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About skelsey

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    Broadcast journalist and BAVirtual Director of Training.

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  1. skelsey

    Several questions about the 737 NGX cockpit

    For a more pilot-friendly formula: SAT = TAT - (V/100)2 Where V is TAS in knots and the SAT and TAT are in degrees Celsius 😉
  2. skelsey

    Several questions about the 737 NGX cockpit

    My understanding is that temperature probes on modern aircraft are TAT probes and the SAT is then calculated from this sensed temperature. Logically this makes sense as the SAT is the temperature of the undisturbed air that the aircraft is about to fly through, so directly measuring that with a probe attached to the aircraft would be rather problematic! The percentage of the ram rise sensed by the TAT probe is known as the 'recovery factor' - a recovery factor of 1 would indicate a 'perfect' instrument which accurately senses all of the ram rise and therefore indicates the exact TAT, whilst a recovery factor of 0 would indicate a probe which senses none of the ram rise (i.e. indicates SAT). Modern probes have recovery factors very close to 1 -- this was probably not the case in the days of the VC10! Although the TAT probes used on modern jet transports are very good at measuring air temperature (ie they are largely unaffected by the heating effect of the sun, for instance) the drawback is that they do require air to be flowing through the probe to obtain an accurate reading, and so they are less accurate on the ground, for instance, unless they are artificially aspirated in some way.
  3. skelsey

    Question for RW GA pilots: Weights and Balances

    You are correct of course to say that the stall speed is higher with a forward CG. However, what you said was that there is a greater risk of stalling with a forward CG. This is probably not really the case for the reasons J35OE outlined - the increased longitudinal stability and greater nose-down moment generally makes recovery much easier and entry characteristics more docile. So whilst the actual stall speed will be a few knots lower than the book figures with an aft CG, the reduced stability and increased difficulty in recovering probably makes a stall easier to enter whilst also making the recovery more problematic. However, we're talking semantics really!
  4. Even 50R is pretty early to even start reducing thrust, let alone be all the way back on the idle stops and, again, most pilots I speak to are of the view that idle thrust at 50R in the real thing is likely to result in an 'arrival'. I'm not sure where the idea that the certification standards are predicated on idle thrust at 50R comes from either, because that's certainly not what Boeing recommend. A light aircraft, of course, is very different and coming to idle 'over the fence' and effectively gliding in with airspeed reducing toward the stall warner is a more valid technique in that environment. Absolutely -- I'm fully in agreement that the thrust levers should (generally) be smoothly retarded rather than 'chopped' for exactly the reason above (as mentioned, I can't think of many MSFS models where the thrust-pitch couple is well-represented so this is one area where the sim can give a slightly misleading impression). As Bertie says, the B747 FCTM suggests starting the flare around 30R by gently raising the nose about 2 degrees and then smoothly retarding the thrust levers to idle to reach the idle stop coincident with main gear touchdown -- this is actually pretty much identical to most if not all of Boeing's other products (with the exception of the pitch increase which I think is a bit less in the B747 compared to other types). Important disclaimer: clearly the atmosphere is rarely idealised and thus one would naturally expect small variations to e.g. the rate at which the thrust is reduced and the exact height the flare is initiated dependent upon the prevailing conditions, but a near-70% increase in flare height (from 30R to 50R), (or a >200% increase from 30R to 100R!), is a lot. As is so often the case, smooth, progressive and controlled inputs (whether in pitch, thrust or any other axis) generally gets a more consistent result than snapping the thrust levers shut/yanking back and hoping for the best -- I see many people fly lovely controlled approaches and then more or less shut their eyes, yank the throttle closed, pull back a bit and wait for the impact when it comes to the landing rather than continuing to fly and control the aeroplane all the way to touchdown (and, indeed, a safe taxi speed)!
  5. 😨 I can think of quite a lot of (in fact, most) transport category aeroplanes where bringing the thrust to idle at 100R would result in the main gear struts being punched through the wings. The FCTM guidance, oddly enough, provides consistent results. If you can find a Boeing (or Airbus) manual, or a rated trainer, suggesting retarding the thrust levers at 100R I'd love to see it.
  6. If you check the landing distance tables there is a bit of variation in Autobrake landing distance with and without reversers. Particularly at low Autobrake settings it is entirely possible that the drag from spoilers/reversers etc will be greater that the AB1 deceleration rate in the early part of the landing roll, thus resulting in a shorter overall landing distance.
  7. skelsey

    EFB vs. FMS VREF

    Because the regulations are different. For planning purposes (ie before dispatch) the aircraft must be able to land within 60% of the available landing distance for a dry runway -- this means you take the actual landing distance at the planned landing weight, multiply this distance by 1.67 and this figure must be less than the available landing distance. If it is not you must reduce the weight until it is. For a wet runway, the factor is 1.92. Once you are airborne, however, these requirements no longer apply and all that is required is that the commander is satisfied that a safe landing can be made (ie actual unfactored LDR <= LDA).
  8. Probably! Sorry, I always forget that this forum includes questions about the -8 -- comments above reference the -400 :).
  9. The 747 is a very different beast to to the 737 in terms of flying characteristics -- the Jumbo is, by and large, extremely stable and surprisingly responsive for an aeroplane of its size. When it comes to control inputs less, generally, is more, particularly in the roll axis. The one area I think may be lacking a little in the PMDG model is the thrust-pitch couple -- my understanding of the real thing is that there is quite a strong coupling (i.e. if you reduce thrust the nose should pitch down quite positively and vice versa) which isn't really replicated well in FS as a whole. However, that said if you are asking why you floated, the answer is quite simple: not so much a late reduction of thrust as too much flare. The pitch change in the flare in the 747 is really quite tiny -- only about two degrees at the most, which is just barely enough to determine that the pitch has changed at all (i.e. the exact moment you see the horizon move down relative to the top of the glareshield -- that's about two degrees and you should stop there!). In your video, if you look at the ADI you will see your pitch change is closer to 4 degrees -- i.e. nearly double the recommended amount. The FCTM contains full details of the recommended technique.
  10. skelsey

    B748 - setting elevator trim

    Rudder trim should be zero for take-off and indeed in-flight unless the airframe is bent (I'm sure PMDG's engineering is impeccable!). The only time it should be needed is for an engine failure. I've no idea about the -8, but on the -400 you would expect to need roughly 4 units for an inboard and 7 units for an outboard failure on takeoff (4-7... hmmm!). Top tip: you get about one unit of trim per second when you hold the trim knob full left/right. Thus if you have an engine failure after takeoff, once you are safely airborne and you want to trim the rudder you can just hold the knob and count to 4 or 7 as appropriate and that should get you around the right ballpark.
  11. skelsey

    Auto-Pilot is NOT Engaging

    Normally I'd agree with your approach to troubleshooting -- the point though is that the fact his joystick isn't centering is not in dispute -- we know, and Ken knows, it is not centering because it has deliberately been made so. Yes, one would expect it to work with the keyboard (perhaps: how does the pitch axis behave when controlled using the keyboard? Does it 'spring' back to centre or if you make an input is the yoke held back in that position, as is the case with the mouse yoke, in which case it still won't work) -- but that won't actually prove anything unless the centering function is restored on the joystick...
  12. skelsey

    Auto-Pilot is NOT Engaging

    Pete, That's exactly what people are saying about it being out of trim. Ken has disconnected the power cable which returns his joystick to the centre postion, therefore when he lets go of it it stays exactly where it is, i.e. it does not return to centre. So yes, it kind of is his joystick but only because he has changed the way it operates. If he restores the centreing function then he will be able to do as you and Bill describe and all will be well!
  13. skelsey

    Auto-Pilot is NOT Engaging

    Bill -- I'm 100% certain it's the trim. To replicate what Ken's situation is, what happens if you hold the stick out of centre and then try and engage the autopilot? That's what he's doing...
  14. skelsey

    Auto-Pilot is NOT Engaging

    Hi Ken, I wrote a piece about trimming here which you may find useful if you had not seen it: In short: even with a GA aircraft, a centering force to pull/push against is essential and not so very far removed, really, from real life. As has been mentioned, as far as airliners are concerned actually the control column will almost invariably be centred when the aircraft is in trim because the whole horizontal stabiliser moves and therefore when the aircraft is in trim the elevator will be in the neutral position: i.e. with the control column centred. Even in a light aircraft equipped with trim tabs, the principle is much the same; hold the attitude and trim off the force you are exerting. If you do not have any centreing force then you will have no feel at all. Saying that, although I don't have a force feedback stick myself, are you aware of FSForce? I gather this replaces the default FS force feedback with a a much more realistic feel so may be worth looking at. Regarding hardware -- I have the Saitek Cessna yoke myself and I find it very good for the money - the springs are solid enough to mean you really do feel it when the aircraft is out of trim -- stalling a light aircraft, for instance, requires a fairly hefty haul to the backstop (or I'm just weedy!). Personally I find the yoke provides excellent control for light aircraft and airliners (although I still prefer my old Sidewinder Pro 2 for the Airbus -- the slightly different flight control system and fly by wire implementation makes the stick a little more intuitive in that setting). Re: sensitivity - always ensure that the sensitivity sliders in FS are set to maximum, because all they really do is limit the maximum input and/or introduce a lag in inputs, neither of which are much fun! It's also worth looking at FSUIPC if you don't already own a registered copy -- this provides the capability to adjust control response curves etc which can be quite useful.
  15. skelsey

    QW 789 Ultra Long Haul Payload?

    Sure the pax weights there don't include bags? I don't know what sort of load factors QF get on this flight but I would be quite surprised if they could take anywhere near full flights -- I would have imagined they'll be making their money off selling a much smaller number of expensive tickets.