F35's cleared for flight!!

[aeropilot]

Ginetta G15 Girl said:

This could never be got to work satisfactorily. Indeed, according to John Farley (the Harrier Test Pilot) it probably never would work.

Beat me too it. I remember JF posting a very informative post (as you'd expect) on PPrune in the JSF/F-35 thread about this.

[Eric Mc]

I thought that this was the problem. Is plenum chamber burning not even possible today?

[Ginetta G15 Girl]

FourWheelDrift said:

What about if it only used the rear nozzles when in horizontal flight, the front nozzles being turned off when swivelled up after take off and forward flight is achieved. Then divert the thrust from the rear nozzles back into the fuselage and into a normal single jet exhaust with a fully functioning reheat.

The Pegasus has 'hot' nozzles (the aft pair) ie 'normal' jet exhausts, and 'cold' nozzles (the forward pair) that utilise bleed air from the compressor. The nozzles thus can't be 'connected' in the way you propose

Apparently there wasn't enough thrust from the Pegasus/Pegasus derivative to achieve supersonic flight in the P1154 with afterburning merely on the aft nozzles.

More importantly, the fuel burn vs fuel required for supersonic flight meant that the weight of the a/c became so great that you needed PCB (Plenum Chamber Burning) on the forward nozzles merely to carry out VTOL!

Eric Mc said:

Is plenum chamber burning not even possible today?

According to John Farley, PCB in itself wasn't a problem as long as the a/c had forward motion. It was in the VTOL regime where it became a problem and especially within the hover. Lack of cooling airflow through the compresser during PCB in the hover meant that the compressor was rapidly destroyed.

Add in the extra problems of hot gas ingestion into the intakes, especially during PCB, and you can see the difficulties.

[Eric Mc]

How does the F-35 avoid ingesting hot gases in the hover (or the |Harrier for that matter)?

[Mave]

FourWheelDrift said:

What about if it only used the rear nozzles when in horizontal flight, the front nozzles being turned off when swivelled up after take off and forward flight is achieved. Then divert the thrust from the rear nozzles back into the fuselage and into a normal single jet exhaust with a fully functioning reheat.

That's essentially what the F35 does. But because you can't just "turn off" the thrust from the fan of a gas turbine, there's a separate fan driven through a clutch.

[ninja-lewis]

Eric Mc said:

How does the F-35 avoid ingesting hot gases in the hover (or the |Harrier for that matter)?

The lift fan at the front generates a column of relatively cold air (invisible in the thermal image below), which prevents the hot gases moving forward from the main engine.



The Harrier worked on the same principle, by sending bleed air (air that has been compressed by the fan at the front but not sent through the fuel burning section) through the front nozzles.

[Mave]

Eric Mc said:

How does the F-35 avoid ingesting hot gases in the hover (or the |Harrier for that matter)?

The jet from the lift fan or cold nozzles acts as a "jet screen"- the plume reduces the forward migration of the hot gases.

[Ginetta G15 Girl]

ninja-lewis said:

The Harrier worked on the same principle, by sending bleed air (air that has been compressed by the fan at the front but not sent through the fuel burning section) through the front nozzles.

Although of course 'Bleed Air' is far from actually being 'cold' - the term 'cold nozzle' is relative. Compress any fluid and it heats up (Boyles Law in action!).

In fact the Harrier could suffer hot gas ingestion in the low hover. It is for precisely this reason that the 'Bona Mates' (Harrier Pilots) dropped the a/c quite rapidly through the last 10 ft or so on a VL (vertical landing), chopping the throttle before the jet had fully settled on the ground/deck.

Edited by Ginetta G15 Girl on Wednesday 16th July 23:12

[Mave]

Mojocvh said:

it cannot match the current generations transonic acceleration ie "running away bravely" It has a single engine that does two jobs, it weights just as much as a current twin engined fighter and has a wing area half that of current aircraft...

I'm guessing the transonic acceleration is better than a harrier (which also had a single engine doing 2 jobs), and I wouldn't base turning performance on wing area; aircraft have been getting significant fuselage lift since the 70s.

[Ginetta G15 Girl]

Mave said:

I'm guessing the transonic acceleration is better than a harrier (which also had a single engine doing 2 jobs)

Between 400kts and 550kts the GR3 was one of the fastest accelerating a/c in the world.

Mave said:

I wouldn't base turning performance on wing area; aircraft have been getting significant fuselage lift since the 70s.

In the cruise maybe, but in the turning fight wing area, or rather wing loading, is crucial.

[S3_Graham]

Ginetta G15 Girl said:

Although of course 'Bleed Air' is far from actually being 'cold' - the term 'cold nozzle' is relative. Compress any fluid and it heats up (Boyles Law in action!).

In fact the Harrier could suffer hot gas ingestion in the low hover. It is for precisely this reason that the 'Bona Mates' (Harrier Pilots) dropped the a/c quite rapidly through the last 10 ft or so on a VL (vertical landing), chopping the throttle before the jet had fully settled on the ground/deck.

Edited by Ginetta G15 Girl on Wednesday 16th July 23:12

Agree with what you say, but Boyles gas law is pressure vs. volume at a constant temp isn't it?

[Ginetta G15 Girl]

Alright, the development of Boyle's Law PV=K

Into: PV/T=K

[Mave]

Ginetta G15 Girl said:

Mave said:

I'm guessing the transonic acceleration is better than a harrier (which also had a single engine doing 2 jobs)

Between 400kts and 550kts the GR3 was one of the fastest accelerating a/c in the world.

Maybe, but that's hardly transonic. As you get close to transonic, the propulsive efficiency drops through the flow because of the 50/50 cold/hot thrust split

Ginetta G15 Girl said:

Mave said:

I wouldn't base turning performance on wing area; aircraft have been getting significant fuselage lift since the 70s.

In the cruise maybe, but in the turning fight wing area, or rather wing loading, is crucial.

I disagree; what matters is effective wing area, and at high alpha the fuselage effectively increase the wing area. So looking at Janes or Wikipedia to get wing area and use that as an indicator of wing loading is misleading because it discounts the effect of the fueselage. It may not be as efficient as an aerofoil, so hurts SEP, but that's no different to a delta at high alpha.

[jimbobsimmonds]

S3_Graham said:

jimbobsimmonds said:

aeropilot said:

FourWheelDrift said:

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

The X-35 first flew in 2000, F-35A in 2006 and the first F-35B in 2008 and the B model is expected to be in service in December 2015 with the US Marine Corps, 1 year before the USAF get their A models.

Now I'm not saying the Eurofighter was a slow development (but I do think it was) but the F-35B has been positively rushed by comparison to it and others.

The trouble is with all this new stealthy high tech fly-by-wire computer controlled gubbins and fire/control weapons kits etc is that the design of it all in the mid 2000's is now so out of date, they almost have to start again just prior to entering service.
F-35 has 8 million odd lines of code or something like that, and the hardware its all mounted on is 'technically' now out of date.

As it the case with all military/civil aerospace avionics though. Even the latest updates to the Typhoon are on ancient hardware (in comparison to what is available). The final updates for Typhoon in 10-15 years will probably be with hardware we recognise today. The time it takes to design, test, redesign, qualify then produce avionics hardware is incredibly long as it HAS to work with near 100% reliability. Component obsolesence (ie: the manufacturer stops making the chip, capacitor or w/e) is a major problem in the aerospace industry.

I'd say that civilian stuff is more up to date than military, based on the fact that they can share components and use 'off the shelf' items whereas most military stuff, as you say, is all made to order when the original order is placed.

My site produces a lot of the avionics for a lot of platforms, civil and military, civil is every bit as much of a problem as military, the COTS items still have to be qualified every bit as much as military items. Certainly for the safety critical stuff.

[MartG]

FourWheelDrift said:

That's the cover lifted up on the cold air lift fan.

mcdjl said:

The computer deals with all that automatically,

"Open the lift fan door please HAL"

"I'm sorry Dave, I'm afraid I can't do that"

[Lurking Lawyer]

I did the same gag earlier in the thread, MartG - it fell flat.

Pearls before swine, eh....?

[Eric Mc]

I got it.

[Ayahuasca]

Is the F35 imperial or metric? Stuff like wrench sizes, bolt sizes, weights and measures, capacities and volumes, maintenance instructions, etc?

Edited by Ayahuasca on Thursday 17th July 22:58

[Mave]

Predominantly imperial.

[RobGT81]

Eric Mc said:

How does the F-35 avoid ingesting hot gases in the hover (or the |Harrier for that matter)?