You're in a glider and realize you aren't going to clear the fence before the runway....

Salty

Touchdown! Greaser!
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Salty
What do you do?

The answer I was given is:

Speed up and close the air brakes.


For the life of me I cannot grasp why this would be the answer, but this comes from a "cheat sheet" from a previous student that took his check ride with this examiner and I don't have any further information.

My answer would be to open the air brakes and attempt to land before the fence, or parallel to the fence after a 90 deg turn. I sure as heck don't want to be going through the fence any faster than I have to.

If I'm going to try to clear the fence, I'm going to fly best glide with the airbrakes off, but I wouldn't be inclined to speed up.
 
Normally, the airbrakes would be deployed coming down final, so closing them would be the correct action if you wanted to extend your glide. I don't know why you would, necessarily increase your speed. I suppose one could argue that the glide could be extended farther in ground effect.
 
Closing the air brake is a given. And speeding up would get you into ground effect quicker where those long wings will fly more efficiently thereby giving you enough of an advantage to hop the fence when you get to it.

Not quite a SWAG, but at least a WAG.
 
Gliders don't have speed brakes, they have spoilers. Not quite the same thing. Retracting the spoilers decreases drag, thereby reducing your sink rate (if you keep the speed constant). That might be enough to clear the fence. The whole speed up so you can "hop" the fence I offer no opinion on, since I don't actually have any glider time (yet).
 
Closing the air brake is a given. And speeding up would get you into ground effect quicker where those long wings will fly more efficiently thereby giving you enough of an advantage to hop the fence when you get to it.

Not quite a SWAG, but at least a WAG.
I considered that, but I still can't see how best glide wouldn't be "best". You can still use ground effect.
 
I considered that, but I still can't see how best glide wouldn't be "best". You can still use ground effect.

You can't do both. You can do best glide speed, reduce the sink rate, and keep your altitude longer. Or you can increase descent rate, increase speed, and get into ground effect sooner. One or the other.
 
Any speed other than best L/D results in a shorter glide, doesn't it? Gaining airspeed converts altitude to energy, and maybe that energy is enough to allow you to pop over the fence. (pretty much what others are saying).

I've heard bad things about hitting a fence in a glider (maybe an urban legend), the wires of a barbed wire fence seem to usually come in right at neck level and if they get through the windscreen the results can be bad. Dunno if that's a valid concern or not, but that's what I've been told. Many years ago our club Blanik L13 went through a fence. It was before I joined the club, but I vaguely remember seeing the damage. The nose went through the fence approx evenly between two fence posts. Each wing was creased by a post, and each wing had been swung back a few inches, far enough to leave a gap at the leading edge where the wing joined the fuselage and a crease in the airframe at the trailing edge joint.

Possibly stalling at about 4 AGL if you hop the fence might be preferable to hitting it.
 
Any speed other than best L/D results in a shorter glide, doesn't it?

In the absence of any other factors, yes. But adding in ground effect for part of the distance definitely changes things.
 
In the absence of any other factors, yes. But adding in ground effect for part of the distance definitely changes things.
RIght, your earlier post about getting into ground effect sooner, and also noted by others, might give you a chance to skim the ground a little farther than you would otherwise.
 
Because the approach speed is probably slower than best glide.
On approach, you will be going the fastest in the flight, with spoilers half deployed. BTW, all the SG 1-26s have spoilers. The 1-26D I sometime flew had SPEED BRAKES. Thats what the placard said.
 
You can't do both. You can do best glide speed, reduce the sink rate, and keep your altitude longer. Or you can increase descent rate, increase speed, and get into ground effect sooner. One or the other.
My point is ground effect is still there, getting into it sooner seems to reduce your options not increase them.
 
My point is ground effect is still there, getting into it sooner seems to reduce your options not increase them.

The slower you're going when you get into ground effect, the less time you'll be there. And then you don't have any options. This is a decision you need to make sooner rather than later. Note that I'm not saying WHICH is a better option, but you don't really get to pick both.
 
Depending upon what you’re flying, approach speed is often below best L/D. If you assume that you’re landing into wind, your penetration speed will be higher yet.

Ground effect in gliders is also a far more powerful tool than most power planes...For demonstration purposes I’ve flown half a mile in ground effect with very little loss of airspeed. To bail out a student approach I’ve flown 400 feet over an uphill grade in ground effect and still had the energy to hop the fence. Spoilers were still required to land in a reasonable distance beyond the fence.

Which also brings up the point that before people realize they’re too low on final, they often raise the nose subconsciously to keep their aiming point, and end up too slow as well. Regaining as much airspeed as possible prior to leveling out a couple of feet off the ground gives the most benefit.
 
Depending upon what you’re flying, approach speed is often below best L/D. If you assume that you’re landing into wind, your penetration speed will be higher yet.

Ground effect in gliders is also a far more powerful tool than most power planes...For demonstration purposes I’ve flown half a mile in ground effect with very little loss of airspeed. To bail out a student approach I’ve flown 400 feet over an uphill grade in ground effect and still had the energy to hop the fence. Spoilers were still required to land in a reasonable distance beyond the fence.

Which also brings up the point that before people realize they’re too low on final, they often raise the nose subconsciously to keep their aiming point, and end up too slow as well. Regaining as much airspeed as possible prior to leveling out a couple of feet off the ground gives the most benefit.
Yes, all that and...

Best L/D is very close to approach speed in all sailplanes. Typically a little higher than the flight manual specified approach speed but often lower than the actual speed flown given a typical head wind and gust factor. In any case, the effect of 5 knots in either direction won’t make a great deal of difference on short final.

Ground effect is very powerful in sailplanes both due to span and to the minimum height that can be flown.

A normal approach would involve having the spoilers partially deployed. If one is a bit short, just closing them will produce an enormous change in one’s prospects.

Most power pilots would be amazed at how easy it is to spot land a spoiler equipped sailplane. It’s far easier than using flaps and that vibrator thing up front. On the other hand, a flaps-only sailplane is considerably more challenging which is why they are no longer produced. And gliders with no approach path control other than a chute are more demanding still which is why none have been produced since the 60s or early 70s.

Then there are some gliders like the Schweitzer 2-22 that has such ineffective spoilers that your main approach path control is a side slip.

Re spoilers versus air brakes; it’s just semantics. They do both to varying degrees. Terminal velocity ‘air brake/spoilers’ are on some gliders (e.g. 1-34 2-32 Mini-Nimbus)

Yeah, and you don’t want to hit a fence, certainly not a barb wire fence. I’m aware of 1 actual fatality that occurred long after I had heard of the danger and other fatalities from barb wire fence encounters. Fences can be hard to spot during an outlanding if there aren’t any livestock working the field.

Sent from my iPad using Tapatalk Pro
 
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Of course on approach you are probably going upwind and therefore optimum speed for covering ground will be approximately l/d max plus half the wind speed. Minor tweak.

Related lesson: We had a guy in our club confuse spoilers and flaps in our l13. When he finally figured it out he had fixated on the only obstacle within a half mile, a chain link boundary fence. Fence 1 blanik 0. There was nothing else to hit. Avoid fixation on the obstacle.
 
Hmm, tough one, seems to me altitude is money (energy) in the bank. I would agree, spoilers off, best glide, but I don't fly gliders.
 
Hmm, tough one, seems to me altitude is money (energy) in the bank. I would agree, spoilers off, best glide, but I don't fly gliders.
It is a tough one to figure out in one’s head. The physics of flying in ground effect are well understood by someone, somewhere, but as a power pilot there’s no way to experience it in a way that makes ‘jumping a fence’ a possibility.

Glider pilots, especially those flying high performance gliders, experience energy as a combination of speed and altitude called total energy (TE). There’s actually instrumentation that provides a continuous readout of TE based not only on speed and altitude but that also integrates the vertical movement of the airmass. The ‘readout’ typically takes the form of a continuous audio tone that tells the pilot, moment to moment, the rate at which they are gaining energy or losing energy and whether they are flying at the optimal speed for the conditions.

All of this continuous calculation is pretty straight forward with current digital technology and miniature pressure transducers. It seemed like magic back in the day when it was done with a pitot tube-like device, a variometer and some tuned constrictors. Essentially an pneumatic analog computer sans electronics.

Anyway, glider pilots that take fly their ship down into ground effect with a little extra speed (and no spoilers or landing flaps) will actually feel the aircraft accelerate slightly as it enters ground effect. Less AOA is required in ground effect and there is less drag than level flight out of ground effect and that change can be felt in the seat of the pants.

At that point one can fly along in ground effect for a considerable distance as one slowly pitches up to maintain altitude as the speed bleeds off.

At some point in that exercise, one could still have enough energy to pull up over a short fence and that point would be further than the point would be if ‘best L/D’ was maintained from the same point on final (it’s rarely best L/D due to wind).

However, the pull up over the fence would probably be ballistic-like followed by a hard landing on the other side where the pilot would probably be slightly surprised in being unable to completely arrest the descent.

Question I wonder about is whether the TE instrumentation would accurately reflect the TE profile of the ground effect maneuver? Personally, turning off the TE audio output was part of my pre-landing checklist. It was a way of totally committing to the landing rather than being distracted by some low level thermal or vertical gust.
 
What do you do?

The answer I was given is:

Speed up and close the air brakes.

This really sounds like one of those questions that doesn't really have a 'correct' answer. There are so many variables. Wind, alt, speed, brakes deployed or not, how far away is the fence...

It just depends, but you kind of need all that information before you make a decision.
 
I got clarification on the context of the question today. It was meant to be when you are very low and close to the fence, not far enough away to continue to stay on best glide. The idea as some already stated is to use ground effect and zoom climb to pop over the fence.
 
I got clarification on the context of the question today. It was meant to be when you are very low and close to the fence, not far enough away to continue to stay on best glide. The idea as some already stated is to use ground effect and zoom climb to pop over the fence.

I was at Lebanon NH a long time ago and heard this whizzing noise, I saw a glider doing a low approach at what looked like 150 knots. He was about 5 feet over the runway, near the end he pulled up, soared to about 500 feet, turned and landed. It was pretty cool. He had lots of energy though.
 
I was at Lebanon NH a long time ago and heard this whizzing noise, I saw a glider doing a low approach at what looked like 150 knots. He was about 5 feet over the runway, near the end he pulled up, soared to about 500 feet, turned and landed. It was pretty cool. He had lots of energy though.
“Bringing the mail”. A buddy did that once, that was a cool thing to hear.
 
True but it can make it easier to not give a crap about hitting the fence.
I had a friend as a kid that got decapitated when he went through a fence on a 4 wheeler. I give a crap about going through a fence.
 
Hmm, tough one, seems to me altitude is money (energy) in the bank. I would agree, spoilers off, best glide, but I don't fly gliders.

Someone finally mentioned this factor.

Thought experiment: imagine you are approaching at 50mph with a 50mph head wind and best LD is 50mph. What speed is going to give you the most distance. Obviously it is not best L/D. Using the rule of thum it would be 75mph. I haven’t ran the numbers to see that actually is the best number.

This is also why I tell power pilots not to speed up when to high on an approach.

So Speed up...

1. Because you probably were unconsciously slowing down to try to make it look like you were going to clear the fence.
2. Speed up get closer to the best glide speed, best L/d + 1/2 the headwind.

3. The distance penalty for flying 5mph to slow is about twice the penalty for fly 5mph to fast.

4. Last resort speed up to get the ground effect a bit sooner and have enough energy to use it.

The Op’s Answer of pull the spoilers and land short, if unsure you can clear the fence is a good answer also.

Brian
CFIIG/ASEL
 
I'd start the engine, 'cuz I'd be in a Stemme.

If you are to the point you are not sure you are going to clear the fence it is way to late to start the engine.

As you know, most non-motorglider pilots don’t realize that you can often safely thermal lower in a pure glider than a motor glider. Because with a pure glider you only need enough altitude to successfully execute a normal landing. With a motor glider you need enough altitude to deploy, attempt a start, stow (when it doesn’t start) and execute a normal a landing. Many motorgliders have been damaged due to the engine not starting and not having enough altitude to execute a safe landing.

To be fair the Stemme is likely a little better at the altitude loss while attempting and engine start than some other glider.

Brian
CFIIG/ASEL
 
I had a friend as a kid that got decapitated when he went through a fence on a 4 wheeler. I give a crap about going through a fence.
Thanks for sharing. I had a childhood friend that had a similar experience but he lived and got a new name. We called him lefty after that day. He was able to have kids. Guess he had empirical evidence that you don’t need two to procreate.

@Salty just remember. .. you and I care about fences but that doesn’t mean anyone else does.
 
Talked with a CFIG about this. Probabbly been covered, I ain't read much of the thread. Spoilers don't really change things like flaps do and you shouldn't have to push the nose down to stay at Max Glide aka best Lift to Drag ratio speed. Yeah, ground effect is pertinent. What ya lose by pointing the nose down can be made up by staying in ground effect longer when you get down there. Down there is kinda high up because of the long wingspan, higher than a typical fence. She likes it when students get into the predicament and she can show them as a learning moment. And she thinks it's fun to.
 
Gliders don't have speed brakes, they have spoilers.

Not necessarily a true statement (from a glider pilot). How about a SGS 2-33 or a Blanik L-23. Spoilers and brakes.

K-21 pr L-33 pr LS anything....spoilers only.
 
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