Helideck takeoff with S92A
I will be at the S-92 Filght Ops Group next month, so will bring this topic up, as it will flow naturally from other related topics.
Jim,
could you explain your reasoning that drop down will increase with wind speed? Given that up to 120 ft drop down, the S-92 is deck edge clearance limited in nil wind, I fail to see how for a given RTOM and ambient conditions, a constant nose down pitch attitude will result in greater drop down with increasing wind speed. What the wind speed will do is allow a greater Vtoss to be attained in the same drop down and therefore a greater MTOM, though as Vtoss tends to Vy this advantage will clearly disappear.
In an etreme case where the Vtoss is equal to the wind speed, then I can see that the application of nose down pitch will be unecessary, and will result in height loss that was not required, but I can't see this being greater than the height loss needed to achieve this airspeed in nil wind conditions.
Luckily, as we have no wind, I don't have to worry too much about this......
Jim,
could you explain your reasoning that drop down will increase with wind speed? Given that up to 120 ft drop down, the S-92 is deck edge clearance limited in nil wind, I fail to see how for a given RTOM and ambient conditions, a constant nose down pitch attitude will result in greater drop down with increasing wind speed. What the wind speed will do is allow a greater Vtoss to be attained in the same drop down and therefore a greater MTOM, though as Vtoss tends to Vy this advantage will clearly disappear.
In an etreme case where the Vtoss is equal to the wind speed, then I can see that the application of nose down pitch will be unecessary, and will result in height loss that was not required, but I can't see this being greater than the height loss needed to achieve this airspeed in nil wind conditions.
Luckily, as we have no wind, I don't have to worry too much about this......
Last edited by 212man; 29th Sep 2008 at 14:34.
Hi 212man,
In fact you capture the phenomena in your penultimate sentence.
It is not absolute drop-down but relative drop-down that is the issue; what we found with a given wind speed - say 30 kts (which was the wind in the iteration cycle that we found the effect and modelled extensively) - a pitch attitude application of 20 degrees showed a drop down below the deck (it was about 50ft as I remember it); with a pitch angle of 10 degrees there was no drop down below the deck (although it did drop down to deck level from an RP of 25ft). There was no real effect on deck-edge clearance.
With a nil wind, a pitch attitude of 20 degrees was required to clear the deck; no secondary effect was modelled because deck-edge clearance (of 15ft) was the primary target.
You concentration at the meeting needs to be with the landing procedure (as previously briefed) - that is much more problematical.
Jim
In fact you capture the phenomena in your penultimate sentence.
It is not absolute drop-down but relative drop-down that is the issue; what we found with a given wind speed - say 30 kts (which was the wind in the iteration cycle that we found the effect and modelled extensively) - a pitch attitude application of 20 degrees showed a drop down below the deck (it was about 50ft as I remember it); with a pitch angle of 10 degrees there was no drop down below the deck (although it did drop down to deck level from an RP of 25ft). There was no real effect on deck-edge clearance.
With a nil wind, a pitch attitude of 20 degrees was required to clear the deck; no secondary effect was modelled because deck-edge clearance (of 15ft) was the primary target.
You concentration at the meeting needs to be with the landing procedure (as previously briefed) - that is much more problematical.
Jim
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Looks like JimL has very high knowledge regarding procedures. Appreciate very much that you share that knowledge.
Just a small thing, I see you yesterday replyed to OMP, OEI during helideck takeoff in a way like that was the original question.
The original question was regarding AEO that is possible to misunderstand when reading the RFM.
In the RFM it states very clearly in case of OEI after TDP you schould rotate the aircraft to 20 degrees nose down. In other words 20 degrees below artificial horizon.
But in the RFM it states not so clearly how to rotate (10-20 degrees) during helideck takeoff AEO (from hover attitude/artificial horizon). But thanks to excellent inputs from you Ppruners I now grasp the concept.
ardbeg
Just a small thing, I see you yesterday replyed to OMP, OEI during helideck takeoff in a way like that was the original question.
The original question was regarding AEO that is possible to misunderstand when reading the RFM.
In the RFM it states very clearly in case of OEI after TDP you schould rotate the aircraft to 20 degrees nose down. In other words 20 degrees below artificial horizon.
But in the RFM it states not so clearly how to rotate (10-20 degrees) during helideck takeoff AEO (from hover attitude/artificial horizon). But thanks to excellent inputs from you Ppruners I now grasp the concept.
ardbeg
I have it on very good authority, that the intent in the wording in the RFM is that for AEO operations the figures quoted (10-20 degrees) are a delta, and that for the OEI case (20 degrees) an absolute value.
E.g you are hovering with 5 degrees nose up, on rotation you rotate to 5-15 degrees nose down on the ADI - the actual value dependant on factors such as pax comfort and day/night operations. If the engine fails, you rotate to 20 degrees nose down on the ADI.
20 degrees is a compromise between maximum acceleration to Vtoss and excessive rate of descent.
It is accepted that there may be some ambiguity in the current description and it will be addressed at a future RFM re-write. Hope that clears that up
E.g you are hovering with 5 degrees nose up, on rotation you rotate to 5-15 degrees nose down on the ADI - the actual value dependant on factors such as pax comfort and day/night operations. If the engine fails, you rotate to 20 degrees nose down on the ADI.
20 degrees is a compromise between maximum acceleration to Vtoss and excessive rate of descent.
It is accepted that there may be some ambiguity in the current description and it will be addressed at a future RFM re-write. Hope that clears that up
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Correct RFM!
Thanks
A statement that corresponds to the RFM. A clarification from Sikorsky might be in place. Maybe with the words JimL proposes "through 10-20 degrees".
Also as S. Coyle says "requirement for the FM to be more clear..."
regards
OMP
A statement that corresponds to the RFM. A clarification from Sikorsky might be in place. Maybe with the words JimL proposes "through 10-20 degrees".
Also as S. Coyle says "requirement for the FM to be more clear..."
regards
OMP
