Vx, Vy, and turnbacks

[Gnarly Gnu]

Next time you are flying, find a nice straight stretch of road about the length of your local runway. Fly above it at slow speed with takeoff flaps but with a safe height.

Should I go over or under the wires? If under how should I handle oncoming traffic?

 

BTW you forgot to mention your bank angle in the hook turn, which aircraft and total height loss. Pretty sure you didn't mean just 100 feet (in a Jab it's more like 400). Also not so clear why you wanted to use a road instead, of you know, a runway?

 

 

[ayavner]

I took it to mean he was already at a safe height over the road, and he was simulating a takeoff up to 500' over where he started... so not down near the wires at all.

 

So he's saying he lost 600'... 100 below his start point.

 

I use roads from height for the same sort of thing - something straight to line up on and practice, without doing so over an airport and annoying traffic in the circuit. At least that's what I got out of Geoff's comment.

 

 

[2tonne]

That's the way I read it as well.

 

 

[Gnarly Gnu]

OK, 600 feet loss sounds like a kinda lazy turn.

 

 

[Geoff13]

OK, 600 feet loss sounds like a kinda lazy turn.

I am not sure what you mean by a lazy turn but as I say that is the best that I have managed to date. The worst puts me somewhere near the bottom of the Mariana Trench. A lot depends on temperature, wind etc. I tend to try it under different conditions and as I said I know when I am going to pull power so there is no oh s**t moment. I dont practice this so that I can turn back if I need to, it is simply my way of instilling into my mind that I can't do it.

 

 

[Ada Elle]

A standard rate one turn takes 2 minutes to perform. Logically that means that if you’re trying to perform 180 degrees (half of a full turn to make a runway) the turn will take one minute to perform. Now when you lose an engine in the Foxbat after take-off you automatically push the nose forward to increase the AIS to 60 kts (that’s the speed I train my students with; yes it’s faster than normal but it’s safer. Your instructor may give you a different speed) increasing the AIS will put you into a descent with a VSI reading of 500fpm minimum. So, if you lost your engine at or below 500 ft it would take you 1 minute to both finish your turn and lose 500ft so you would end up impacting the runway before completing the turn (This doesn’t include increase in weight in a turn greater than rate 1 on increased IAS, but either way you wouldn’t make it). The same thing will apply to both Vx and Vy just be aware of how far your nose will have to drop to bring the ASI back to a safe speed which should make your descent rate greater than 500fpm.

Rate 1 is pretty slow turn in these aircraft. Time taken to turn 180 degrees should be pi * v / (10 tan(bank angle)), where v is in m/s (1 m/s == 2kt, roughly). so at 30 degrees of bank, it should take roughly 20s at 60 knots.

 

What this means is that when you are flying at low level you fly at normal cruise speed or higher so in the Foxbat I will be at at-least 80 kts so that if I lost an engine I would convert my excess speed to height which produces about 200-300ft of height which I get to play with. This; however; will change if you fly better aircraft. I asked Matt Hall how much height he would gain if he lost the engine in his aerobat. The answer he gave me was circuit height; that is with an aerobatic aircraft he would be able to gain roughly 1000ft and have plenty of time to do a full circuit before having to land.

Not necessarily better, but faster. 80kts should only get you 180ft though (assuming you have 40kt of airspeed at the end of the zoom.

 

This however, changes when you reach top of climb where you adjust the attitude first (push the stick forward and gain airspeed), then power (reduce RPM back to cruise) then trim. This is because in heavier aircraft C150, C172s whatever you flying you must increase ASI so that you are fast enough to avoid stalling the aircraft. If you adjusted power first instead of attitude at the top of your climb there is a very real chance you could stall the aircraft and at 1000ft AGL when you are also entering a turn to make a down wind leg you could also enter a spin. So the question is; can you could get out of a spin or stall at 1000ft AGL or lower?

This confuses me.

 

If you have the plane trimmed for flight in a particular regime (say at Vx) and you suddenly cut power, two things should happen:

 

1. The reduced airflow over the tail should induce a nose down pitching moment

 

2. As the plane slows and noses over, the winds unload and the stall speed is reduced by this reduction in wind loading

 

If your stick isn't in the stick stall position, how does it stall?

 

 

[diesel]

Get out and do some thermaling in your powered buggy. With practice you will be able to wrap up those turns at only a couple of kts above stall speed. None of this 80 kts stuff as you wont be able to do it. As your stall speed is under 45 kts 80 you are basically at max manovering. Why all this fear of stalling and spinning? If you feel the stall approach just back off a bit and keep going. Reluctance to bank and over ruddering the turn is what will kill you. Chas

 

 

[Letitia]

Hi Ada,

 

Could you please let me know where you got your formula from? After looking at the FAA Aerodynamics of flight PDF I can’t seem to find the formula you’re referring to.

 

I would like to point out that I wasn’t particularly concerned about how much time it would take to you to perform 180 degree turn. I’m more worried about your VSI is doing during a steep turn and what happens to it when you increase AoB. The only safe, practical way I can see of making the turn would be by carrying out a stall turn; which we aren’t allowed to perform so it’s sort of a moot point.

 

Don’t forget about how angle of bank affects your stalling speed. If you were below 500ft and you lost your engine right after take off your initial reaction should be to lower your nose and gain much needed airspeed and if you landed straight ahead you would be on the ground a minute after losing your engine. If you then decided to put your aircraft into a 30-60 degree turn you would also have to increase your ASI because the increased AoB causes an increase in LF which increases your stalling speed. The example I used was that if you were flying at 60kts it should give you a descent rate of at least 500fpm. If you were to increase your turn by 60 degrees you increase your LF to 2; so if the aircraft originally stalled at 45 kts it will now stall at 90 kts. So to compensate for this you push your nose further forward to increase your ASI and because you have done this your VSI will increase to greater than 500fpm; lets use 600 fpm then it would take you 50 seconds to land. Plus if you have a delayed reaction of 2-5 seconds that’ll cost you a hundred foot or so. So after you’ve lost an engine at 500 ft then you’ve lost at least 100ft to delayed reaction then you decide to perform a 180 degree turn you’ll only have 400 left that you can perform a turn in and straighten up in and land which you would have to do in 40 seconds. Why don’t you test it out with an instructor? Go out to the training area and fly at 3000AGL add 300-500 ft to that so that you’re at 3300-3500AGL simulate an engine failure and see if you are able to perform a 180 degree turn in 300-400ft. And no, don’t stall turn the aircraft.

 

With the point on LL. I was not trying to say that flying along the runway at 80 kts is a good idea and is a fail-safe for loss of height or that you shouldn’t learn how to fly at a slower ASI at LL. Flying at various airspeeds is essential knowledge whether it is at 50ft or 30,000 ft.

 

I’ve trained mostly low time RAA pilots in LL (Yes they meet the minimum requirements set by RAA) and these pilots often end up; once completing training; west mustering cattle in RAA aircraft. The reason I get them to fly fast is because I know a lot of them will while mustering do something silly like look over their shoulders or fly into the sun or get distracted by drift or whatever. The point of making them fly fast is to ensure they transition into and out of low level smoothly without too much hassle and without spending too much time down there before they get back up to height and spot cattle or whatever it is they’re doing.

 

The point I was trying to make; and I’ll use it in an example; is that if I was flying along at 50ft above the ground and lost an engine and I pulled back the stick to gain height (I have no experience gliding and do not have an opinion on how to operate them. I assume the EFATO for a glider is similar to a Thruster where it’s stick forward and try and gain airspeed and land pretty much underneath yourself) say 200ft so I was now at 250AGL all I would have succeeded in doing would be giving myself an extra 3 seconds to think and increase my ASI before I would have to land again.

 

If you look at the other point that was made of flying at low airspeed at LL no change to this assumption would be made except that instead of being to gain some height I would be landing right where the engine stopped, so there is no time to turn back.

 

And with your last point RAA is different to GA. They have aircraft which are half a ton in weight; minimum. You would have noticed that when you fly the Foxbat you get no real lag between when you apply power and the aircraft climbing. This doesn’t happen in GA aircraft. When you fly GA aircraft you’ll get beaten over the head by instructors who will tell you that once you retracted one stage of flap and before you retract the next stage you must ensure you have a positive indication on your ASI. This is due to delay in reaction of the larger aircraft. While I was doing circuits in a C210N on the weekend I had this problem. After I applied full power I have to wait for two seconds or so for the ASI to increase and the VSI to show a positive rate of climb indication before I retract flaps and undercarriage etc and even then you wait after each retraction which can scare you a bit if you’re not used to it. The same thing applies to the circuit procedure right after take-off. Before you pull back power you check to ensure you have enough airspeed (or you lower the nose) before you reduce power. This can become an issue if pilots haven’t done a proper weight and balance chart. If someone were to have loaded the aircraft so that it exceeded maximum weight or so that its CofG was aft of its limit you increase the risk of stalling or spinning the aircraft.

 

Don't forget as I said in an earlier post I am in the process of finishing a CPL and as such I'm still and will always be learning. So if you think I've made a mistake with the explanation please let me know and we can clarify the issue.

 

 

[Ada Elle]

Could you please let me know where you got your formula from? After looking at the FAA Aerodynamics of flight PDF I can’t seem to find the formula you’re referring to.

You take v^2/a = r for the radius of the turn; in a coordinated turn a = g tan (aob) and the time taken to turn 180 degrees is pi * r / v. Substitute it all in...

 

I would like to point out that I wasn’t particularly concerned about how much time it would take to you to perform 180 degree turn. I’m more worried about your VSI is doing during a steep turn and what happens to it when you increase AoB.

Push the nose down a few degrees.

 

If you then decided to put your aircraft into a 30-60 degree turn you would also have to increase your ASI because the increased AoB causes an increase in LF which increases your stalling speed. The example I used was that if you were flying at 60kts it should give you a descent rate of at least 500fpm. If you were to increase your turn by 60 degrees you increase your LF to 2; so if the aircraft originally stalled at 45 kts it will now stall at 90 kts. So to compensate for this you push your nose further forward to increase your ASI and because you have done this your VSI will increase to greater than 500fpm; lets use 600 fpm then it would take you 50 seconds to land. Plus if you have a delayed reaction of 2-5 seconds that’ll cost you a hundred foot or so. So after you’ve lost an engine at 500 ft then you’ve lost at least 100ft to delayed reaction then you decide to perform a 180 degree turn you’ll only have 400 left that you can perform a turn in and straighten up in and land which you would have to do in 40 seconds. Why don’t you test it out with an instructor? Go out to the training area and fly at 3000AGL add 300-500 ft to that so that you’re at 3300-3500AGL simulate an engine failure and see if you are able to perform a 180 degree turn in 300-400ft. And no, don’t stall turn the aircraft.

60's a lot. The simulator trials suggest that theoretical optimal is 45, and 35 is probably better for most pilots.

 

http://www.csgnetwork.com/aircraftturninfocalc.html says that at 60 knots, with a 45 knot stall speed, and a 35 degree angle of bank, you can do a rate 4 turn (180 degrees in 15 seconds), increasing the stall speed to 50 knots. If your VSI is reading -600, you've lost 150ft during the turn.

 

I'm not talking about a turnback at 500ft, I'm talking at a turnback when I only have 1500ft of runway left. If I'm at 300ft at YWOL, I'm going to land straight ahead because there should be 3500ft of runway left if I've done the takeoff right, so I'm going to land straight ahead At 700ft, landing straight ahead on remaining runway is no longer an option but the turnback should be an option at this point, _ I think_. These numbers differ between aircraft and runways, of course.

 

(I'm usually at about 800ft at the end of the runway when doing a climb at 80 knots, which is a sort of performance climb situation; 15 faster than BROC).

 

And with your last point RAA is different to GA. They have aircraft which are half a ton in weight; minimum. You would have noticed that when you fly the Foxbat you get no real lag between when you apply power and the aircraft climbing. This doesn’t happen in GA aircraft. When you fly GA aircraft you’ll get beaten over the head by instructors who will tell you that once you retracted one stage of flap and before you retract the next stage you must ensure you have a positive indication on your ASI. This is due to delay in reaction of the larger aircraft. While I was doing circuits in a C210N on the weekend I had this problem. After I applied full power I have to wait for two seconds or so for the ASI to increase and the VSI to show a positive rate of climb indication before I retract flaps and undercarriage etc and even then you wait after each retraction which can scare you a bit if you’re not used to it. The same thing applies to the circuit procedure right after take-off. Before you pull back power you check to ensure you have enough airspeed (or you lower the nose) before you reduce power. This can become an issue if pilots haven’t done a proper weight and balance chart. If someone were to have loaded the aircraft so that it exceeded maximum weight or so that its CofG was aft of its limit you increase the risk of stalling or spinning the aircraft.

I was asking about the aerodynamics of the stall in this situation, not the numbers on the instruments. I've not flown anything heavier than a Warrior.

 

 

[facthunter]

Higher drag planes will lose more height as they have an inferior glide ratio so you will need a greater rate of turn to compensate. 45 degrees of bank , or a bit more may prove best. It becomes a time thing Using excess speed (if you have any) would require instant use to gain anything. Don't forget there is more turn than 180 degrees Usually 180 + about 30 to regain runway Centreline and then 30 degerees back again to align with runway. AND at this stage you are going downwind so you have a higher groundspeed if things go wrong. Most consider a turn back a bad recommendation. You can run the figures through a simulator and get some theoretical height/ over distances where it can be achieved. Pick a very draggy plane as most U/l's don't achieve a better glide angle in still air than 1 in10. In the real world the success rate appears to be very low, with most stalling in the turn where the pressure is on to make it. Landing straight ahead or turning into wind and avoiding major obstacles may damage the plane but you should walk away from a plane that stalls at 45 knots, landing into wind. The message seems to be retain control of the aircraft and you come off better, always. Nev

 

 

[Gnarly Gnu]

60's a lot. The simulator trials suggest that theoretical optimal is 45, and 35 is probably better for most pilots.

For a power-off hook turn 60 degree bank is ideal, 45 is minimum, 35 would be only if you have plenty of height to spare (or power still available).

 

 

[Guest Andys@coffs]

I fly a Jab and while I'm aware of Vx and Vy the reality in a jab (well at least mine that is) is I climb at the speed that gives me the required engine cooling If I look after the engine then there is a better chance it'll look after me.......If I was to extended climb at best angle of climb Id be in fear of cooking the heads regularly..... I climb such that CHT doesn't exceed my predetermined maxima's on any head. (in my case old thick finned heads with pushrods, so hotter than more recent models of the engine)

 

From memory in my 230 they are Vx 65 Kts Vy 70 Kts .... generally I try to not go slower than about 80 for climb after flaps away and for extended length climbs not slower than 100..... so those things (Vx and Vy) are relatively moot depending on Aircraft and load

 

 

[Head in the clouds]

The turnback is an entirely different aspect that has already been evaluated and discussed on this forum, (and many others) so a link would be good. It's a big discussion in it's own right. ...

I think the OP and a couple of others might like the lengthy and informative thread we had on the EFATO subject last year - EFATO Reference Thread

 

 

[Ada Elle]

I think the OP and a couple of others might like the lengthy and informative thread we had on the EFATO subject last year - EFATO Reference Thread

I've read it. It doesn't address the question I originally posed.

 

http://www.recreationalflying.com/threads/e-f-a-t-o-reference-thread-quality-information-only.40773/#post-429411 describes the notion of the 'non-maneuvering area'. My question originally posed, is:

 

- Does climbing at Vx reduce the non-maneuvering area?

 

- Does it reduce it by enough that the decreased stall margin is made up for?

 

 

[facthunter]

Think in sink rate rather than stall margin. That gives you an easy way to determine the time to ground contact from a known height. You have to increase speed =height loss, plus provide increased lift= drag for the time you are in the turn to reverse direction. Best not to increase the speed much before you turn for obvious reasons You are going away from where you want to get to.. Things are changing all the time. The optimum bank angle is more than you think it will be as the first turn is the critical one. Nev

 

 

[Ada Elle]

Think in sink rate rather than stall margin. That gives you an easy way to determine the time to ground contact from a known height. You have to increase speed =height loss, plus provide increased lift= drag for the time you are in the turn to reverse direction. Best not to increase the speed much before you turn for obvious reasons You are going away from where you want to get to.. Things are changing all the time. The optimum bank angle is more than you think it will be as the first turn is the critical one. Nev

I'm not asking about after EFATO! I'm asking about how to fly, on climbout, that maximises your choices after EFATO. The possible/impossible turn is a distraction.

 

Imagine (assuming that I've tested it in an aircraft and I lose 400ft on the turn):

 

- climbing at Vx, the height at end of runway is 700'. The impossible turn becomes possible.

 

- climbing at Vy, the height at end of runway is 500'. The impossible turn is impossible.

 

Should I climb at Vx so that I have the option of turnback? This is the question.

 

 

[facthunter]

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

 

 

[Head in the clouds]

Ada Elle, flying isn't a perfect world.

 

If you were flying a jet in nil wind conditions your 'flying by the numbers' formula might have some relevance but the reality of flying a very light aircraft in varying wind conditions completely negates any use of Vx, Vy or anything else. In the real world you fly these small aircraft according to your experience in the differing conditions on each day. Your airspeed indicator has a delay that prevents you being able to fly the 'perfect scenario' in any case. If you spend your time chasing the ASI you'll not be looking outside, nor will you be taking best advantage of lift and sink, and wind gradients as they affect you.

 

And - you'd need a sensitive variometer rather than just an RoC indicator to tell you when to fly faster in sink and slower in lift - if you really want to nail this one you would benefit from going gliding ...

 

Get to know the aircraft you fly and you'll make much better height/distance gains than you ever will by trying to fly the numbers.

 

 

[fly_tornado]

the quickest turn around requires a 360˚ turn, a 270˚ turn followed by 90˚ turn in the opposite direction. a 180˚ turn will put you on a parrallel course but a couple hundred feet away from the runway.

 

Its a big ask in a plane without an engine and a full load of fuel.

 

 

[ev17ifly2]

Hi there Ada Elle, what is your profession and back ground ? You come across as being very clinical and analytical .

 

I think Head in the Clouds may be someone you can learn from.

 

When I first started in spent too much time worrying about what was happening below the windscreen rather than looking through it.

 

 

[Zibi]

I'm not asking about after EFATO! I'm asking about how to fly, on climbout, that maximises your choices after EFATO. The possible/impossible turn is a distraction.Imagine (assuming that I've tested it in an aircraft and I lose 400ft on the turn):

 

- climbing at Vx, the height at end of runway is 700'. The impossible turn becomes possible.

 

- climbing at Vy, the height at end of runway is 500'. The impossible turn is impossible.

 

Should I climb at Vx so that I have the option of turnback? This is the question.

You have two more variables, in that situation, that you are not including: initial speed and initial pitch angle.

Climbing and Vx you might be at 700' as in your example, but you are also pitching up higher and going slower so you have drop your nose through a higher angle and you have less energy to carry you on as you are dropping your nose.

 

So even though you might have started higher, by the time you get to your glide speed you might lose more height than what you gained by climbing quicker.

 

I don't have any practical experience with either of those situations (apart from simulated engine failures during training) but the way I was taught was that unless you have a very good reason to climb out at Vx (i.e. a hill ahead) it is generally not worth it.

 

 

[Russ]

Don't mean to hijack this thread.........but, my query is sort of aligned.....

 

to "learn" just how FAR i can glide........eg, 5000ft back to idle, set up speed at 60, then note distance covered, then same again 65, again 70 etc etc.

 

Is this going to cause too rapid engine cooling, and cause me grief.

 

I would like to "know" in air, that, that particular area in the distance.....is reachable......if you get my drift.

 

Ive read my POH.......best glide is not showing, maybe i just missed it. ??

 

russ

 

 

[Kununurra]

Ada Elle

 

It seems your question has been answered many times already.

 

As you will find on any forum there will be lots of hypothethis on every subject.

 

It may be best if you divulge what your answer is and how you support that answer. I am almost sure that will generate even more discussion on this thread.

 

Enjoy your flying

 

 

[facthunter]

Russ, best distance achieved in a glide is very dependent on wind component. If into wind glide at a faster airspeed and with a tailwind component glide at a slower airspeed. If you haven't had this pointed out in your training , we can discuss it. The principle applies to X country flying too, but then it's your chosen cruising speed affected. Nev

 

 

[Russ]

Yes, thanks nev.....I was seeking cooling dangers in the "exercise"...

 

Jab engine.....treat nicely