Calculating Approach speed --additions

[Pilot DAR]

for gusts, wind, people in the back, plagues of frogs or anything else UNLESS the POH so advises!

Well.... For plagues of frogs, I would be adding a few knots. All of those gizzards smeared all over the lifting surfaces can affect stall speed...

[RansS9]

"because the POH recommended approach airspeeds in all the common trainers, provides plenty of margin. "

Margin for what?

Please correct me if I am wrong but !.3 is the margin the designers make to Vso for the approach speed. If it is not for gust protection (which I understand it is not) what is it for? And does a degradation of that margin
matter when in my trainer (Vso 50kt app 68kt wind down the runway 10kt gusting20kt) I lose 10kt headwind as I am starting the flare?

TIM

[mad_jock]

You put a nudge of power on which you get instantly.

A jet on the other hand would take 10-15 seconds to give you any extra thrust to help you out so they add a bit to give a bit more energy to play with.

To be honest in my experence its not the decrease of wind speed that cause problems with inexperenced pilots. The dramatic increase in sink rate makes them shove the throttle forward.

Now an increase gust doesn't give the same effect especially if there back at idle anyway. They balloon up then panic put the nose down the gust goes and everything is setup for a nose wheel landing. If they do manage to correct it we are into a PIO situation now. And excess energy is just going to make matters worse.

[Robin400]

Worried

Mad Jock your last paragraph is correct

This post worries me, i do hope student pilot are not reading this post and listen the their instructor regarding safe speeds.

[mad_jock]

Unfortunately I think that Instructors are teaching this procedure.

Hell if they can't get a job or afford to pay to fly a jet they can pretend to fly one.

Sorry Haz just spotted your question. I will give you each aircraft has its own picture on approach (but most ga aircraft it will be within a ball hair the same). And under some circumstances eg steep appoach the configuartion points will be different. But I don't make a change generally be it a huge space shuttle sized runway or some titchy just in limits regional airport/grass strip. As I have stated inside the operating enevelope I do the normal appoach. I always land with full flap, none of this pish of reducing some cause its gusty or xwind.

[Mark1234]

And does a degradation of that margin
matter when in my trainer (Vso 50kt app 68kt wind down the runway 10kt gusting20kt) I lose 10kt headwind as I am starting the flare?

From those numbers I think we might be considering the venerable PA28, perhaps this might allay some fears:

Considering a PA28-161:

• 50kts is the clean stall speed - try 44 with full flap.

• You're probably at something less than MTOW, so can grab a few more knots off the stall speed (placarded stall speeds are at MTOW, and there's a chart in the manual somewhere that deals with factoring them for reduced weight)

• Who can read 68kts, so you're probably flying at 70(ish) anyway..

(also, according to the last checklist I looked at, 63kts vref for the 2nd and 3rd stages of flap)

So the reality is that you're probably doing 70kts when stall is a bit above 40. Suprising? That's the problem with all the cumulative 'err on the safe side' assumptions. Given the above, a 10kt loss is neither here nor there really; pull back a bit on the yoke. Worst case you touch a bit harder than normal.

If you're faster, 1) you still have to stop, and 2) you spend more time skimming the ground slowing down - where you're far more likely to PIO and break something.

Lastly, when did you last stall an aircraft - you might remember that it actually takes a pretty concerted effort

[Robin400]

Pa 28-140

Touch down speed is between 47-56 kts at max weight.
Approach speed 75 kts
So you need to reduce speed by 19kts before touch down.
If you loose 28kts. you will be at minimum touch down speed.

[Big Pistons Forever]

Rather than add a bunch of extra airspeed when flying in gusty unstable days, IMO for light training/touring aircraft using less flap works better. This is particularly for true for Cessna's, because of their big, effective flap system. For the Cessna 150/172 series I personnally use flaps 10 deg on those ugly windy days.

[Maoraigh1]

"You put a nudge of power on which you get instantly."
But you don't accelerate instantly. You accelerate at the same slow rate as from lift off, to climb out speed. If the gust is enough to take you well below stall speed, you're in trouble at low altitude. Look at the effects of gusts near thunderstorms.

[Piltdown Man]

This month, I tried the effect of coming low over the fence, but with 70 kts, on a flat 700m runway, in flat calm. Without using brakes, I used all but about 30 metres.

In a full F50, touching down in the TDZ I also didn't need brakes, but I'm probably 15-19 tons heavier. For a 41ton E190 at Flaps Full and moderate braking, I'd expect a similar field length performance. So something is wrong here!

May I suggest that what is broken is the training. It certainly was none too hot when I was being taught in bug smashers. The approach speed was always 65, the climb speed was 65 etc. Neither the weight nor wind etc. was ever dialled in as a parameter. Then we have the some for "Mum & the kids" Safety Brigade (aka "Some for the wire, hedge and ditch brigade").

What did I teach? I taught what the book said. Use the weight from the plan and the approach speed from the book and add half the wind strength up to a maximum of 15kts. At maximum landing weigh in the 172 model I flew , that would be 44kts plus a maximum increment of 15kts would give a maximum approach speed of 59kts. No hedges were ever seen vertically although we had lots of fun watching the safety merchants go farming.

Ugly, windy days if I had to fly, I used to do the same. And just like everyone else, I used less runway to stop.

PM

[RansS9]

"From those numbers I think we might be considering the venerable PA28, perhaps this might allay some fears"
---I think you might be wrong and no it doesn't allay any fears. The figures were chosen for a hypothetical trainer (I've never flown A PA-- anything.) SO if the Vso is 50 1.3 is approx 68. Agreed being a low hours PPL I'd be flying 70 (not for the kids, or plague of frogs, just because there is likely to be a mark on the ASI to indicate it) but you know what PPruners' are like some wag would have corrected us saying it was actually 68! This makes the energy excess over the stall slightly less "surprising".

"Lastly, when did you last stall an aircraft - you might remember that it actually takes a pretty concerted effort "
--- 6 months ago. But then I haven't flown since. Actually as I remember it doesn't but then my airplane has a powerful elevator in part to help bring it to the stall quickly. In other aircraft the effort I supposed depends and how fastidious you are in your trimming. My memory maybe playing me tricks but since I'll be seeing an instructor down your way(White Waltham) next week for a pre-reason wake-up call (involving almost certainly repeated departures in almost every conceivable aircraft attitude/energy state...OH JOY!?!) I'll let you know.

"This post worries me, i do hope student pilot are not reading this post and listen the their instructor regarding safe speeds"
---It does me to..... Conversely I do hope Student Pilots read the post (I count myself as one being low hours.) Why? Well perhaps you could illuminate as to which particular instructor we students should be listening to. Todate I've heard everything from forget airspeed and airspeed indicators"feel the force Luke"; Vso1.3 irrespective of gusts; Vso1.3 plus the whole gust factor; Vso1.3 plus half the wind (which wind ..the total or the resolved component down the runway) no mention of gusts; do what it says in the POH(unfortunately many POH's say nothing); and finally add a bit for the wind add a bit for the kids blah blah!

Oh and before anyone pipes up this information is earnestly given by pilots with lifetimes worth of experience, in all manner of aircraft. Yes..it worries me. Perhaps they are all right and that there is more than one way to "skin a rabbit". Alternatively perhaps they are not all right ...just exceedingly lucky!

Interesting post on the sister thread in Flight Testing about when 1.3 first started to appear in the literature .

TIM

[mad_jock]

You don't need to accelerate you just need to increase you slip stream. The combination of that and ground effect will sort the problem out.

And your into a wind sheer event if your getting that much instant change in wind speed.

And your all focusing on "stall speed" when you should be thinking about stall attitude. If you have the picture right and maintain it you won't stall.

And the size of gusts you are talking about 30-40knts you will only get in gust front infront of continetal CB's. And in those conditions I would be questioning your airmanship attempting an approach anyway. Yes we do get gust of 20-30knts in the UK but its in wx conditions that no GA will be airbourne. Thats middle of winter western isles and Shetland wx when the seagulls are grounded.

It seems to me the we have a group of experenced instructors and big tin drivers who have flown in these conditions many times saying don't add anything. And a group of GA only drivers who say add it in or you will die.

[one dot right]

Mad Jock, have you been on the sauce?

You don't need to accelerate you just need to increase you slip stream. The combination of that and ground effect will sort the problem out.

Er, how is increasing slipstream over the fuselage and tail going to increase your lift?

And as for ground effect helping you out, don't you think it's a bit last minute ish to be sitting there thinking, 'it's ok, sink rate's a bit high, airspeed's a bit low, but ground effect will intervene in just a sec, oh wait, i'm in a high wing 152/172/182/Partenavia/Tripacer/insert as appropriate, BANG "oh bother"'

I'm not just a 'GA only' driver, and my last turboprop had 5000 horsepower on the wings (whatever difference that makes)!

[mad_jock]

Engerises the airflow over your wings and decreases your stall speed. Also the thrust line helps you out.

Stalling exercise ppl course.

Again it is not your airspeed which makes you stall it is your angle of attack.

If your not in ground effect you have enough room to lower the nose a bit add a bit of power and sort it out.

And if you have driven a machine with that much power on the wing you should know that its your power to weight ratio which counts not the sum total of your SHP.

What size of gusts are we talking about here? Your normal GA pilot aint going to be flying in more that 25-30 Knots of wind anyway, the most likely situation would be 10G20 knots which has already been proved makes cock all difference in the grand scope of things. Now if it was 10G30 or maybe even 10G40 your average PPL after they get on the deck is more than likely going to flip it taxying.

[Robin400]

Er, how is increasing slipstream over the fuselage and tail going to increase your lift?

The slip stream from your 5000shp over the wing area behind the prop arc....try closing the thrust levers before touchdown dash and thump.

sorry mad jock you posted whilst was typing

[mad_jock]

Nae bother.

And your always meant to be at flight idle by the time you put the wheels on the deck. A bit like this discussion there are some out there that recommend you leave a bit of power on for a gusty landing.

Similar to this situation all that does is add energy into the equation which means when you do actually want to stop flying you end up 2 foot off the deck trying to control the aircraft in ground effect while bleeding the energy off.

[Robin400]

all simple stuff.

[one dot right]

Robin 400 and Mad Jock. Do try to keep up chaps, this is about light aircraft the majority of which are single engine.

Single engines are generally in the middle of the aeroplane, attached to the fuselage not the wings, so the concept of energising the airflow over the wings is irrelevant

And if you have driven a machine with that much power on the wing you should know that its your power to weight ratio which counts not the sum total of your SHP.

Yup, well aware of that, but you were using your turboprop experience to compare to a tomahawk. My old turboprop was gloriously overpowered as probably is yours, a Tomahawk is not. My old turboprop responded to the power in the blink of an eye, a Tomahawk does not.

[Pace]

Again it is not your airspeed which makes you stall it is your angle of attack.

Mad Jock

I thought you guys up in the wilds of Scotland were experts with wind 50 kts is light up there

Of course its the angle of attack which causes the aircraft to stall but it is the airflow over the wing which allows you to reduces or increases the AOA while maintaining flight.

In any flight we are looking at energy management. In the case of a glider using potential energy in still conditions trading off altitude for airspeed.
Glider pilots seek lift from air movement. In rising air they can reduce the AOA to maintain altitude which will give an increase in speed or use that energy to climb.
In descending air to maintain an altitude they will have to increase the AOA with a reduction in airspeed and an increase in drag.

The only way around this is to increase the rate of descend tapping into potential energy and reducing the AOA and drag.

The powered aircraft follows the same principals but has an extra energy source from the engine. I always think of the aircraft having two throttles, one for the engine one in the elevator, both allow you to access energy.

What happens in gusty conditions near the ground is no different, with rising and falling pockets of air.
Hence it is a matter of tapping into both energy sources as conditions require.

Normally 1.3 x The landing stall speed is all that is required in normal conditions. Bring in windshear and you have the .3 of airspeed over the stall the potential energy in the aircraft and the energy from the engine.

That may not be enough. You only have so much engine power available! You can tap into the potential energy in the aircraft which may put you in the ground or you can increase your approach speed to 1.3 plus X kts the X kts giving you an extra source of energy to tap into.

It then comes down to how good a pilot is at sensing those movements and how accurate he is at juggling all the parameters available to him.
Sadly many are not and become mere passengers to the aircraft rather than the commander of the aircraft they should be.

Pace

[mad_jock]

I am taking about single engine pistons, One dot I suggest you go and have a look at your principles of flight or get a FI to go over stalling part 1 & 2 with you.

And yes it is about energy management. The book speeds give you the required amount end of story.

If it wasn't the required amount for gusty conditions it would say so in the POH.

And yes I am no stranger to windy conditions 20G30 is a normal days work out west. 40G60 a bit less so and a couple of times 40G70. But as you say its light aircraft which won't be flying in those conditions.

Per say there is nothing wrong with strong winds until your taxi limit is reached or its from the wrong direction. Its gusts we are talking about you have the same issues with 5G20 as you do with 40G55.

If the pilot is not capable of controlling the aircraft on approach at the correct speed they have no buisness being PIC of it.

Adding extra on, landing with power on just points out how talent limited the PIC is.

And to add i have 700 hours in tommy's flying in the Highlands of Scotland summer and Winter. I used to send students solo with 15knt gusts down the runway. Why because they were taught how to fly properly and it wasn't a factor, added to the fact you would be limited to when you could send them solo for 50% of the year. Even Pink Aviator used to be able to handle 15knts of gust without adding to the approach speed.