gardiner@umn-cs.CS.UMN.EDU (David Gardiner) (06/30/89)
From: gardiner@umn-cs.CS.UMN.EDU (David Gardiner) A rule in the board game "Flight Leader" indicates that the engines used in US F-15s are only smokeless if they are tuned appropriately. Apparently, this limits engine life so that most or all of the engines have been "detuned" to extend engine life. Does anyone know (a) if this is true and (b) any more details? BTW, for those who are interested in jet fighters but don't have ready access to one, the "Flight Leader" (by Avalon Hill Game Company) is an interesting game. The rules are 20+ pages of small print and contain a substantial amount of technical information, all of which I believe to be reasonably accurate. David Gardiner
shafer@drynix (Mary Shafer) (07/01/89)
From: Mary Shafer <shafer@drynix> David Gardiner writes: >A rule in the board game "Flight Leader" indicates that the engines >used in US F-15s are only smokeless if they are tuned appropriately. >Apparently, this limits engine life so that most or all of the engines >have been "detuned" to extend engine life. Does anyone know (a) if this >is true and (b) any more details? The term is "de-rated" and I'm probably going to tell you more about this than you really want to know. When the F-111 first came out, it had a _terrible_ problem with engine stalls. The engine would stall during ground engine runs, even. This was due to a bad inlet design. A lot of work went into fixing this and if you look down the inlet of an F-111 you'll see vortex generators all around the inlet. This is the most visible fix. Engine stalls aren't the same as aircraft stalls, but they are caused by airflow problems. When the engine stalls, the thrust drops off rapidly. Damage to the engine is also possible, mostly from overheating. The Air Force and the Navy were so alarmed by all this that they decided, when the F-14 and F-15 came along, that they weren't going to take the chance of having fighters that were prone to compressor stalls. The solution was to de-rate the engine to the point that it _couldn't_ stall. The way to do this is to adjust the stator vanes (the fixed vanes in the compressor stage) so that they won't stall. However, doing this means that the engine isn't going to operate to its full capacity. Also, since you're not using the full capacity, you'll have lower pressures and lower temperatures and, hence, less wear and longer engine life. But you will also have less thrust and/or more fuel burn, since efficiency also is reduced. The smoke would result from an out-of-spec engine, because you would be so far off the design point that you would get incomplete combustion. However, I've never seen a smoking F-15 or F-16, either here at Edwards or at Langley AFB. I assume that the tolerances are fairly broad and that you would see other engine problems like elevated temperatures, in addition to the smoke, that would make you down the a/c and fix it. The F-15 HIDEC (Highly-Integrated Digital Engine Control) project here at Dryden uses a digital engine control system to run the engine. By scheduling the engine parameters on aircraft parameters like angle of attack, a non-derated engine can be used, since the engine control system takes care of avoiding stalls. Thus the HIDEC gets over 10% more thrust because it can use the thrust available without engine stalls. Here's a quick explanation of the compressor. The compressor stage of a jet engine consists of several sets of moving and stationary vanes. The front vanes are relatively small and the space between the moving and stationary vanes relatively large. As you proceed through the stage, the vanes get larger and the space gets smaller, so the air is compressed. -- M F Shafer shafer@elxsi.dfrf.nasa.gov NASA Ames Research Center arpa!elxsi.dfrf.nasa.gov!shafer Dryden Flight Research Facility DON'T use the drynix address Of course I don't speak for NASA A MiG at your six is better than no MiG at all. --Unknown US fighter pilot.
cyrius@cs.utexas.edu (Juan Chen) (07/05/89)
From: ut-emx!walt.cc.utexas.edu!cyrius@cs.utexas.edu (Juan Chen) I recall reading an add for Phillips 66 years ago (~10) that mentioned that they had developed THE additive to jet fuel that inhibits smoke and vapor trails. So I never though the engine itself had to do anything with smoke production. Anyone knows of this additive? ----------------------------------------------------------------------- Juan G. Chen cyrius@dopey.cc.utexas.edu University of Texas@Austin (or grumpy, or doc, or happy...) P.O. Box 8362 Austin, TX 78713 =======================================================================
bsmart@uunet.UU.NET (Bob Smart) (07/05/89)
From: vrdxhq!vrdxhq.verdix.com!bsmart@uunet.UU.NET (Bob Smart) In article <7874@cbnews.ATT.COM>, gardiner@umn-cs.CS.UMN.EDU (David Gardiner) writes: > > > From: gardiner@umn-cs.CS.UMN.EDU (David Gardiner) > A rule in the board game "Flight Leader" indicates that the engines > used in US F-15s are only smokeless if they are tuned appropriately. > Apparently, this limits engine life so that most or all of the engines > have been "detuned" to extend engine life. Does anyone know (a) if this > is true and (b) any more details? > > David Gardiner The answer got long so there is a one line summary at the end :-) Having put in 6 years fixing Eagles from 1976-82 I think I may have a few details that can help here. The answer to a) is YES. In 1976-77 one of the biggest problem areas we had (besides lack of parts) was the engines. THe F-100 was having stagnation problems on a regular basis. at the same time the engines were not lasting as long between overhauls as they expected. at the time the overhaul interval was very short because of the engines was new to the inventory. The stagnation problems were causing the engines to be removed even more often. To reduce wear &tear they retuned the engines at about 97%. The stagnation problems were fixed and things stayed hunky-dory. Then about 1980 there was a SEVERE engine shortage. TheCarter administration had made deep cuts in spares procurement and in long leadtime procurement for new aircraft. Then there was a labor problem either at Pratt & Whitney or one of there major suppliers. The pipeline for F-100 engines dried up completely. At one point we were removing engines from existing aircraft and sending them to St Louis to be installed in new aircraft that were coming off the assembly line. You see engines are GFE (government furnished equipment) and the Air Force had to provide them to keep from being charged for storage of the A/C. At one point our wing ( and I was told every other F-15 wing) had to send 23 aircraft to Warner Robins AFB to have all removable systems like radar radio, ECM, and engines stripped from them 'temporarily' to restock the supply system. We finally got the planes back about a year later but some of them never were 'right' again. It was easy to tell which planes had been used for this, most of the fleet had 4,000+ hours on the planes these birds had about 1,500. Anyway in the midst of the 1980 engine shortage the word came out to detune the engines to about 95% to extend the time between overhaul. The first detuning caused some smoke on some engines but the second one caused most to smoke. But the problem is relative. a smoky F-15 puts out only a little more than an F-4 with the new 'smokeless' engine mod. and the F-15 can be fixed on the trim pad in about 2 hours peacetime ( 10 minutes if the engine troops know that it's the real thing). I know planes that were preped for exercises like Gallant Eagle and Red Flag to 100% aand the smoke went away ( as well as markedly better performance according to the pilots) of course there were no official records kept of this since the book required the lower settings. The short answer is smoky engines last longer in peacetime flying since the engines aren't being stressed to their limits. But if the whistle blows the engines will be back to clean & mean. Bob Smart (bsmart@verdix.com)
ps01%gte.com@RELAY.CS.NET (Paul L. Suh) (07/05/89)
From: "Paul L. Suh" <ps01%gte.com@RELAY.CS.NET>
>From: gardiner@umn-cs.CS.UMN.EDU (David Gardiner)
%A rule in the board game "Flight Leader" indicates that the engines
%used in US F-15s are only smokeless if they are tuned appropriately.
%Apparently, this limits engine life so that most or all of the engines
%have been "detuned" to extend engine life. Does anyone know (a) if this
%is true and (b) any more details?
This is the only place where I have seen any indication of the engines
being de-tuned. All of the other sources which I have read (quite a
few, since I have been toying around with writing a flight simulator)
give no indication of this whatsoever.
%BTW, for those who are interested in jet fighters but don't have ready
%access to one, the "Flight Leader" (by Avalon Hill Game Company) is an
%interesting game. The rules are 20+ pages of small print and
%contain a substantial amount of technical information, all of which
%I believe to be reasonably accurate.
A much better boardgame is Air Superiority, from Game Designers'
Workshop. I own both of these games, and AS beats FL by miles. Also,
there is a second AS module available, which covers air-to-ground
missions and SAMs quite well, along with an historical module covering
the Arab-Israeli Conflicts.
Finally, for those who want a quick fix and feel like Flying An Electric
Jet Right Now, I recommend Falcon, available for about $30 from
MacConnection, PCConnection, or many other mail order places, in
versions for many different machines.
(Bill, feel free to excise this next paragraph)
Speaking of Falcon, one of my pet peeves when playing it is that when a
MiG is at my 10 0'clock and we're in a hard scissoring fight, there's no
really good way to get a look at it without easing off on the G's, which
may not be such a good idea. This is because although you can look
level left and level right, when you're banked into a hard turn, your
target is going to be 45 deg to 90 deg above the plane of the aircraft.
Does anyone have a solution, or failing that, will someone please let
the people at Sphere know?
[mod.note: I figured I'd leave it in... it might be a realistic
feature, not a bug 8-) Any comments on the gaming aspects should be
kept to email, unless you're sure it's appropriate here. - Bill ]
%David Gardiner
--Paul
ps01@gte-labs.COM
ps01@bunny.donn@entropy.ms.washington.edu (Donn F Pedro) (07/10/89)
From: mcgp1!donn@entropy.ms.washington.edu (Donn F Pedro)
With all the talk about the F-4 and smoke...
I was a member of an Air National Guard Combat Communications unit
stationed at Volk Field in Wisconson a few years ago. We were providing
air traffic support with out MPN-14 radar unit.
The first squadron to arrive for excercizes was a F-4 recon group.
They had two types of F-4's, regular and "smokeless".
You could easly spot the regular F-4 up to four or five miles away
due to the smoke trails. However the "smokeless" F-4 was *much* harder
to find. Side by side it was almost impossible to see the "smokeless" jet.
What was intresting about these F-4's was that they carried no armement
whatsoever. They were loaded with recon cameras and terrain following
radar. One of the pilots told me that the standard operating procedure
was to fly in low, pop up vunerable and weaponless for the pictures,
and proceed back to the deck and run like hell.
He indicated that his type of F-4 was the fastest model due to it's
lighter weight. I don't recall if the engines were more powerful or not.
As a side note, the pilots who flew the unmodified smokey engines went
by the nickname or "Smokey", "Fodder", and "Bait".
Donn F Pedro ....................a.k.a. mcgp1!donn@Thalatta.COM
else: {the known world}!uunet!nwnexus!thebes!mcgp1!donn
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