Two useless speeds [Archive]

Nunc

2nd Apr 2014, 21:38

Pretty big call to state Vx and Vy are irrelevant unless you are happy to drag your gear through the trees one day (or worse still power lines), Im sure Cessna, Piper et al are just wasting their time working out these speeds.

Why not have these speeds filed away in a handy document in the cockpit that can be revised on the day or quickly referred to if needed- they might just save your life. The author may have 5000+ hours of bush flying but if he thinks these speeds are crap he has never really had to do any serious bush flying.

As an aside re the cylinder head temps being increased (refer article in link) Vx is usually used to to deal with obstacles so will only be flown for a very short period of time (at least in my experience in "the bush") so CHT will not be a factor.

The problem with these sort of articles in these forums is that student and inexperienced pilots take this sort rubbish as gospel without thinking.

Mach E Avelli

2nd Apr 2014, 21:57

Saying "could be" is not the same as saying "are". Think about why I would have used the conditional.
In general I do agree with him, but at the little 400 metre strip where I have based the bugsmasher there are power lines almost at the thresholds. Of course I have to fly best angle..... but only until the wheels have cleared the wires.
If the engine quit before then it would be seriously bad, but I would be trying to crash under the wires rather than through them.

The author's point - if I read it right - is that flying Vx or Vy very close to the ground when it is not necessary is taking an unjustified risk and of little relevance for climbing en route.

Bladeangle

2nd Apr 2014, 22:29

Its as simple as what triathlon said. Instructors are only following suite.

Imagine going into an instructor rating test/renewal with CASA and putting your own theories on the board... There would be only one result.

I reckon if an engine failed on climb out in a single (for the average pilot), close to the ground, it wouldn't matter what speed you were doing, the result would have a lot to do with luck as it would skill. There are so many external factors.

Old Akro

2nd Apr 2014, 22:30

Its good to see John Deakins back writing again. I've missed his thought provoking articles.

My criticism of many of John''s articles is that they are about 90% correct and he fudges a bit which can be misleading. I also wish he would move on from red boxes.

For high performance aircraft, I agree completely that that Vx, Vy should never be used. However, if the engine stops and you need to glide. an understanding of which are the efficient speeds for the airframe is pretty important.

For high performance aircraft the work that Bernard Carson (ex US Naval aerodynamics professor) did on fuel efficiency and the "Carson Speed" is a much more valuable concept.

Peter Garrison (Flying Magazine) did a summary of this in 2007. See here:

http://www.flyingmag.com/very-best-speed-fly

The cafe foundation has one of his original 1980 papers (not a red box anywhere) on their website:

http://cafefoundation.org/v2/pdf_tech/MPG.engines/AIAA.1980.1847.B.H.Carson.pdf

A very nice summary is in the Aerostar magazine:

http://www.openclip.net/Benchmark/AOALog2012SummerSweetSpot.pdf

Carson wrote a number of papers and you can find them all in the proceedings of the AIAA conferences. Some of them are hard work, but for high powered aircraft and extended climbs to altitude, Carson is THE authority.

In a light twin, I want to get above blue line, cleaned up with enough altitude to give a safety factor as fast as I can, although this varies a bit with runway length and terrain. For 3 or 4 minutes the thermal mass of the engine and cowl flaps will protect the cylinder heads. After that, its all about Carson speed & leaning according to the Deakins bible.

In a low performance aircraft (especially an underpowered antique type) flying to Vx or Vy accurately might mean the difference between climbing or not climbing. Those of us who did multi training in aircraft like Travelairs know that a couple of knots off Vy will mean the difference between climbing and not climbing. So, Vx & Vy are important concepts that must be understood.

43Inches

2nd Apr 2014, 22:30

I wouldn't say Vx and Vy are useless, they give information to the pilot regarding the maximum performance of the aircraft. The pilot must know the points at which the aircraft will achieve best rate/angle of climb so you can manage your climb appropriately. This does not mean you have to use them though.

Should Vy and Vx be adopted on a take-off regularly?

I think what is being pushed is that if you are having to use Vx on take-off maybe you are cutting it too fine.

Cylinder heads aside, in many high performance aircraft Vx especially will be at a very high nose attitude, and usually very little stall margin. As the article states if an engine should fail at low altitude in this configuration an aerobatic manuevre would be required to successfully land, and that is still most likely with substantial damage. Read the thread on the Arrow accident at Orange. Considering you were doing this to avoid an obstacle, you probably just went through it as well. Flying at a higher speed you will have more time to adjust to glide, more visibility to avoid obstacles and find a suitable landing zone.

Where is Vy useful?

As already stated most light twins need to be flown accurately at this speed following an engine failure to get any climb performance. Climbing below blue line in a light twin means you will have to trade altitude for speed in most pistons at high weight following a failure.

If you are trying to get to absolute ceiling, possibly for maximum range.

If you just want to get to altitude quickly.

Where is Vx useful?

Avoiding an obstacle is about it. Why are you pointing at it? This is a speed to be flown if you have stuffed up, ie put yourself in a situation that you are trying to get out of. You use it after a terrain warning, or you suddenly realise you are in the wrong place and need to climb back to a safe altitude without hitting something. If a strip is so short with an obstacle that requires a Vx climb to negotiate then why are you there?

This discussion is very different when applied to transport category aircraft though.

Old Akro

3rd Apr 2014, 00:06

There are Carson speeds for most efficient cruise and most efficient climb. I have all his original papers on file, but in an effort to find hyper-links quoted only the cruise related papers.

In an effort to find the climb articles, I've just found this recent article specifically on efficient climb. The author has done a really nice job of this and its worth reading.

http://www.openclip.net/Benchmark/IntroducingVz.pdf

The author is proposing a new speed (Vz) for the optimal climb speed.

Aussie Bob

3rd Apr 2014, 02:44

Imagine going into an instructor rating test/renewal with CASA and putting your own theories on the board... There would be only one result.

Got a laugh out of me! :ok: But, not that bad, the FOI's I have dealt with with would be approachable on differing methods so long as you knew your stuff 100%. Its only a blackboard brief for the purpose of demonstration.

Now picture this, you are on an airstrip in a single with trees that require exactly the precise angle and all that. You paced it out. My question is what are you doing there in the first place? You are a crash waiting to happen.

Worse still, you wait until Vx appears on the ASI before rotating. This is sadly what I was taught.

Wally Mk2

3rd Apr 2014, 04:32

All good stimulating inputs here but I'd like to think that any pilot whom might be considering using either speeds for a T/off might look at the whole picture not just some number/s written in the POH. There's lots of variables here to also think about b4 launching off a very short strip, old machine, prop less than efficient, same goes for the donk, instrument inaccuracies, bloody nasty turb where the speedo is all over the place anyway, pilot skills & apart from the surface & wx conditions what about an escape path if it all goes tits up? Don't just assume that holding such a book figure will save you!
Not much point having the machine pointed towards the moon in order to clear the tall pine trees at the end when the donk fails & you fall from grace into the trees anyway.

Big picture stuff, not many of us are test pilots in nice new machines

Wmk2

Captain Nomad

3rd Apr 2014, 04:36

Some of you may be familiar with an old distinguished FOI of the Newcastle area who I had the pleasure of doing several instructor rating tests and renewals with. He was very much of the school of flying what 'felt about right' and was not big on flying published 'certification' figures. This would inevitably launch into a long conversation about the difference between certification flying and operational flying. While this approach and the associated apparent uselessness of Vx and Vy might be applicable to a lot of pilots and their Australian experience, there is something about this discussion that gets under my skin. Just because you can't see use for it doesn't mean it doesn't have an application somewhere, somehow to some aircraft. Breeding an attitude in lesser experienced pilots of 'I know better' could also result in inefficiencies at best, or worse, putting themselves in danger.

Perhaps the best argument would be for me to explain by way of example times when these speeds ARE useful both 'low to the ground' (not necessarily the same as 'low level') and at higher altitudes. Flying a fully loaded piston single in PNG there were many times I did fly Vx climbing with within confines of terrain and positioning to cross ridges. Granted, I sometimes had the luxury of JPI instruments and the timeframe and temperatures were monitored. It may not have been flown for the entire climb but in cases where performance is critical, this speed IS important. For example, Cessna even publish two Vx speeds for the TU206 - one at SL and one for 10,000ft - why? They are six knots apart and it makes a difference. They don't make up these numbers just to fill manuals with 'useless' information!

If you want to talk high performance aircraft it becomes perhaps more important, not less. Take for example a single engine turboprop. ATC asks you for 'max rate' climb through 10,000ft. What speed are you going to fly? In one SE TP that I know there are at least 3 Vy speeds published depending on altitude. The speeds can easily vary by 10 knots between SL and 20'000ft. Does it make a difference? You bet! Now what about when you are sitting in cruise and start encountering moderate/severe icing and you need to climb straight away to get above a layer of cloud (if you don't act fast you will lose the ability to climb at all). What speed are you going to fly? The one I would hope you pick would be the one the manufacturer gives you as being the appropriate speed for that altitude that also gives you stall protection in icing conditions!

I say again, manufacturers do not write this 'useless' stuff just to fill manuals - ignore at your peril.

lilflyboy262...2

3rd Apr 2014, 06:06

Some interesting points raised, but a little common sense could be put into play here.

1) If you are operating an aircraft into and out of a strip that a few knots is so critical that you may or may not collect the terrain, trees or obstacles at the end without being familiar with that aircrafts performance... then you are a much braver man than I.

2) Practical applications of Vx and Vy are used often as some have already alluded to. Climbing towards terrain (And where I am right now, there is some serious terrain that needs to be cleared which leads to sustained Vx climbs), climbing through weather (My current Vy gives around 35-40kts protection between it and stall), or when being asked by ATC to give best rate through to a certain altitude.
Perhaps either of the two could be used for climbing to MSA before entering IMC as well.

3) I'm sure most of the pilots on this forum have the ability to adjust the speeds a little to give that particular aircrafts Vx/Vy due to its age/wear and tear/general straightness of the airframe.

Jabawocky

3rd Apr 2014, 06:38

This is a very interesting thread. :ok:

Wally Mk2

3rd Apr 2014, 06:42

Hey Jabba took ya a while to front up here buddy, careful though don't add any material that could be construed as free advertising:E:ok:

It would be unusual for ATC to say "max ROC" to a particular Alt more like Best ROC & that 'rate' will be at the discretion of the commander not what some book figure says due all sorts of reasons.

Wmk2

CaptainInsaneO

3rd Apr 2014, 10:04

I hope no one takes this guy seriously - it's pub talk.

"I went and did 3 flights with a doctor (to help me record the time and draw 3 graphs) and I have proved all the engineers and test pilots in Cessna and Beechcraft wrong" - seriously??

He mentions that Vx is close to stall speed - ever heard of Take Off Safety Speed? The manufacturer states this is the minimum speed until 50' to ensure controllability of the aircraft in the event of an EFATO.

For aircraft where the Vx is lower than Vtoss, the manufacturer states you should fly at Vtoss, then adopt Vx for obstacle clearance. Maybe this bloke should just read his POH.

Vy is there for a reason in singles, maximum height in minimum time. If you have an engine failure after 5 minutes, you got as high as you possibly could to give you maximum gliding range and maximum gliding time.

Has anyone got a link to the report about the Caravan out of Townsville that had that happen to him? VH-PSQ I think it was. I'm sure he was glad he had time!

Also if you're engine is getting hot at Vy, get it sorted out by the engineers. Leave your mixture at full rich and if it's still too hot, get them to tweak it so it gives you more fuel when the lever is fully in, lean back once you adopt a cruise climb.

I could go on all night and pick this rubbish to pieces, but I've got better things to do.

There are very good reasons for Vx, Vy and especially Vtoss.

Instructors just don't make it up or teach it because they were taught it. They read the POH and research credible information and don't listen to pub talk...well the good ones do anyway.

Cheers.

601

3rd Apr 2014, 11:31

1) If you are operating an aircraft into and out of a strip that a few knots is so critical that you may or may not collect the terrain, trees or obstacles at the end without being familiar with that aircrafts performance... then you are a much braver man than I.

Not braver, just superior by using the POH for the figures and flying the aircraft to the book figures.

Jabawocky

3rd Apr 2014, 12:47

Insaneo

Perhaps in the morning you will read it again. And realise what you think you read was not actually what was written.

If you want to be constructively critical, go right ahead, but use a little science with it.

Just your comment regarding engine temps and reading the article shows you need to read again with better comprehension.

As for the C208 out of Townsville, just doing some quick back of beer coaster maths, there is no way he was doing a Vy climb. Had he done so he would have been at about 7000' by 8 miles when you allow for the takeoff on typical runway heading and departure from TL, either visual or SID.

So with all due respect to whatever your flying experience is, and quite likely far more than mine, I think you owe it to yourself to at least read with the view this guy might know some stuff, and do not try to apply it to B777 ops....coz it was not written for that. You might find it contains a few gems :ok:

By the way Dr Rogers research work was just a tad more detailed than a few jollies in a 172. I have read the whole research paper for Embry Riddle, so I guess I have an unfair advantage.

Cheers :ok:

jdeakin

3rd Apr 2014, 14:55

"I went and did 3 flights with a doctor (to help me record the time and draw 3 graphs) and I have proved all the engineers and test pilots in Cessna and Beechcraft wrong" - seriously??
I've never met the gentleman, except on the Internet. We've arguedly good-naturedly for 30 years over the wisdom of doing "The Impossible Turn," and since he is a well-known writer and professor at the US Naval Academy, I figured his charts would be better received than mine.
He mentions that Vx is close to stall speed - ever heard of Take Off Safety Speed? The manufacturer states this is the minimum speed until 50' to ensure controllability of the aircraft in the event of an EFATO.
I've never heard of Vtoss, but that doesn't mean much. Sounds like a step in the right direction. It may be unique to Australia? In any event, I tried to confine myself to Vx and Vy.
For aircraft where the Vx is lower than Vtoss, the manufacturer states you should fly at Vtoss, then adopt Vx for obstacle clearance. Maybe this bloke should just read his POH.I assure you that I have, and have written a number of them, too. We go through about a dozen common POHs in courses we teach, and anyone who sits through that will never view POHs as holy writ again.
Vy is there for a reason in singles, maximum height in minimum time. If you have an engine failure after 5 minutes, you got as high as you possibly could to give you maximum gliding range and maximum gliding time.
I'm sure CASA and the FAA will applaud that. It's mainstream thinking. My point was that it provides shockingly little difference and you might be better off with an alternative.
Also if you're engine is getting hot at Vy, get it sorted out by the engineers. Leave your mixture at full rich and if it's still too hot, get them to tweak it so it gives you more fuel when the lever is fully in, lean back once you adopt a cruise climb.Well said! But many/most POHs limit this, for Marketing Reasons, rather than sound engineering. Pesky POHs, again.
I could go on all night and pick this rubbish to pieces, but I've got better things to do.
I'm sorry to hear that, but my email is running about 20 to 1 the other way, to my shocked surprise. I thought there'd be FAR more protests like yours.
Instructors just don't make it up or teach it because they were taught it. They read the POH and research credible information and don't listen to pub talk...well the good ones do anyway.
I wish we had a lot more like that in the USA! The vast majority here are simply time-builders who cannot find any other way to do it. They got their training from a long line of 400-hour wonders, and towards the end of it, they pass on their misconceptions to to newbies before going on to the airlines.

Best...
John Deakin

43Inches

3rd Apr 2014, 21:45

He mentions that Vx is close to stall speed - ever heard of Take Off Safety Speed? The manufacturer states this is the minimum speed until 50' to ensure controllability of the aircraft in the event of an EFATO.

Most manufacturers POH for light aircraft refer to lift-off speed and 50 foot barrier speed ( which is usually close to Vx). There is no mention of Vtoss.

The Bonanza POH states "set desired climb speed once clear of obstacles", assuming the obstacles were deemed clear on lift off there is no need to fly Vx or Vy.

Piper breaks up take-off into take-off and climb; for take-off they recommend accelerating to Vx to clear obstacles then Vy or just accelerate Vy if no obstacle, something to note is they do not say to accelerate and maintain these speeds, they are implying a minimum speed. En-route they state the Vx and Vy speed but usually have a recommended higher speed. They do not state where take-off ends and en-route climb begins, one can assume that is at a safe altitude once obstacles/terrain is no longer a threat.

From the PA-32R-300 POH (1987 copy);

"Allow the airplane to accelarate to 52 to 62 KIAS depending on weight of the aircraft and ease back on the control wheel to rotate to climb attitude"; end of normal take-off procedure.

Climb procedure next; "The best rate of climb at gross weight will be obtained at 92KIAS. The best angle of climb may be obtained at 87 KIAS. At lighter than gross weight these speeds are reduced somewhat**. For climbing en-route, a speed of 104KIAS is recommended"

So based on that if obstacles are not an issue the manufacturer is basically saying lift of and accelerate to 104 KIAS for a normal take-off, Vx or Vy only if required.

Old Akro

3rd Apr 2014, 23:32

He mentions that Vx is close to stall speed - ever heard of Take Off Safety Speed? The manufacturer states this is the minimum speed until 50' to ensure controllability of the aircraft in the event of an EFATO.

Someone will correct me if I'm wrong (DJPil?), but I'm pretty sure that take-off safety speed is a uniquely Australian manifestation probably going back to the old DCA. It used to be in the old uniquely Australian performance charts, but I' can't recall ever seeing it on a manufacturers chart.

The bit about "The manufacturer states..." is wrong. The take-off safety speed is defined as 1.2 x stall speed. Co-incidently, 1.2 x stall speed is used in FAR 23 as a performance hurdle, but its not intended to be a target speed used by the pilot, its more of a certification protocol.

See here:

eCFR ? Code of Federal Regulations (http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&rgn=div5&view=text&node=14:1.0.1.3.10&idno=14#14:1.0.1.3.10.2.60.8)

I'm with John Deakins that for relatively high performance aircraft like the Bonanza that vx & vy have very little practical relevance, I'd disagree with low powered aircraft.

Take off in a C150 (yes C150, not C152) from Bang Pra airport on a hot day in Thailand with high tension wires in front of you and I can guarantee the only speed you want to know is Vy.

But, take-off in pretty much anything retractable and its Carson speeds that you want to understand.

43Inches

3rd Apr 2014, 23:56

Someone will correct me if I'm wrong (DJPil?), but I'm pretty sure that take-off safety speed is a uniquely Australian manifestation probably going back to the old DCA. It used to be in the old uniquely Australian performance charts, but I' can't recall ever seeing it on a manufacturers chart.

Pretty much how I understand it.

Take Off Safety Speed? The manufacturer states this is the minimum speed until 50' to ensure controllability of the aircraft in the event of an EFATO.

The lift off and 50 foot speeds are purely performance related, ie, you must attain these speeds to achieve performance.

The only mention of a safe speed with regard engine failure is usually found in section 10-Operating tips, of a Piper manual. For instance the the Arrow III states, Section 10-10.3 (b); "The best speed for take-off is about 70 KIAS under normal conditions. Trying to pull the airplane off the ground at too low an airspeed decreases the controllability of the airplane in the event of engine failure"

Considering the lift off speed flap 25 on the chart is max weight 59 KIAS (62 KIAS at the barrier) and the stall speed is calculated at around 55 KIAS full flap at max weight, this is not 1.2 x the stall.

CaptainInsaneO

4th Apr 2014, 01:03

Jab: Perhaps in the morning you will read it again. And realise what you think you read was not actually what was written.

You're probably right there.

I didn't blow the dust of my text books last night when I read the story. A quick look at it and I could see holes in it - if you consider Vx and Vy useless speeds to all aircraft that is.

As for PSQ though, I wasn't there but I think it's a bit harsh to say that 'no way was he climbing at Vy'.... I've flown Caravans where some don't climb nearly as well as others, especially if that engine had a higher than normal ITT. It might of also have been an SOP thing to climb out at a certain ITT, he might of backed off the Tq and relied on Vy to get him up there as quickly as possible - I don't know though, I wasn't there.

I don't mean to be so critical of somebody's story, yes some theories might hold true to a particular aircraft, but I would hate for a student pilot or fresh PPL/CPL pilot to believe that Vx and Vy are useless to the aircraft they fly.

My point is: just take it with some salt. Just because 95% of Ppruners think it's true - doesn't mean it is true! This story does not prove that Vy and Vx are useless air speeds as this thread title suggests.

If people are reading the story, then reading their POH and flight manual to find the truth for their aircraft - well then I'm a fan of the story and I'm glad I stirred people up a bit.

Happy researching everybody and safe flying!

john_tullamarine

4th Apr 2014, 02:27

Most manufacturers POH for light aircraft refer to lift-off speed and 50 foot barrier speed

Probably because most manufacturers endeavour not to go too far beyond what the design standards require ... Also it is reasonable to presume that OEM paperwork is structured with a very close eye on liability ..

I'm pretty sure that take-off safety speed is a uniquely Australian manifestation

Probably not quite the case. 1.2Vs for singles has long been held as a reasonable balance between too slow and too fast in the event of a failure. The US regs (http://www.ecfr.gov/cgi-bin/text-idx?SID=091eb5121ff771cbbc74b8584ebd24f8&node=14:1.0.1.3.10.2.60.9&rgn=div8) reflect this. I expect djpil will endorse my view ...

Probably reasonable to opine that Oz has, for many years, used the Vtoss abbreviation as a convenient shorthand.

this is not 1.2 x the stall

Be careful of PEC. The 1.2 is not applied to IAS. As PECs can get more interesting in the near stall regime, this is a common error amongst the pilot fraternity. Indeed, we proably have all flown Mr Cessna's fine products and enjoyed the observation of "zero" IAS with the nose pulled way up above the horizon .. doesn't mean anything useful though ... and most certainly doesn't indicate that the aircraft is traveling along with no airspeed.

43Inches

4th Apr 2014, 03:15

Don't have access to the flight test data. The Piper POH I was quoting refers to IAS for stall speed calculation, max weight only. The calibration chart lists negligible change for flaps, possibly 1 kt less calibrated than indicated, and a slight decrease for flap zero at low speed changing to slightly higher at high speed. Although at low speed close to the stall this is probably a little more out than the chart indicates.

If you take the calibrated flap zero stall speed and adjust 1.2 you pretty much get the flap zero lift off speed in this aircraft. 1.2 x 59 = 71

For flap 25 1.2 x the 55 kts listed speed arrives at 66. There would have to be a big difference between CAS and IAS for this to achieve 1.2Vs, lift off being stated at 59 kts.

It makes sense why piper advises 70kias as a more appropriate speed to aim for as it is close to the Vs clean x 1.2.

One thing that's got me thinking of is how much difference is there in accuracy at various flight attitudes and configs of the Piper pitot static head vs Cessna static port and pitot tube.

Aussie Bob

4th Apr 2014, 06:26

In my humble opinion, liftoff speed is another useless speed for most piston singles. Far better to raise the nose wheel (if flying a nose dragger) slightly, keep all eyes outside and let the liftoff happen.

Tis a pleasure when you get it right which will be always with practice. In a tail dragger of course it is even more important to keep all eyes outside and again, from a tail low position liftoff is automatic.

waren9

4th Apr 2014, 07:00

Take off in a C150 (yes C150, not C152) from Bang Pra airport on a hot day in Thailand with high tension wires in front of you and I can guarantee the only speed you want to know is Vy.

eh?

45678910

triathlon

4th Apr 2014, 10:06

Vx and Vy. Useless speeds ?
Deary me.

djpil

4th Apr 2014, 12:54

From FAR 23: (4) The takeoff safety speed, V2, in terms of calibrated airspeed, must be selected by the applicant so as to allow the gradient of climb required in §23.67 (c)(1) and (c)(2) but must not be less than 1.10 VMC or less than 1.20 VS1.so definitely not a unique Australian term but perhaps the old Department thought that it was a more meaningful set of words to use in their standardised AFMs rather than V2 or whatever.

Apart from the climb requirements referenced in that paragraph there are one-engine inoperative performance requirements as appropriate. I'm sure that others can give examples of where they need to be able to get the climb performance provided in the AFM and that is only achievable at the right speeds.

Operating a 300 hp Pitts in the Rocky Mountains I didn't need to know Vx or Vy, I'd just point the nose over the mountain and we'd get over it. Different thing in a heavily loaded 172 taking off at 8,000 density altitude - not much rate of climb at Vy. Not going anywhere useful at any slightly higher speed.

Walter Atkinson

4th Apr 2014, 15:32

Trent 972

4th Apr 2014, 21:34

"Rotating" a piston is poor form and has dangers associated with it's use.
Operating off a prepared sealed surface perhaps, but if operating from a 'contaminated', soft unprepared surface, is your advice poor, and has dangers associated with its use?

Aussie Bob

5th Apr 2014, 00:05

Operating off a prepared sealed surface perhaps, but if operating from a 'contaminated', soft unprepared surface,

I don't actually think so Trent, I think it is even more relevant.

Get the nose wheel up early off the poor surface, eyes outside looking for the best takeoff run, let the plane fly, lower the nose if required, finish takeoff in the air.

Trent 972

5th Apr 2014, 00:30

Thanks for that Bob, just one question though.
Are you able to explain the difference between
1. not rotating - "Get the nose wheel up early off the poor surface….. let the plane fly..." (yourself)
2. not rotating - "by placing them in the proper attitude…..the aircraft will simple lift upwards away from the runway..." (Walter)
(Full quotes are found in the posts above)
.. and the general theme of 'not rotating' a S/E piston on take-off?
Also remember to be specific to cover every eventuality or otherwise acknowledge when the advocated technique is not applicable.

Mach E Avelli

5th Apr 2014, 00:37

I hear you Aussie Bob. Bugsmashers are bugsmashers, not jets.
By Vr, a transport category aircraft is already committed to continued flight. As opposed to merely breaking the surly bonds of earth at some minimum speed determined by the airframe's performance on the day and accelerating to a safe margin above the stall while in ground effect and before attempting to climb. With no commitment to continued flight possible.
As for those who say that using airstrips which require short field techniques are pushing their luck, what about those who fly high performance singles over built up areas? If their engine quit, could they really get into that park or football field?
40 knots or less is a very desirable stall speed for any single.

43Inches

5th Apr 2014, 00:47

**In my humble opinion, liftoff speed is another useless speed for most piston singles. Far better to raise the nose wheel (if flying a nose dragger) slightly, keep all eyes outside and let the liftoff happen.

Tis a pleasure when you get it right which will be always with practice. In a tail dragger of course it is even more important to keep all eyes outside and again, from a tail low position liftoff is automatic.**

Lift off speed is not a speed to aim for lift off to "pull" the aircraft off the ground. If you read the recommended take off procedure it says to accelerate to around this speed and set take-off attitude. All things calculated correctly and the aircraft should become airborne at close to this speed.

There are three types of take-off technique usually mentioned in the POH, normal, short field with obstacle and soft field. Soft field raising the nose at the right point is important, rotate too early and the mains will be pushed further into the muck by the downward tail force. Raising the nose too early on the other forms of take-off will increase aerodynamic drag at a point where the aircraft is not able to fly yet and will consume more runway then necessary. The lift off speed gives you a rough rotate speed to achieve this.

Aussie Bob

5th Apr 2014, 03:32

1. not rotating - "Get the nose wheel up early off the poor surface….. let the plane fly..." (yourself)In effect raising the nose wheel is rotating I guess but not in the conventional sense. I would open the throttle, apply up elevator as required to lift the nose wheel, probably to the full extension of the oleo and wait. Ease off back pressure as required during acceleration to maintain this attitude. Lift off happens in a most pleasing manner :).

Also remember to be specific to cover every eventuality or otherwise acknowledge when the advocated technique is not applicable. In the (land) singles I fly, this is the only technique I ever use anywhere ever. Not applicable for seaplanes!

A brilliant book on the subject and highly readable is "Take Offs and Landings" by Leighton Collins. I got my copy from the Kindle Store onto my Ipad.

Aussie Bob

5th Apr 2014, 03:40

Raising the nose too early on the other forms of take-off will increase aerodynamic drag at a point where the aircraft is not able to fly yet and will consume more runway then necessary.

You have to raise it pretty high to get a substantial drag penalty. In the POH for my tail dragger the recommended technique is to take off from the three point attitude. It may be marginally shorter raising the tail in the takeoff run but not much. The three point attitude is very close to the stall. IMHO raising the tail in this aircraft is a better technique than the POH recommendation.

Walter Atkinson

5th Apr 2014, 15:43

It may be worthwhile to note that from The Wright Brothers to the advent of jets, the term "rotate" was not used in flying. How do you reckon we managed to fly for over 50 years without ever "rotating" an airplane on takeoff? <g>

Trent 972

5th Apr 2014, 21:43

Here's a little bit of a hint for you.
"Rotate" is just another way of saying "pull the stick back".
How did you ever manage 50 years of aviation without "pulling the stick back".
It's not like you've discovered a new form of aviation.
As for letting it roll down the runway at full noise without ever having to pull the stick back, maybe, maybe not, but will it achieve the POH numbers with regards to take-off distance required in a limiting situation, probably not.

Challenge for you, next time you're here, visit your good mate Jaba at Caboolture and go for a spin in his mighty RV10. Give yourself min book runway distance figures for takeoff, don't touch the stick, and tell me at what point everybody's @rse starts to pucker.