Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Helicopter crashes at Lumberton airport

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Helicopter crashes at Lumberton airport

Old 16th Sep 2017, 07:18
  #41 (permalink)  
 
Join Date: Jun 2016
Location: Brantisvogan
Posts: 512
Just thinking out loud. A higher ROD would imply more energy is required to maintain RRPM with the engine out vs at idle. At the idle detent you're getting 50-60% Ng which is providing a fair amount of drive to overcome some of the inherent drag and friction in the rotor system/drive train. With no engine you would need to overcome 100% of the forces via autorotation, which would require a higher ROD.
Bell_ringer is offline  
Old 16th Sep 2017, 07:48
  #42 (permalink)  
 
Join Date: Dec 2006
Location: UK and MALTA
Age: 56
Posts: 1,201
Some strange ideas cropping up on this thread. Maybe some clarity would help:

1. Autorotation (AUTO) - The rotors are driven only by the airflow up through the disc.

2. EOL - the thing you do at the bottom of an autorotation. (If the engine is running with zero TQ (typically at idle) it is a"Simulated" EOL.

3. During autorotation, if the engine is producing ZERO Tq, the only friction difference between that and the engine shutdown, is the increased rotational Delta speed of the inner and outer race of the freewheel. Compared to the Autorotational forces acting on the rotor I suggest this difference is inconsiderable. Assuming of course the freewheel is serviceable and the TQ during autos with engine at idle is zero.

4. Having spouted this, I have no idea how a H300 works. Saw one once from about 300 yards.

Sad for this guy but I would say if he planned a deliberate entry into auto, something we all practise a lot in our initial and other training, it's difficult to assume the pilot screwed this bit up. Maybe something else, like seized freewheel, intervened.
DOUBLE BOGEY is offline  
Old 16th Sep 2017, 08:39
  #43 (permalink)  
 
Join Date: Nov 2015
Location: Canada
Posts: 105
Originally Posted by Old Farang View Post
Hmm, I am now too ancient to fly anymore, but I just wonder how some people with correlators, electric fuel shutoff valves, hydraulic controls etc.,
would have managed with older piston machines that had none of them!

Cannot remember which way the H300 engine is mounted, but I do remember that my old Hiller was vertical. As an engineer I cannot agree about "friction" being the cause of a difference in ROD. But there will certainly be some differences in forces because of the gyro effect of an engine between running or stopped. May not be the cause, but it should be considered.
The 300 engine is mounted horizontally to a belt system at the back.
cncpc is offline  
Old 16th Sep 2017, 09:45
  #44 (permalink)  
 
Join Date: Jan 2005
Location: yorkshire uk
Posts: 1,503
TC says ..If you committ to an EOL at the top of the slope, you physically switch the engine off. In an Auto - you don't.
Also "So he apparently opts for an EOL (not an auto as some state - an auto would drive the Nr off the clock and damage the blades
Is this correct ? It appears he believes an auto is done with the engine on . I may be wrong ( again !!) but I thought autorotation was just an aerodynamic state regardless of engine state ? So you can have engine on autorotation or engine off autorotation ....just as 212 said .
Lastly I also thought EOL was relevant just to the pull at the bottom being with engine OFF with no reference to the descent part .
If in idle it is actually a simulated EOL .
Please no TC type of replies ....as I genuinely would like to know if I have had a 35 year misconception!!!
nigelh is offline  
Old 16th Sep 2017, 10:02
  #45 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,475
Many of TC's EOLs, like mine, will have been in a Gazelle where you enter auto and, when sure of making the landing area, retard the throttle to ground idle.

It is an EOL in that there is no assistance possible from the engine, since we were actively discouraged from advancing the throttle again in case of surge or damage to the clutch ( have done it once though to avoid a mid air).

Back to the drag issue - I don't know what sort of freewheel arrangement the 300 has, I assume it has some sort of centrifugal clutch/ramp and roller gizmo that does the job.

With the engine running, but at idle, there is a small rotational speed difference between driving and driven parts so drag will be minimal - with the engine stopped there will maximum speed differential so there must be more friction and drag. Engine ancillaries (pumps, generators, alternators etc) may also contribute to the 'dead load' depending on the layout.

Out of interest, the Brit Mil still do some EOLs on the Squirrel, they call them EOLs in that again the engine is back at idle but the throttle can be quickly opened to save embarrassment.
crab@SAAvn.co.uk is offline  
Old 16th Sep 2017, 10:15
  #46 (permalink)  
 
Join Date: Jan 2005
Location: yorkshire uk
Posts: 1,503
Crab ....Thanks . It would be interesting to get an actual figure on the % extra friction and therefore rod . As I said in the ones I have done I didn't really notice any change . I was slated by TC for saying that an auto with engine in idle is the same as off ...!! By that I just meant there was no connection due to freewheel. I accept I was wrong with regard to some extra friction..ok ?
Now the same man who slammed me for my " oversight " is calling engine ON landings ...engine OFF landings !!!!! Are you certain landing with engine in idle is IDENTICAL to landing with engine OFF ? So how many genuine EOL,s has our resident expert really done ??!!!
If you want to be pedantic and aggressive here you had better make sure you never make a mistake !!
nigelh is offline  
Old 16th Sep 2017, 10:40
  #47 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,475
It would be interesting to get an actual figure on the % extra friction and therefore rod
Nige, I think there are so many variations of transmission across helos that might be difficult - I am also transferring what I know from turbine aircraft across to piston but there may be differences - eg on the R22 with that weird squirrel cage and drive belt arrangement, I have no idea what drag there might be through that system.
crab@SAAvn.co.uk is offline  
Old 17th Sep 2017, 05:00
  #48 (permalink)  
 
Join Date: May 2016
Location: Bangkok
Posts: 106
Originally Posted by [email protected] View Post
Nige, I think there are so many variations of transmission across helos that might be difficult - I am also transferring what I know from turbine aircraft across to piston but there may be differences - eg on the R22 with that weird squirrel cage and drive belt arrangement, I have no idea what drag there might be through that system.
Crab, you appear to be one of the few that know what they are writing about(also double bogey). Please look up the definition of both ''friction" and "drag". If there is any of either when ANY type of freewheel device is activated, then there is a fault with the device.

I do not know about turbines, but with the R22 the squirrel cage sprag clutch most definitely does not have any contact when disengaged. No contact, no friction, no drag. I doubt that any Helicopter would be certified if there was not an approved freewheel device that completely disconnects the power input source from the rotor system.

The poster that has concerns about the MR over speeding when in auto rotation has either not been trained correctly, or has never been in auto rotation! Cheers.

edited to add the following: http://www.rotorandwing.com/2010/02/...a-sprag-thing/
Old Farang is offline  
Old 17th Sep 2017, 06:29
  #49 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,475
Old Farang, I don't claim to be a scientist or an engineer, I am just passing on what was taught to me many years ago by people who were; if it is wrong then so be it.

I know how a freewheel works and I also know they don't always operate perfectly - some friction drag is quite possible if the sprags don't completely disengage.

Perhaps you can come up with an alternative answer as to why some have experienced higher RoD in auto without the engine running compared to with it at idle.
crab@SAAvn.co.uk is offline  
Old 17th Sep 2017, 07:31
  #50 (permalink)  
 
Join Date: May 2016
Location: Bangkok
Posts: 106
Perhaps you can come up with an alternative answer as to why some have experienced higher RoD in auto without the engine running compared to with it at idle.
Well, I did make suggestion in a previous post. But it may depend on what else is still rotating such as the cooling fan or other engine driven attachments rather than driven from the gearbox. I do not know, but would be inclined to think that a turbine may also show a diffence for the same reason, especially a H500 with the engine at an angle.
Better ask Nick Lappos!

Also the orientation of the cylinders in a piston engine. It is too long ago to recall just what the H300 did, but I have more time in an old Hiller, and I just do not remember if there was any difference. The point being here the difference in the engine layout between the two examples. I do know that it was quite easy to stretch the glide in the Hiller, but then the rotor system was more akin to a Huey.

The first R22 that I owned was before the tip weighted blades were introduced, and that required immediate and judicious use of the collective to the extent that it would not have been noticeable either way! Never did one with the engine stopped, just at idle.
Old Farang is offline  
Old 17th Sep 2017, 09:14
  #51 (permalink)  
 
Join Date: Jan 2005
Location: yorkshire uk
Posts: 1,503
TC seems to have gone very quiet since having very strong views on my comment about autos without engine ( EOL) . See below ...

"Nihelh - there you go again egg on face in public talking rubbish, transmitting and then thinking about it afterwards.
You'll never learn will you (well not in all the years you persistently continue to make these silly naiive remarks on a public forum)."

Now it appears that many others here have the same view that there should NOT be a large increase in rod with engine off as against idle . ( I think we all agree there will be some difference due to hydraulic pump still being turned but not enough to put 20% onto RoD ). It now appears that his million EOL,s have been with engine on and not Off as he implied .
Does anyone else have any idea ?? Maybe a member could actually do both , one after the other , and compare ?!!
Ps . Hyd pump still works on 350 in auto I think ....but maybe I'm being naive ...
nigelh is offline  
Old 17th Sep 2017, 10:42
  #52 (permalink)  
 
Join Date: Nov 2008
Location: UK
Age: 61
Posts: 905
Correct me if I'm wrong, but I was under the impression the ROD was controlled by the pitch on the main rotor blades? If the engine is at idle or stopped, surely the rotor blades and weight of the a/c will still determine ROD?
Is someone telling me if the engine stops on the way down during a practice autorotation the ROD suddenly increases? Or because a possible increase in friction on the spragg will slow the rotor rpm thus requiring more down lever which then becomes the reason for increased ROD?
Having said that, slowing the rotor RPM a little during the descent would reduce ROD, no?
chopjock is offline  
Old 17th Sep 2017, 10:43
  #53 (permalink)  
 
Join Date: Jan 2009
Location: Sweden
Age: 52
Posts: 156
Friction in freewheeling unit

The story of high friction in the freewheeling unit can't be true.
Some, low friction yes of course.

Long time, but I still remember the MR continue to turn forever after engine is shut down and you walk away from the 300. It would'nt ever stop. If there was anything more than 'almost no friction' the stopped engine would effectively act as a rotorbrake, and stop the MR.

For twin engine helos with NG-oriented idle, when selecting one engine to idle( the other engine in flight) the free turbine of the idle-ing one would be driven backwards via the freewheeling unit and show a lot higher NF when MR at 100% than when both engines at idle. But it doesnt, on the types i flown. When selecting idle on one, the NF reduces for example to around 70%, when the other engine is selected to idle, and NR decays, it still show the same number until rotor is driven by both eng on idle(a small reduction of nf caused bu the load of the drive line of course).

Was you guys ever shown a freewheeling unit bu the flight engineers in basic traning? Was allowed to turn it both ways? Remember any significant amount of torque when turning it the frewheeling direction? I don't.
AAKEE is online now  
Old 17th Sep 2017, 11:00
  #54 (permalink)  
 
Join Date: Jan 2009
Location: Sweden
Age: 52
Posts: 156
Autorotation with engine(-s) in idle vs flight

Something that Nigelh and Reely340 also mentions and is very inportant:
If you do an autorotation with engines in flight you arent performing a true auto before the nf shows lower rpm/ disconnected to rotor rpm on the two-/threeneedle gauge. Most turbines continue to drive the rotor until somwhere in the 102-105% ng mark. Rotor rpm has to be higher than this, otherwise the engine(-s) still are driving the rotor, very much affecting the rate of descent and glide angle.

In an auto with engine(-s) at idle, the rotor drives itself and the freewheeling unit already put the said drag( but very,very low) on the system.

I fore sure hope tou guys train autos with engines at idle. I did training somewhere where the pilots newer did this. They actually also only did the simulator autos with engines in flight( ). If you ever should be in the need for a real auto I think tou would feel very fooled, seeing a much much higher rate of descent and a lot shorter glide, and efter this tou die :-(
AAKEE is online now  
Old 17th Sep 2017, 11:46
  #55 (permalink)  
 
Join Date: Jun 2013
Location: Thaïland
Age: 62
Posts: 183
When you perform an autorotation, the first thing is: "RPM rotor"... So when you put the pitch down, you "normally " desynchronize RPM/NG UP or DOWN....And so, you check
the freewheel...Better if your RPM rotor are higher than your RPM NG In turbine engine, when you perform an autorotation descent with engine runing but desynchronized ( free wheel runing normally ), and then you put the turbine on idle, i admit you feel a little increase of the rate of descent. What else ,
BOBAKAT is offline  
Old 17th Sep 2017, 12:02
  #56 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,475
I think we have got a bit over the top on this freewheel question - the amount of friction I was suggesting would be very low unless there was some problem with the freewheel disengaging properly.

AAKEE - I agree with what you say about needing an NF/Nr split to be in true auto and maybe this is where the higher RoD issue has come from - it is always difficult on these forums comparing apples with apples without detailed explanations of exact circumstances.

Chopjock, you are correct about the RoD in auto and the only way a freewheel would affect that following an engine failure, would be if the freewheel had not fully disengaged - it can happen.

Out of interest, how many people actually check the functioning of their freewheels on a regular basis - we had specific checks for it on the Sea King but on a single you would need to enter auto and flare to split the Nr from the Nf (or equivalent).
crab@SAAvn.co.uk is offline  
Old 17th Sep 2017, 12:54
  #57 (permalink)  
 
Join Date: Sep 2011
Location: USA
Age: 50
Posts: 221
Originally Posted by [email protected] View Post

Out of interest, how many people actually check the functioning of their freewheels on a regular basis - we had specific checks for it on the Sea King but on a single you would need to enter auto and flare to split the Nr from the Nf (or equivalent).
H300 run up checks include a throttle chop to check disengagement of sprag clutch.
Sir Korsky is offline  
Old 17th Sep 2017, 13:01
  #58 (permalink)  
 
Join Date: Nov 2008
Location: UK
Age: 61
Posts: 905
H300 run up checks include a throttle chop to check disengagement of sprag clutch.
That's good for pistons as a throttle chop splits the needles quickly. Different on a 500 though as the turbine takes a while to wind down and the light inertia blades slow down with it and you don't get much of a split.
chopjock is offline  
Old 17th Sep 2017, 15:03
  #59 (permalink)  
 
Join Date: Apr 2010
Location: Kansas
Age: 33
Posts: 89
Gentleman, your discussion on freewheel drag has truly been entertaining... but it is a waste of time. Rate of descent is a function of density altitude, gross weight, and rotor RPM. anyone who has shut down a helicopter at the end of a flight knows that those blades continue to spin quite freely (as in "freewheeling"). The primary difference in the autorotation with and without the engine running, is the touchdown. With the engine at idle, the helicopter will fly the same down to the touchdown point, but... when you apply the collective and droop the rotor rpm for the landing, it will eventually meet back up with that idling engine. Most of the turbines I fly will idle around 90-92% power turbine speed. Once the rotor slows to that 90% speed, it couples with the idling engine and the droop will be drastically slower(0.5 - 2 seconds) in terms of how long we can cushion that landing. With the engine off, the rotor droop is faster and if you have never attempted this, it will feel as if the aircraft drops much faster during the touchdown since the rotor reaches the stall much faster. My speculation is that this professional entered autorotation and misjudged the approach, Stretched the glide, or got slow and pulled the cushion too early. Either way, the NTSB has video of the incident and I'm sure they will use sound analysis, video analysis, and all GPS data to rebuild exactly what occured.
army_av8r is offline  
Old 17th Sep 2017, 15:30
  #60 (permalink)  
 
Join Date: May 2016
Location: Middle England
Posts: 69
Originally Posted by [email protected] View Post

Out of interest, how many people actually check the functioning of their freewheels on a regular basis - we had specific checks for it on the Sea King but on a single you would need to enter auto and flare to split the Nr from the Nf (or equivalent).
In the R66 it's part of the shutdown checklist. Look for positive split of needles when you pull the fuel.
FlimsyFan is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.