Vx, Vy, and turnbacks

[Ada Elle]

I've always been taught to do the initial upwind climb at Vy to maximise total performance available. However, on a longish runway (5000ft) you might be able to get to 500ft and the crosswind turn just past the end of the runway. Would climbing at Vx (so that you got to 500 ft later time-wise, but earlier distance wise) be safer in case of EFATO?

 

The logic here is that by chewing up less runway per height gain, you can either land on remaining runway or turn back more easily. The tradeoff is that if you have an engine failure you need to nose down to not stall on the turn.

 

 

[Happyflyer]

Climbing at Vx is dangerous. Getting to height as soon as possible (Vy) is safer. Height is safety. Play the odds.

 

 

[ayavner]

if you have an engine failure, its nose-down anyway..

 

 

[Ada Elle]

That's not the point.

 

YWOL, for example, has just under 6000ft of runway.

 

In a Foxbat, Vx is 49kt (650fpm) and Vy is 54kt (690fpm). So if you have an engine failure 45s into flight, at Vx you've gone 3700ft and are 430ft up; at Vy you've gone 3900ft and are 460ft up. So if you've been climbing at Vx, you might have a situation where you either have runway ahead of you (including slipping/flaps/etc) or you can turn around. At Vy you might consume all the runway before you have enough altitude to turn around.

 

 

[Ada Elle]

http://www.planeandpilotmag.com/pilot-talk/more-pilot-talk/guest-speaker-safe-turnarounds.html discusses the advantages of climbing at Vx to give you a chance at turning around.

 

Also, one thing that may be required is a plane that has a better glideslope than climbslope. A J160 has 10:1 glide and about 10:1 climb, so turning around might not be advisable. 7.5:1 climb and 11:1 glide (published numbers for the foxbat) give you better chances. An Alpha Trainer has 6.2:1 climb and 17:1 glide, so as long as you can do the turn without losing too much altitude, you should be able to essentially turn back or go ahead on a lot of sealed runways.

 

 

[diesel]

Get used to flying off sub 1000 ft runways and you will think differently. Do some glider winch training and get some real power failures behind you. years ago we used to use number 12 gauge fencing wire on an interesting field. Learning to do something with an old wooden glider sharpened the sensers. I fly power the same way. Bank, balance, speed will get you home. Chas

 

 

[facthunter]

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.

 

Climb rate in a circuit in the average plane is going to determine circuit size to a certain degree. If you want to keep it small climb at close to best rate at least. If you are departing the circuit and tracking en route you might go a bit faster for time and engine cooling considerations. unless obstacle clearances are a consideration..

 

If you have a very high performance aircraft you could reach a height where you may conflict with aircraft joining the circuit over head, crosswind, so be aware of that. Nev

 

 

[diesel]

Hi Nev, I dont disagree with you. What scares me is watching people trying to claw their way into the air with heavy for the aeroplane loads and going straight into max angle if they manage to keep airborne. They do not make use of ground effect. Acouple of dings in the last couple of weeks. One heavy c182 never got airbourne. At the other end of the scale a kitfox. Two stroke engine out probably at 400 ft. We dont have long runways but have gullies and rivers. In reality vx and vy are very close for most aircraft. If crap happens its more like a basic camera. Piont and shoot.I have had a few genuine ones over the years. Just keep it flying and keep looking. Marconi is second. Chas.

 

 

[Aldo]

I've always been taught to do the initial upwind climb at Vy to maximise total performance available. However, on a longish runway (5000ft) you might be able to get to 500ft and the crosswind turn just past the end of the runway. Would climbing at Vx (so that you got to 500 ft later time-wise, but earlier distance wise) be safer in case of EFATO?The logic here is that by chewing up less runway per height gain, you can either land on remaining runway or turn back more easily. The tradeoff is that if you have an engine failure you need to nose down to not stall on the turn.

Ada

 

My opinion for what it's worth (talk to your instructor/mentor for your personal situation).

 

Get Turn Back out of your thinking altogether it has killed more pilots than you have had hot dinners (I'm assuming you're not 95). Concentrate on taking off in the manner prescribed in the POH for the take off that you are doing for that particular field and if you ever happen to have an engine out on take off pick somewhere 10 deg either side of the nose and put it there.

 

Aldo

 

 

[Downunder]

Foxbats climb really well. I climb out at 60kts as taught, WOT (1 stg flap until 50kts) and use longish fields.

 

As mentioned above, don't be too high mid field as you may conflict with crosswind joining aircraft.

 

I make an effort to fit in with other aircraft and generally climb upwind to 1000 before turning because I'm still over the field/rwy at 500.

 

Not had any issues with that where I fly.

 

 

[Ada Elle]

The traditional attitude regarding turnbacks is in aircraft with lower performance than the ones we fly, though. How many GA aircraft can be at 1000ft while still over the runway?

 

(not counting runways sized to take A380s).

 

 

[facthunter]

Probably not many unless there are significant headwinds unless at places like Darwin. Nev

 

 

[Ada Elle]

The glider rope-break procedure seems to have two decision points:

 

1. Is there enough runway to land straight ahead?

 

2. Is there enough altitude to turn back?

 

In a sufficiently high performance aircraft or long runway, these might overlap - so you might have enough altitude to turn back, as well as runway to land ahead. but if they don't, how can we fly to minimise the time between (1) and (2)? because that is the region where you might not have options (houses etc straight ahead).

 

 

[facthunter]

You may have neither. A glider has L/D ratios much better than a powered plane of the type we operate, so a course reversal loses less height and you glide further with the height you have.

 

It's a distance height consideration. Turn back is nearly always a risky path to take, moreso it you have a significant headwind component, where an into wind landing will be at slow groundspeed, so less kinetic energy, especially with low stall speed aircraft, so less damage to you and the plane. Nev

 

 

[Ada Elle]

This discussion came from flying an aircraft that is near glider territory (17:1) off long runways, and doing some gliding. I don't have any actual experience trying to simulate this, but I will try the next time I have an instructor in the plane (currency revalidation etc).

 

http://williams.best.vwh.net/turnback_seminar_Oct_2008.pdf says this:

 

'You can turnback if: 1) you height when crossing the departure end of the runway exceeds the altitude required to make the turn, AND 2) Climb ratio is more than glide ratio.'

 

Traditional GA aircraft tend to not meet this criteria. Most high performance RA types (100hp rotax, or amazing wings) do.

 

 

[Letitia]

Dear Ada,

 

Hope this helps.

 

I had a friend explain the reasoning behind this problem to me mathematically;

 

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.

 

This reasoning doesn’t include the 2-5 seconds it takes for you to act after an engine failure. Usually the initial surprise and shock make you hesitate slightly and will cause you to delay your reaction.

 

Also remember what type of aircraft you’re flying. I have a low level endorsement for RAA and while I was training for the endorsement part of the training involved simulating an engine failure while at low level. What I was trained to do in the event of an engine failure at low level was to pull the stick back to gain height. One of the things you’re taught in low level training is “If you want to fly low, fly fast. If you want to slow, fly high”. 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.

 

Also, have a look at performance charts. When you were training for straight and level flight your instructor should have mentioned the PAT and APT graph. P=Performace, A=Attitude and T=Trim. This represents the ways to adjust your controls during every stage of flight. That is everywhere in circuit except when you level out you adjust your controls in the following sequence; power first (apply full power), then attitude (at right ASI pull the stick back and climb off the runway) and finally trim.

 

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?

 

Just so you know CASA applies restrictions on novice aerobatic pilots for both training and competing. From what I’ve read novice aerobatic pilots who compete in the championships are required to perform manoeuvres at a minimum height (which I believe is 3000ft AGL) which includes both stalling and spinning manoeuvres.

 

Letitia

 

 

[ayavner]

further to the above - just curious, since i've not done the maths nor been in that situation... but... you would be doing more than a 180* turn in such a case right? Unless there were a parallel runway under you at whatever point you roll out of your 180, wouldn't there be an additional loss in then getting yourself back to the runway you were on? I'm envisioning a turn that looks a bit like an enlarged question mark or an upside-down J.

 

worth mentioning, or am i overthinking?

 

 

[ev17ifly2]

further to the above - just curious, since i've not done the maths nor been in that situation... but... you would be doing more than a 180* turn in such a case right? Unless there were a parallel runway under you at whatever point you roll out of your 180, wouldn't there be an additional loss in then getting yourself back to the runway you were on? I'm envisioning a turn that looks a bit like an enlarged question mark or an upside-down J.worth mentioning, or am i overthinking?

From what I have read and been told you are correct. There is one school of thought which says to take off and climb on an angle to the strip ie. Down the leg of your upside down J.

 

That way the degree of turn back is not as great.

 

I would be interested on what some of our more experienced members think.

 

 

[Oscar]

A glider cable-break response is (almost) unique to gliders for several reasons.

 

Firstly - you are climbing at a very steep angle and a slow speed - and the sensation of that is increased because you are basically laying down - it feels as if your feet are above your head, and in some gliders, that is probably true. Believe me - and I have four cable-breaks to my experience, two of them NOT student training exercises. It genuinely feels as if you are about to slide backwards and there is NO way you can 'convert speed to height', you mash the stick forwards as a reflex action - forget the 2-5 seconds to react thing. Then - and we are taught this very, very strongly, you get the nose well down and DO NOT other than perhaps marginally ease the stick back until you feel your weight back on your bum. By that time, you are looking at the ground not much in front of you - and if at less than about 600 feet, that means a goodly amount of strip.

 

Start pulling back the stick to stabilise speed to say around 55-60 kts and look at the options. One thing you have in gliders that isn't in most other aircraft is speed brakes, and you also - in most gliders - have the ability to enter a very decent side-slip to further shorten your landing distance. A straight-ahead landing is almost always possible, even if you need to add in a split-ar$e S turn. I've had cable-breaks at about 400 and 600 feet; in both, I was stopped before the winch. In the two others, I had sufficient height to do a full turn back in one case - with a very truncated circuit - and in the other, a thermal happened at a decidedly propitious moment and I was able to climb away.

 

Slide-slipping plus an S turn gives you a fairly good appreciation of how much height you are losing, so you can roll out of the first phase of the turn and get the aircraft back in line by simply keeping your eye on the arrival point. If you commit to a 180 turn, you CAN'T judge the arrival point until you are deeply committed. Finding that your arrival point is way off the side of the airfield would be extremely unpleasant in some situations - e.g. Wedderburn.

 

The mantra of 'convert speed to height' is very much affected by the nature of the aircraft involved. If you are in a high-drag, low-inertia device, there is bugger-all improvement in your situation available. In something like a Janus with full water-ballast, you can convert 120 kts into 1200 feet height gain as a matter of course; in a Schneider Arrow, you can convert max. rough into a height gain of about one ham-sandwich, with coleslaw if you're flying really accurately.

 

In the biography of Sidney Cotton - an amazing guy - it is recounted that he had an engine-out in his Lockheed 12A when climbing out; he pulled it vertical (so no lift required from the wings) and powered-over using the good engine, for a complete 180 turn requiring only the pull-out and landing. I reckon you could do that sort of recovery in maybe a Pitts... or if you're Matt Hall.

 

For me, I will go the 'pick the best achievable soft spot' option.

 

 

[ayavner]

.. in my night circuit lesson the other day, the instructor said basically if the fan stops, pick a dark spot (assuming reaching the field not an option)

 

 

[poteroo]

Also remember what type of aircraft you’re flying. I have a low level endorsement for RAA and while I was training for the endorsement part of the training involved simulating an engine failure while at low level. What I was trained to do in the event of an engine failure at low level was to pull the stick back to gain height. One of the things you’re taught in low level training is “If you want to fly low, fly fast. If you want to slow, fly high”. 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

Don't take this personally, but I would question the relevance of this 'fast' flight . Flying fast at LL means you shorten the available reaction time to decreased forward visibility, and you increase your radius of turn. It's not what I teach. My syllabus is CASA approved for LL, and I've done 150+ of them. Perhaps we need to shift this to another thread because it might explain, in part, why many pilots collide with obstacles and terrain? cheers,

 

 

[diesel]

If you push over too quickly you are adding drag. Its a baic manover no a panic one. Have had more cable breaks over the years than I care to remember. If in doubt turn cross wind. This way you are not eating up airfield and may even drift back. Chas

 

 

[Oscar]

No more than parasitic drag, because you have no induced drag, you are going through a period of neutral/negative G in the push-over. At cable-break speeds, parasitic drag is relatively low. Yes - always turn into-wind, even in the preliminary part of the S turn, to reduce distance to the landable ground.

 

 

[SDQDI]

Don't take this personally, but I would question the relevance of this 'fast' flight . Flying fast at LL means you shorten the available reaction time to decreased forward visibility, and you increase your radius of turn. It's not what I teach. My syllabus is CASA approved for LL, and I've done 150+ of them. Perhaps we need to shift this to another thread because it might explain, in part, why many pilots collide with obstacles and terrain? cheers,

I haven't finished my ll endo yet but was definately being taught to use the whole 'envelope'. My instructor was basically saying he wouldn't sign me off unless he was sure I was competent being low AND slow, which seems to make sense to me for all the reasons you mentioned plus a few more.

 

 

[Geoff13]

Dear Ada,

Hope this helps.

 

I had a friend explain the reasoning behind this problem to me mathematically;

 

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.

 

This reasoning doesn’t include the 2-5 seconds it takes for you to act after an engine failure. Usually the initial surprise and shock make you hesitate slightly and will cause you to delay your reaction.

 

Also remember what type of aircraft you’re flying. I have a low level endorsement for RAA and while I was training for the endorsement part of the training involved simulating an engine failure while at low level. What I was trained to do in the event of an engine failure at low level was to pull the stick back to gain height. One of the things you’re taught in low level training is “If you want to fly low, fly fast. If you want to slow, fly high”. 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.

 

Also, have a look at performance charts. When you were training for straight and level flight your instructor should have mentioned the PAT and APT graph. P=Performace, A=Attitude and T=Trim. This represents the ways to adjust your controls during every stage of flight. That is everywhere in circuit except when you level out you adjust your controls in the following sequence; power first (apply full power), then attitude (at right ASI pull the stick back and climb off the runway) and finally trim.

 

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?

 

Just so you know CASA applies restrictions on novice aerobatic pilots for both training and competing. From what I’ve read novice aerobatic pilots who compete in the championships are required to perform manoeuvres at a minimum height (which I believe is 3000ft AGL) which includes both stalling and spinning manoeuvres.

 

Letitia

 

further to the above - just curious, since i've not done the maths nor been in that situation... but... you would be doing more than a 180* turn in such a case right? Unless there were a parallel runway under you at whatever point you roll out of your 180, wouldn't there be an additional loss in then getting yourself back to the runway you were on? I'm envisioning a turn that looks a bit like an enlarged question mark or an upside-down J.worth mentioning, or am i overthinking?

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. When you get to the start of the straight stretch allow a few seconds to simulate building speed to the point if on the runway then apply full power and and climb as if you are taking off. At 500 feet pull power. get best glide speed, turn 210 degrees the back another 30 degrees so that you are back over the road. Then check your height. The best that I have ever done even when I pull power on myself so I know it is coming puts me at about 100' below my start point as I get back in line with the runway. Thats not good odds in my book. If I loose power at 500 I am going straight ahead unless there is a cross runway, that can change things. I practice for that as well.