Helicopter Glide Ratio
Joined: Feb 2006
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From: Rapunzel's tower
Given the use of terms, like 'impact' and 'hopefully surviving' I assumed you do not fly helicopters.
Thanks for replies, always good to further one's knowledge
Joined: Jul 2005
Posts: 912
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From: UK
Too complicated for me. I was taught to look out the chin bubble if the engine failed cos that was probably where I would land! Just dumping the collective quick has to be the first priority,not calculating glide ratios.
"Just a pilot"
Joined: May 2001
Posts: 633
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From: Jefferson GA USA
"Glide ratio" is like the EPA mileage on the window sticker
Numbers, based on theory, pulled out of some tests that I won't ever be repeating.
I don't know exact distances or absolute altitude, en route.
"That" field is my next forced landing site, based on the angle of reference observed in performing autorotations, and varies from airframe to airframe. Never thought about that point being 5000 feet across the ground versus 5500 feet, just that it's within the cone (as someone has termed it). Seems to work at all altitudes, except very low and very fast. Gaining altitude makes the area included larger and a wind shifts it downwind.
My experience is that GPS positions lag actual, so distances derived therefrom to known points in a dynamic, non-surveyed situation can be dangerous.
I don't know exact distances or absolute altitude, en route.
"That" field is my next forced landing site, based on the angle of reference observed in performing autorotations, and varies from airframe to airframe. Never thought about that point being 5000 feet across the ground versus 5500 feet, just that it's within the cone (as someone has termed it). Seems to work at all altitudes, except very low and very fast. Gaining altitude makes the area included larger and a wind shifts it downwind.
My experience is that GPS positions lag actual, so distances derived therefrom to known points in a dynamic, non-surveyed situation can be dangerous.
Last edited by Devil 49; 10th July 2013 at 12:31.
Joined: Jan 2009
Aviation Qualifications: ATP+Mil
Posts: 344
Likes: 105
From: Sweden
Glide ratio varies a lot with airspeed and Rotor rpm.
Min allowed NR and max allowed IAS in auto gives the best glide ratio.
Can differ quite much from 'standard' 70kts and 100% NR...
Min allowed NR and max allowed IAS in auto gives the best glide ratio.
Can differ quite much from 'standard' 70kts and 100% NR...
That's Life!!
Joined: Feb 2004
Posts: 396
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From: Out of the sand pit, carving a path through our jungle.
Having come from the Chippie 10, to Culdrose for the 'wings course', the main thing I remember from the famil flight in a Hiller12e was the auto to EOL. I thought 'farkinell' that was quick'!
Eventually got used to that, and on moving to the Whirly 7, (showing a bit of age there!), was amazed at how gentle the auto was, almost enough time to have a ciggie on the way down!
Eventually got used to that, and on moving to the Whirly 7, (showing a bit of age there!), was amazed at how gentle the auto was, almost enough time to have a ciggie on the way down!
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
The glide ratio for an S-76 is about 4.2, at min rate of descent and maybe 4.7 at best glide.
The lowest rate of descent in the glide is driven by the power required to fly at best rate of climb speed, since the engine is no longer the power source, the power is taken from the potential energy of the helicopter - its altitude. Lowest rate of descent is at or close to Vy (best rate of climb) but might read differently on the airspeed indicator due to calibration differences between the steep descent of auto and the steep climb of a max climb rate. In other words, the airspeed might READ differently in auto, but most likely the actual airspeed is the same as a climb.
Similarly, the best angle of descent is close to the best range speed, for the same reason. Best range is where the fuel burned takes you the farthest. If you substitute fuel burned for altitude lost (same thing, really - energy consumed is energy consumed) then best glide is farthest flown for a unit of descent.
The steep glide angle relative to an airplane is due to the basic inefficiency of the rotor as compared to a wing. Most airplanes have a glide ratios of 8 to 12 to 1, and sleek airplanes can be 18:1. Gliders can be impossibly efficient, with 40:1 in the world class ones.
Rotors are less efficient than wings onlu until the winged machine tries to hover, that is.........
The lowest rate of descent in the glide is driven by the power required to fly at best rate of climb speed, since the engine is no longer the power source, the power is taken from the potential energy of the helicopter - its altitude. Lowest rate of descent is at or close to Vy (best rate of climb) but might read differently on the airspeed indicator due to calibration differences between the steep descent of auto and the steep climb of a max climb rate. In other words, the airspeed might READ differently in auto, but most likely the actual airspeed is the same as a climb.
Similarly, the best angle of descent is close to the best range speed, for the same reason. Best range is where the fuel burned takes you the farthest. If you substitute fuel burned for altitude lost (same thing, really - energy consumed is energy consumed) then best glide is farthest flown for a unit of descent.
The steep glide angle relative to an airplane is due to the basic inefficiency of the rotor as compared to a wing. Most airplanes have a glide ratios of 8 to 12 to 1, and sleek airplanes can be 18:1. Gliders can be impossibly efficient, with 40:1 in the world class ones.
Rotors are less efficient than wings onlu until the winged machine tries to hover, that is.........
Last edited by NickLappos; 12th July 2013 at 17:44.
Joined: Aug 2004
Posts: 2,105
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From: Aberdeen
Gliders can be impossibly efficient, with 40:1 in the world class ones.
Joined: May 2002
Aviation Qualifications: ATP+Mil
Posts: 18,633
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From: Downeast
You can't see the surface at 10 miles from 1000' due to the curvature of the earth.
