. Accelerate/Stop distance and the surface required was about the same for a Twin Otter with the same payload. Also figured out why the T5 repeaters and the ASI is in a funny place as well. So you can see them on the way down as I think the torquemeter became irrelevant. Training was done at high weights with ballast so no fudge factor involved. Have always wondered about the Canadian operations from decks at sea level with pax. Surely must be Cat B departure and arrival.
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One of the main points about the Category A procedure is repeatability.
That is what drives the numbers and the numbers drive the profile - not the other way around.
The problem is that helicopter pilots are used to only using what is necessary, not like fixed wing pilots who use takeoff power every time.
As Nick says, the procedure is developed for hot, heavy and high as possible, and may need some change for light, low and cool (hey, they all have an 'L' in them).
But just 'flying the profile' is not the answer - the procedure has to be done with the power settings and attitudes to ensure the ability to land safely or fly away to meet Category A.
Otherwise, how is it repeatable?
That is what drives the numbers and the numbers drive the profile - not the other way around.
The problem is that helicopter pilots are used to only using what is necessary, not like fixed wing pilots who use takeoff power every time.
As Nick says, the procedure is developed for hot, heavy and high as possible, and may need some change for light, low and cool (hey, they all have an 'L' in them).
But just 'flying the profile' is not the answer - the procedure has to be done with the power settings and attitudes to ensure the ability to land safely or fly away to meet Category A.
Otherwise, how is it repeatable?
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John, I can't speak for the Canadians, but in the US Gulf it's all Cat B. I've been flying helicopters since 1971, both military & civilian, working on 12,000 hours, & I have never done, nor seen, a single Cat A takeoff.
Thread Starter
Shawn,
You are correct. I think it comes down to attitude mostly. All the power in the world will not help you if your mindset during the proceedure is not focused on moving the aircraft from one phase to the other. It is most dependant on good crew co-ordination to follow the prescribed flight path and stay out of the avoid curve.
As far as Cat A off the platforms. I know that the profile is designed with an reject area ( ie: airfield ) so that dictates that anything offshore is going to be Cat B. Generally you are starting with a 100+ ft of altitude as well.
On another similar issue. I have seen a Vertical profile departure that is not designated a Cat A departure. The takeoff is a climb to 100ft AGL and then a 10 degree nose down attitude to fly away. The initiation of the 10 degrees nose down is considered the committed point and subsequently is termed as 'CDP'
Its my opinion that CDP is Cat A terminology and use of CDP in this profile is incorrect. It is not Cat A so a change is vocab is required.
True or False?
You are correct. I think it comes down to attitude mostly. All the power in the world will not help you if your mindset during the proceedure is not focused on moving the aircraft from one phase to the other. It is most dependant on good crew co-ordination to follow the prescribed flight path and stay out of the avoid curve.
As far as Cat A off the platforms. I know that the profile is designed with an reject area ( ie: airfield ) so that dictates that anything offshore is going to be Cat B. Generally you are starting with a 100+ ft of altitude as well.
On another similar issue. I have seen a Vertical profile departure that is not designated a Cat A departure. The takeoff is a climb to 100ft AGL and then a 10 degree nose down attitude to fly away. The initiation of the 10 degrees nose down is considered the committed point and subsequently is termed as 'CDP'
Its my opinion that CDP is Cat A terminology and use of CDP in this profile is incorrect. It is not Cat A so a change is vocab is required.
True or False?
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False,
CDP terminology is not necessarily a 'CAT A' namesake. It dosen't matter what twin you drive, or in what profile, if you lose a donk prior to a critical point (I will call this the 'Critical Decision Point'
) you do not have an option.... You must (be forced too) reject the take off.
Cheers
CDP terminology is not necessarily a 'CAT A' namesake. It dosen't matter what twin you drive, or in what profile, if you lose a donk prior to a critical point (I will call this the 'Critical Decision Point'
) you do not have an option.... You must (be forced too) reject the take off.Cheers
Last edited by rotorque; 29th Aug 2002 at 13:17.
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GLSNightPilot,
I do vertical takeoffs with accountability in an Agusta 109E Power. Can't call them "Cat A" correctly but "Cat A profile". Cat A after all belongs to FAR Part 29 Transport category helicopters. It will do these profiles up to 3500' DA at gross weight. Of course there are compromises for this performance in other areas.
I do vertical takeoffs with accountability in an Agusta 109E Power. Can't call them "Cat A" correctly but "Cat A profile". Cat A after all belongs to FAR Part 29 Transport category helicopters. It will do these profiles up to 3500' DA at gross weight. Of course there are compromises for this performance in other areas.
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Steve76
Two weeks on vacation and this topic is still hot!!
Good One!
Just wondering. For those pilots that want to pull max pwr, why?
I know the profile has limited dimensions but hover Q + 10% does the job nicely.
If I had an engine failure on take off my first choice is to reject if I can. The way I have seen some of the profiles flown lately it seem like the goal is to fly away.
What about the failure post CDP? I am not that crazy about the nose down attitudes either. We already have an altitude of 40' (55 rad. alt.) minimum. Why give it up? Why dive back at the ground? Maintain your altitude, (a slight decent is acceptable if the airspeed is really low,35 kts), adjust your pwr setting, set the Nr to 96% wait for the increase in airspeed ( its not long really)and the subsequent rate of climb.
Just a few thoughts MATE.
Go Leafs Go!
Two weeks on vacation and this topic is still hot!!
Good One!
Just wondering. For those pilots that want to pull max pwr, why?
I know the profile has limited dimensions but hover Q + 10% does the job nicely.
If I had an engine failure on take off my first choice is to reject if I can. The way I have seen some of the profiles flown lately it seem like the goal is to fly away.
What about the failure post CDP? I am not that crazy about the nose down attitudes either. We already have an altitude of 40' (55 rad. alt.) minimum. Why give it up? Why dive back at the ground? Maintain your altitude, (a slight decent is acceptable if the airspeed is really low,35 kts), adjust your pwr setting, set the Nr to 96% wait for the increase in airspeed ( its not long really)and the subsequent rate of climb.
Just a few thoughts MATE.
Go Leafs Go!
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Of course there are compromises for this performance in other areas.
What's the most you can carry?
When is the latest you can depart?
We take off at max gross most every time, & it's often a struggle to hover, much less do a vertical or Cat A takeoff. We get right at the edge of the heliport, & if it's a 412, hold it steady at a 3' hover until it starts to rise a little, or if a 76, pull 100% TQ & 'ride the bubble' off the heliport, after having verified that we can at least hover. Having the luxury of excess power to do anything else is rare.
Thread Starter
I am still not convinced that 'CDP' is not specifically a Catagory A term. Not trying to say your a dummy Rotorque; but what do others think.
Stan:
Offshore drivers around the globe are nodding their heads in sympathy. Its an unfortunate truth.
Xnr:
My thinking is to get to the better side of the curve. At 35kts and 96% you are really pulling the arse out of the machine and the remaining engine. Closer to 74kts we gain by moving to the bottom of the power required curve and attain advantageous airspeed that can be traded for height (in opposition to gravity) for avoiding obstacles further down the road.
My order of preservation will aways be RRPM, Airspeed and Height in that order. Ya gotta give one to get some of the other, but in the end its the RRPM that will soften the crunch.
Stan:
Offshore drivers around the globe are nodding their heads in sympathy. Its an unfortunate truth.
Xnr:
My thinking is to get to the better side of the curve. At 35kts and 96% you are really pulling the arse out of the machine and the remaining engine. Closer to 74kts we gain by moving to the bottom of the power required curve and attain advantageous airspeed that can be traded for height (in opposition to gravity) for avoiding obstacles further down the road.
My order of preservation will aways be RRPM, Airspeed and Height in that order. Ya gotta give one to get some of the other, but in the end its the RRPM that will soften the crunch.
Last edited by Steve76; 30th Aug 2002 at 02:30.
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Steve76
Are you suggesting that you should trade your 40' (55 rad alt ) for 74 knots?
Keep your altitude , the aircraft will accelerate (if you haven't let it decelerate less than 35 knots in the climb) and if you have calculated your max gross weight for a Cat A procedure. The second you level the nose after CDP the aircraft is already accelerating. Probably in the area of 40 knots +. A dive to gain airspeed is not neccesary.
What kind of obstacle are you trying to clear? Most procedures are designed to clear a 50' obstacle. You already have 40' of that minimum.
BROC is 74 knots at sea level and it does give you your best rate of climb. In that you are correct, but this is for your climb to altitude if you are forced to go enroute OEI, not to clear a 50' obstacle on departure.
Don't get me wrong, I am not suggesting to fly around at 40 knots. Just don't trade the altitude you already have in search of 74. It will come and a positve rate of climb is evident long before that.
If you are facing the CN Tower make a turn.
Just my humble opinion of course.
Cheers Mate
Are you suggesting that you should trade your 40' (55 rad alt ) for 74 knots?
Keep your altitude , the aircraft will accelerate (if you haven't let it decelerate less than 35 knots in the climb) and if you have calculated your max gross weight for a Cat A procedure. The second you level the nose after CDP the aircraft is already accelerating. Probably in the area of 40 knots +. A dive to gain airspeed is not neccesary.
What kind of obstacle are you trying to clear? Most procedures are designed to clear a 50' obstacle. You already have 40' of that minimum.
BROC is 74 knots at sea level and it does give you your best rate of climb. In that you are correct, but this is for your climb to altitude if you are forced to go enroute OEI, not to clear a 50' obstacle on departure.
Don't get me wrong, I am not suggesting to fly around at 40 knots. Just don't trade the altitude you already have in search of 74. It will come and a positve rate of climb is evident long before that.
If you are facing the CN Tower make a turn.
Just my humble opinion of course.
Cheers Mate
Last edited by Xnr; 30th Aug 2002 at 20:22.