Busting the big two myths about the Harrier

[BrySkye]

For todays lesson, a write up I made over a year ago. :P

THE TWO BIG HARRIER MYTHS
1.

“Harriers don’t do vertical take-offs very often because it burns too much fuel, reducing their range”

The most common myth about the Harrier.
In reality, a vertical take off doesn’t necessarily burn more fuel than a conventional take off.

Let’s go back to Harrier 101 first.

Although it has four nozzles, the Harrier only has a single engine.
So there are no extra ‘lift’ engines using fuel while hovering.
All you are really doing when hovering is rotating (vectoring) the nozzles and so the direction of the thrust.

Fuel consumption is mainly dictated by engine power.
The throttle lever.

This is pretty much universal for any internal combustion engine.
Basically, it doesn’t matter which direction you are squirting the hot air, be it downwards or aft. If the engine is at full throttle (in the same conditions) then it will consume the same amount of fuel.

Hovering doesn’t magically mean the fuel pipes can suddenly pump more fuel into the engine.
You could be hovering or you could be in a low-level dogfight at 500 kts with the throttle firewalled to maintain energy. You’ll be using similar amounts of fuel.

Probably more because hovering in most circumstances doesn’t require full throttle.

So where does this myth come from?

While it’s true that a Harrier performing a short or conventional take off can fly much further than one performing a vertical take off, the reason is very different, but so much more straight forward.
The truth is that a Harrier is weight limited in performing a vertical take-off.
To do so, the aircrafts weight must be less than the amount of thrust the engine can produce.
Harriers fitted with the most powerful version of the Pegasus engine can just about take off vertically with full internal fuel, but no payload at all.
If you want to strap any kind of weapons to it there is only one option.
Remove fuel.
This is the reason why Harriers have less range when performing a vertical take off.
Not because they burnt extra fuel in doing so.
But because the aircraft was loaded with less fuel to begin with.

We can create a scenario where a Harrier II, with no payload at all (clean) and say half a tank of fuel, performing a vertical take off and transition to cruising speed of 420 kts will consume less fuel than a Harrier II which is fully loaded ‘dirty’ (full internal fuel, external fuel & weapons up to Maximum Take Off Weight) performing a completely conventional take off.
This is because the fully loaded Harrier is not only heavy, but also draggy.
The result of which is that it will accelerate more slowly and so have to use a higher power setting. It will also have to use that higher power setting for longer in order to reach 420 kts.
That means more fuel consumed.

Don’t get me wrong. The fully loaded Harrier will probably still fly a greater distance at the end of the day.
But that’s because it would have been carrying 3x the fuel in the first place.
Though it wouldn’t fly 3x further, because it was burning more fuel per minute.
The actual fuel *consumption* would still be higher in order to over come the drag.
This is the F-35B scenario. Although it has far greater range than the Harrier II, this is by virtue of a much larger fuel capacity, not a more effecient engine.
Based on published figures, despite being a design that is decades newer, the F-35's Pratt & Whitney F135 still burns more fuel per minute than the Rolls Royce Pegasus, especially the Mk.107.

I got some approximate figures for the fuel consumption of a Harrier GR3 from a retired RAF IV Squadron pilot who flew Harriers in Germany and even over the Falklands after the war ended.

A GR3, so the 70's vintage Pegasus Mk.103, used 50 lb/min at high level cruise (M0.80), 100 lb/min at low level cruise (420 kt) and 200 lb/min in the hover.

Remember that low level cruise at 100lb/min would not be at such a higher throttle setting. But if it was pushed up, such as to dogfight, then it would match or exceed the 200 lb/min figure.

As food for thought, an F-16C Block 50 using MIL power at sea level burns about 280 lb/min of fuel.
So a hovering Harrier GR3 (first generation Harrier) is actually still using less fuel every minute than an F-16C.
As a bonus, that same F-16C, at sea level, in full afterburner would be using 1,600 lb/min.
That rate would empty the Harriers fuel tanks in less than 3 minutes.

[BrySkye]

2.

”A Harrier can only hover for 90 seconds.”

Yeah… OK, first watch this.

https://www.youtube.com/watch?v=CM9rinzB1C8

https://www.youtube.com/watch?v=A4CFuKKUwh4

Good, now you know this one has been blown well out of the water.
…and riddled with bullets and rockets on it’s way down.
For the record, this display won the Steedman Display Sword (Best UK Participant) at RIAT 2002 for Royal Navy pilots Lieutenant Commander Rob Schwab and Lieutenant Will Hynett of 899 NAS.

We can thank the History Channel for this one. A more recent myth that managed to gain a lot of traction thanks to the internet.

The 90 seconds number comes from how long the aircrafts 50 gallon water supply will last.

In obtaining maximum thrust, the engine is temperature limited.
To enable the engine speed and thus thrust to be increased, water is sprayed into the combustion chamber to keep the blade temperature down.
With water on, the engine rpm is increased by about 2.6% for a given throttle setting.

The myth is that water is *required* for hovering.

It’s not. Remember that the Harrier and it’s engine was designed and built in Britain, for use over the Western and Northern European theatres if the Cold War had turned hot.
Especially for CAS over Germany, destroying Soviet tanks.

In these conditions, with cooler ambient temperatures, Harriers can generally hover without approaching the engines limits.
The same was true during the Falklands War. It was COLD in the South Atlantic.

It’s worth pointing out that this myth came from an American documentary on the Harrier.

USMC Harriers are based at locations like MCAS Cherry Point in North Carolina and often fly from bases in Arizona, Florida and Nevada.
These locations, along with the likes of where it has operated in combat such as Iraq, have considerably higher ambient temperatures or in the case of Afghanistan, much higher altitudes. 'Hot and High' is the double whammy for VSTOL aircraft, as the Soviets found out dearly with the Yak-38 when they trailed it in their own Afghanistan operations.

It is for this reason that USMC Harriers have to use the water considerably more often than those in the UK did, in order to keep the engine from exceeding it’s temperature limits, which in turn limits its time in the hover.

The use of water injection is also the reason why USMC AV-8B displays at American airshows are typically far more smokey than RAF/RN Harrier displays in the UK were.

[heartc]

Originally posted by BrySkye:

For todays lesson, a write up I made over a year ago. :P

THE TWO BIG HARRIER MYTHS
1.

“Harriers don’t do vertical take-offs very often because it burns too much fuel, reducing their range”

Haha, lolz, who would say such a thing? One second on the afterburner in an F-16 probably burns more fuel than 10 vertical take offs in a Harrier would haha.

[Jimmy6]

I agree with the sentiment of the statement that a vertical takeoff doesn't use more fuel than a conventional one, but it's never quite as simple as that.
The Pegasus actually operates to a higher RPM and temperature limit when in the hover than it does during a conventional/short take off. Same goes for a vertical landing; there's a logic in the engine control software that increases the engine limts depending on whether the nozzles are deflected, whether the water is selected to take-off or ldg, and whether or not the gear has been cycled during the sortie.
So I guess if I was going to be a pedant then I would say you would burn more fuel during a vertical take-off and acceleration to cruise speed than you would during a conventional/short takeoff due to the engine running faster and hotter. If I was going to be really pedantic, I would probably bang on about jet engines being more efficient at higher airspeeds (closer to the jet efflux velocity) hence saving even more fuel on a conventional/short takeoff.

But going back to the original point, yes - vertical takeoffs were not routinely flown due to payload limitations more than anything else. In general on a standard UK summer day, you would only be able to perform a vertical takeoff once the jet had burnt about half its internal fuel. Of course, there were many factors that would gain you several hundred pounds of performance here and there; headwind, actual engine installed performance (some jets were just more powerful than others) as well as the main ones - temperature and pressure.


As for the water, you're absolutely correct. Even the small engined jet (Pegasus 105) would still hover on a hot day after running out of water, but the fatigue counts on the engine would be fairly high. You would never plan to land without water if you were "wet committed", but the jet would still hover even if you ran out - most of the time!

With the bigger engine jet (Pegasus 107) the water was only needed when the temperature got significantly above 25 dec C (memory failing me here - it may have been higher). In fact, it could actually be a hindrance, carrying around an extra 495lbs of water that you didn't need. Having said that, it was always carried on sorties due to centre of gravity issues etc.

Hope that's of interest.

[BrySkye]

Obviously if you were to go into every fine detail, there a dozens upon dozens of factors that can have an alteration on the outcome. These things are seldom black and white.
Though to be honest, this applies to any aircraft and jet engine, not just the Harrier.

While the engine limits may be increased, that doesn't mean that increase has to be exploited.

So in absolute laymans terms, the general myth is that in performing a VTO, the Harrier is an bonafide gas guzzler, not just in relation to it's own performance, but compared to other jet aircraft, and that is what is specifically being addressed.

Before originally posting this, I laid out the scenario with that GR3 vet and he concurred that, in general terms, sfc can be better in an aircraft performing a lightly loaded VTO vs a heavy and draggy aircraft performing a STO or even CTO.
It still wouldn't get very far, but *fuel consumption* wasn't the reason why.

[Jimmy6]

Agree with you there mate.
But I will maintain that in performing a VTO that the engine will be running faster and hotter than one operating to "normal" limits. The increase would absolutely be exploited because full power is selected for every VTO.
Like I said, being pedantic and absolutely splitting hairs- not trying to start an argument!

[BrySkye]

Originally posted by jamiemac:

Agree with you there mate.
But I will maintain that in performing a VTO that the engine will be running faster and hotter than one operating to "normal" limits. The increase would absolutely be exploited because full power is selected for every VTO.
Like I said, being pedantic and absolutely splitting hairs- not trying to start an argument!

Let's just remember the full scenario depicted wasn't just the take off, but reaching a specific cruise configuration.
Even if it was using that extra power, the aircraft in that scenario is going to have transisitioned to conventional flight well within a minute (especially John Farley style) and, with no external weapons, can throttle right back during it's climb and acceleration compared to the aircraft carrying a heavy Harrier II load of drop tanks, lightning pod and a selection of laser guided bombs, etc.

The weight and drag is going to require a much higher thrust setting for a protracted period of time, unless you want to climb at about 500fpm in which case even a modern jet airliner (except for an A340-200/300 with its hairdryers under the wings) is going to be s♥♥♥♥♥♥ing as it outclimbs you.

[Jimmy6]

OK, if you're talking about a jet at MTOW carrying out a STO and accelerating to cruise speed versus a clean jet with about 2000lbs of fuel on board then I would agree with you, the heavier jet would burn more fuel by the time it reached cruise speedl. Probably ;)
All I said was that a VTO burns more gas than a STO, certainly by the time you've transitioned to, let's say, 5nm from your point of departure. Not trying to start an argument, just pointing out that there's a bit more to the problem than initially meets the eye.

But I totally agree, a VTO is not practical with any kind of payload on board. Much better to point it at a ramp and get airborne in less than 200'!

[damson]

Originally posted by jamiemac:

All I said was that a VTO burns more gas than a STO, certainly by the time you've transitioned to, let's say, 5nm from your point of departure.

Thats pretty obvious as with STO you have additional lift (created by an airflow around wings during STO) which isn't available during VTO. So the engine needs to do "more work" to counteract the gravity. Not to mention that getting to 5nm out of the starting point is faster with STO than with VTO.

[Atlantis]

Ive seen a Harrier land vertically, then take off vertically on a bridge in the Florida Keys, fly to downtown Miami, hover around a lot of skyscrapers, while engaging terrorists from floor to floor, have its tail slammed into the window of one of the buildings, get shot up, take out a helicopter by launching a missle through a building with someone attached to said missle, and land vertically in downtown Miami. No concern for fuel consumption, weight, etc etc.
Man what an aircraft!

[damson]

"You're fired" - classic!

[Atlantis]

Love that scene!

[Jimmy6]

Arnie can actually VTO with any fuel /stores load...

[Nilboggen]

Uh and clearly it takes more thrust thus more fuel for a vertical take off.... I mean think about it. Put your car in neutral and give it a push now pick it up, see how the forces to gain momentum are drastically different. It is easier to gain forward momentum and gain lift by pushing air over the wings than it is to provide direct lift and gain flight. Its not a myth its just how things work.

[udidwht]

The Harrier does indeed have higher fuel consumption rate when in VTOL mode. When in VTOL mode the wings are creating zero lift to aid in reducing overall power output to maintain a given speed. I worked on various aircraft when in the US Navy (1986-1996) as an AD-1 jet engine mechanic.

[BrySkye]

Not sure why this is getting looked at again 4 years later...

If anyone feels the need to say:

"A Harrier flying level has less fuel consumption than one hovering because the help from the wings means it doesn't need as much thrust to stay airborne, thus a lower power setting and less fuel burn."

Then you kind of missed the point and what the myth is actually talking about.
I'm also a little disappointed someone saying that wouldn't first stop and think.
"That's so obvious, maybe I'm missing something?"

You're actually making the same overall point.

Just with the addition that you can create circumstances where that same point also applies in the opposite direction, hence the example of lightly loaded VTO vs MTOW CTO in a race to reach a designated cruise altitude and speed.
Once its transitioned, the lightly loaded VTO jet can climb at a much lower power setting than the MTOW aircraft by the exact same principle already described.

This *should* be simple and obvious stuff, and maybe some people are overthinking it a bit which is causing the problem.

The myth comes from an oversimplification, that is all.
That the reason VTO's are impractical and that the aircraft has a reduced range is because it *used* so much fuel during the VTO.
The real reason is that in order to perform a VTO in the first place, the aircraft has to carry a reduced fuel load.
Less fuel to burn in the first place, not drastically more fuel being used by the engine.

In a 1:1 scenario, yes, a VTO is going to use more fuel than a CTO by virtue of requiring more time at a higher power setting.
Though even then, the difference is often greatly exaggerated, saying as a VTO and transition to wing-borne flight can be concluded in 30 seconds.