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The importance of speed on final

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The importance of speed on final

Old 26th Jul 2015, 19:19
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" Many SLMG pilots select full airbrake early, then control the approach on throttle."
Really? Well, every day's a school day. I never knew that. And in my own limited experience (only about a dozen different types of SLMG, ranging in performance from T-61 to S-10) Its throttle to idle and airbrakes only.
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Old 26th Jul 2015, 19:30
  #22 (permalink)  
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That's how I was taught to fly them too, but appears to not be universal when I've been preparing for the flight testing.

Won't work with this aircraft - the airbrake won't stay out without continuous pull, which would scupper anything but the technique you've just described, but ultimately, you test the aeroplane that's there, and need to be open to the conclusion that the aeroplane is safe but requires non-standard handling techniques.

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Old 26th Jul 2015, 19:57
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John, Deefer, Genghis and Mack, I believe you chaps do most of your flying in power? correct me if not the case.

I think best to simply quote Ken Stewart, from his book The Glider Pilot's Manual, he discusses the use and effect of the airbrake.

Says Ken, page78, "Due to the low drag of the glider and the resulting low rate at which it uses energy, it would be very difficult to land, requiring a very large landing area. ....When extended, ....airbrakes increase the drag dramatically and disrupt the airflow over part of the wing, thus reducing the lift produced....steepening the angle of approach and making the glider easier to land in smaller areas. The amount of airbrake can be varied over the complete range, between fully closed and fully open, giving an infinite number of settings and allowing the glide angle to be adjusted to match the approach path required....
Apart from their use as an approach aid, some airbrakes have another, less used purpose, that of "speed limiting" or DIVE BRAKES. ....and can be used to limit the airspeed of the glider should control be lost while cloud flying or carrying out aereobatic maneuvers."

Certainly beginners may end up "rowing" down the approach, with airbrakes rising up and down, but the airspeed is controlled by the attitude of the glider. The term airbrake does lead to confusion.
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Old 26th Jul 2015, 20:14
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You're quite right only a small portion of my flying is on sailplanes, although I've certainly had adequate reason over the years to understand unpowered flight, and powered sailplanes, and your quote matches my normal understanding.

The approach of full A/B, partial throttle surprised me also, but it does appear to be how some pilots operate SLMG / SSS on approach and was something that came into my pre-trials research.


Being able to use the A/B as speedbrakes is a further issue, and relies upon a degree of drag which may not exist on every design (present aircraft again, etc. etc).

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Old 14th Sep 2015, 21:58
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What speed and how you get it...

I'm afraid I've too often heard that 65 is the magic number used by PPL holders for an approach, unless it's windy when they add a few more knots. But very few will tell you their stall speed for their actual landing weight. It's a shame really because as the OP suggested, getting the speed right for an approach is critical. But right in this context means getting it "Goldilocks" right; not too fast and not too slow, just right.

As to how you get there, I'm in the Farley camp. Yes, I do adjust the pitch when I change speed, but the speed is controlled by use power or adjusting the airbrakes. The pitch adjustment is required to maintain or correct the approach angle. And as John pointed out, how do you correct an under-speed close to the ground? Lastly, what happens when you side slip? If you are too slow do you lower the nose or stop the slip?

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Old 15th Sep 2015, 03:50
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Air Brakes and Airspeed

Once you have full air brake out, you can let the nose down to increase speed and drag (by the square of the speed).

Once you level out the speed drops rapidly with full air brake same applies to Cessnas with 40 flap.

Not to be done until you reliably flare at the correct height lest something get bent.
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Old 15th Sep 2015, 09:58
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My Monnet Moni had a ventral airbrake and opening it caused a marked nose up pitch, so on final I used to set airbrake open and rpm 4,500, which gave me about 60mph. I would shut the throttle over the hedge and fly it on ie no flare; I did this a couple of times and it dropped like a stone and I heard that several US designed homebuilts eg Quickie Q2 needed to be landed this way.
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Old 15th Sep 2015, 14:23
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PM

Too slow with side slip!
The gliders (sailplanes) that I have side slipped loose the ASI once the side slip has developed due to the airflow around the pitot.
I have also tried to stall a glider whilst in full side slip...never achieved it. I presumed because of partial blanking of the elevator.

As to airbrakes or speed brakes;
I used the latter term when I returned to gliders after years of big jets...had no end of criticism and wasn't allowed solo until I used them like airbrakes to control the rate if descent rather than speed brakes to control the speed.

The reason the BGA is so strict is because the number of undershoot accidents with pilots putting the nose on where they want to land and in a progressive undershoot case they can end up stalling trying to reach the threshold.

When I stopped instructing the current philosophy was to teach a half to two thirds airbrake approach...any less close them completely until you reached the "slot" ...any more pick another aiming point.
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Old 30th Oct 2015, 22:56
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One thing I emphasize with new students is to never ever let the nose come up to the point where they cannot see the runway touchdown point. If the nose remains down below the horizon the airplane cannot stall (unless the airplane has a very high bank angle, not likely while on final).

I also tell them that if the stall warning comes on during approach they are too slow. If it does not come on during the flare to land they are too fast.

Don't need no steenkin airspeed! (joke)
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Old 6th Nov 2015, 17:15
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Originally Posted by boofhead
If the nose remains down below the horizon the airplane cannot stall
I think this statement needs to be qualified, in much the same way as "the stall speed is XXXkts" - it's only correct under certain conditions.

Q: What happens in a stall recovery if the pilot is too aggressive pulling out of the ensuing dive?
A: A (secondary) stall - with the nose below the horizon.

Q: What happens if the stick is held fully back in some gliders?
A: A rapid, fully stalled, descent with the nose WELL below the horizon.

OC619
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