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Gliding with a Boeing 737

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Gliding with a Boeing 737

Old 2nd Nov 2008, 18:27
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Gliding with a Boeing 737

Hello everybody,

I've tried some searching around on the web, but not finding answares for my questions. As a glider pilot I'm a bit interested in how the airliners glide etc.

For a Boeing 737-700 with wing lets:
- What is the best L/D ratio?
- What are the best speeds for best L/D at given weights?

Would it be possible to save fuel, descending earlier at a lower speed?
Are there any requirements of how long an typical 737 engine has to run before max power (take-off)?

Sorry if there questions have been asked earlier, I'm new here...

Best regards,
Bluescan
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Old 2nd Nov 2008, 18:37
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I do not have the 737 numbers for you -
xxx
For the 747-200 Classic - we are close to 20:1 ratio.
We could glide some 220 km from FL 360, assuming "no wind".
Typical glide speed would be some 200 KIAS.
I often mention the above to people who say that "jets glide like a brick"...
xxx

Happy contrails
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Old 2nd Nov 2008, 19:02
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jets glide like a brick"...
Its all relative, the first single seater (glider) I flew had a ratio of about 18:1 K-8

The plastic twin seater I lfirst flew in had a ratio of 36:1 Grob 103

As for a metal glider of 74 classic vintage, the Blanik has a ratio of ca. 28:1. On a tangent, it also has forward swept wings...

iX
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Old 2nd Nov 2008, 19:45
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The classic was somewhere cited to be around 1:22, the NG seems to be quite a bit better, its a goddamn gliderplane really, cant slow it or get down fast enough (glides too good), especially if heavy.

Learned to fly on an old Bergfalke 2, then Ka 8, Ka6 and ASW 15, the old stuff Sadly no time anymore to fly gliderplanes (except the NG of course).
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Old 2nd Nov 2008, 21:09
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You should have tried the Grunau Baby, it could even sink in a thermal !
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Old 2nd Nov 2008, 21:27
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Wot about the T31!!
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Old 2nd Nov 2008, 22:36
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Thank you BelArgUSA and Denti!

So, what I see here is that the L/D is quite good, up to 22 on a newer 737. BelArgUSA, you expected the best L/D speed to be quite low. Then I wonder what a realistic speed would be on a 737.

And second question, do the jetengines need to run for x minutes before going full? If you started your engines on the runway, just completing the checklists and then full throttle. How healthy would it be?

-----
We also have a Ka8 in our club, a fun glider to fly, but don't it have a l/d closer to 26-27?
You may watch my gliding videos here
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Old 2nd Nov 2008, 22:42
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About the same amount of healthiness as you waking up from a deep sleep, immediately jumping out of bed and being forced to run a sprint 200m run. How does that sound to you?????
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Old 2nd Nov 2008, 23:01
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As close as damit, rule of thumb -

V2 plus 20 KIAS gives you the best L/D ratio on a 737.

Green dot on the Airbus

Therefore the best glide speed for still air.
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Old 2nd Nov 2008, 23:09
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AOA indicator

Bluescan -
xxx
Best glide speed obviously lower for a 737 than a 747.
I hate to give uneducated numbers, but certainly could be 160-180 KIAS.
Wish airliners had an "angle of attack" indicator. Learjets have one.
With such instrument, you do not even worry about approach speeds.
Heavy or light, fly the attitude...!
xxx

Happy contrails
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Old 3rd Nov 2008, 01:53
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Angle of Attack

My B747-400 has FPV on the PFD. The angle of attack is the difference between aircraft symbol and the FPV (flight path vector).

Likewise, Airbuses with FBW are all FPV equipped.
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Old 3rd Nov 2008, 10:58
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On the classic the glide speed is around 210kn, on the NG it is around 200kn. Also the classic has a higher descent rate, it is close to 1:20; the NG does 1:22; that is the -800 I am talking about.
 
Old 3rd Nov 2008, 10:58
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V2 plus 20 KIAS gives you the best L/D ratio on a 737.
Does that assume you are gliding with flaps down since V2 is usually associated with a take off flap setting. I would have thought that any drag systems would increase the glide angle. For dead stick approaches in the 737 Classic we normally use 210 knots clean to reach vicinity of the airfield then flaps 5 and gear as required to fine tune the approach. This is pure "about yea" guesswork and not based on any specific figures from a manual
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Old 3rd Nov 2008, 11:17
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747 clean would be V2+80 KIAS.
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Old 3rd Nov 2008, 12:40
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737 clean speed is at Vref40 + 70, so perhaps V2 + 40 give or take?

Yipoyan - wouldn't you also have to consider the wing incidence to the fuselage before you can use that method? I'm running on the assumption it's non zero for a 747 else it would eat up a hell of a lot more runway at 400t than it does no?

Last edited by Port Strobe; 3rd Nov 2008 at 15:44.
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Old 3rd Nov 2008, 13:12
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V2 + 20 is a clean speed
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Old 3rd Nov 2008, 15:55
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Do you mean an 'idle power descent' or a 'no-engine glide'? Many of the glide angle figures being quoted are more appropriate at flight idle and the 'real gliding' L/D will be substantially less, I would hazard in the 15-18:1 range.

Normal holding speed is a good point to start but in reality, the speed for best glide (under power) will reduce as the residual thrust increases.
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Old 3rd Nov 2008, 16:06
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V2 on a B737 is not a speed when the AC is in clean configuartion..... +20 you might get when you Take Off with F1 + 20 kts.... could be clean, with F5 + 20kts you are not clean for sure.

Fly safe and land happy

NG
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Old 3rd Nov 2008, 16:52
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Time limit for higher power setting (extract from 737CL AMM):

After the engine start, operate the engine at low idle power
for two minutes minimum before you accelerate the engine above
idle power.
NOTE: Taxi time at or near idle power can be part of the two
minute warmup period.


And some useful doc. for "heavy" gliders...

http://www.casa.gov.au/fsa/2003/jul/22-27.pdf
http://www.wadenelson.com/gimli.html
http://www.rvs.uni-bielefeld.de/publica ... ransat.pdf
http://www.moptc.pt/tempfiles/20060608181643moptc.pdf
http://versa.bmvit.gv.at/uploads/media/ ... 0_2_01.pdf



Last edited by františek dobrota; 3rd Nov 2008 at 17:03.
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Old 3rd Nov 2008, 17:06
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Understood, 'V2 is a speed you fly at with flaps down.'

Ignore the flaps thing, just take the V2 figure the manual gives you at the appropriate weight then completely forget it happens to be called V2.

Then add 20 kts

Then fly that number on the speed dial in the CLEAN CONFIG.

Best L/D occurs at approximately whatever the V2 figure is in Knots plus twenty - (this gives you the 737-300 CLEAN best L/D approximately).

Other jets, configs etc will all be slightly different.
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