F-35 Cancelled, then what ?

[Engines]

Courtney, Dat, JTO, DD,

Perhaps I can help out a bit here. What I can't do is improve on JF's succinct and 'spot on' comments about ski jump takeoffs. They are, by some distance, the lowest workload way of getting a combat jet into the air. The flat STO presented many more challenges to the F-35B team, and the lack of aft control surface movement shows how straightforward the evolution is.

However, it's a lot more than 'straightforward'. It's a little surprising, given that this is a pilots' forum, how few people mention the significant advantages it delivers. Firstly, operational: the ski jump will allow the F-35B to launch on task with at least another ton and a half of fuel and/or weapons. That's a ton (or two) of pure military goodness. Secondly, safety. As JF points out, the aircraft leaves the jump nose up and climbing without the pilot having to do anything. If anything does go wrong, the pilot has many more precious seconds to dump stores/jump out. At night, or in bad weather, or from a pitching deck, that's also a lot of goodness.

I do understand why some posters think this looks like a 'pucker' heavy evolution, but it's really, honestly, not. Every Harrier pilot I worked with said that it was a complete non-event. What's really amazing is that these gains come without penalty to the aircraft, which is fairly rare. The Harrier needed no mods to do ski jumps, save extra servicing checks on the nose leg. The F-35B has needed none. The flat deck STO drove the design, the ski jump came basically free.

Oh, and don't forget that it's another brilliantly simple and effective naval aviation idea from the UK's Fleet Air Arm. Respect.

JTO: Yes, the aft nozzle is definitely moving. I am not familiar these days with the F-35B control laws. but I would guess that what is happening here is that the aft nozzle is being left as far 'up' as possible to get to ramp exit speed in the shortest time (and distance), then programmed 'down' after ramp exit to support the 'fly away' profile. The Harrier did this manually, with the pilot selecting nozzles down to an adjustable 'STO stop' as it neared the ramp exit. F-35B does this for him/her.

For those that might not be familiar with the way a ski jump STO works, the key thing to 'get' is that the aircraft leaves the ramp BELOW flying speed. So the rate of climb starts to decay after ramp exit, depending on how much wing lift and jet lift is being provided. However, the aircraft is still climbing. As it accelerates, wing lift increases and jet lift can be reduced by altering the angle of the propulsion system's nozzles. At some point after ramp exit, the aircraft reaches an 'inflexion point', and the rate of climb starts to increase again. That distance between the end of the ramp and the 'inflexion point' is essentially a 'free runway in the sky' - around 1 to 1.5 km, depending on launch weight, temperature and other factors. That 'free runway' delivers the payload improvement.

The UK legacy performance limit for Harrier ski jump STOs was a minimum ROC of 400 feet per minute at the 'inflexion point'. Other nations have different limits.

A powered lift aircraft can 'schedule' (adjust) wing and jet lift so as to maximise the payload that can be delivered from the ramp. It can also be controlled well below wing borne flying speeds. Unfortunately, conventional aircraft can't do either of these. They have to launch at a speed at which they can fly controllably on wing lift alone. Their only option (with all thrust already applied) to arrest ROC decay is to apply more pitch, which increases drag, which slows the aircraft, which.....you probably get the picture. That's why the STOBAR option, being used by the Chinese and others, is, in my view, always going to be severely limited in effective payload.

Good questions on USN/USMC non-use of the ramp. The answer I always got was that the operational concept for the 'Gators' was a mixed air wing, with the requirement to carry out mass helicopter launches driving the flight deck layout. I know for a fact that many USMC aviators would love to have a ramp for F-35B. They aren't at all hard to fit, and ship handling wasn't affected. The loss of the most forward spot was not a problem for the UK - in any case, trying to operates helicopters from '1 Spot' in anything more than light airs was, in my experience, a bit of a mare. However, I gladly cede to the USMC, who know what they want.

However, there is no doubt that for a given deck (or say, a short expeditionary runway) a ski jump gives improved combat efficiency plus safer operations.

It's interesting that with the advent of the MV-22, short rolling takeoffs (STOs) are being considered as a standard shipboard operating procedure. Perhaps they could use a ramp as well?

Hope this lot of drivel helps - I'm always happy if it fills in any (quite understandable) gaps in some posters' knowledge. After all, that's what a 'forum' is supposed to do.

LO, I hope this isn't a 'meme' - whatever that is.

Best regards as ever to the clever folk who think up this sort of stuff,

Engines