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

Helicopter Glide Ratio

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

Helicopter Glide Ratio

Old 29th Jun 2012, 16:04
  #1 (permalink)  
Thread Starter
 
Join Date: Oct 2007
Location: Far from home, but not far from here
Posts: 49
Helicopter Glide Ratio

Hi all just updated my Sky demon to find they have added a glide safe option. Not really that much help for us as we should know it out the window. But did get me to thinking just what is thaverage glide ratio for a helicopter.

Cheers Chippy
ChippyChop is offline  
Old 29th Jun 2012, 16:23
  #2 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,563
Always less than you think!
crab@SAAvn.co.uk is offline  
Old 29th Jun 2012, 16:28
  #3 (permalink)  
 
Join Date: Nov 2006
Location: UK
Posts: 444
Should be in the POM.

R44 is 4.7:1 on an average day. (4700ft horizontal for every 1000ft vertical.) But depends on airspeed at start of glide....
JimBall is offline  
Old 29th Jun 2012, 16:30
  #4 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,563
It's not gliding - it's falling with style! Apologies to Toy Story
crab@SAAvn.co.uk is offline  
Old 29th Jun 2012, 16:52
  #5 (permalink)  
 
Join Date: Mar 2002
Location: Kings Caple, Ross-on-Wye.orPiccots End. Hertfordshire
Posts: 459
Auto descent

Hi Jim ... are you sure we are right! Heli descent in auto circa 1800 to 2000 fpm so from 1000 feet we hit the ground in circa 35 secs, which at 60 mph auto speed gives a range of around 2500 feet! Sounds mor elike 2.5 to 1. OR where have I gone wrong! DRK
DennisK is offline  
Old 29th Jun 2012, 18:29
  #6 (permalink)  
 
Join Date: Nov 2006
Location: UK
Posts: 444
Well, great DK, I want to bow to you. But the POM for R44 Raven II states 4.7:1.

And, from my experience over the past 9 years flying them, I'd say it's spot on - in average circs. As I intimated, going into a glide from a hover is a different thing - and the ratio shortens.

A 90/90 R44 auto (as taught by the factory on the safety course) gives astonishing results - 90kts at 90% rrpm.
JimBall is offline  
Old 29th Jun 2012, 19:29
  #7 (permalink)  
 
Join Date: Jun 2012
Location: North America
Posts: 20
Quote: A 90/90 R44 auto (as taught by the factory on the safety course) gives astonishing results - 90kts at 90% rrpm.


I would imagine the low-rpm horn would be going off.
OffshoreHeli-Mgr is offline  
Old 29th Jun 2012, 20:12
  #8 (permalink)  
 
Join Date: Mar 2002
Location: Kings Caple, Ross-on-Wye.orPiccots End. Hertfordshire
Posts: 459
Auto range

Hi again Jim ... I spent yesterday at Dunsfold doing nothing more than practice autos (hi speed-low speed and hi & lo rrpm) and must confess that even the humble Hughes 300C at 60 knots into wind seems to make better than my 2.5 to 1 theory. But figs are figs. Anyone out there who can offer something definitive? Dennis K.
DennisK is offline  
Old 30th Jun 2012, 02:04
  #9 (permalink)  
 
Join Date: Jun 2002
Location: Canada
Posts: 67
Rate of descent varies with size/weight too. I remember seeing 3800 fpm on a Vertol!
Corax is offline  
Old 30th Jun 2012, 04:41
  #10 (permalink)  
 
Join Date: Sep 2007
Location: I am not sure where we are, but at least it is getting dark
Posts: 273
R44 ROD in Auto at 60kts is less than 1800fpm. The published figure of 4.7:1 can be achieved when using the max. range configuration (90%RRPM/90kts)
At 90kts (= 9,100ft/min) forward speed, you would get 4.7:1 at a descent rate of just under 2,000fpm.


I would imagine the low-rpm horn would be going off.
Yes. Minimum allowable RRPM in autorotation is 90% though, so you are within limits.

Last edited by lelebebbel; 30th Jun 2012 at 04:45.
lelebebbel is offline  
Old 30th Jun 2012, 14:40
  #11 (permalink)  
 
Join Date: Jan 2001
Location: UK
Age: 66
Posts: 1,368
I wonder whether the R44 may be a rather atypical helicopter, with a low RoD in autorotation.

I haven't flown one for many years, but recall that although the limitations section include a max DA of 14,000ft, there is another "altitude" limitation of 9,000ft agl "as the aircraft would otherwise take more than 5 minutes to land in the event of a fire". I suspect this implies a low RoD (rather than a rapid escalation of a fire in this type). I cannot recall a similar limitation in other types.
Helinut is offline  
Old 30th Jun 2012, 15:19
  #12 (permalink)  
 
Join Date: Jul 2007
Location: within a range of RPG
Age: 45
Posts: 181
in mi-17 speed is 65kt and descent around 2000ft/min, but when you start flare(110-120ft agl), it takes some time and distance to get speed down for touchdown.
zlocko2002 is offline  
Old 9th Jul 2013, 20:30
  #13 (permalink)  
 
Join Date: Feb 2006
Location: Rapunzel's tower
Posts: 458
Rule 5 & alight clear

Just curious, if you were cruising in a single (let's say 80kt?) in slack wind, and suffered engine failure (total), what height agl would you need to be to travel 1nm before impact/hopefully-surviving!?

Last edited by good egg; 9th Jul 2013 at 20:42.
good egg is offline  
Old 9th Jul 2013, 22:47
  #14 (permalink)  

Purveyor of Egg Liqueur to Lucifer
 
Join Date: Nov 2002
Location: Alles über die platz
Posts: 4,615
I think we need a hymn sheet to sing off, how about;
R22 autorotation engine off landing to a power recovery | Helicopter Lessons

Once we’re into wind at 70 knots, we lower the collective lever (with right pedal for yaw), roll the throttle off, and check up on the collective to prevent the rotors overspeeding, and add a touch of aft cyclic to achieve airspeed of 60kts.

So we’re now in a descent at about 1650feet per minute, with the rotor speed needle at 100%, the engine speed needle at idle, the wings level relative to the horizon, in trim, and looking out for drift. It’s quite a stable and manoeuvrable flight condition, as long as we are careful to keep the rotorspeed accurate. So we can put turns in (as in the video here) to shorten our travel over the ground, we can even do a 360 orbit if we have enough height.
60 kts @ 1650'/min sound ok?

1 mile at 60 kts would take 1 minute, then it starts to get complicated
SilsoeSid is offline  
Old 9th Jul 2013, 23:49
  #15 (permalink)  
 
Join Date: Mar 2002
Location: Iceland
Age: 54
Posts: 811
Talk about complicated



Glide ratio for BH206 is 4:1 @ 69kts.

Discussed here: http://www.pprune.org/rotorheads/489...ide-ratio.html

.

Last edited by Aesir; 9th Jul 2013 at 23:59.
Aesir is online now  
Old 10th Jul 2013, 00:32
  #16 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,530
From 1000' you will be on the ground in about 30 seconds, give or take a few. Doesn't leave you much time to enter autorotation, make a mayday call, turn towards a safe spot, hopefully into wind, adjust your glidepath to make that spot, flare and land. About as much time as it took to read that.

You should have a good idea of where your "cone" of landing spots is, under and forward of your machine, and where in the window is the cutoff between making it and being impossible to get there.
Ascend Charlie is offline  
Old 10th Jul 2013, 02:05
  #17 (permalink)  
 
Join Date: Oct 2012
Location: Canada
Age: 48
Posts: 215
A simple answer for the OP: a good rule of thumb is a 4:1 glide ratio in a helicopter (not perfect but close enough). So to glide 1 nm you need 1/4 nm, or roughly 1500', of altitude.

Given the use of terms, like 'impact' and 'hopefully surviving' I assumed you do not fly helicopters. Some glide better, some worse, but the biggest deciding factor will be pilot actions.

Last edited by pilot and apprentice; 10th Jul 2013 at 05:06.
pilot and apprentice is offline  
Old 10th Jul 2013, 04:00
  #18 (permalink)  
 
Join Date: May 2002
Location: "Deplorable but happy as a drunken Monkey!
Age: 71
Posts: 16,431
Glide Ratio.....about equal to a set of streamlined car keys!
SASless is online now  
Old 10th Jul 2013, 04:08
  #19 (permalink)  
 
Join Date: May 2002
Location: Wanaka, NZ
Posts: 2,076
If I had a 20nm over-water crossing and I was flying a 206L without floats I'd always climb to 10,000' thinking if the donk quit half-way I'd be able to make it to one shore or the other (using the best wind option of course). You "should" be able to go 10nm from that height if you bleed the RRRM back and keep the speed up, assisted by any tail wind in your favor.

Last edited by gulliBell; 10th Jul 2013 at 04:09.
gulliBell is offline  
Old 10th Jul 2013, 05:38
  #20 (permalink)  
 
Join Date: Dec 2000
Location: midcoast US
Posts: 154
Helicopter glide ratio

Would that qualify as an oxymoron?
rotorfan is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

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