Time to talk about Allegro's

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Dangeruss
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Re: Time to talk about Allegro's

Postby Dangeruss » Fri Apr 08, 2016 10:29 am

I've flown a few hours in the Allegro with the 80hp rotax. Its a good airplane. 4800rpm take off would be a breeze with one person on board. The one at my flight school had over 4000 hours on the airframe. It is very light on the controls and has to be flown with your feet entering turns. Glides really nice. Landing procedure was to cut the power abeam the numbers, and glide the rest of the pattern incrementally adding flaps. I didn't like the cockpit layout with the center stick and the radio on the right. Since Its not much of a "hands off" aircraft, it was a pain to hold the stick with my left hand and get the radio with my right.
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Re: Time to talk about Allegro's

Postby drseti » Fri Apr 08, 2016 2:10 pm

Dangeruss wrote:Landing procedure was to cut the power abeam the numbers, and glide the rest of the pattern incrementally adding flaps.


That's how I was taught a half century ago in an Aeronca Champ (except, for the flaps, substitute slips). And, that's the way I teach now in an Evektor, Sport Cruiser, Gobosh, etc. So, I approve of that technique in an Allegro.
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Re: Time to talk about Allegro's

Postby Dangeruss » Fri Apr 08, 2016 2:55 pm

drseti wrote:
Dangeruss wrote:Landing procedure was to cut the power abeam the numbers, and glide the rest of the pattern incrementally adding flaps.


That's how I was taught a half century ago in an Aeronca Champ (except, for the flaps, substitute slips). And, that's the way I teach now in an Evektor, Sport Cruiser, Gobosh, etc. So, I approve of that technique in an Allegro.


Hmm, good to know. Imo, that seems to be the safest way to fly the pattern but I didn't know that technique was so wide spread. The Remos GX I'm currently flying feels like a comparative brick, and requires power over the fence. I guess its mainly a matter of Instructor preference.
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Re: Time to talk about Allegro's

Postby drseti » Fri Apr 08, 2016 3:54 pm

Dangeruss wrote:The Remos GX I'm currently flying feels like a comparative brick, and requires power over the fence. I guess its mainly a matter of Instructor preference.


Pilot preference cannot be ignored, but in fact no airplane requires power over the fence. If it did, you'd never be able to land after an engine failure! The power-off landing may not be smooth, or pretty, but as long as you find and stick to best glide speed, it's never unsafe.

My instructor preference is to have every student do power-off landings from day one. The Law of Primacy says that, in a crisis, your mind reverts to what you learned first, and everything else goes out the window. If you have an actual engine failure in flight, and have to land off-airport, power off, for real, that certainly constitutes a crises. So, you automatically do what you were taught to do at the outset, which is to glide, and land the plane. Those who've never done a glider landing before have to teach themselves how to do it for real, and do it right, the very first time!

Of course, to reach the airport power-off, you need to fly a very tight pattern. None of this flying downwind a mile away from the runway. Not even a half mile is likely to work -- you have to set up your downwind a quarter mile out, to be assured you're going to make it. Thus, everything happens fast in the pattern (you travel only a quarter mile from abeam the numbers to turning base, only a quarter mile on base, and a quarter mile on final between turning and touching down).

In most LSAs, best glide speed is around 60 knots. Ignoring wind, at 60 knots (a mile a minute) that three quarters of a mile is going to take you three quarters of a minute. So, from abeam to touchdown, you only have 45 seconds to sort everything out. This is why you nail that best glide speed when first entering downwind, and don't let your speed vary at all until the flare.

If you started out 1000 AGL, during those 45 seconds you need to descend that 1000 feet. So, your average rate of descent is 1000 feet per 45 seconds, or 1333 FPM. I know of no SLSA that sinks faster than that at best glide speed. In fact, you have to do something to get the plane down before you use up too much runway -- and that's where flap management comes in. You must not point the nose down and dive for the runway -- that will speed you up so much that you'll float all the way down the runway, and land in the trees off the departure end! You control your descent with flaps alone. But, in a real off-airport landing following an engine failure, this is exactly what things are going to look like, so isn't it helpful to already know how to do this before the emergency occurs?

My opinion; YMMV.
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Re: Time to talk about Allegro's

Postby Flocker » Fri Apr 08, 2016 5:11 pm

drseti wrote:My instructor preference is to have every student do power-off landings from day one. The Law of Primacy says that, in a crisis, your mind reverts to what you learned first, and everything else goes out the window.


Great point. I'm going to do a power-off approach into DNL on Sunday in your honor.

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Re: Time to talk about Allegro's

Postby drseti » Fri Apr 08, 2016 5:17 pm

I am indeed honored, Flocker.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
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Re: Time to talk about Allegro's

Postby zaitcev » Fri Apr 15, 2016 3:48 pm

drseti wrote:In most LSAs, best glide speed is around 60 knots. Ignoring wind, at 60 knots (a mile a minute) that three quarters of a mile is going to take you three quarters of a minute. So, from abeam to touchdown, you only have 45 seconds to sort everything out. This is why you nail that best glide speed when first entering downwind, and don't let your speed vary at all until the flare.


I find myself questioning the wisdom of sticking to Vbg in case of a power-off landing, because you cannot do anything to extend your glide if you're already at Vbg. It's just not possible. But what if anything at all happens that requires you to extend the glide a little bit? For example, what if you underestimate the wind?

In most LSAs and traditional light singles, there's quite a bit of drag to be called on command. You can crank down the flaps, for example. So, it adds a margin to be a little faster. If you overshoot, you slip it in. If you undershoot, you can slow down a little bit and that actually makes the glide a bit flatter as it approaches Vbg. You also have a bit of extra kinetic energy stored that can be handy.

Unfortunately if you're a little slow and want to _accelerate_ to Vbg, you lose a lot of altitude to re-accelerate and typically you don't have that luxury, so I'm not considering that side of the curve. But being faster is good, in case you aren't nailing the turns with 100% precision.

Now of course there's an excess of everything, and barreling down at 100 knots is a sure way to float through whole runway and end in the mud if now worse. You really don't want to exceed your ability to slow down on final. But being a little bit faster on downwind and through turns feels safer to me, because things happen.

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Re: Time to talk about Allegro's

Postby FastEddieB » Sat Apr 16, 2016 7:35 am

zaitcev wrote:
I find myself questioning the wisdom of sticking to Vbg in case of a power-off landing, because you cannot do anything to extend your glide if you're already at Vbg. It's just not possible. But what if anything at all happens that requires you to extend the glide a little bit? For example, what if you underestimate the wind?



I've read this a few times and I'm still not sure what you're getting at.

Gliding at a speed greater than best glide will, by definition, always bring you up shorter than just sticking to that speed*.

Parasitic drag increases as the square of the increase in velocity, so gliding faster to "hold a little in reserve" will always be counterproductive. You may be a be able to "zoom climb" a bit - trading speed for altitude - but that tradeoff will always result in a net negative to just holding best glide.

Best hint is to hold best glide, and see what your intended touchdown point is doing in the windshield. Moving up in the windshield? You're coming up short. Moving down? You're overshooting and may end up needing more flaps or slips to get down - just don't be in a hurry - once that altitude is gone, its gone. Lots of of ways to get down if you're high, no way without power to correct if you end up low. The sweet spot is where it just stays in the same spot, just getting larger and larger.



*The speed in the POH is generally given at max gross. If you're lighter, then that speed needs to be adjusted downward. Then again, if gliding into a headwind, that speed needs to be adjusted upward. But if gliding with a tailwind, that speed needs to be adjusted downward. In general, in an emergency it will be hard juggling all the factors, and best glide is likely a good approximation.
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Re: Time to talk about Allegro's

Postby 3Dreaming » Sat Apr 16, 2016 8:43 am

Eddie, what he is saying is if you are gliding at a speed greater than best glide you can adjust to either extend your glide by going to best glide or shorten your glide by slowing beyond best glide and slipping. This gives an adjustment on both sides of the touchdown point. By flying at best glide if you don't calculate your touchdown correctly and come up short there is nothing you can do, except pick a closer spot. This is not good if you picked the only suitable spot in the area.

I don't necessarily agree with this. If you practice like Paul suggest you will be more likely to be able to hit your point in an emergency. If it is a true emergency and the prop is stopped you will likely glide farther than you are used to anyway.

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Re: Time to talk about Allegro's

Postby FastEddieB » Sat Apr 16, 2016 9:12 am

Thanks.

I was thinking about that and think I understand where he was going.

I was thinking of a power off final, where anything other than best glide is counterproductive. He's talking about routine patterns where a bit of extra speed is fine.

For standard patterns, usually 1.3x the stall speed in any given configuration is a good starting point, giving a 30% margin above the stall. If Vso is 40k, let's say, 52k would be the result. And 1.2x the stall speed for short field is pretty standard, in this case 48k.

The speeds in the POH take precedent, however, but will often be pretty close to the above.

As an additional complication, I don't think any POH's list best glide at anything other than flaps up.

But much of this reminds me of measuring a board with a micrometer, marking it with a crayon and cutting it with an axe. IOW, extreme precision is rarely needed.
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Re: Time to talk about Allegro's

Postby Wm.Ince » Sat Apr 16, 2016 10:52 am

FastEddieB wrote:
zaitcev wrote:I find myself questioning the wisdom of sticking to Vbg in case of a power-off landing, because you cannot do anything to extend your glide if you're already at Vbg. It's just not possible. But what if anything at all happens that requires you to extend the glide a little bit? For example, what if you underestimate the wind?
I've read this a few times and I'm still not sure what you're getting at.

Gliding at a speed greater than best glide will, by definition, always bring you up shorter than just sticking to that speed*.

Parasitic drag increases as the square of the increase in velocity, so gliding faster to "hold a little in reserve" will always be counterproductive. You may be a be able to "zoom climb" a bit - trading speed for altitude - but that tradeoff will always result in a net negative to just holding best glide.

Best hint is to hold best glide, and see what your intended touchdown point is doing in the windshield. Moving up in the windshield? You're coming up short. Moving down? You're overshooting and may end up needing more flaps or slips to get down - just don't be in a hurry - once that altitude is gone, its gone. Lots of of ways to get down if you're high, no way without power to correct if you end up low. The sweet spot is where it just stays in the same spot, just getting larger and larger.

*The speed in the POH is generally given at max gross. If you're lighter, then that speed needs to be adjusted downward. Then again, if gliding into a headwind, that speed needs to be adjusted upward. But if gliding with a tailwind, that speed needs to be adjusted downward. In general, in an emergency it will be hard juggling all the factors, and best glide is likely a good approximation.
Concur with Eddie.
To me, fiddling with the best glide speed is equivalent to "moving the goal posts."
Once I have the best glide speed established, I know what my aircraft capability is, good or bad. I can then make a decision based upon a predictably accurate outcome, that being, we are short, long or spot on, where we want to be. Once established at best glide, "what you see is what you get," in real time, no guessing. Much easier juggling one ball than five.
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Re: Time to talk about Allegro's

Postby snaproll » Sat Apr 16, 2016 2:32 pm

Have enjoyed the discussion and comments. Guess I am a little "old School" like Paul. To this day, I still cut power midfield and dead stick to touchdown. A well prepared pilot practices closed throttle with no flaps, with each increment of flaps, and with slips both with and without flaps landing on a specific spot on the runway. Randomly cutting power at various positions in the pattern and planning to touch down at that same spot no matter what hones pilot skills and prepares a pilot for the inevitable engine out emergency landing. My old instructor was “really” old school and randomly cut power away from the airport and said “find a place to land” (OK - it was the 60's). I was not allowed power until I touched the mains down, whether it be in an open field, dirt road, river bottom, etc. The preparation was invaluable with my first, second, and succeeding engine failures – never scratched an airplane. Years back, most aircraft I flew did not have flaps and practicing slips to hit a spot on the runway was important. My flying habits have not changed in the last 50 years, I always approach either high or hot insuring I make the runway without power, and yes, I typically slip the airplane. My techniques may not be textbook, may not match the current teaching, but have always managed to keep me safe and not having to add power to make a landing spot. I fly my Remos GX the same way as a J-2 Cub (except the Remos glides better and has brakes) and squeak it on 50 ft. beyond the threshold consistently.

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Re: Time to talk about Allegro's

Postby MrMorden » Mon Apr 18, 2016 8:47 am

zaitcev wrote:I find myself questioning the wisdom of sticking to Vbg in case of a power-off landing, because you cannot do anything to extend your glide if you're already at Vbg. It's just not possible. But what if anything at all happens that requires you to extend the glide a little bit? For example, what if you underestimate the wind?


The only reason you'd need to "stretch" a glide is if you are coming up short. If your approach is already at best glide, you are getting the maximum distance out of the airplane's glide that is possible. Worst case scenario at best glide you end up high and have to add flaps or slip to make your intended touchdown point.

If you are not going to make your intended touchdown point at best glide speed, here's a spoiler: you are not going to make it at any other speed, either. :cry:
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