F15 questionalbe flight model in vertical and speed
willem 'PaleRider'
Hi,
Well,i know you're an F15 pilot so who am i to argue....and i don't
have the sim..yet...ggggg
But i can't refrain from commenting anymore:)
I thought the CFT's weren't supposed to have the huge impact on
performance you describe here.(when the fuel inside of them is used
that is)
The max speed and load factor remains the same when these things are
bolted on.
They were designed to give an extra fuel load with _very_ little
increase in drag...
The C/D can also carry the CFT if so desired,if i'm not mistaken it
takes about 20 minutes to put them on/take em off.
The basic weight difference between the E and C is only about 5000 lbs
About half of the E models have the 229 (60000lbs thrust) engine the
other half's got the 220 (50000lbs thrust) .Don't know what's modelled
in the sim but if it's the first ( i hope it is) this thing should
defenatly be able to climb and gain speed in the vertical.
If it's the second and you're low on fuel and don't carry any stores
it should be possible to maintain airspeed or even gain in the
vertical for a while.
The F15E is no C,but it's not a flying brick either.
I shouldn't say this cause i haven't flown the sim yet but
when i read what Clutch is writing,a clean plane and i pressume light
fuel load and it looses a lot of speed very fast judging by the term
'SOOOOO' in the vertical then i think that's strange.
Cheers,
Willem 'PaleRider'
$$$ in email is antispam.
>>CLUTCH24 wrote:
>> I have a question on 2 issues thus far regarding the F-15 flight model.
>> Someone correct me if I am wrong but the F-15 thrust to weight ratio is better
>> or at LEAST 1:1...
>> Thus, a CLEAN aircraft will accelerate in a climb or at least
>> close to it. Well....dumping all stores.....checking pylons and weapon load out
>> in the MFD to insure nothing is hanging around...:) I cannot come close to
>> keeping acceleration in a verticle climb. My AB's are lit...My engine gauge
>> shows 109%...Full burner I hope? My acceleration drops SOOOO rapidly in a
>> verticle climb....I know something is wrong here. I have been in an actual 2
>> seat F-15 trainer a few times and this verticle rocket maneuver in this sim is
>> way off.
>Sean Long wrote:
>Sorry, not the F-15E. Those CFT's add a bunch of weight and a TON of
>drag.
>The F-15E maintains it's energy quite differently from a plain
>F-15A/b/c/d. More weight, lots more drag.
Andy Hollis
willem 'PaleRider' <willem$$$@bart.nl> wrote in article
<352520f6...@news.arnhem.bart.nl>...
> Hi,
>
> Well,i know you're an F15 pilot so who am i to argue....and i don't
> have the sim..yet...ggggg
> But i can't refrain from commenting anymore:)
[snippage]
> The F15E is no C,but it's not a flying brick either.
> I shouldn't say this cause i haven't flown the sim yet but
> when i read what Clutch is writing,a clean plane and i pressume light
> fuel load and it looses a lot of speed very fast judging by the term
> 'SOOOOO' in the vertical then i think that's strange.
Ok, so you are not a real F15 pilot and you have not yet flown Jane's F15,
but you feel that you can refute the claims of the real pilot and the
game's designers and comment on the sim you have no first-hand experience
with?
Hmmm, that's sounds like I must have tuned into the Usenet! :-)
--Andy
willem 'PaleRider'
Hi,
So,your not happy that i based a post on what someone else was
writing about the sim.
Well...you have a point...i am sorry and i regret sending it before
having the chance to try it out myself
But i did warn that i was judging by someone else's post...and the use
of the drastic 'SOOOOOO' in it.
In my post i also emphasized that [quote: *When your low on fuel and
have a clean plane * end quote]
So..if you leave the bearing this has on Jane's F15 out of this...and
you just evaluate this comment i made in that post about the F15E in
real life [*quote:.Don't know what's modelled in the sim but if it's
the first(229),i hope it is,this thing should defenatly be able to
climb and gain speed in the vertical.
If it's the second(220) and you're low on fuel and don't carry any
stores it should be possible to maintain airspeed or even gain in the
vertical for a while* end quote]
the would you say i'm full of bullshit?
When i get it myself i'll try it out,if what my post was based on is
untrue i'll pupblicly apologize.
If i still think it's strange i hope to get a more friendly answer.
As for refuting an F15E pilot and game's designers...i didn't and
don't mean to offend anyone but if you go buy a car you wouldn't
solely base your buying descision on what the car salesman tell you.
I'm a complete SU27 fan,but that doesn't mean i don't want another sim
out here with just as good or an even better flightmodel
I'm not a person who constantly trashes other sims out there...or
people for that matter.
The rare posts i did here about sims...were about ADF..and that didn't
say "it sucks"..but a few things i noticed about
sams/missilePK/reactiontimes/stealth...and a post about F18..with it's
wierd inverted flight etc.
If only F15E pilots and experienced game designers are allowed to
share thoughts about Jane's F15 it would turn very quiet out here.
Willem 'PaleRider'
$$$ is antispam.
*Isp's news server is wacko...so i seem to miss out on some posts*
On 28 Mar 1998 20:15:18 GMT, "Andy Hollis" <aho...@origin.ea.com>
wrote:
pleg...@earthlink.nospam.net
Hey Palerider you were incorrect and just a little off base to post
about a sim that you dont have....
1. Its modeling the 220's so its the lower thrust model. The REAL LIFE
tm F-15 Pilot explained why extremely well....
2. You should be very careful about using other peoples experiences with
the sim to judge it. I know you to be extremely thorough in Flanker and
you would not judge it the same way. Do you know for example that many
people running around here dont know the difference between indicated
and true airspeed....big difference. Or did you know that many people
here also arent very good at checking their weight before flight
testing...fairly important if your gonna check climb performance wouldnt
you think. So instead of speculating about a sim you dont
have...wait...you will like this one. I bet.
PAPA DOC
>Hi,
>So,your not happy that i based a post on what someone else was
>writing about the sim.
Pierre PAPA DOC Legrand
Infamous
Pink Flamingo Pilot...<G>
pleg...@earthlink.net
willem 'PaleRider'
On Sun, 29 Mar 1998 03:54:43 GMT, pleg...@earthlink.nospam.net wrote:
Hi PD,
Well as i said...i am sorry i did that...i should have waited for it
to fall on my doorstep before commenting on what anybody thought of
the flightmodel.
I'm just so damned curious...and that post got me interested.
I haven't seen anything on what engine is modelled,so it's the
220...thanx for telling....but i did take that into account when i
wrote my post.
Anyway....once you've posted it...the evil is done:(...and once the
ball starts rolling it's hard to stop.
You are right about the weight checking and speed...i just figure it's
normal to do that...for me it is when i do testing in a sim.
I do expect a great flightmodel...i really hope it's awesome.
Cheers,
Willem 'Palerider'
$$$ is antispam.
CLUTCH24
>Hi PD,
>
>Well as i said...i am sorry i did that...i should have waited for it
>to fall on my doorstep before commenting on what anybody thought of
>the flightmodel.
>I'm just so damned curious...and that post got me interested.
>I haven't seen anything on what engine is modelled,so it's the
>220...thanx for telling....but i did take that into account when i
>wrote my post.
>Anyway....once you've posted it...the evil is done:(...and once the
>ball starts rolling it's hard to stop.
>You are right about the weight checking and speed...i just figure it's
>normal to do that...for me it is when i do testing in a sim.
>I do expect a great flightmodel...i really hope it's awesome.
>
>Cheers,
>Willem 'Palerider'
>$$$ is antispam.
>
brunt of the insult....The ORIGINAL post to the JANES GOD's was out of
curiosity about how I thought the flight dynamics felt....My post was NOT
based on attitude. That gets people killed in my business.
Regards,
Victor "Clutch" DiCosola
Former USAF Spec Ops
Engineer Northrop Corp, B-2 Div.
pap...@ix.nospam.com
You are incorrect...you were not the brunt of the insult. But now that
you mention it.....that wasnt an insult...Im really much better than
that at insults.
PAPA DOC
>I DID check the weight of the A/C and loadout of the planform. Sorry I was the
>brunt of the insult....The ORIGINAL post to the JANES GOD's was out of
>curiosity about how I thought the flight dynamics felt....My post was NOT
>based on attitude. That gets people killed in my business.
>
>Regards,
>
>Victor "Clutch" DiCosola
>Former USAF Spec Ops
>Engineer Northrop Corp, B-2 Div.
Pierre PAPA DOC Legrand
Infamous
Pink Flamingo Pilot...
pleg...@earthlink.net
willem 'PaleRider'
Hi Clutch,
Thanx for droppin in,as for the performance of the real life F15E in
the vertical i mentioned in my first post....it still stands.
But as you'll understand i don't want to get in any deeper before
having seen it in the sim myself ,and i probably don't wanna get
into it at all anymore<VBG>
Maybe you can do some more test runs and write down the details and
share those here.
There's still free speech .
Willem 'PaleRider'
CLUTCH24
>Hi Clutch,
>
>Thanx for droppin in,as for the performance of the real life F15E in
>the vertical i mentioned in my first post....it still stands.
>But as you'll understand i don't want to get in any deeper before
>having seen it in the sim myself ,and i probably don't wanna get
>into it at all anymore<VBG>
>Maybe you can do some more test runs and write down the details and
>share those here.
>There's still free speech .
>
>Willem 'PaleRider'
Thanks for your reply Willem, still doing LOTS of testing...stop watch etc. he
he I will be DEFINATELY POSTING BACK. Have a few F-15 jockies I know and will
be talking with them this week.
Regards,
Vic
Micheal Smith
On 28 Mar 1998 20:15:18 GMT, "Andy Hollis" <aho...@origin.ea.com>
wrote:
>Ok, so you are not a real F15 pilot and you have not yet flown Jane's F15,
>but you feel that you can refute the claims of the real pilot and the
>game's designers and comment on the sim you have no first-hand experience
>with?
>
>Hmmm, that's sounds like I must have tuned into the Usenet! :-)
>
>--Andy
>
thrust that the engines produce, then it will accelerate vertically.
Does anyone know what the approximate weight of an F15E with no
external stores and a low fuel load would be? I'd be curious to find
out.
Mike
willem 'PaleRider'
Hi,
It's well below the 48000 lbs the 220 engines give.
and far below the the 58000 lbs of the 229 engines.
Probably somehwere around 40000-42000lbs,no externals (except for the
empty CFT and the lantirn pods) and a light fuel load...
So if you have Jane's F15 try it out...
I still don't have it.....waiting very very eagerly to see what
happens in the sim myself,but i allready have a good idea of what i
will see...<VBG>
Willem 'PaleRider'
sm...@interhop.net (Micheal Smith) wrote:
>Actually, Willem has a valid point. If the A/C weighs less than the
>thrust that the engines produce, then it will accelerate vertically.
>Does anyone know what the approximate weight of an F15E with no
>external stores and a low fuel load would be? I'd be curious to find
>out.
>Mike
>On 28 Mar 1998 20:15:18 GMT, "Andy Hollis" <aho...@origin.ea.com>
Andy Hollis
Micheal Smith <sm...@interhop.net> wrote in article
<351eb8c1...@news.ican.net>...
> Actually, Willem has a valid point. If the A/C weighs less than the
> thrust that the engines produce, then it will accelerate vertically.
> Does anyone know what the approximate weight of an F15E with no
> external stores and a low fuel load would be? I'd be curious to find
> out.
Go to the custom loadout screen and take everything off the plane. Then
look at the weight readout. That should be pretty close.
--Andy
Robin G. Kim
Micheal Smith <sm...@interhop.net> wrote:
>"Andy Hollis" <aho...@origin.ea.com> wrote:
>Actually, Willem has a valid point. If the A/C weighs less than the
>thrust that the engines produce, then it will accelerate vertically.
No, not in general. In vertical flight, you have a thrust vector
pointing upwards fighting against gravity _and drag_ vectors pointing
downward. What you say is true only when the plane is hovering in
midair.
>Does anyone know what the approximate weight of an F15E with no
>external stores and a low fuel load would be? I'd be curious to find
>out.
In the sim, the plane weighs about 37000 lbs with zero fuel and no
ordnance.
What you really want to do is try to get the plane pointed straight up
at as low an altitude as you can (lower = more thrust) and going as
slowly as you can (slower = less drag, but it also means less thrust, so
I'm actually not sure about this part).
Anyway, I ran just this test. With 1600 lbs of fuel (38600 lbs total
weight), I pulled up into the vertical, achieving 90 degree pitch at
about 1500' MSL. I waited until I slowed to about 30 KIAS, than firewalled
the throttle. I accelerated _very_ slowly to about 65 KIAS before I
"lost my balance" and fell away.
I'd say the flight model is a little off here, both in terms of thrust
vs. weight and controllability at extremely low airspeeds (I'm not that
good a pilot). Even assuming I am right about all this, I personally
consider neither shortcoming to be worth worrying about. I would never
dream of impinging on the rights of others to rant about minutiae,
however--been there, done that. :^)
Olen Goodwin
Micheal Smith wrote:
> On 28 Mar 1998 20:15:18 GMT, "Andy Hollis" <aho...@origin.ea.com>
> wrote:
> >Ok, so you are not a real F15 pilot and you have not yet flown Jane's F15,
> >but you feel that you can refute the claims of the real pilot and the
> >game's designers and comment on the sim you have no first-hand experience
> >with?
> >
> >Hmmm, that's sounds like I must have tuned into the Usenet! :-)
> >
> >--Andy
> >
> Actually, Willem has a valid point. If the A/C weighs less than the
> thrust that the engines produce, then it will accelerate vertically.
> Does anyone know what the approximate weight of an F15E with no
> external stores and a low fuel load would be? I'd be curious to find
> out.
>
> Mike
You are right about Willem having a point, however, it takes quite a bit more
than 1 to 1 thrust/weight ratio to allow accelleration in the vertical. You
also have to overcome the drag involved in going whatever speed you started at,
which would be considerable.
You can get the weight by editing the stores in the game.
org
razor
Richard Cowl
In article <351eb8c1...@news.ican.net>, Micheal Smith
<sm...@interhop.net> writes
>On 28 Mar 1998 20:15:18 GMT, "Andy Hollis" <aho...@origin.ea.com>
>wrote:
>>Ok, so you are not a real F15 pilot and you have not yet flown Jane's F15,
>>but you feel that you can refute the claims of the real pilot and the
>>game's designers and comment on the sim you have no first-hand experience
>>with?
>>
>>Hmmm, that's sounds like I must have tuned into the Usenet! :-)
>>
>>--Andy
>>
>Actually, Willem has a valid point. If the A/C weighs less than the
>thrust that the engines produce, then it will accelerate vertically.
>Does anyone know what the approximate weight of an F15E with no
>external stores and a low fuel load would be? I'd be curious to find
>out.
>
>Mike
Am I right in thinking that the thrust rating of an engine is the thrust
it produces standing still ( static thrust ) and at sea level air
pressure and nominal air temperature ( probably 20deg c )?
If so, then any forward movement of the engine through air will
surely result in reduced thrust. Will increased altitude also reduce
thrust significantly i.e going from 0 to 10000 feet as in a typical
vertical full AB climb? Also I think very high air temperatures (
typically 40 deg c in the region modelled in F15 ) will also conspire to
downrate performance.
If the above is correct then it is hardly surprising that the
F15 modelled in this sim, does not climb quite as well in the vertical
as the figures in the 'brochure' would have us believe!
I am NOT an expert, so if the above is a lot of rubish then I
appologise! - interesting thread.
--
Richard Cowl
Snow White
I got the thing to climb vertical during my test.
min. fuel, and stripped of everything I went vertical at 2000'@450kts
and climbed to 40000'. It wasn't accelerating though but the speed was
decreasing gradually.
Bas Jansen
Richard Cowl wrote:
> If so, then any forward movement of the engine through air will
> surely result in reduced thrust.
Wrong. Speed will augment in building pressure forward of the compressor
and will ultimately end up in a higher pressure behind the last stage.
Higher pressure will have a positive effect on engine thrust.
> Will increased altitude also reduce thrust significantly i.e going from 0 to 10000 feet as in a typical
> vertical full AB climb?
I am not 100% sure but I think that the lower temps. may actually have a
positive effect on engine power as well... I think it outweighs the
decreaing pressure.. to a 'certain' altitude, that is...
Also I think very high air temperatures (
> typically 40 deg c in the region modelled in F15 ) will also conspire to
> downrate performance.
Yup.
CJ Martin
>Am I right in thinking that the thrust rating of an engine is the thrust
>it produces standing still ( static thrust ) and at sea level air
>pressure and nominal air temperature ( probably 20deg c )?
> If so, then any forward movement of the engine through air will
>surely result in reduced thrust. Will increased altitude also reduce
>thrust significantly i.e going from 0 to 10000 feet as in a typical
>vertical full AB climb? Also I think very high air temperatures (
>typically 40 deg c in the region modelled in F15 ) will also conspire to
>downrate performance.
> If the above is correct then it is hardly surprising that the
>F15 modelled in this sim, does not climb quite as well in the vertical
>as the figures in the 'brochure' would have us believe!
Bingo!
>I am NOT an expert, so if the above is a lot of rubish then I
>appologise! - interesting thread.
You are doing a lot better than some of the other "experts" here.
;-)
-CJ
Micheal Smith
On Tue, 31 Mar 1998 13:52:40 GMT, ent...@SPAMREG.quake.at (Alexander
Sanda) and a whole bunch of others :) wrote:
> In article <351eb8c1...@news.ican.net>,
> sm...@interhop.net (Micheal Smith) wrote:
>
>>Actually, Willem has a valid point. If the A/C weighs less than the
>>thrust that the engines produce, then it will accelerate vertically.
>>Does anyone know what the approximate weight of an F15E with no
>>external stores and a low fuel load would be? I'd be curious to find
>>out.
>
>I'am not an expert in flight physics, but didn't you forget the drag ?
>
>
>--
># /AS/
># My email adress is valid as written. Please don't remove SPAMREG, as #
># this is used to catch spammer domains. Thank you.#
># #include <std_disclaimer.h> http://privat.schlund.de/entropy/ #
Okay, I have been severely trounced for forgetting drag :). Yes
you're right, the drag vector would also have to be considered in this
calculation, however I would imagine the magnitude of the drag vector
would be very small at low speeds, such as Robin was trying (<100 kts
IAS). If you want, I could calculate, very roughly, what that drag
would equal in force (which is what we are really talking about here)
and then we could add that to the A/Cs weight. That would certainly
help to answer whether the F15E should be able to accelerate
vertically. But you are all right, drag would indeed increase the
amount of thrust needed.
Mike
Micheal Smith
On Mon, 30 Mar 1998 20:47:54 +0100, Richard Cowl
<Ric...@kilawen.demon.co.uk> wrote:
>snip...
>Am I right in thinking that the thrust rating of an engine is the thrust
>it produces standing still ( static thrust ) and at sea level air
>pressure and nominal air temperature ( probably 20deg c )?
Yes, that is the way engines are rated by the manufacture. I don't
remember what standard day conditions are though, I think 101.325 KPa
@ 20C.
> If so, then any forward movement of the engine through air will
>surely result in reduced thrust.
Actually no. As the engine is moved forward, it's efficiency will
increase due to higher intake air speeds and this will actually
produce slightly more thrust than if the engine was static. That
being said, there is a limit as to the velocity of the intake air that
the engine can withstand so there is an upper limit to this increase
in thrust. That whole subject requires it's own post. It's ok, I
will spare you :).
>Will increased altitude also reduce thrust significantly i.e going
>from 0 to 10000 feet as in a typical vertical full AB climb? Also I
>think very high air temperatures (typically 40 deg c in the region modelled in F15 )
>will also conspire to downrate performance.
Yes. Increases in altitude and temperature will decrease thrust.
However, due to the physics involved, this perfectly suits turbojet
engines, particularly those with multiple spools like all modern
fighters have. Even though they experience a decrease in thrust as
you gain altitude, they deliver more bang for your buck (same power
produced for less lbs of fuel burned) which makes them ideal for high
altitude flight. Another diatribe I'm afraid :).
>If the above is correct then it is hardly surprising that the
>F15 modelled in this sim, does not climb quite as well in the vertical
>as the figures in the 'brochure' would have us believe!
You have that right. Always read the fine print :).
>I am NOT an expert, so if the above is a lot of rubish then I
>appologise! - interesting thread.
>Richard Cowl
Not at all. You raise very valid points.
Mike
Robin G. Kim
Micheal Smith <sm...@interhop.net> wrote:
>Richard Cowl <Ric...@kilawen.demon.co.uk> wrote:
>Increases in altitude and temperature will decrease thrust.
>However, due to the physics involved, this perfectly suits turbojet
>engines, particularly those with multiple spools like all modern
>fighters have.
This is a very minor nit, but I believe most modern fighters (and certainly
the F-15E) sports turboFAN engines, not turbojets. Does your comment apply
equally well to turbofans with medium to high bypass ratios? I'm genuinely
curious.
>Even though they experience a decrease in thrust as
>you gain altitude, they deliver more bang for your buck (same power
>produced for less lbs of fuel burned) which makes them ideal for high
>altitude flight. Another diatribe I'm afraid :).
I don't know about anyone else, but I'd love to hear an explanation of
why this is the case.
Leo
On Tue, 31 Mar 98 15:15:06 GMT, cma...@origin.ea.com (CJ Martin)
wrote:
>In article <UdFJwIAqb$H1E...@kilawen.demon.co.uk>, Richard Cowl <Ric...@kilawen.demon.co.uk> wrote:
>
>>Am I right in thinking that the thrust rating of an engine is the thrust
>>it produces standing still ( static thrust ) and at sea level air
>>pressure and nominal air temperature ( probably 20deg c )?
>> If so, then any forward movement of the engine through air will
>>surely result in reduced thrust.
almost...but not quite!......in the simplest of terms, yes, an
increase of air *velocity* will mean that the thrust is
reduced.....but.......you have to consider other factors...such as
*mass airflow*...which is dependent on air density (thus temperature
and pressure).
Because of *Ram Effect* (when the engine is moving forwards)
increasing the airspeed also increases the pressure of the air and
airflow to the engine.
The net result is.....that at a certain point...(will vary according
to design of the inlet, and choke effect at the jetpipe) thrust
*increases* as the aircraft goes faster and faster......
It will also compensate for some of the loss in thrust due to reduced
pressure at altitude.
>>Will increased altitude also reduce
>>thrust significantly i.e going from 0 to 10000 feet as in a typical
>>vertical full AB climb?
the thrust lapse rate is more or less constant up to around 36 000 ft,
and then increases in value above that....because air temperature
stops falling off , while air pressure continues to drop.
will it be reduced significantly????.....well.....depends on how fast
you're going.....and what you consider a 'typical' vertical climb in
full reheat....:)
>> Also I think very high air temperatures (
>>typically 40 deg c in the region modelled in F15 ) will also conspire to
>>downrate performance.
ok.....so what we really really want is an add-on campaign scenario
set in the Aleutians during midwinter......<ggg>
>>
<snippage>
>Bingo!
>
>>I am NOT an expert, so if the above is a lot of rubish then I
>>appologise! - interesting thread.
>
>You are doing a lot better than some of the other "experts" here.
>
>;-)
>
>-CJ
CJ: Does the Sim model thrust?.....if so.....is it a constant factor,
with temp and pressure affecting a/c aerodynamic flight model only....
or are environmental conditions (including Ram effect) a factor in
engine performance (in the Sim) ?
(no agenda here....just interested to know... )
cheers,
FastPants
Leo
On 31 Mar 1998 17:23:47 GMT, op...@marconi.ih.lucent.com (Robin G. Kim)
wrote:
<snippety snip>
>This is a very minor nit, but I believe most modern fighters (and certainly
>the F-15E) sports turboFAN engines, not turbojets. Does your comment apply
>equally well to turbofans with medium to high bypass ratios? I'm genuinely
>curious.
>
>>Even though they experience a decrease in thrust as
>>you gain altitude, they deliver more bang for your buck (same power
>>produced for less lbs of fuel burned) which makes them ideal for high
>>altitude flight. Another diatribe I'm afraid :).
>
>I don't know about anyone else, but I'd love to hear an explanation of
>why this is the case.
>
>Rob
>opu...@lucent.com
Me too........though can i hazard a guess at one factor?....bypassed
air must be of great benefit to the use of afterburners......if it's
colder and denser, then mixing it with the exhaust is certainly going
to boost the performance of reheat.......??
FastPants
leo...@dial.pipex.com
Bas Jansen
Bas Jansen wrote:
> a turbojet). This is the main reason why todays engines use bypass
> ratios of varying degrees (which is also dependent on fuel prices,
> believe it or not..)
I meant to say that the diameter of the fan is dependent on, amongst
other things, fuel prices....
anyway..
Bas Jansen
Robin G. Kim wrote:
>
> Micheal Smith <sm...@interhop.net> wrote:
> >Richard Cowl <Ric...@kilawen.demon.co.uk> wrote:
> >Increases in altitude and temperature will decrease thrust.
> >However, due to the physics involved, this perfectly suits turbojet
> >engines, particularly those with multiple spools like all modern
> >fighters have.
>
> the F-15E) sports turboFAN engines, not turbojets. Does your comment apply
> equally well to turbofans with medium to high bypass ratios? I'm genuinely
> curious.
Turbofans are using less fuel for a given amount of thrust (compared to
a turbojet). This is the main reason why todays engines use bypass
ratios of varying degrees (which is also dependent on fuel prices,
believe it or not..) Obviously there are drawbacks as well...
I don't see the relation between the original posters comment about
multiple spools and "physics involved".
As far as I've been taught, multiple spools are introduced to counter
problems in engine operation (for instance compressor stall, surge
etc.). It also results in smoother accelleration of the engine and a
host of other benefits.
regards
Bas Jansen
CJ Martin
>CJ: Does the Sim model thrust?.....if so.....is it a constant factor,
>with temp and pressure affecting a/c aerodynamic flight model only....
>or are environmental conditions (including Ram effect) a factor in
>engine performance (in the Sim) ?
>
>(no agenda here....just interested to know... )
>
>cheers,
>FastPants
Now we are fast getting into an area that I am not sure of, and our
Flight Model Guy (tm) is on vaction...but I do know we model the
effects of pressure (varying with altitude). Mil thrust at sea level
will be higher than at 20,000 feet. Ram effect, I honestly don't know
the answer to that one. Sorry, but I don't want to give out bad
information.
-CJ
Micheal Smith
On 30 Mar 1998 03:27:16 GMT, "Andy Hollis" <aho...@origin.ea.com>
wrote:
>Go to the custom loadout screen and take everything off the plane. Then
>look at the weight readout. That should be pretty close.
>
>--Andy
Thanks Andy, that makes it easy.
Mike
Micheal Smith
>This is a very minor nit, but I believe most modern fighters (and certainly
>the F-15E) sports turboFAN engines, not turbojets. Does your comment apply
>equally well to turbofans with medium to high bypass ratios? I'm genuinely
>curious.
>
>Rob
>opu...@lucent.com
Yes, you're right. Turbofans. They are all turbojets, meaning the
operation of the core is the same principle. Throw a free turning
fan/turbine on a turbojet and it becomes a turbofan of the twin spool
type. Put on another fan/turbine and it is a triple spool. The ratio
of air that bypasses the combustor determines if it is a low, medium
or high bypass turbofan engine.
Yes, the efficiency of a bypass turbofan is affected the same way as a
pure turbojet regarding altitude and temperature. Turbofans however,
are able to maintain a higher efficiency over a broader range of
altitude than turbojets, making them ideal for most military and
civil craft.
Mike
Matthew V. Jessick
CJ Martin wrote:
> Ram effect, I honestly don't know
> the answer to that one. Sorry, but I don't want to give out bad
> information.
>
> -CJ
If your takeoff rolls are anything close, it's in there.
- Matt
Joakim
Micheal Smith wrote:
>
> On Tue, 31 Mar 1998 13:52:40 GMT, ent...@SPAMREG.quake.at (Alexander
> Sanda) and a whole bunch of others :) wrote:
>
> > In article <351eb8c1...@news.ican.net>,
> > sm...@interhop.net (Micheal Smith) wrote:
> >
> >>Actually, Willem has a valid point. If the A/C weighs less than the
> >>thrust that the engines produce, then it will accelerate vertically.
> >>Does anyone know what the approximate weight of an F15E with no
> >>external stores and a low fuel load would be? I'd be curious to find
> >>out.
> >
> >I'am not an expert in flight physics, but didn't you forget the drag ?
> >
> >
> >--
> ># /AS/
> ># My email adress is valid as written. Please don't remove SPAMREG, as #
> ># this is used to catch spammer domains. Thank you.#
> ># #include <std_disclaimer.h> http://privat.schlund.de/entropy/ #
>
> Okay, I have been severely trounced for forgetting drag :). Yes
> you're right, the drag vector would also have to be considered in this
> calculation, however I would imagine the magnitude of the drag vector
> would be very small at low speeds, such as Robin was trying (<100 kts
> IAS). If you want, I could calculate, very roughly, what that drag
> would equal in force (which is what we are really talking about here)
> and then we could add that to the A/Cs weight.
Remember that drag does not always decrease as air speed decreases
towards zero. There is a speed below which drag *increases* as air speed
*decreases*. This is due to the fact that drag consists of two
components: induced drag and parasite drag. Induced drag increases as
air speed decreases and becomes significant at low speeds. Parasite drag
increases as air speed increases and becomes significant at high speeds.
Consequently, the minimum controllable air speed of an aircraft is flown
with full throttle. This can be very counter-intuitive. It's easily
demonstrated in a single-engine piston propeller aircraft - don't know
how this manifests itself in F-15E's (or the sim, for that matter).
...Joakim
Robin G. Kim
Joakim <avi...@mv.mv.com> wrote:
>Micheal Smith wrote:
>> Okay, I have been severely trounced for forgetting drag :). Yes
>> you're right, the drag vector would also have to be considered in this
>> calculation, however I would imagine the magnitude of the drag vector
>> would be very small at low speeds, such as Robin was trying (<100 kts
>> IAS). If you want, I could calculate, very roughly, what that drag
>> would equal in force (which is what we are really talking about here)
>> and then we could add that to the A/Cs weight.
>
>Remember that drag does not always decrease as air speed decreases
>towards zero. There is a speed below which drag *increases* as air speed
>*decreases*. This is due to the fact that drag consists of two
>components: induced drag and parasite drag. Induced drag increases as
>air speed decreases and becomes significant at low speeds. Parasite drag
>increases as air speed increases and becomes significant at high speeds.
>Consequently, the minimum controllable air speed of an aircraft is flown
>with full throttle. This can be very counter-intuitive. It's easily
>demonstrated in a single-engine piston propeller aircraft - don't know
>how this manifests itself in F-15E's (or the sim, for that matter).
While all this is true, it does not apply to vertical acceleration tests,
which are done at zero G--no induced drag.