Airborne_Again wrote:
How come? I would say the opposite. In the descent the wing actually has to provide less lift than in cruise as drag has a vertical component.
On a controlled descent, at constant speed, like in any other steady state of flight, lift is always the same, and is exactly equal to the weight of the aircraft :-)
(of course, this is for the vertical component of lift, it gets complicated when lift is not straight vertical)
hmng wrote:
lift is always the same
Lift is reduced.
Interesting picture, thanks. What if the plane is descending, but the nose is pointing up? In fact, the picture assumes that ‘angle of descent’ == ‘deck angle’ which is probably wrong?
Airborne_Again wrote:
Well… Langewiesche had half a point only. You need both power and pitch to climb. No amount of power will make the aircraft climb if you pitch down!
Nitpicking your nitpick, power alone might help a bit with climbing, if the thrust vector has vertical component, but I guess that is marginal, and it’s the increased speed that increases lift, and power is only increasing your speed. At high speeds, even with the nose pointed down (but AoA still positive) the plane will climb. So the “elevator” does control your vertical motion, but because it changes your speed, which then changes your lift. Or course it change the AoA at the same time, so there are second order effects.
What I am trying to get at, is not to say who is right or wrong, but that “it depends” can be applied easily to equations with 3 or 4 dependable variables, and we can all be right and wrong in several observations. Heck I am sure I am wrong in many things here.
But I want to defend Langewiesche in this; the way I see it he is trying to present a mental model that he believes can help people fly safer by making the right decisions and actions based on that mental model. And as they say, all models are wrong, and some are useful :-)
As for the AoA when descending, I think that for the typical slow speed descent, the AoA is higher, but maybe not for a cruise descent, and the pictures in the book are quite good illustrating it:
@hazek and @172driver. If you were in a car heading towards a slight bend or if you were to do a low level 20’ to 50’ fly past along a runway would you turn the steering wheel or level off before applying power smoothly or would you cram on full power first and then take the turn or the level off.
By pitching up/levelling off first (or starting to.) and then applying power smoothly you a) reduce the force needed on the yoke or stick b) I use less reserve power in order to maintain level flight. c) once levelled off I can control the speed at which I pass over the runway. If I add a bit more power the aircraft will rise,that’s if I don’t pitch the nose down to pick up speed. And if I want to climb quicker at the end of my fly past I can pitch up for Vy or Vx adding power smoothly as I go.
If you add power first there will be a lag because the engine has to grab a bit more fuel and a bit more air that then has to enter the cylinders and be burnt to drive the crankshaft to drive the prop for the prop to grab the air and finally drag you into a climb.
This is just my opinion. I very much agree that one can and should be able to do 2 things at once and those things should be done smoothly which is why for a go round I start by raising the nose to level flight and once that move is in motion I before I begin adding extra power.
I quite realise that angle of attack and pitch are not necessarily the same thing but I don’t remember, ever reading of a stall where the nose is pointing below the horizon.
I may be old, I may be a dinosaur, as hazek suggests but not opening myself to change and different ideas to my anecdotal experience of around 40 years of flying light aircraft SEP, MEP . Homebuilt, experimental ULM , IFR and VFR, is simply bs.
Airborne_Again wrote:
How come? I would say the opposite. In the descent the wing actually has to provide less lift than in cruise as drag has a vertical component.
If you’re in a constant descent then the wing is providing the same amount of lift as during cruise – 1g. If it wasn’t you’d be accelerating towards the ground (your rate of descent would be increasing).
So long as you stay at 1g (you’re not further loading or unloading the wing) there is a relationship between airspeed and angle of attack. You’re slower and at 1g during descent so angle of attack is higher.
Another way to see this is is that you actually trim not for airspeed but for angle of attack. To fly at a lower airspeed during the approach you need to trim nose up.
That’s also why stall spin accidents tend to happen during approach to landing, you’re closer to the critical angle of attack and loading up the wing (say during turn the base to final turn) pushes the wing over the limit. If you’re well trimmed and you don’t pull on the yoke during the turn you won’t stall (but your descent rate will increase).
gallois wrote:
I don’t remember, ever reading of a stall where the nose is pointing below the horizon.
It is unrelated to this discussion, but in a secondary stall the nose usually points down below the horizon.
Can you describe the circumstances of a secondary stall, it’s not a phrase I have come across?:)
RV14 wrote:
a near fatal incident involving a new SR22T flown by an accomplished businessman and freshly minted pilot into a place where there is no go around. He didn’t spare expenses on flight training, platinum grade instructors etc.
A few truths here catch my attention: “Accomplished businessman” generally is a more senior, type A person, who has built himself up in life, and is unaccustomed to starting back at square one to learn and master the basics, before declaring himself a master at the new skill – when he’s still many hundreds of hours of practiced experience away from having adequate skill. A number of memorable fatal accidents come to mind with this consideration.
And, “spared no expense on flight training…”. Yeah, but did he learn? Did the platinum grade instructor assure that he retained taught knowledge, and remained humble to the task of piloting?
Learning to fly, and in particular transitioning to a new type, maybe with a cockpit full of self protection gadgets, is not; “you’re done your training, you’re released to the skies”, it’s; “you’re on your way, go fly with great caution, in easy conditions, and then gt more training and practice.”.
I’ve had four happily memorable type conversion “students” (though they were pilots, two were class one instructors) who, after I declared them adequately trained to go solo, asked me for more yet training, and fly along for skill and experience building. Each of these four pilots asked me for more practice at forced approaches, once I had mentored them through a few, and each asked for more practice with approach to stall, and recovery – knowing that two were instructors! This is an attitude I commend.
As to this resolution into infinite detail of flying characteristics, sure, when it’s a philosophical discussion in an advanced classroom, but you’re now doing the student any favours with over thinking it. I recall during my helicopter training (when I already had about 6000 hours fixed wing as a basis) my very competent instructor teling me that he was going to give me “stuck petals” as a training exercise while we were on downwind to an approach. I thought about the lefts and the rights, the torque effects, watching which way the rotor was turning, and compensating with some cyclic control. I had the helicopter flying half way sideways through the sky. He looked at me and said: “I haven’t given yo the stuck pedals yet!”. He was laughing and watching me think myself to death, forgetting to simply fly the helicopter for a failure which had not happened yet! It was a memorable exercise in simply being aware of what was actually happening, and having a clear mind for what could happen next, rather than clogging your mind up thinking through all the classroom work, and forgetting to fly the plane!
Can you describe the circumstances of a secondary stall,
Stall recovery goes:
1. Stick forward to unload wing and break stall
2. Stick gently back to return to level flight
(I’m ignoring power here, let’s suppose we’re flying a glider).
At #2, you’re still slow. If you pull a bit too hard, you will stall again. That’s a secondary stall. No idea what it’s called in French (décrochage secondaire seems obvious, but who knows).
In a Cessna, you would have to pull hard to make this happen. But in e.g. the Marchetti, the wing design is such that it is VERY easy. You have to let plane accelerate a bit before pulling at all.
