Jschill

The Marine Corps AV-8B Harrier demo, Reno 2017
Jason

Ruizmilton

My Feedback: (29)

Wow, was this a single flight? Of course there is some editing in the video, if it is a single flight, total time with the nozzles down is over four minutes and the prolonged hovering was a bit over three minutes, I was under the understanding that the Harrier was limited to about two minutes of hovering per flight, this was dictated by the capacity of the internal water tank, water that is injected into the pegasus engine intake to keep it from overheating while in hover mode. What is the actual limit of hovering time per flight for the Harrier?

Jschill

Yes, this was from a single flight demo.
Jason

paulhat

Awesome!!

FalconWings

My Feedback: (57)

Water is necessary on extremely hot/humid days.
On cooler days hovering is limited by engine oil temps...as long as you dont exceed it..you can hover.

Typhoon Phil

I am an ex RAF Harrier engine engineer and the only factor that determines the length of time it can hover for is the amount of fuel it can carry...... that is why our display jets were in the clean configuration so thAt they could carry more file to hover with ie. Less drop tanks and pylons weight.... more fuel to carry for same equivalent all up weight.

One point that someone has made here is that it carrys water to cool the engine... this is not entirely true as the system works in such a way that water is injected into the engine (when the system has been turned on by the pilot) only after the RPM rises above 92.5% and its purpose is 2 fold.... firstly it does reduce the cool it but what that means is that more fuel can be added to raise the temperature again but because of the more fuel , you actually get and increase in thrust for the same RPM.... secondly thrust is determined by the Mass Airflow through the engin and as water is sprayed into the engine then the Mass of that air is increased and so you get an increase in thrust..

Hope this further explains how and why the Harrier can hover for so long......

cmp3cantrj

I'm guessing that the extra thrust produced by the water injection is only needed when the aircraft is heavy with fuel. Once the fuel weight is reduced then the thrust required is also reduced and the water injection can be switched off. I presume that this is the reason why running out of water is not an issue.

Typhoon Phil

Yes that is generally correct in that the water system is used as a way to enhance thrust..... if the pilot uses too frequently then it can become a problem as he will run out too early..... the system will still add the extra fuel to compensate for the water but because the water has run out then the Jet Pipe Temperature will increase to potentially a critical level and he will need to throttle back to save the engine..... so the time with water flowing is carefully monitored.

FalconWings

My Feedback: (57)

The concept is you pump water into the combustor to use as an oxidizer, and it lowers the combustion temperature significantly, resulting in lower EGT (you get more bang for the buck). This improves both high altitude and hot day performance (which can be translated to more thrust, more payload, more fuel). The company I work for owns the patent to use peroxide as the oxidizer, but more for high altitude performance than anything.....but using peroxide has it's own set of issues. :-)

On a side note, I've witnessed testing of Peggies on the dyno at Cherry Point.....and it beats the living crap out of me how that engine can sustain having a T exhaust and not break apart. Incredible. That sure was a hot test cell!

Cheers!
David

David Gladwin

[QUOTE=FalconWings;12383747

On a side note, I've witnessed testing of Peggies on the dyno at Cherry Point.....and it beats the living crap out of me how that engine can sustain having a T exhaust and not break apart. Incredible. That sure was a hot test cell!

Cheers!
David[/QUOTE]

All down to the brilliance of a British engineer, Sir Stanley Hooker, who, in his own words was " Not much of an engineer"

Two of his other designs, the Olympus ( the only aircraft jet engine Iknow of which runs at full throttle throughout the cruise ) and the RB 211 have powered me for thousands of hours without a single failure.

David.

David Gladwin

For anyone interested in jet engines, or engineering, Sir Stanley's ( few people have been more deserving of a knighthood) autobiography, "Not much of an engineer" is a brilliant read, ideal for the Christmas holidays.

It it is published by Airlife isbn 0906393 35 3. ( may have been updated, Google or Amazon will resolve)

David.

FalconWings

My Feedback: (57)

Absolutely, credit where credit is due. RB-211 easily the best commercial engine ever produced, almost making the 757 competitive with modern day NGs and NEOs.

cmp3cantrj

Yet in spite of all that his own favourite was the very first thing he did at Rolls-Royce, which was the re-working of the Merlin Supercharger (as used on the Spitfire). This was because it was the only project he ever got to do all on his own.

We probably all have cause to be grateful for that one!

David Gladwin

Totally agree. Perhaps we should be most grateful, too, that, he solved the problems on the RB 211 and saved Rolls Royce in the process.

Few people know that another brilliant aspect in the development of the engine that eventually became the Trent was the creation by RR of the single crystal turbine blade, which allows higher turbine temperatures and hence thrust. On my last visit to RR at Derby, they showed me one but wouldn't tell me how it was made !

Don't know of Sir S H was involved in that but he was truly a a brilliant engineer.

That said, the Pegasus would not have been needed without the brilliant engineering of Sir Sydney Camm, chief designer of the Harrier, who started his aviation career with model aircraf design and construction, as did Sir Frank Whittle at Cranwell, I am sure they would be delighted to see the extraordinarily high level of model aviation now.

David.

JP-1

Have to concur on that David, very interesting read.

Alistair