SCAT15F
Topic Author
Posts: 468
Joined: Fri Feb 09, 2007 8:34 am

Lack Of "turkey Feathers" On F-15 And B-1B

Fri Apr 06, 2007 3:04 pm

Since about 1980 the P&W F100 turbofans on the USAF F-15 Eagle Fleet have had their afterburner nozzle covers "turkey feathers" removed. About 10 years ago the same was done to the GE F101 turbofans on the B-1B fleet.

The USAF "reasoning" was given as weight and complexity issues.

The F-16, also using the F100 was allowed to "keep" its "turkey feathers" as was the Israeli F-15I

Now I've heard people say "oooh, it looks technical and cool" but the reality is, it increases drag and most importantly takes the beautiful lines of both the F-15 and B-1 and makes them look DAMN UGLY AS SIN!!! For God's sake, if you want to save weight remove the paint like the Russians, at least it would maintain the flow and integrity of the design! I guarantee that if the AF was to take the turkey feathers off of the F-16 they would be shamed into putting them back on by AF personnel and the public alike.

Would anyone buy a corvette without a hood or perhaps without fenders?!!

I had hopes that when the AF started installing the F100-229 in the F-15E they would change their ways; I was wrong.

All I can say is stupid is as stupid does!!!

I'm sorry, but someone had to say something...
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checksixx
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Sat Apr 07, 2007 1:37 am

Taken off the 15's and B-1's because they were loosing panels from them. Better to just remove them all. I'm pretty sure the F-15I doesn't use a baseline 100 and thats why you see them on there.
 
DeltaGuy
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Sat Apr 07, 2007 12:35 pm

I agree with you, the lack of feathers (or as technically called, Divergent Nozzle External Segments), looks ugly. It's an increase in drag, no doubt. But it's one less thing to work on, and a few pounds spared. Those internal segments get awfly hot and the Gaspath (the white lining that coats them) gets burned quickly, so replacing those segments is a recurring thing. Most things go to depot now though.

Back in the day when I went to tech school to work on the F100 motor, I asked my puzzled instructor about this (her best initial explanation of an afterburner to our mostly inexperienced class was "those fire nozzles on Top Gun"). It was explained to me by her that the reason the Eagle dropped those was because of airflow issues, and at certain power settings the petals were getting too hot, or melting, something along those lines. I still don't believe the logic but to this day we still don't have a single one in the shop. I'm sure there's a good reason, I'll ask and get a good answer, this is a good question.

Now, get around some of those oddball block F-16's with the F100, you'll always see them. Then again, the 16 has some very clean lines and needs them. The 15 has some choppy lines towards the tail and I'll bet their benefit wasn't worth the weight- not to say the plane is striving to be light to begin with  Wink The -229 is a sweet motor to begin with, easy as hell to work on. It came with a newer augmenter duct, but like it's older cousins the -100 and -220, no external segments. I guess some things never change.

DeltaGuy

[Edited 2007-04-07 05:38:31]
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
UA777
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 03, 2007 3:17 pm

I have a question. In full afterburner, do these turkey feathers close or open? I've seen pictures of F-16's taking off and some show the exhaust outlet closed and some open. The same with inflight photos I've scene. There's a video on YouTube of an F-16 in full afterburner tests, achored to the ground of course. During the video you see these open and close, but I can't make out in what order it's happening.

Thank you.
 
DeltaGuy
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 03, 2007 5:04 pm

UA777, to answer your question, those nozzles move alot. If you ever hear an F-15 at idle thrust landing over your house, you can hear a very loud whine occasionally, almost like the sound a whip makes...it's called the CENC, or Convergent Exhaust Nozzle Control. It's basically a little motor powered by 13th stage bleed air, that causes the nozzle to open and close based on the computer's needs.

The nozzle is almost constantly moving to improve optimum flow. At idle, the nozzles are fully open, to prevent a compressor stall. As power is increased, the nozzles will close a tad more, creating a more convergent duct, thus increasing the velocity of the exhaust gasses. At full military power, the nozzles are completely tight, meaning they are as constricted as far as they'll go, almost to 18" or so...alot of pressure flowing through such a small opening. When the augmenter is engaged, they open to the full open position as the purpose of the convergent duct is no longer required considering there's a 20-foot plume of white-hot fire coming out the tail end.

Hope that helps, it is quite awe inspiring to see in test cell....hang on to your eyebrows.

DeltaGuy
(Former F100 engine troop)
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
UA777
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 03, 2007 5:36 pm

Thank you. You've been extremely helpful.
 
AAR90
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 03, 2007 5:49 pm



Quoting DeltaGuy (Reply 4):
When the augmenter is engaged, they open to the full open position as the purpose of the convergent duct is no longer required considering there's a 20-foot plume of white-hot fire coming out the tail end.

IIRC, they BEGIN opening as AB is applied and will be FULL OPEN at FULL A/B setting. These are not the "throw fuel in the back" afterburners but rather multi-staged controlled A/B's that require the nozzles to adjust to the amount of A/B being used.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
YANQUI67
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 03, 2007 6:36 pm

Back in my Hornet days the VENs Variable exhaust nozzles would always get wrinkled up and would cause a lot of maintenance. The panels would not retract to the right position and crush the panels on top of each other. Later a mod was made were a notch was removed from the edge of the panel on the aft part of the VEN. Problem solved!! No more wrinkled VENs.

View Large View Medium
Click here for bigger photo!

Photo © Guilherme Bystronski

 
DeltaGuy
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Tue Dec 04, 2007 1:20 am



Quoting AAR90 (Reply 6):
IIRC, they BEGIN opening as AB is applied and will be FULL OPEN at FULL A/B setting.

You're right sir, I should have been more specific.

The F100 has seven fuel sprayrings in the augmenter, and will provide varying amounts of fuel for the desired amount of burner. Older afterburning motors weren't so refined IIRC.

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
Blackbird
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Fri Dec 07, 2007 1:51 am

Can one of you guys show me like an old version with the turkey feathers and a new version without or something?

Andrea Kent
 
grandtheftaero
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Sun Dec 09, 2007 10:03 pm



Quoting SCAT15F (Thread starter):
All I can say is stupid is as stupid does!!!

Geez...

I'm glad someone with a career in "forestry and writing" could become so adept at the intricacies of variable exhaust nozzle mechanics and aerodynamics. So adept that they could second guess the decisions made by both Pratt and GE regarding engines that they designed... not to mention the many scientist and engineers at NASA and the Pentagon who helped to resolve this issue.

As you pointed out they are a fairing to cover the many and varied mechanisms that articulate the VEN. However on the the Pratt-powered F-15s and later the B-1, they experienced vibration/harmonic issues related to higher-than-expected dynamic loads and shock interaction with the airframe. All this was causing premature failure and, in some cases, causing them to depart the aircraft in flight, as Checksixx pointed out. As I mentioned earlier, this was not an easy problem to diagnose/solve.

If you've ever had the pleasure of assembling/disassembling nozzle flaps and seals you know that they along with their related hardware easily weigh more than a hundred pounds per engine. In the end, the weight saved by by removing the outer flaps not only solved the vibes issues but also shaved enough weight off the airframe that it offset the loss of smooth aerodynamic lines. In the end it was a win/win situation.

Please think before you call people in our industry stupid. There is more time, energy, and analysis put into making these decisions than you can possibly image.

--Shane
 
AAR90
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 10, 2007 3:25 am



Quoting DeltaGuy (Reply 8):
The F100 has seven fuel sprayrings in the augmenter, and will provide varying amounts of fuel for the desired amount of burner. Older afterburning motors weren't so refined IIRC.

That's definitely an improvement(?) over the 5-stage systems in acft from "my generation." And significantly better than the RF-8G's "dump in the fuel = BOOM" that I was introduced to as a midshipman.  spin 
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
DeltaGuy
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RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 10, 2007 4:44 am



Quoting GrandTheftAero (Reply 10):
If you've ever had the pleasure of assembling/disassembling nozzle flaps and seals you know that they along with their related hardware easily weigh more than a hundred pounds per engine. In the end, the weight saved by by removing the outer flaps not only solved the vibes issues but also shaved enough weight off the airframe that it offset the loss of smooth aerodynamic lines. In the end it was a win/win situation.

You ain't kidding, I remember tearing those sections down. The Augementor is it's own module in itself, and a quick peek inside will soon reveal why- the mechanisms and actuators required to move that nozzle so smoothly is very very intricate. Add to that, the coatings required to keep the metal from burning through from the burning exhaust, it's quite amazing.

Quoting AAR90 (Reply 11):
And significantly better than the RF-8G's "dump in the fuel = BOOM" that I was introduced to as a midshipman.

Oh but how I would love to hear that on a daily basis..have to settle for the one on gate guard at NAS Jax I guess....

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
AAR90
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Joined: Fri Jan 21, 2000 11:51 am

RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 10, 2007 1:23 pm



Quoting DeltaGuy (Reply 12):
Oh but how I would love to hear that on a daily basis

Hear? No.... FEEL ! ! ! No matter where you were aboard JFK, your body told you everytime a VFP-63 Det-B plane took off! Makes quite an impression upon a young 21-yr old Naval Aviator wannabe. yes 
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
SCAT15F
Topic Author
Posts: 468
Joined: Fri Feb 09, 2007 8:34 am

RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 10, 2007 4:40 pm



Quoting GrandTheftAero (Reply 10):
Please think before you call people in our industry stupid. There is more time, energy, and analysis put into making these decisions than you can possibly image.

OK, then explain why the IAF and the Saudis still have their turkey feathers on. I guess they just don't realize they have a problem yet.

Oh, and by the way, I was in the Navy for 4 years and did maintenance work on the TF-30 and F-110 at Miramar.
 
grandtheftaero
Posts: 247
Joined: Sat Nov 29, 2003 1:05 pm

RE: Lack Of "turkey Feathers" On F-15 And B-1B

Mon Dec 10, 2007 10:01 pm



Quoting SCAT15F (Reply 14):
OK, then explain why the IAF and the Saudis still have their turkey feathers on. I guess they just don't realize they have a problem yet.

Stupid is as stupid does?

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