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View Full Version : do jets benifit from pushing trottle past 100%?



thefruitbat
01-17-2008, 04:15 PM
pretty much in the title http://forums.ubi.com/images/smilies/16x16_smiley-tongue.gif

recently, i've been flying jets alot, as its fantastic flying low and v fast in slovakia!!

I'm only interested in the proper jets though*, ie me262, he-162-a2, ar-234 (my fav, what a plane), yp80 and the mig9.

* = real combat record http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Anyway, is there any benifit in pusing the throttle past 100%, they all do?

On an aside, would anyone apart from me be more than happy to pay double full wack to have a F86 and a Mig 15, with a coulpe of maps of Korea, to the level of slovakia? I would pay money.

cheers fruitbat

VW-IceFire
01-17-2008, 04:34 PM
I think they do...only some of the jets will go past 100% so there must be a reason for that. I don't actually know...good question!

Yes Korea would be fantastic...and the rumors indicate that its on the way. But it'll be some time off yet because they are using the same engine as Storm of War: Battle of Britain.

na85
01-17-2008, 04:39 PM
set up a test:

trim for level flight, go into wonderwoman view, put throttle to 100%, record TAS, then push to 110% and watch to see if TAS changes.

thefruitbat
01-17-2008, 05:00 PM
Originally posted by na85:
set up a test:

trim for level flight, go into wonderwoman view, put throttle to 100%, record TAS, then push to 110% and watch to see if TAS changes.

Who is this wonderwomen?!? http://forums.ubi.com/images/smilies/mockface.gif

I obviously havent tested belligerently, as i wouldn't of asked othewise! However from personal observations, made of the cuff, please dont record this, i dont think they do.

I guess i just dont understand why jets go past 100% and what it means, where as i do understand what it means in most props.

Even if they do gain, why the 110%?

cheers fruitbat

Waldo.Pepper
01-17-2008, 05:07 PM
In my experience they do. You get a little bit faster, but only under rare circumstances. But you have to be going crazy fast before you notice it.

Don't overheat. Take a Heinkel 162 up for a spin. Get to 5000m. Dive down to 1000m at 100%. IIRC you can get to about 930kmph. And stay there.

thefruitbat
01-17-2008, 05:19 PM
Originally posted by Waldo.Pepper:
In my experience they do. You get a little bit faster, but only under rare circumstances. But you have to be going crazy fast before you notice it.

Don't overheat. Take a Heinkel 162 up for a spin. Get to 5000m. Dive down to 1000m at 100%. IIRC you can get to about 930kmph. And stay there.

Thats the odd thing i've found with jets. I can get to, an HOLD all of there respective top speeds, but not by LEVEL acceleration. If i climb above, as you describe, and say shallow dive to my desired height, the speed will bleed off until top speed, and hold. Level acc, i get no where near.

fruitbat

stalkervision
01-17-2008, 05:37 PM
do jets benifit from pushing trottle past 100%?

Not in real life.... http://forums.ubi.com/images/smilies/disagree.gif

Viper2005_
01-17-2008, 05:42 PM
The meaning of power setting in IL2 is contextual.

All that 110% means is that you're asking for 110% of some power setting variable, whatever that variable may be.

Therefore, the chances are that if 110% is available it's probably useful.

(It would be more useful to talk about ratings, but ratings are a somewhat technical subject. I can go there if you want, but you probably don't. Suffice it to say that engine models in IL2 are considerably simplified...)

You might be asking for 110% rpm, you might be asking for 110% EPR, you might be asking for 110% T4 or T5. In the case of T4, the chances are that it's not measured but calculated.

Each of these variables (rpm, EPR, T4 and T5) have been used as power setting variables in jet engines, and this list is by no means exhaustive.

Recent engines have effectively been controlled by auto-throttle, with the thrust lever "asking" the auto-throttle to deliver a certain quantity of thrust. It's very easy to envisage a system wherein the thrust lever becomes a "go" lever which controls the set-point of a speed-holding autopilot which in turn controls speed via an auto-throttle which modulates a series of power setting variables in order to achieve the desired result as efficiently as possible...

If you want to take the subject a little further,

http://en.wikipedia.org/wiki/Jet_engine_performance

This may usefully be followed up with:

http://www.amazon.co.uk/Gas-Turbine-Performance-Philip-Walsh/dp/063206434X

Metatron_123
01-18-2008, 12:31 PM
Originally posted by thefruitbat:

I'm only interested in the proper jets though*, ie me262, he-162-a2, ar-234 (my fav, what a plane), yp80 and the mig9.

The Yak-15 is a 'proper' jet. If you mean those that actually saw action, why is the Mig-9 in that list? I think China never used them in the Korean war.

And yes Korea would be great, provided we get to fly La-9s, Seafuries, Seafire 47s as well as the jets!

Waldo.Pepper
01-18-2008, 03:38 PM
Did some testing the other day. Might have been last night. (Getting old when the days merge into each other like that.)

Anyway at medium altitude (7500m) I got one of Heinkels 162c to max speed at 100%. Then I pushed throttle to 110%, and tried to keep alt steady. Within a few hundred meters.

So what happened was an immediate speed increase and an immediate spike in engine temperature that I could not avoid. The speed increase was kind of startling. It went from about 800kmph TAS to over 900 kmph TAS. But overheating was unavoidable, at least by myself.

Usually I do not fly this plane. If it did not see service in the war. (No matter how limited) I normally don't fly it. (Unless its online with a group or something.)

So is that a benefit? If you need to get away I guess it is.

Bremspropeller
01-18-2008, 07:05 PM
Originally posted by stalkervision:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">do jets benifit from pushing trottle past 100%?

Not in real life.... http://forums.ubi.com/images/smilies/disagree.gif </div></BLOCKQUOTE>

Yes, they do.
Depends on wiring and thrust-rating.

In airliners, you have TOGA (Take-Off/ Go Around) and MCT (Max Continuous Thrust).
MCT is an unlimited thrust-setting (well, virtually, the higher the throttle-setting, the sooner your engine's gotta be overhauled). MCT thus represents 100%.
TOGA, however, is time limited. It's needed for MTOW take-offs with short, or "hot'n high" runways, or go-arounds when you need every pound of thrust avaliable.

TOGA may only be applied for a few minutes (usually 5mins) to prevent engine damage or costly overhauls.

I've seen a 737-300 having both engines changed b/c the pilot thought running the TOGA setting for ten minutes was a good idea.

There are military aircraft that can run their engines at overspeed or have a special "pursuit" mode.
The F-15 is one of them.

Engine life-time is very critical in RL ops.
Even "chip tuning" may have a large impact on the engines.
For example: the CFM 56-5B can be taken for the whole A32X-family.
Normally, it's rated at rougly 27k lbs (also depends on the customer). That's what it was designed for.
Hanging that thing on an A319, you'll only need 23k lbs for the same performance. Thus, you'll downrate the engine in order to safe lifetime.
An A318 may go forever on that engine (needs even less juice), whereas an A321 is always critical with it's uprated engines.
33k lbs is just not what the engine was initially designed for - and you'll recognize that when you're doing a borescope inspection.
The combustion chambers and "hot parts" virtually melt away http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif
Same goes for the 1st gen. A340 engines (56-5C).

Short question, long answer, i know http://forums.ubi.com/images/smilies/winky.gif

stalkervision
01-18-2008, 09:01 PM
alright bremspeller if you must be picky for a short time.. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

DrHerb
01-18-2008, 09:44 PM
How many cycles did the engines go through on the B-737-300? before hot section inspection?

BSS_Vidar
01-18-2008, 09:55 PM
100% is full power also known as "Military Power". Anything past 100% is Afterburner, or as our British friends like to call it, "Reheat".

I am unaware of any jet aircraft during this period having afterburner. The 110% in-game is a mistery to me.

V

VW-IceFire
01-18-2008, 10:20 PM
Originally posted by BSS_Vidar:
100% is full power also known as "Military Power". Anything past 100% is Afterburner, or as our British friends like to call it, "Reheat".

I am unaware of any jet aircraft during this period having afterburner. The 110% in-game is a mistery to me.

V
That'd be a modern day combat jet. 110% doesn't have to represent afterburner just a setting beyond maximum sustained.

Bremspropeller
01-19-2008, 06:47 AM
Originally posted by DrHerb:
How many cycles did the engines go through on the B-737-300? before hot section inspection?

No hot section inspection, they just put on an entire new engine on each side.


If you mean the inspections on the A321. Well, those occur in a normal timeframe, but you'll see a difference between a normal rated 27k engine and those 33k ones.

Taylortony
01-19-2008, 08:53 AM
100% on a gas turbine does not mean 100% and yes they do exceed this....

as for the british "reheat" it tends to be refered to as dry thrust prior to reheat (wet).....u can also have reheat in the dry band, the Jaguar had PTR which is part throttle reheat, this meant you could go 100% dry power then into reheat, but then be able to pull it back to about 80% dry power whilst remaining in partial reheat.......ie still lit, this was to enable rapid power tweaks during inflight refuelling......... see you lot learn something every day :}

Viper2005_
01-19-2008, 01:52 PM
I always thought there was something rather Monty-Python about using reheat whilst refuelling, pumping fuel in at one end whilst pumping it out almost as fast at the other...

Matching must have been fun with PTR; it's very easy to see failure modes associated with the scheduling of engine non-dimensional speed, reheat fuel flow and nozzle position, especially if the reheat was to suddenly go out amidst all the excitement...

And of course, the kind of rapid throttle movements to which you allude would further compound the complexity (and adversity) of the scenario by bringing the poor engine into hot reslam country.

What were the failure rates like?

Surely airbrakes would have been cheaper?

Taylortony
01-19-2008, 08:23 PM
Used to get the odd pop surge at high angles of dangle and low speeds, but cannot remember ever changing an engine due to the reheat or reheat module in 4 years... used to often have to change the cats though.

The reason they used it was the Jag was a bit underpowered so it gave it more control. It needed more oooomph, not slowing down with A/brakes

Haigotron
01-20-2008, 10:04 AM
I think I'm one of the few who actually LOVES the jets, and I have to agree with you, the 234 is one hot momma http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif has a very sexy cockpit too http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Viper2005_
01-20-2008, 11:07 AM
Originally posted by Taylortony:
The reason they used it was the Jag was a bit underpowered so it gave it more control. It needed more oooomph, not slowing down with A/brakes

The idea of brakes would be to engage reheat and then leave the engines alone, and control drag with airbrakes instead of controlling thrust with PTR to attain the same end result as regards specific excess thrust control.

The reason I bring this up is that this was the generally accepted strategy for approach control in the early days (especially for carrier ops), providing both improved speed stability (thanks to the parasite drag) and allowing the engines to operate at reasonably high rpm, thereby easing the acceleration problems which otherwise plagued the early engines due to their lack of surge margin.

It therefore seems interesting that PTR was selected as the best way of providing rapid modulation of excess thrust, since I would have though that it implied some quite scary development work when compared with airbrakes which are fundamentally simple devices and which were already understood...

Didn't the F-4 community just engage one reheat and finetune thrust with the dry engine? Whilst it's a slightly scary concept in some ways, it would be easier on the engines than PTR.

PTR really seems like a very technically difficult way of attacking the problem; kind of "because we can" stuff if you see what I mean...

How did PTR work in the cockpit? The idea of rocking through a gate at the end of the dry thrust range to access reheat seems a bit strange if you're then going to pull back on the thrust levers again to use PTR...

Taylortony
01-20-2008, 04:04 PM
Putting the Air Brakes out on a Jag you might as well just pull onto your local forecourt as you will have for want of better words, ceased to go forth......... A Herc tanker would be seen to be pulling away from you http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

In the cockpit you would go through the gate into the wet range and upon coming back through the gate the reheat would remain lit down to about 80% if memory serves me correctly, that way you did not have any lag due to it having to relight if you needed the extra thrust.

PTR was originally concieved as a go around fix on one engine, full reheat being to much but when doing and I quote someone who used to use it now


"Jaguar PTR was indeed introduced as for AAR. It was found that the need to throttle the RH engine back at altitude to prevent surging left the driver without sufficient fine control of his airspeed on the LH engine- effectively he would have been at max dry or thereabouts, and any further increase in airspeed would necessitate going to Min reheat. This made the aircraft too fast. http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif Solution was to provide reheat from 80%Nh or Part Throttle Reheat, thus giving the driver a much greater degree of control at a critical point in AAR. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif To ease commonality it was applied to all Jaguar engines and only required a bit of extra electrical string as far as the airframe was concerned. Think its the only type to have that facility but then when you look at the origins of the FCU its hardly surprising that little extras had to be added on to make it a militarily user friendly engine".