View Full Version : Quick Blackhawk question
NGPogue
14th Jul 2008, 22:32
Anyone know why the #4 tail rotor drive shaft (the one in the pylon between the intermediate and tail rotor gearbox) is so much larger in diameter than the other drive shafts?
Regards,
Phil
(Sorry, I'm in a UH-60 maintenance class and these things keep popping up...) ;)
ShyTorque
14th Jul 2008, 23:17
It's been some years since I flew the 'Hawk. Does the intermediate gearbox reduce the rpm? If so, you need a larger diameter / stronger shaft to withstand the increased Tq.
maxeemum
14th Jul 2008, 23:17
The drive shaft component is one that was previously manufactured for the CH-53 Super Stallion. Because the part was already available, ready to go and a known quantity, Sikorsky popped it onto the Black Hawk and it has stayed there ever since.
:)
Max
not the same as a 53 shaft.
Blackhawk9
15th Jul 2008, 03:47
Maybe the reason as Shytorque said input to IGB 4116 rpm output from IGB 3319rpm and ive seen the IGB to TGB shaft larger on other Helos too just can't think which.
(found my S-70 course notes from 1987!!! I do collect junk!)
Dan Reno
15th Jul 2008, 08:32
Army studies of VN era gun fire hits always showed most rounds hitting aft and mostly in the pylon. (Guess there weren't many NVA duck hunters back then). To lower the threat, ballistic tolerance in the tail was increased by the use of a larger diameter DS between the IGB and TB.
S70IP
15th Jul 2008, 10:42
Mxeemum is correct. CH 53 part.
Blackhawk9
15th Jul 2008, 11:51
If it is a 53 part thats new to me , but i don't remember any part numbers on the shaft starting with 65.... or 80.... (S-65 and S-80 's) .
Most part numbers start with the Sikorsky number of the first aircraft that part was fitted to 61...,70...,76...,92... etc
Jack Carson
15th Jul 2008, 16:26
Torque is a function of shaft speed (rpm) and horse power required. Decreasing the shaft speed from 4166 rpm to 3319 would increase the torque that the shaft would experience by 18%. I don’t know the specifics of the dimensions for the upper shaft but I would expect its diameter to be approximately 18% greater that the forward shafts. Form my experience at Sikorsky, I do not remember the Hawk line sharing any parts with the Super Stallions.
ShyTorque
15th Jul 2008, 16:40
Thankyou, Jack. I was beginning to think the laws of physics were different over on that side of the Atlantic.
Jack Carson
15th Jul 2008, 17:55
It is pretty simple. You just need to watch the water, after you flush, to see which way it turns.:)
Dan Reno
15th Jul 2008, 21:13
SA instructor Glenn Magoon (sic) taught a lot of aircrew my version of that DS. Those SA instructors were usualy in the back pocket of the engineers when prepping for a course. Another myth shattered! RIP Glenn.
ShyTorque
15th Jul 2008, 21:27
You got flushing toilets as well as Blackhawk! What more could a man ask for?
;)
NGPogue
15th Jul 2008, 22:27
Looking at the parts breakdown the drive has a 70 series part number. I guess I'll have to measure them tomorrow - the section I through III shafts look to be about 4" in diameter and the section 4 is about 6".
Thanks, all!
Regards,
Phil