Vx, Vy, and turnbacks

[Ada Elle]

The trouble with over educated people is they over complicate things, I have seriously intelligent engineers work for me but have to teach them what to do to get the results I need, if I left them to their own devices all I would have is 10,000 pages of calculations and nothing I could sell to anyone.Just listen to what your instructors tell you, follow the rules and listen to good information passed on by people with lots of experience and you will have a long and enjoyable flying career/hobby. You don't need to know the in's and out's of a rats backside to be a very competent and capable pilot.

By all means if aerodynamics is what turns your crank go study it to your hearts content but stick time will count ten fold when the noise up the front stops.

Over-educated pretty much describes me.

 

I'm sure that a lot of people in Sydney will know who my ab initio instructor if I say that the first page of my logbook consists of hundreds of circuits, almost all glide approaches. This was good for me - it turned me into a safe pilot - but not into a confident pilot. I was scared of steep turns, of incipient spins, of flying out of balance more than a ball's width. Add to that three years away from flying, and when I came back to flying I was a very nervous pilot, with my head in the cockpit - flying speeds, and watching the AI, etc.

 

Gliding, and doing some proper spins/unusual attitudes and discovering just how hard it is to spin a lot of aircraft, has given me more confidence in flying nearer to the edges of the envelope. But it's also led me to realise that lots of instructors have been teaching time honoured techniques without necessarily understanding the basic sciences and why. In my day job I love thinking about how to translate basic science knowledge into understanding what is going on with the patient, and I've been blessed with many good teachers who both know their basic anatomy and physiology really well, as well as having good technical and patient skills. But I can't expect flight instructors to be surgical professors!

 

 

[Ada Elle]

Can you actually achieve these differing results? Headwind will affect what you can achieve too. as will tracking off runway heading on climb out ( you only need ONE turn of less than 180 degrees then) I'm not suggesting it in a normal traffic situation because you won't be doing what most other traffic would expect.Also your faster climb gives you a greater manouver margin more quickly, so you don't arrive at the different heights with the same ability to do things. You total energy is PE(height) plus Kinetic energy (V squared) Cancels out a bit of the advantage of the extra height. Nev

I don't know. Vx is 55 with flaps hanging out; Vy is 75 clean. I could easily imagine having a couple of hundred feet different after a mile with those speeds. (RoC at Vy is 1220fpm, so that's 976 ft per mile at Vy; AoC at Vx isn't published but it would have to be better than 976ft per mile and worse than 1161.)

 

On a glide approach, abeam the numbers, 0.9nm out from the airport (The Oaks) I had to do a wide left turn onto my end of base location, 2 180 degree turns, then sideslip, then apply full flap to get it down. Next time it's not busy I'll have to see what sort of glide racetrack circuit I can fly.

 

 

[Ada Elle]

Can you actually achieve these differing results? Headwind will affect what you can achieve too. as will tracking off runway heading on climb out ( you only need ONE turn of less than 180 degrees then) I'm not suggesting it in a normal traffic situation because you won't be doing what most other traffic would expect.Also your faster climb gives you a greater manouver margin more quickly, so you don't arrive at the different heights with the same ability to do things. You total energy is PE(height) plus Kinetic energy (V squared) Cancels out a bit of the advantage of the extra height. Nev

I don't know. Vx is 55 with flaps hanging out; Vy is 75 clean. I could easily imagine having a couple of hundred feet different after a mile with those speeds. (RoC at Vy is 1220fpm, so that's 976 ft per mile at Vy; AoC at Vx isn't published but it would have to be better than 976ft per mile and worse than 1161.)

 

On a glide approach, abeam the numbers, 0.9nm out from the airport (The Oaks) I had to do a wide left turn onto my end of base location, 2 180 degree turns, then sideslip, then apply full flap to get it down. Next time it's not busy I'll have to see what sort of glide racetrack circuit I can fly.

 

 

[facthunter]

Those are still air figures which you rarely get. Do a few calcs with a couple of headwind components. It's a height /distance situation but also the speed you have initially affects your ability to turn instantly. Continuing to go away from the field while gliding makes the successful return much less likely . I'm not with your 2x180 degree turns. Do power off course reversals and see what altitude you lose each reversal. Nev

 

 

[facthunter]

Those are still air figures which you rarely get. Do a few calcs with a couple of headwind components. It's a height /distance situation but also the speed you have initially affects your ability to turn instantly. Continuing to go away from the field while gliding makes the successful return much less likely . I'm not with your 2x180 degree turns. Do power off course reversals and see what altitude you lose each reversal. Nev

 

 

[Ada Elle]

Do power off course reversals and see what altitude you lose each reversal.

Two idle-power course reversals lost about 700ft in total. I might have cheated and made them about 160 degrees. This was with about 20 degrees of bank.

 

Like this:

 

But it's in a plane with 17:1 glide ratio, so I wouldn't try to do this in a Jab.

 

 

[Ada Elle]

Do power off course reversals and see what altitude you lose each reversal.

Two idle-power course reversals lost about 700ft in total. I might have cheated and made them about 160 degrees. This was with about 20 degrees of bank.

 

Like this:

 

But it's in a plane with 17:1 glide ratio, so I wouldn't try to do this in a Jab.

 

 

[facthunter]

I see (said the blind man) Don't try it in a Gazelle or Thruster either. That's a good glide ratio 10:1 is about average . You're in gliding paradise.. Nev

 

 

[facthunter]

I see (said the blind man) Don't try it in a Gazelle or Thruster either. That's a good glide ratio 10:1 is about average . You're in gliding paradise.. Nev

 

 

[Ada Elle]

That's a good glide ratio 10:1 is about average . You're in gliding paradise.

Yep, love the plane, but moving between it and a Jab I always muff up my approaches the first couple of times because it's so slippery it's hard to get down and slow. Same potential energy, just can't bleed it off as fast.

 

 

[Ada Elle]

That's a good glide ratio 10:1 is about average . You're in gliding paradise.

Yep, love the plane, but moving between it and a Jab I always muff up my approaches the first couple of times because it's so slippery it's hard to get down and slow. Same potential energy, just can't bleed it off as fast.

 

 

[Contact Flying]

I teach the basic low ground effect takeoff for all situations. Like diesel, I have seen too many fully loaded airplanes, like the Cessna 150, pitch up to either Vx or Vy pitch attitude too early and go behind the power curve while trying to overfly an obstacle by too much vertical distance. They have given up a lot of free kinetic energy in low (less than a meter) ground effect. They have bled off what excess engine thrust for climb they had at liftoff. Now the only safe option is to push forward on the stick to continue going up or at least stay level. This is something humans have a hard time doing.

 

Especially when there are obstacles at the end of runway, we need all the energy (both engine and natural) available. If we get the nose wheel just off the surface or tailwheel airplane level as soon as possible, we have eliminated significant drag. If we get the mains off as soon as possible, we have eliminated significant friction drag. The design of the airplane is to fly, not to roll on the ground. Finally, and perhaps most important, airplanes accelerate best level in low ground effect. This, millimeters off the beach, is where test pilots set the max speed for airplanes.

 

Like the crop duster in low ground effect in the paddock, we need not climb until near the obstacle. Now we can use both excess engine thrust for climb and kinetic energy of low ground effect to zoom just over the obstacle. No! This is not necessary on every takeoff, not even most. It is just needed when needed. Perhaps heavy, hot, and high. Perhaps here or there. If you cannot predict the future, do you want to be hanging on the prop when you need it?

 

It has probably become obvious that the stuff I teach is not for the flight test. It is for the safety of the pilot. However, in the US, the Practical Test Standards have changed from no mention of low ground effect on normal and obstacle clearance short field takeoff to "accelerate to Vx or Vy as appropriate in ground effect." If you have had any experience with our FAA, you know that is real progress.

 

 

[facthunter]

Flying in ground (or water) effect is the most efficient flight regime you can have for our types of aircraft. The best example of it's use is a soft field take off, where you lift off as soon as possible. What you don't gain is initial height which you won't achieve well if your climb speed is too low as the extra drag makes your situation not the most efficient. Once you have achieved a higher speed you can climb (or turn) better. Nev

 

 

[Contact Flying]

Well said facthunter. Ground, or water, effect flying boats get 40% lift out of their ground effect because they stay in low ground effect. Our over emphasis on getting up quickly causes us pilots to waist most of our ground effect by not staying as low as possible. As you astutely said, the soft field takeoff is the most efficient short field takeoff. That is not true, however, if we allow the airplane to climb above a meter and struggle in a high pitch attitude. We need get off as soon as possible, but then we need push forward on the stick, especially in more powerful airplanes, to stay in low ground effect.

 

The worst aircraft for teaching good technique are powerful ones.

 

 

[Contact Flying]

Explain "Nev" to this dumb hillbilly.

 

 

[Contact Flying]

I read back through the posts and figured out it his name. I think.

 

 

[facthunter]

Most of what we fly under RAAus rules is underpowered, some single seater and exotic ones excepted. We also get some "HOT" aerodromes that knock performance and heat engines up if you climb at low speed. Instructors fly close to the weight limit as there is always 2 aboard so hardly ever get a "light" plane to fly.

 

Over the years here there hasn't been a lot of comment on take off technique here except when someone goofs it up on the sand. There's quite a bit to learn about it. Most of our fields are grass. Nev

 

 

[Kamloops]

Every take off is different.

 

How heavy are you?

 

Obstacles?

 

Field length and surface type?

 

Wind speed and direct on the nose or severe cross.

 

Pilot skill?

 

Aircraft type?

 

And the list goes on and on....

 

I would say 50 percent of the time I try to just add enough back pressure to let it fly off when ready. Then accelerate in ground effect, and then start to climb out at best rate and not best angle, while getting rid of the gear as soon as i have about 20 or 30 feet under me or if a short strip when out of runaway, whichever is first.

 

That is assuming no big obstacles in the windscreen. Then i go to cruise climb after about 1000 feet agl....and by about 2000 i reduce power to. I hate running the engines flat out for extended periods of time.

 

I frequently go in and out of Courtenay and its a very nice strip.

 

But despite a lack of obstacles except for a 4 or 5 foot fence people do stupid stuff because its only 1800 feet long.

 

But it's the easiest 1800 feet you will ever find.

 

I never use best angle unless I must outclimb an obstacle.

 

What i consider to be my home strip is listed as 2500 feet of grass....but there is really about an extra 100 at each end if you want it....so i call it 2700 feet. The valley is narrow.

 

The ends have hillside to out climb if you stay straight.

 

But a gentle turn to the east either direction puts you over lower ground.

 

I watch so many stay straight ahead and consider rhe hills an obstacle to out climb.....and why?????

 

A gentle turn removes the obstacles and adds safety IMO.

 

The real question should be....what technique do you use in examples A to Z for take off.....as no 2 are the same.

 

Asking vx or vy is very misleading IMO.

 

I consider vx dangerous if not any obstacles.

 

 

[facthunter]

In a high drag aircraft, climbing at max angle unless required by an obstacle (and you really shouldn't be at those places) means you are going to injure yourself if your engine quits at low altitude. (say below 300')

 

If you are taking off in a significant crosswind don't unstick until you are sure you won't contact the ground subsequently.Nev

 

 

[Contact Flying]

Kamloops,

 

You are certainly right about airplanes flying better level or even down hill. A good technique at short fields with crooked departure paths is the rudder turn in low ground effect. Keep the wing level with ailerons while pushing the nose around with rudder. This misses high terrain and obstructions, keeps the wing from hitting something, and retains the kinetic energy of ground effect.

 

C

 

 

[Kamloops]

Hi Jim.

 

True my friend.

 

But at my little grass strip I am well above ground effect by the hillside....i just don't want to then worry about a 300 foot hill so i swing east about 30 degrees as soon as safe to do so....usually about the time i am darn near out of runaway.

 

I am the only twin there.

 

Many think it is nuts to have my seneca there.

 

But it is perfectly fine for me.

 

Would I suggest a low timer....or even a high timer not used to short strips use it....no way.

 

But I have come to regard anything over 2000 feet now as long.

 

The seneca is a dog at take off....but still doable.

 

My new 182 will feel like I am cheating when on a strip that long.

 

But its new home should have the same sort of feel since its 1400 feet of dirt.

 

Will be great only driving 3 minutes to the strip, instead of the 30 i drive now.

 

Obstacles at the new strip are a low slope hill, and very small trees.

 

The owner of the land just makes us users sign a liability waiver.

 

He has a beautiful cub crafter kit cub that uses so little runway if he was at a regular airport he could just use the ramp or a taxi way and forego the runways.

 

Sorry if this is considered off topic....and a moderator is welcome to delete this posting if they feel it interupts the flow of this topic.

 

Cheers

 

 

[Sloper]

Acturley tried a turn back last week.

 

Declared 2000ft ground and attempted it at 3000ft

 

Lost 400ft climbing clean and 500ft with flaps, learnt a lot.

 

Consider better options at 1000ft to 1200ft.

 

regards Bruce

 

 

[Contact Flying]

I turned back to the paddock next to the one my Ag student was spraying in from only one meter altitude in the first field. The student in the front hadn't switched tanks yet in a 135 hp Super Cub. The energy management or crop duster turn is what makes this possible. Zoom reserve from cruise, and ground effect in the field or on the runway, is what makes this possible. I had it on the ground in the next field by the time he had switched the tank.

 

Going back to the runway? No! This is not possible as it requires a P crop duster turn. First, we are spraying crosswind starting the first swath on the downwind border. The P turn involves clearing the wing coming out of the field. We don't want to put the wing down into a wire or tree. Once the obstacle goes under the downwind wing, we turn (fall off the target) downwind. This is for offset. We turn about fifteen degrees in light crosswind and much less in a strong crosswind. As soon as we bleed much energy from this pitch up, we either level with a near full load or start the upwind turn if zoom reserve still remains. Either way we now trade airspeed for altitude in the upwind turn. This reduces our airspeed (the slowere we go the faster our turn rate) and groundspeed. The now headwind helps reduce the diameter of the turn back. We do not pull back on the stick in the turn except to prevent a great deal of nose tuck in a very steep (toward 90 degree) bank. We do, however, use a great deal of rudder in the turn to counter adverse yaw and to now (on our side with the upwind wing pointed toward the ground) help push the nose down. In a near 90 degree bank, our rudder controls the up-down pitch of the nose somewhat. Forward elevator here would only delay the turn. We are in a bit of a rush to get the nose pointed down the desired crop row before the down wing strikes something. And we certainly do not try to pull up with that wing down, causing the graveyard spiral effect. We want to level the wing going over wires, trees, and such.

 

Having lots of practice turning at low altitude, I have had little trouble with the twelve engine failures I have had. However, the only time I put it down on a runway was straight ahead. As I had used the basic low ground effect takeoff I always use, I was at one meter with plenty of runway left when the motor stopped.