<meanwhile in a distant/nearby underground/subsea/suburban/London/volcano-based lair/log-cabin/tent/basement-flat-under-a-pillar-box-outside 221B Baker Street>
"What's that Lassie/Penfold/Oddjob? Some children are stuck down a well? No? There's an SRVL discussion on PPRuNe? Golly! Something must be done! Alert the Peoples Liberation Army Navy (and coincidentally anyone else who reads PPRuNe) for incoming rumours..."
Originally Posted by
stilton
The approach speed is so slow it brings up the obvious question though, I think it’s about a 30 knot overtake, assuming 20 knots wind over the deck that’s around 50 knots IAS
At such a low speed I don’t see how you’re generating any worthwhile, additional wing lift so what’s the point if the idea is to allow higher landing weights ?
50 KIAS (other numbers are available, but it's not my place to repeat them here) on a wing as big as the F-35B's generates significant lift when compared to the mass of things like (expensive) stores rather than in comparison to the mass of the whole aircraft. I.e. at F-35B/QEC SRVL airspeeds (look them up, or just watch the TV footage carefully), the extra lift is worth having.
Originally Posted by
safetypee
If a simplistic view of F35 VL control is that lateral stick controls left-right motion and the thrust lever fwd-aft; the conventional stick input for pitch, controls vertical rate (thrust), then there is no direct pitch change control.
I suspect that there is some automatic integration within the control law, but again not very much pitch change would be available if the nozzle height is critical. Similarly that wing lift with forward motion / WOD may not decrease the thrust required for landing / nozzle clearance to have any benefit.
Are F35 VLs essentially made at constant attitude ?
At SRVL speeds, waggling the stick fore/aft pitches the nose down/up. The control law (with support from PW/RR) ensures that the flightpath follows, given that the aircraft is mostly jet-borne and hence the change in wing-lift isn't going to give the required flightpath change by itself. If radically changing pitch attitude is seen as a problem close to the deck, then one might design the manoeuvre such that the required flightpath doesn't waggle around much, and back that up with a (not-just-fortuitously) suitable flight control system and appropriate visual landing aids and pilot procedures/training. However, what of actual VLs? Many moons ago, the (at the time) response to longitudinal stick inputs of a simulation of an aircraft involved in the development of control strategies for what (eventually) became JSF, elicited expressions of concern and even criticism from some test pilots who flew it, including TPs from the USA. It was felt that not properly exploiting the wing lift available at modest airspeeds was, well, wrong, and hence having the aircraft pitch in response to stick inputs intended to change flightpath, even at speeds where pitch changes themselves did not do much to flightpath, would be right. A decision was required as to what constituted the minimum speed below which having the nose pitch up and down in response to longitudinal stick inputs was silly ("Chaps, am I doing a VL or not?"). Subtleties were raised. Ships were mentioned. Anxious glances were made at pocket watches as yet more subtleties were raised and the faint sound of covers being removed from beer pumps in nearby villages could be discerned. Faced with this potentially awkward situation, a decision was taken, stuff was implemented, the aircraft flown, positive reviews recieved and the issue was never spoken of again. Well, OK, obviously "Team JSF" reviewed this stuff and designed an appropriate control law including stuff to address lessons learned from the research programme, but you get the gist of it anyway. Probably.