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Older Style 707 And 737 Engines  
User currently offlineHermansCVR580 From United States of America, joined Jul 1999, 510 posts, RR: 1
Posted (1 year 12 months 3 days 16 hours ago) and read 6748 times:

If you look at the front outer areas on the engines on 707 and older 737-200's they have what appear to be openings on the out side of the engines. What are they for? Can they be adjusted during flight?

Older 737-200
http://www.airliners.net/photo/Aer-L...d=622b9d5c895be3dc4df43b403d688aab

Newer 737-200
http://www.airliners.net/photo/Expre...d=c769f095bede66487a9c1a45be584520


The right decision at the wrong time, is still a wrong decision. "Hal Carr"
30 replies: All unread, showing first 25:
 
User currently offlineAF1624 From France, joined Jul 2006, 665 posts, RR: 0
Reply 1, posted (1 year 12 months 3 days 14 hours ago) and read 6698 times:

This is adjusted in flight simply my moving the throttle levers to a higher power setting. These doors open so that, basically, more air gets sucked in.

I'm sure someone will come up with a detailed explanation but that's the basics.

[Edited 2012-12-26 08:07:19]


Cheers
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (1 year 12 months 3 days 11 hours ago) and read 6558 times:

Quoting HermansCVR580 (Thread starter):
What are they for?

They're called blow-in doors. They allow more air into the inlet at low airspeed and high power. Old inlets didn't work well at low speed (low ram pressure) so they had auxiliary doors to let more air in when inlet pressure drops below ambient.

Quoting HermansCVR580 (Thread starter):
Can they be adjusted during flight?

Not directly. They're sprung doors and just respond to pressure changes across the inlet wall. They close up on their own when inlet pressure gets high enough (appropriate relationship of airspeed and engine thrust).

Tom.


User currently offlineHermansCVR580 From United States of America, joined Jul 1999, 510 posts, RR: 1
Reply 3, posted (1 year 12 months 3 days 11 hours ago) and read 6526 times:

Very interesting, see I learn something new everyday.

So for example on the 737's some of the same planes that had these blow in doors in earlier pictures, then years later the exact same place no longer has them on the engine. Was the aircraft re-engined even though its still the older style straight pipe Pratts?



The right decision at the wrong time, is still a wrong decision. "Hal Carr"
User currently offlinetimz From United States of America, joined Sep 1999, 6903 posts, RR: 7
Reply 4, posted (1 year 12 months 3 days 10 hours ago) and read 6516 times:

Some early 747s had them too-- for some reason they could meet noise rules better without the blow-in doors and later 747s didn't have them. Maybe 737s were quieter without them too?

(Don't call 737 JT8Ds "straight-pipe"-- bypass ratio was around 1.)


User currently offlineSpacepope From Vatican City, joined Dec 1999, 2989 posts, RR: 1
Reply 5, posted (1 year 12 months 3 days 10 hours ago) and read 6510 times:

Quoting HermansCVR580 (Thread starter):
f you look at the front outer areas on the engines on 707 and older 737-200's they have what appear to be openings on the out side of the engines. What are they for? Can they be adjusted during flight?

They were also present on early 747s.


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User currently offlinedlednicer From United States of America, joined May 2005, 547 posts, RR: 6
Reply 6, posted (1 year 12 months 3 days 10 hours ago) and read 6471 times:
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Blow-in (or more properly, suck-in) doors were also used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage), Dassault Mirages (side of inlets), IAI Kfirs (side of inlets), Sukhoi Su-22s (side of inlet), Su-27s (bottom of inlets), later model MiG-21s (side of fuselage ahead of wing), Mikoyan-Gurevich MiG-29s (top of inlets), Lockheed F-117s (top of inlets), General Dynamics F-111s (side of inlets) and many other military aircraft.
:

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User currently offlineDL_Mech From United States of America, joined Feb 2000, 1992 posts, RR: 9
Reply 7, posted (1 year 12 months 3 days 4 hours ago) and read 6288 times:

Here are the "sucker" doors in action:

http://www.youtube.com/watch?v=Sf3mo3QROC8



This plane is built to withstand anything... except a bad pilot.
User currently offlineViscount724 From Switzerland, joined Oct 2006, 26021 posts, RR: 22
Reply 8, posted (1 year 12 months 3 days 3 hours ago) and read 6271 times:

More discussion of the "blow-in doors" in this 2007 thread.
737-200 Engine Modifications (by CTRL_ALT_DEL Jun 25 2007 in Tech Ops)


User currently offlineamccann From United States of America, joined Mar 2008, 175 posts, RR: 0
Reply 9, posted (1 year 12 months 3 days 2 hours ago) and read 6242 times:

Quoting dlednicer (Reply 6):
Mikoyan-Gurevich MiG-29s (top of inlets)

I'm not positive, but I believe the inlets on the leading edge upper surface of the Mig 29 are auxiliary inlets used when the main inlets are closed to prevent the "injection" of FOD from the main inlets.


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What one person receives without working for, another person must work for without receiving. - Ronald Reagan
User currently offlinerwessel From United States of America, joined Jan 2007, 2416 posts, RR: 2
Reply 10, posted (1 year 12 months 3 days ago) and read 6188 times:
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SR-71 too.


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User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 11, posted (1 year 12 months 2 days 19 hours ago) and read 6112 times:

Quoting Viscount724 (Reply 8):

Thats a real oldie thread......

Auxiliary inlet doors were fitted to early JT8D's around the nose cowl. These were spring loaded and opened automatically whenever the pressure differential between inlet and external static pressures was high, ie slow speed, high thrust conditions (takeoff) to give additional engine air and closed again as airspeed increased causing inlet static pressure to rise.



Think of the brighter side!
User currently offlineHermansCVR580 From United States of America, joined Jul 1999, 510 posts, RR: 1
Reply 12, posted (1 year 12 months 2 days 16 hours ago) and read 6071 times:

Wow to me this is really amazing. I also never knew that military aircraft had these also, but after learning about them a bit they are a really simple device on a high tech engine. And to think now days there really is no need for them with the high bypass engines. We sure have come a long way.


The right decision at the wrong time, is still a wrong decision. "Hal Carr"
User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 13, posted (1 year 12 months 2 days 11 hours ago) and read 5953 times:

Quoting HermansCVR580 (Reply 12):
We sure have come a long way.

We sure have advanced a lot technology wise......but sadly the glory days of Aviation will never return.



Think of the brighter side!
User currently offlineViscount724 From Switzerland, joined Oct 2006, 26021 posts, RR: 22
Reply 14, posted (1 year 12 months 2 days 9 hours ago) and read 5905 times:

JT3Ds on 707s and 720Bs had two types of blow-in doors.

This early version.


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And this later type mounted further forward on the nacelle.


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User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 323 posts, RR: 0
Reply 15, posted (1 year 12 months 2 days 5 hours ago) and read 5833 times:

The E-8s here in the Deid also have these doors on them. An E-8 is basically a 707, and we've got the old engines on them. I've watched them a few times during engine run-ups/maintenance, and the doors definitely do not open and close symetrically! Some lag behind the others though they do all eventually open and close.

User currently offlineJAGflyer From Canada, joined Aug 2004, 3583 posts, RR: 4
Reply 16, posted (1 year 12 months 2 days 4 hours ago) and read 5821 times:

Here is a great video showing the doors moving on a 707.

https://www.youtube.com/watch?v=5dpFLssaSXw



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User currently offlineTupolevTu154 From Germany, joined Aug 2004, 2186 posts, RR: 27
Reply 17, posted (1 year 12 months 10 hours ago) and read 5527 times:

I never really knew how they worked either but then I sat next to them for an hour or so back in September and it was certainly a noise I won't soon forget! Here's a short video I took on my phone showing how they flap around on high power settings. I was fascinated watching them;

http://youtu.be/dnxgdKX6SzU



Atheists - Winning since 33 A.D.
User currently offlineJoeCanuck From Canada, joined Dec 2005, 5478 posts, RR: 31
Reply 18, posted (1 year 12 months 4 hours ago) and read 5436 times:

Quoting DL_Mech (Reply 7):

I find the suction vents on the Hawker Harrier very prominent.

Open;

http://3.bp.blogspot.com/-qKSAn7CIbns/T5TIHI6zm9I/AAAAAAAACJg/LlGCMnyv8mg/s1600/AV+8B+Harrier+II+Aircraft+4.jpg

Closed;





What the...?
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (1 year 12 months 2 hours ago) and read 5404 times:

Quoting JoeCanuck (Reply 18):
I find the suction vents on the Hawker Harrier very prominent.

Harrier was a corner case because it had enormous thrust for its size and had to run at full thrust with zero (or even negative) forward airspeed. Even that giant inlet wasn't enough to move the requisite mass of air without blow-in doors.

Tom.


User currently offlinedlednicer From United States of America, joined May 2005, 547 posts, RR: 6
Reply 20, posted (1 year 11 months 4 weeks 1 day 23 hours ago) and read 5365 times:
AIRLINERS.NET CREW
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Quoting tdscanuck (Reply 19):
Harrier was a corner case because it had enormous thrust for its size and had to run at full thrust with zero (or even negative) forward airspeed. Even that giant inlet wasn't enough to move the requisite mass of air without blow-in doors.

The original P.1127 prototype even had inflatable inlet lips, to provide a better shape for high thrust/no speed operation:


The early prototype YAV-8Bs had two rows of blow-in doors to cope with these problems:
http://upload.wikimedia.org/wikipedia/commons/d/de/YAV-8B_Harrier_testing_a_ski_jump.jpg


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17185 posts, RR: 66
Reply 21, posted (1 year 11 months 4 weeks 1 day 23 hours ago) and read 5358 times:

Quoting dlednicer (Reply 20):
The early prototype YAV-8Bs had two rows of blow-in doors to cope with these problems:

I love how the pilot is leaning way forward in order to see over the nose.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinemusang From United Kingdom, joined Apr 2001, 872 posts, RR: 7
Reply 22, posted (1 year 11 months 4 weeks 1 day 17 hours ago) and read 5310 times:

Quoting tdscanuck (Reply 2):
They're sprung doors and just respond to pressure changes across the inlet wall

To give an idea of how "sprung" they are, you can push them in manually.

(And while on the tangential subject of things you can do manually, you can lift the thrust reverser shutters on a DC-8-50!)

Quoting dlednicer (Reply 6):
used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage),

Interesting. If they're so far back, presumably they're not allowing air into the intake, but augmenting (adding) airflow into the exhaust duct?? Does the exhaust section demand more if after burning (reheating)?

Quoting Viscount724 (Reply 14):
JT3Ds on 707s and 720Bs had two types of blow-in doors.

The narrower type of door looks hinged at the rear, almost as if its a dump vent, i.e. letting air out. It would appear that this type forces the air to make an "s" turn into the intake.

Quoting KC135Hydraulics (Reply 15):
doors definitely do not open and close symetrically

Different spring pressure, hinge lubrication might contribute, but I'd contend that uneven vent opening would be likely due to the uneven pressure inside the intake, which I would further guess might be caused by airflow interference due to the proximity of the ground, and any crosswind. Most of that was conjecture!

Regards - musang


User currently offlinedlednicer From United States of America, joined May 2005, 547 posts, RR: 6
Reply 23, posted (1 year 11 months 4 weeks 1 day 9 hours ago) and read 5206 times:
AIRLINERS.NET CREW
DATABASE EDITOR

Quoting musang (Reply 22):
Quoting dlednicer (Reply 6):
used on Spey-engined Phantoms (side of aft fuselage), Northrop F-5Es (side of aft fuselage),

Interesting. If they're so far back, presumably they're not allowing air into the intake, but augmenting (adding) airflow into the exhaust duct?? Does the exhaust section demand more if after burning (reheating)?

The engines on the F-5 are mounted very far aft, so the doors are at the inlet:
http://img828.imageshack.us/img828/2442/northropf5etiger2upgrad.jpg


User currently offlinemusang From United Kingdom, joined Apr 2001, 872 posts, RR: 7
Reply 24, posted (1 year 11 months 4 weeks 1 day 8 hours ago) and read 5198 times:

Thanks for that, it sorts out the F-5. I had no idea they were so far aft.

However the Phantom doors are way aft of the engine face. Could they be to do with ventilation of the engine bay due to overheating of the RR Spey engines in the Royal Navy variant?

Regards - musang


User currently offlinefrancoflier From France, joined Oct 2001, 3848 posts, RR: 11
Reply 25, posted (1 year 11 months 4 weeks 1 day 8 hours ago) and read 5245 times:

Quoting TupolevTu154 (Reply 17):
Here's a short video I took on my phone showing how they flap around on high power settings.

Ouch, that fluttering can't be too good. I'm guessing the spring that counteracts the pressure differential is mostly worn in that case.



Looks like I picked the wrong week to quit posting...
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 26, posted (1 year 11 months 4 weeks 22 hours ago) and read 5111 times:

The blow in doors are there to help with the conflicting sizing requirements of the inlet at no or low speed and high speed. The problem is very well shown in the Harrier flow pictures, at low speed you need very broad and round lips as you are sucking air from a larger area then your inlet, even from behind the inlet lips at start. If the air does not follow the lip around to the inside you get inlet air separation which gives an airflow meeting the fan or compressor face which is uneven, can lead to surge.

At high speed it is the inverse, there is so much air available due to your forward speed stuffing air in the inlets that you can't consume all of it, ie you have air spilling over the sides of the inlet and if it does not attach around the outside lip you get drag. This problem is bad for an airliner (Inlet Mach range 0 to 0.85) but even worse for a fighter (Inlet should work over a Mach range 0 to 1.5).

For airliners advanced inlet lip shapes has given a good enough compromise so that you can do without the doors nowerdays, for fighters the Mach range is most of the time to large, especially if you have an inlet which has an optimized high Mach design like those with variable shock lips or bodies, these have almost invariably suck-in doors. Notable is that the JSF35 does not have doors (would cause radar reflections) or variable inlets (once again difficult to do with a low radar signature), therefore it has problems flying faster then M 1.5, today it better to be slower and not be seen then the opposite.



Non French in France
User currently offlineHermansCVR580 From United States of America, joined Jul 1999, 510 posts, RR: 1
Reply 27, posted (1 year 11 months 4 weeks 17 hours ago) and read 5048 times:

Do these blow in doors make the engines any more louder or do they have no effect on engine noise?


The right decision at the wrong time, is still a wrong decision. "Hal Carr"
User currently offlineViscount724 From Switzerland, joined Oct 2006, 26021 posts, RR: 22
Reply 28, posted (1 year 11 months 4 weeks 10 hours ago) and read 4973 times:

Quoting HermansCVR580 (Reply 27):
Do these blow in doors make the engines any more louder or do they have no effect on engine noise?

If not mistaken, one of the reasons they were eliminated on later engine versions was to reduce noise.


User currently offlineGr8Circle From Canada, joined Dec 2005, 3130 posts, RR: 4
Reply 29, posted (1 year 11 months 4 weeks 1 hour ago) and read 4913 times:

I remember doing a pre-flight walk around of an AI B707-337, and as he walked past the engine, he pushed in one of the blow-in doors on the P&W engine and shone his torch inside for a quick inspection........it just moved in easily, and swung shut on being released, as though it was held back in place by a spring.......

User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 30, posted (1 year 11 months 3 weeks 5 days 20 hours ago) and read 4715 times:

Quoting Viscount724 (Reply 28):
If not mistaken, one of the reasons they were eliminated on later engine versions was to reduce noise.

Franking speaking the noise reduction vide Noise supressors or Vortex generators may not be humanly noticeable due to the small variation in db levels.But exists when measured using test equipment.



Think of the brighter side!
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