After Take off climb attitude

[scramjet]

Gday!

I was told that after take off in a Light Twin (I fly c310) hold 7 deg pitch up till clean and then 10 deg pitch up would give you the right climb performance and it does seem to work well after acceleration it will hold about Best RofC speed.

However, since then I have been reading some Trevor Thom manuals and another Light Twin book and they say to accelerate aircraft to blue line in ground affect then climb away at blue line +10 to 15 kts (assuming no obstacles). ***Airspeed is everything***

Now the first option sounds more like what Airline type aircraft would need, and while the speeds work out well in the c310, would the latter approach be a safer option for GA light aircraft?

[john_tullamarine]

Scramjet (are you tied up with the QLD project by any chance),

Good meaty stuff.

I presume that you are referring to Dave Robson's book in the Trevor Thom series. Dave is a very experienced TP, instructor and a nice guy (as is Trevor) .. he took me for a chase plane ride in a somewhat faster aeroplane many years ago which was the highlight of my little life ...

I haven't had a chance to read his book although I did manage a 30 second skim through it some weeks ago and it appears to say the sensible sorts of things which I would expect. Certainly Dave's background warrants consideration of what he might have to say.

Some thoughts of my own directed to your questions/comments.

(a) try not to mix procedures relating to light and heavy aircraft. The certification bases are quite different and to do so generally creates more confusion that illumination.

(b) runway environments (lengths and splay obstacle profiles) will dictate what is the range of sensible and practical options for takeoff in a light twin.

(c) the general design, certification and operational requirements address the AEO case which, if the pilot hasn't given enough thought to the possible OEI situation, can lead to some degree of surprise.

(d) if the runway environment is benign .. ie lots of distance and a good end of strip gradient, consider the advantages of accelerating to a speed a little above blue line (actual or gross weight doesn't matter too much in this case) while you have both engines and then plan on cleaning up at a suitable height without too much delay ..

(i) hopefully, the available distance will permit the aircraft to be landed in the remaining distance or, at least, brought to a low speed overrun situation if something untoward occurs prior to achieving a useful climb speed. If the takeoff is continued OEI configuration can be achieved without delay. Much more importantly, the operational decision process can be made very much simpler for the pilot.

(ii) a big problem with an early airborne failure, especially if you don't do a LOT of OEI practice, is that you can lose an embarrassing amount of speed very quickly due to mishandling, indecision, and unnecessary delay. Given the marginal performance of this class of aeroplane with any decent gross weight and at any density height much above sea level, this is not a very desirable thing to have happen. Hence the reference to "airspeed being everything" ... the aircraft may only climb under stable conditions within a comparatively narrow airspeed band .. it is quite easy to lose speed, but a devil of a job to get it back without descending .. therefore, is it not better to start a little bit faster ? Leaves you with an ace up the sleeve.

(e) if there is plenty of runway, consider using nil flap for takeoff. Although there may be some certification issues overlooked by doing this, it does avoid the problems associated with reconfiguring at low level in a very dynamic situation following a failure. The question of approximate distance required can be addressed from first principles without too much trouble, keeping in mind that distance bears a relationship to speed squared. One would do this conservatively to allow for the fact that the piston installation provides a notionally constant power, not thrust, output. If this is desired for routine takeoff operation, it becomes appropriate to investigate a suitable STC to cover the non-standard takeoff configuration. This has been my preferred approach for many years and I prefer to stay on the ground, if that is appropriate for the particular aircraft, until I have a suitable higher takeoff speed in hand.

(f) consider pitching to the OEI body attitude during takeoff. Generally this works well in the event of a subsequent failure and gives an acceptable acceleration AEO. If there is no failure, once you achieve the desired AEO climb speed, then maintain it by adjusting body attitude to suit the conditions. For the range of light piston twins with which I have played over the years, a nominal 10 degrees seems to be a useful default target body angle.

(g) if the runway, by contrast, is tight (shortish and with a nasty obstacle profile) then you have very few options -

(i) can I use a longer runway ?

(ii) can I takeoff somewhat lighter or wait until the wind and/or DH is more favourable ?

(iii) can I go by car ? .. my preference in this case ...

If you decide that you are stuck with it, then there is little to be done other than follow the available book procedure until the obstacles are cleared, accelerate and clean up, and climb away at the desired AEO speed, preferably something in excess of blue line.

If the engine fails prior to this, you have a big problem .. one for which you must have decided your immediate actions prior to commencing the takeoff....

(i) can I land ahead without hitting something terribly hard ?

(ii) can I turn left or right to get over benign terrain and continue the takeoff ? If this is the case, why were you planning on a straight ahead takeoff anyway ?

If you don't have one of these two options available, and the AEO case was pretty limiting, then you are almost certainly about to become a statistic. In all cases it is worth keeping in mind that one is far better off crashing under control than out of control.

[yxcapt]

Forget about compairing techniques of light twins to transport jets there are too many differences. With that said let me continue.

In light twins, I fly a pitch attitude that holds Vy or Vyse+10 which ever is greater. This technique allows me to gain the most altitude in the shortest amount of time. Altitude is your friend! Flying Vy/Vyse+10 (the greater of the two) Allow a buffer above Vyse if an engine should fail. You may recall that drag increases with the square of airspeed> You don't want to climb at too fast of an airspeed becouse your climb performance decreases.

If an engine should fail when climbing at Vy/Vyse+10, airspeed and climb performace decrease very quickly. I have found that with a decrease of pitch of about 5 degrees (+/-), the airspeed will stablize very close to Vyse (right where I want it).

Now weather or not the airplane climbs the way you want it to depends on your preflight planning!

Since your in the Cessna 310, ever look at the accelerated go chart? Ever notice that chart leaves you hanging at 50 feet AGL at an airspeed below Vyse? (I don't recall how close the airspeed was to Vxse).

Anyway, this is the technique I use, It's kept me out of the dirt though 4 engine failures.

[411A]

Scramjet, read and understand J_T's thoughts, they just might save your skin. Also realise that light twins and transport twins are NOT the same....forget the body angle business and look for that blue line....airspeed leads to directional control, very important where performance is not all that great.

[big pistons forever]

I was lucky enough to do a Cessna 340 training course at SIMCOM in Scotsdale Arizona. It changed the way I fly light twins. One of the big problems with light aircraft is the decision speed is not defined like the way it is in transport catagory aircraft ( ie you have definite go/ no go criteria which have been tested ) . This combined with the marginal SE performance of light twins makes an EFATO a pretty ugly thing to have happen. Their method takes the ambiguity out and really works.

The Drill

1. Use full lenght of Runway ALWAYS preferably with no flap
2. Apply full power and check engine Instruments,
leave hands on throttles, if any sign of engine problems while hands on throttle, retart both throttles and max brake.
3. Rotate at BLUELINE
4. AFTER rotation and with positive rate of climb verified your hand goes from throttles to gear handle which is immediatelly selected up , then hand goes to prop levers.
5. if engine fails control yaw with rudder , verify with dead foot and then immediately select apropriate prop lever to feather.
6. Do nothing further but fly the aircraft straight ahead at BLUELINE with yaw controlled and banked 5 deg into dead engine. At 500 AGL complete engine failure checklist.

A light twin will not accelerate from a speed below Blueline in level flight. Therefore an engine failure below blueline means an automatic abort. After blueline is attained the aircraft is climbing and the gear is retracting the only thing left is to feather the failed engine. Most twins will not climb with a windmilling prop prop so it is vital to get it feathered ASAP. In effect a blueline rotation ensures positive climb performance ( V1,VR ) and your hand becomes the auto feather system. This is as close as you can get to duplicating the performance guarantee you will get with transport catagory aircraft V1,VR,V2
calculations.

[john_tullamarine]

Some interesting observations here ... if I may stir the pot just a little more ...

(a) GAMA style POHs which include various sorts of go/stop data ought to be viewed more as a serious admonition to stop rather than encouragement to go. One needs to keep in mind the very litigious environment within which the US manufacturers operate and consider their need to provide a measure of defence during litigation while not making their aeroplanes look too down market in the performance arena.

The pragmatic operational view in a light twin at high gross and density height is that it goes fine on two (some obviously better than others) and, on one, not too badly once it is cleaned up at altitude and on speed. Low and slow continuation of flight OEI, especially in the hands of a marginally proficient pilot in conditions requiring extremely critical flying, is an invitation to an eventual Vmca departure and a crash totally out of control. Far better, I suggest, to consider in such extreme circumstances a controlled forced landing with a moderate degree of available thrust to provide some choice of crash site.

(b) the 340, while being one of my fondest light twins, often is described in unflattering terms in respect of its reluctance to leave the ground. While the comments ascribed to a particular training organisation possibly make a lot of sense for that particular Type, I believe that it is dangerous to attempt to make the takeoff procedure too much of a rote sequence. Circumstances dictate appropriate procedure. The preferred procedure on a particular takeoff might well be quite undesirable for a different set of conditions. I guess that what I am saying is that

(i) many pilots receive inadequate instruction in asymmetric operation during their training

(ii) individual pilots need to read widely within competent literature to obtain a more detailed appreciation of the problems .. so that they are better able to make sensible decisions for particular circumstances.

(c) 5 degrees into the live (I do hope your post involved a typo) engine relates to Vmca determination limits in the certification process. For the normal continued climb at higher speeds, climb performance wings level is very similar to that achieved with 5 degrees bank ... there is little to be gained by making the flying somewhat harder by targeting the bank angle. However, a skilful pilot might squeeze just a little more climb out of the aircraft by using an intermediate bank angle sufficient to eliminate sideslip caused by the rudder force vector. This generally works out to be around 2-3 degrees into the live engine.

(d) one ought not just blindly climb ahead without very considerable thought to terrain problems. Again this must be part of the pre takeoff briefing process.

(e) in some circumstances, a failure a little below blue line might be handled better with a continuation. It all depends on the circumstances .. in this case the overrun environment compared to the terrain further out. Clearly, though, if the aircraft is at a decent weight and density height and the speed is much below blue line, then, in general, it is not going to go anywhere ... something about being between a rock and a hard place. Similarly, there may be circumstances where one would still abort from a speed above blue line. For instance, a takeoff from a very mountainous airstrip with close in good forced landing areas but high tiger country further out. Again .. horses for courses and an individual decision for an individual takeoff.

(f) I take the view that FAR25 performance is not necessarily a guarantee .. only information relating to specific conditions. The jet can easily find itself in circumstances where it may not be able to complete an OEI takeoff satisfactorily .. windshear being the most obvious.

(g) .. and, in all cases, there is little to be accomplished if undue haste in shutting down the engine involves shutting down the wrong one ....

[ 30 December 2001: Message edited by: john_tullamarine ]</p>

[Grogmonster]

Big Pistons, I tend to agree with most of what you say except that we teach our pilots, in Cessna 310R's, to rotate at TOSS(takeoff safety speed)and to keep hands on throttles until blueline is achieved at which point gear is selected up. This Gear Up point is the Go, NO Go, decision point as far as continuing is concerned. Any engine failure prior to that point is going to result in the land straight ahead scenario. There is one other thing that we do. Keeping in mind that blue line is calculated for maximum weight we have calculated lower blue line speeds for lighter weights by interpolation. The only reason that I have pulled you up on this is that I'm sure you will agree that trying to hold a C310R on the runway till it reaches 107 kts and full power is a mission that some pilots may not be able to handle without damaging the aircraft. Also this is not the technique called for in the POH.

[bookworm]

We use the technique Grogmonster outlined on the Twin Comanche. While for many aircraft it's natural to associate the rotation speed with the speed at which the decision to fly or land ahead is made, it just doesn't work practically for others. In the case of the Twin Comanche, it wants to fly a good 10 to 15 knots below blue line, and trying to keep it on the runway, particularly in a crosswind, is exciting. So we accelerate after rotation before climbing. I don't think it has to be "in ground effect" as such, as long as the action in the event of an engine failure can be to close both throttles and land ahead.

[411A]

Large (old) piston twins of yesteryear (Convair 440, Martin 404) used autofeather to ENSURE that the windmilling propellor was feathered. Even these aircraft would NOT climb if the prop was not feathered at high weights, and if autofeather was inop, the MTOW was reduced by a large factor.
These aircraft were certified to CAR4b (now FAR25)and generally had good engine out performance. Most light piston twins, sadly, do not.
Now, if you have turboprops (Cessna 441 is a good example), the picture changes greatly.

[BEagle]

....all of which makes one wonder why the Trislander wasn't more of a success!

These comments about the marginal peformance of light twins (an aeroplane class I actively avoid having anything to do with!) remind me of the brief I received when flying in the back of a 3 tank Meteor 7: "I will plan to take-off and accelerate to a speed at which it'll climb on one, holding it on the ground for as long as I dare. Once airborne, I'll climb at the least gradient I can until we achieve SE climb speed - if we lose an engine before then, I'll close both throttles and we'll force land straight ahead, I'll dump the ventral if I've got enough hands. Once we've achieved SE climb speed, we should be able to climb if we lose one; however, it won't be easy. After my initial blasphemy, I'll say 'Left' or 'Right' and I want you to push the rudder fully forward in that direction. I'll dump the ventral, get us away from the ground, shut down the offending engine and complete a cautious circuit. Committal height will be around 650ft, once we're below that it'll be more or less a glide landing. We will then bravely bug ger off to the Mess and get thoroughly pi$$ed!!"

Lift is a gift, but thrust is a must!

[OzExpat]

The other problem about trying to compare GA and airline type aircraft techniques is that the pilot skill level is different. Airline pilots get to practice OEI operations under a variety of conditions on a regular basis, in simulators that, for the most part, pretty accurately reflect the real aeroplane.

How often does the average GA twin pilot get to practice the same thing? I believe that this must be part of the planning for each take-off. The only way to incorporate it safely, IMHO, is by reference to speed, but not speed alone.

Speed is the first important factor but, as has been said already, there are many GA twins that want to leave the ground well below "blue line" speed. This pretty much ensures that you are going to have a portion of your airborne time devoted to the consideration to close both throttles and crash as gracefully as possible.

I've personally found that "gear up" speed really is the most practical "decision speed" in most circumstances. The major operational problem that I've faced over the years is that the strips in Papua New Guinea are never long enough and often don't have good obstacle-free climb paths.

This presents the "horses for courses" scenario that means just about every take-off is going to be that bit different. That's really what GA flying is all about, when you come right down to it. And it's one major reason why airline techniques shouldn't be confused with GA twin techniques.

[big pistons forever]

Lots of good stuff in this thread. A couple of points. I guess my original post was not very clear. When the pilots hand is taken off the throttles it selects gear up and then goes to the props. Engine failure means pull back what ever handle you are touching, throttles = abort, props equals fly. The placement of your hand in effect performs the same function as the V1 call in a multicrew transport aircraft. I think it is important to emphasize that in transport catagory aircraft no thinking is required, if below V1 you stop if above V1 you go. If the regulatory agencies and industry has decided that it is unrealistic for a 30000 hr 747 Capt to think through what are the approrpriate actions at such a stress filled and critical time , I don't think a light twin driver is any more equiped to adjust his actions in real time.
Also you are right I did situate the actions to the airplane I usually fly in the winters, A VG equiped C340 ( VMC=100 kts ) . A 100 kt rotation works very well in this aircraft, however it would be more accurate to say rotation speed is not that important , what matters is that a engine failure below blueline means the throttles are automatically retarded. I still think delaying the rotation to the highest possible speed is desirable because you are more likely to still be on the runway when the failure occures and therefore will have an easier time controlling and stopping the plane. Certainly airplanes which have signinicant nose up attitude on the ground like Twin Comanches or Seneca's this speed will be lower. Also this is not practicle for aircraft with a high blueline speed like Aerostars ( 115 -118 ks ). SIMCOM's 1.5 million $ US simulator has what is in my experience very good performance fidelity to the actual aircraft. I am convinced it is a practicle impossibilty to reliably be able to get the aircraft to accellerate from a speed below blueline , to blue line and then climb away for an engine failure during the takeoff run even at loadings significantly below gross weight. And this was with me primed to expect a engine failure. Therefore in my opinion
you must treat this scenario the same as an engine failure in a single engine aircraft. Obviously good airmanhip also applies. If there is a mountain in front of you don't climb straight ahead and short fields will require flap and lower rotaion speeds. But I stand by my original assertion. If you don't have blueline, positive rate, gear selected up, and hand's on the prop levers ready to feather then continuing with the flight in the event of an engine failure is unlikely to be sucessfull. It is far better to crash wings level in control with the no thrust than to lose control stall and spin as seems to happen all too frequently. If your hand is on the prop lever than by my definition you are past decision speed and will keep going, now the MOST important thing to do is feather the failed engine, Nothing else matters as a light twin WILL NOT climb away from the runway with a windmilling prop. I would also suggest that all your attention should be focused on controlling the aircraft, that is the rational to so far as possible climb straight ahead and not worry about any other engine failure drills untill the aircraft is at 500 feet AGL. Even if you do everything perfectly the aircraft may still not climb thereby forcing you to close the throttles and do your best in the ensuing forced landing. I believe however that this method wil give you the best chance of sucess.

[ 30 December 2001: Message edited by: big pistons forever ]</p>

[john_tullamarine]

BPF ..

I think that we are basically aligned in our operational thinking.

I would take issue with the claim that the FAR25 situation is a totally programmed decision process. There are situations which can arise where the pilot has to think laterally. However that starts to get dreadfully off the original topic ...

... and surely we would all agree that the Trislander is one of the best noise generators around ...

[ 30 December 2001: Message edited by: john_tullamarine ]</p>

[Chuck Ellsworth]

I have another question:

How many instructors teach light twin pilots to leave the gear down until there is no runway left ahead to land on?

...............

:) The hardest thing about flying is knowing when to say no. :)

[big pistons forever]

CAT DRIVER

I used to, but now I teach the method outlined in my earlier post. The problem is how do you make the judgement? In any case it doesn't matter. If the airplane won't fly after it is cleaned up, land it on the runway or any other suitable place gear up. I think the important thing is to minimize the number of decisions because I am sure the shock of an actual failure will not allow you the luxury of puzzling out the best course of action is. And the simulator showed me how important it was to quickly get the aircraft properly configured if contiuing the flight is a realistic possibility. The other problem is training is unfortunately somewhat unrealistic in that the student is expecting a failure and for obvious safety reasons you are not going to kill an engine close to the ground. The advantage of a good simulator is ALL of my engine failures were in the ugly area close to the ground and at or near blueline. Incidently I crashed on the first one the sim instructor gave me using the traditional: Control , Power ( check throttles full forward ), Drag ( check gear and flaps up) , identify ( dead foot dead engine ), Verify (with throttle), Feather . By the time I got to the Verify with throttle, it was all over. He suggested I use their method and I was sucessfull on the next 20 + . Rapidly feathering the failed engine was the key. He said that almost all first time SIMCOM students crash but most of the graduates of the course who are back for recurrent training do not. Obviously he is biased but I believe him, Their method works.

[ 31 December 2001: Message edited by: big pistons forever ]

[ 31 December 2001: Message edited by: big pistons forever ]</p>

[Chuck Ellsworth]

B.P.F.

Its nice to see you changed your teaching methods, any idea where the goofy idea of not cleaning up a multi engine airplane as soon as safe came from?

There is one other facror that comes into the equation when flying any airplane and that is inertia, when training waterbomber pilots I used to be amazed at how fast some of them would immediately go through their rote learned engine failure exercise with no thought process at all.

Here is the engine failure checklist I teach.

(1) What the fu.. is this thing doing now.
(2) Fly it under control, and really identify what the fu.. it is doing.
(3) When the problem is identified carry out the procedure that will solve the problem.


A fully loaded PBY waterbomber with the critical engine failed and propellor windmilling would only lose approximately two knots in the first five seconds, providing the speed at failure was at or above best single engine climb speed.

Five seconds will give you time to think, all you do is fly it straight while thinking and looking. Of course it is always easier with a well trained and co-ordinated crew of two.

Bottom line is do everything right the first time, dont just rush into something you may not be able to fix.

.................


:) The hardest thing about flying is knowing when to say no. :)

[yxcapt]

What I like about this board is the varity of techniques that come up. I few things caught my attention:

Rotation speed: I use what is recommended in the POH or a minimum of Vmc+5 which ever is greater. Depending on the type of day (hot) and load (heavy) I may bump Vr up to Vsse. Compare this speed with the speeds used on the performace charts (T/O dist, Acc stop, Acc go) notice that in some airplanes these numbers differ from the normal procedure section and the speeds used for performance. If an incident occures the investigating authorities will figure out you did not use the manufactures recommended procedures. Then you will have some explaining to do.

If you accelerate the airplane to Vyse before rotation you could encounter severial problems a pilot might need to deal with: Wheel barrowing, excessive tire speed (tires have limition speed above which a tire will fail), Brake energy limits (something transports use but light twins seldom discuss),reaction times and procedures and needless to say all performance numbers are thrown out the window.

If you rotate farther down the runway you miss out on the altitude above you, and reduce the climb gradient profile (obstical clearance).

When an engine failes in a light twin there is a decision to be made, to stop or to go. This decision needs to be made from all availble information. This means digging in the performance section of the POH and evaluating the departure profile before the flight. Take these numbers and add a safety factor. On some flights I have made my "go" point 500 feet AGL. This was based on available climb performance and the Obstical departure procedure.

Climbing at "Blue line": The Blue line as marked on the airspeed indicator is Vyse at sea level conditions at gross weight. Vyse changes with a change in altitude, tempature and weight. You compute Vyse from the POH before every takeoff (some rules of thumb exist for older aiplanes with out good POH info). When the engine quits fly this Vyse not Blue line.

First and formost Fly the airplane.

Think before you react. Most of us are wired for and engine failure. But wait, do you have a complete failure or an engine that is still producing reasonable power? Do I have a propeller overspeed or underspeed? If an engine is surging in and out, which engine is it? If I shut down that engine what other limitation/problems will I have to work with?

Fly, Think, Fly, Think..........

[OzExpat]

A turbocharger failure can seem like an engine failure. Gotta keep thinking, to work out "wtf is this thing doing now?".

[scramjet]

Read in a Forum on AVWEB about a bloke who did some sim training at Flightsafety and reckons that instead of the "Dead Leg-Dead Engine" method used Engine Failure- "Nose Yawed right-Right Engine Failed, Nose Yawed Left -Left Engine Failed".

Any company's actually use this method as SOP??

[john_tullamarine]

I would hope not. If this technique involves significant yawed flight for a period during which the pilot works out what is going on ... and the failure occurs at a lowish speed, then there is likely to be generated an undesirable bank angle and a "gotcha" increase in Vmca.

It doesn't take too much adverse bank to see the aircraft continue yawing and then roll away into the ground.

[OzExpat]

I agree with JT. I dunno about the rest of you, but as soon as the aircraft starts to yaw, I'm on the rudder to correct it. At about the same time, I'm saying "wtf"...

I'm not one of the folks lucky enough to make periodic use of a sim, so my own engine failure technique gets kinda rusty between required demonstrations. I've found that it really pays to fly the aeroplane first, then THINK about "wtf".

The point here, of course, is that by the time I'm thinking "wtf", the aircraft isn't yawing anymore. I'm back to "dead foot = dead engine", and confirming with engine instruments.

You need to be pretty swift with all the vital actions, more so when closer to the ground. But it ain't a great idea to rush anything, or to use methods that may or may not work as the instructor intended. IMHO, the "dead foot" method is still the most consistently safe one to use.

[pigboat]

I'm really not qualified to comment here, since the last light twin I've flown was a Queen Air in 1972.
There is at least one instance where dead foot - dead engine would not apply. If you have a runaway prop, something you would most certainly want to get rid of, the aircraft would yaw toward the good engine.
I just brought this up because I think the nose yawed left - nose yawed right procedure is a flawed one.

[big pistons forever]

PIGBOAT,

Not sure I follow your reasoning. I would think a significant prop overspeed would result in a net loss of thrust so there would be a yaw into the dead engine. In any case their will be a very noticable change in the sound of the aircraft as the props go massively out of sync and the TACH would hopefully provide an unequivical indication of which one is the problem. Lots of folks have pointed out the necessity of makeing sure you take the time to do things right. I heard a wonderfull story from an airline buddy:

The Scene.

SIM check ride in heavy airliner for very experienced Capt. Check pilot is brand new to training dept,young and very keen. Before proceding he tells Capt he wants fast action to deal with any incidents which arises, and then makes a comment about how some of the old guys are having trouble keeping up with his program.

Start SIM sesssion with max weight departure on runway just barely long enough. Just as FO calls VR , check pilot grenades one engine, engine fire bell goes and a whole bunch of BAD annuciator lights blink on. Capt ( While nailing pitch atitude and maintaining perfect heading ) leans forward and spends about 3 sec winding the panel clock ! He then calmly deals with all the action and checklist items as aircraft climbs away. The check pilot can't believe what he has just seen ,freezes the SIM and says " What the @$#%$#^#$ are you doing winding the clock when an engine has just blown up !! ??.

The Captains reply: " Son, ain't nobody killed themselves winding the clock , But lots of folks have died by pulling levers or pushing buttons before the figured out what their problem was :)

[john_tullamarine]

mmmmmm ..

I've had a runaway prop during the landing flare ... fortunately, even if procedurally very inappropriate, the FE had it identified and the handle pulled before we two knew quite what was going on (as I recall, he only said one word at the time ... and that was said quite loudly with an interesting cadence) .. it was a bit hard to work out exactly what the yaw sequence was.. certainly the yaw was significant.. more so than, for instance, landing with an outer feathered on the same aircraft .. which I had following a oil cooler problem. Had a decouple on another occasion .. but that is a bit different to a runaway ..

Following on from BPF's comments ... presuming that we are talking about a governor failure of some sort here for a light twin, I would have expected that the runaway would involve an increase (and, for a big engine, especially a direct drive turboprop .. this is quite a significant increase) in drag and, consequently, an alarming yaw to the side of the runaway.

Consider two instances where this drag increase is the case ..

(a) many larger prop units have either autofeather or autocoarsen systems to minimise the yaw associated with the governor trying to maintain RPM by fining the blade angle.

(b) some SE tug/jump pilots (and I was guilty of this as a youngster) descend with a very coarse prop setting and then use the pitch control (towards fine) as a defacto airbrake to help slow down on (short) final ... a bit like running into a brick wall. As an aside, do pilots on singles with CSU pull full coarse for a forced landing ? .. always seemed sensible to me and reduces the descent rate by a few hundred feet per minute.

If this is a general situation, then I would have expected the aircraft experiencing a runaway to yaw towards the runaway and the pilot's initial interpretation (noise notwithstanding) to be similar to a straight fuel failure. Or did I miss something important somewhere along the way ?


.. I do think that "The Scene" has a VERY important message for us all in respect of the need for sitting on hands while the brain is given time to engage ... may I relate a tale in a similar vein ? ... on a recent sim endorsement session, I had set up

(a) a gear fire sometime after takeoff .. which had been handled appropriately

(b) then, during the subsequent RTB with the gear down and still well within the nominated gear cooling period ... a predictable miss on short final ... followed by a not entirely surprising engine failure during the early climb ... the crew observed that things weren't going terribly well (with the gear still down). Eventually the penny dropped and the gear was selected up .. that being an alternative preferable to the increasing likelihood of impending death.

To emphasise the need for lateral thinking (as opposed to mindless following of the standard checklists), the gear fire warning, naturally enough, came on again. The trainee captain, who was doing a good stick and rudder job at the time and working pretty hard, wasn't quick enough to stop the (very keen) FO from dropping the gear (checklist item) and, first time politely, directed that it be retracted.

After another fire warning and a similar sequence of events, the trainee captain made a quite impolite comment to the (very keen) FO and the problem went away. As a result, the FO, I suspect, hopefully learnt a useful lesson about doing things too quickly without enough thought .. not to mention the need for crew co-ordination.

I never cease to be amazed at just how much I learn from the back of the cab by watching what others do under high workload.

[ 02 January 2002: Message edited by: john_tullamarine ]</p>

[OzExpat]

Having not yet had the pleasure <img src="eek.gif" border="0"> of a runaway prop, I'm a bit in the dark. But, thinking about it, I figure it would be producing more thrust than the engine and prop thats running normally. This suggests to me, unless I'm missing something more salient, that the yaw would indeed be toward the engine and prop thats operating normally.

Thus, it seems that "dead foot = dead engine" is not right for that situation. But, as I've already said, far better to stop the yaw first, then figure "wtf" by confirming with engine instruments. This would tell me straight away that, for the situation outlined by pigboat, I have one engine/prop misbehaving rather than an outright engine failure.

This would undoubtedly create a moment of confusion in my otherwise irrelevantly overly cluttered mind, because of wanting to believe in "dead foot = dead engine". But the tach would be telling me the right story and, by then, I'd probably also have picked up on the difference in engine noise (perhaps I'm not the sharpest tack in the box, huh?) due to the props being massively out of synch.

I'm sure that these cues would lead me to the correct actions in the circumstances, but that might not be true in all multi-engine types. I reckon it would be a pretty safe bet in the B200 that I fly, anyway. Maybe there's more truth in "horses for courses" than first imagined!

JT...

[quote]As an aside, do pilots on singles with CSU pull full coarse for a forced landing ?<hr></blockquote>

I had an engine failure, back in 1987, in a Piper Arrow. Oil line let go on me - engine oil dumped on windscreen, but that's not the point I'm trying to make. I was quite a ways from the closest airport and nothing suitable on the land in between me and there. So, while I still had oil pressure, I left the prop in fine pitch in order to close with the airport.

But, when I saw that I wasn't going to reach the airport and total engine failure was imminent (that certain smell associated with burning got into my nostrils), went straight into full coarse and headed for the longest, widest runway in the world - the water.

First thing I found with coarse pitch selected was that the aeroplane seemed to accelerate, momentarily. I'd lost heaps of drag and was gliding most acceptably. I'm sure that it had the effect of extending the glide, just as I used to teach it to students! Nice to know that such things actually work, huh!

[ 02 January 2002: Message edited by: OzExpat ]</p>

[Chuck Ellsworth]

Runaway props can be the result of two different problems.

(Piston engine A/C.)

If the runaway is caused by a malfunctioning govenor and there is a high enough power setting there could well be a yaw toward the good engine.

If on the other hand the runaway is because the prop has become disconnected from the crankshaft or nosecase reduction then the yaw will be enormous toward the failed engine.

When I flew for Austin Airways we lost one of our PBY's due to a runaway prop they could not feather. In that case it was a prop disconnect ( Nosecase failure )and the crew could only keep straight by slowing to just above stall speed, however the driftdown was quite signifigant and they crashed in the bush. This type of a runaway must be frightening as the prop speed would be awesome, with a corresponding drag that is almost impossible to overcome with the flight controls.

( That was C-FAAD Pigboat. )

So it is possible to have either a yaw into the failed engine or into the good engine, depends on a lot of factors.

However most of us agree that no matter what happens think before you act. I like the wind the clock one!!

Pilots who automatically snap into rote learned checks and actions without first thinking about W.T.F. is happening should never be given command in my humble opinion.

.................

:) The hardest thing about flying is knowing when to say no. :)

[pigboat]

BPF, I just threw that runaway prop scenario in there to show that the nose yaw right - right engine failed - etc. procedure may not be correct in every instance. I've never had a runaway in anger, but in the sim they almost always occur just as the gear is getting into the wells, before the initial power reduction. The initial yaw toward the good engine is as pronounced as the yaw of an engine failure toward the dead engine. You could get yourself into the deep stuff if you went ahead and just did it by rote. As you say, the tach and the noise does get your attention PDQ. A manual feather must be carried out, as the conditions for an autofeather are not met with the runaway condition.
Cat, I just saw your post. I've done the driftdown exercise at Flight Safety with the G1. They used to set it up at ten or fifteen thousand feet, give you a runaway prop with a failure to feather, either auto, manual or induced autofeather. The drag is something to behold.

[ 02 January 2002: Message edited by: pigboat ]</p>

[yxcapt]

I worked for a charter operator for a few years which used the yaw method for determining the failed engine. When an engine failed you did what was required to keep the airplane in the attitude you wanted it in. When it came time to Identify the engine, you relaxed controll pressures slightly. Yaw left, left engine. Yaw right, right engine. This procedure works very well in reduced power situations (instrument approach, short final) and during moderate to steep bank turns (I don't want to open a debate about turning in to the inop engine but there is a FAA certifcation requirment for demonstrating turns in to the dead engine FAR 23.???)

Any way, I looked at the Yaw method being just one step above the dead foot, dead engine method.

[OzExpat]

I saw JT's post earlier, about the runaway prop in the flare and just HAD to go away and think about it over a few glasses of very high quality saki.

I thought about the fact that his FE had it sorted pretty much before the Capt and FO knew anything about it. I thought about how it might be for a two-crew, or even single pilot, operation. The more I thought about THAT, the more saki I needed.

I couldn't see an upside to that situation. You would need to act very quickly, simply to maintain directional control, at a time when your airspeed is reducing quite rapidly. To be blunt and patently obvious, the situation had NEVER occurred to me before.

Geez, you've maybe just shot the ILS to minimums, got visual and, at least subconsciously, you've started to relax a bit because you've just got away with another leg of the flight. Now, all of a sudden, you've got a runaway prop just as you're falring! Sheeeeeeit.

How much reaction time have you got? Certainly not enough to wind a clock first, tho I DID enjoy the concept. Had JT's FE not been right onto it, I can only wonder at what might have happened. Anyone else care to comment and, thereby, further enlighten this ignoramus?

How did I get this far with my career, without having given this aspect some thought? <img src="eek.gif" border="0">

[Centaurus]

From the above replies, one thing is clear. No one sticks to the procedures recommended in the POH. Why not?

Surely one cannot do much better than lift off the ground at the recommended rotate speed for the weight - then select gear up as soon as positive rate of climb is noted. Avoid deliberately holding down in ground effect just to reach blue line. At night this could be positively dangerous as you are flying awfully close to the runway and could get a prop strike if the height mis-judged.

No point at all in leaving the gear down until you judge that you can no longer land ahead. Because unless you have a very long runway there is no way you can judge accurately how much you will need for what is going to be a single engine flapless landing at high speed maybe on a wet runway as well. Try it at night...

Anyway, the gear down theory to blue line only delays the airborne acceleration which puts the end of the runway that much closer.

Whether you keep your hands on the throttles, pitch controls or something more personal, doesn't really matter. You have to accept that in most light twins there will be a short period after lift-off when the aircraft is transitioning from gear down to gear up and where only superb flying skill will save the day ie airborne abort ahead or slow climb away.
A lot depends how quickly the engine failure is identified and the prop feathered. There is probably a 5-10 second critical period immediately after lift off where an engine failure could go either way.

Certainly I would avoid deliberately holding the aircraft on the ground past the POH recommended lift off speed. After all, if you hold it on the runway until blue line or beyond, and a failure occurs at rotation, you still have the gear dangling and the prop windmilling and you will lose speed very quickly indeed.

So what have you gained? An abort at blue line rotation may mean an over-run. Yet you cannot lift off and go, because you will never climb with everything hanging out at that moment and the speed bleeding.

Far better to stick to the correct POH procedure for take off and accept that there is a danger period of a couple of seconds which hopefully you will quickly accelerate past by adopting normal take off attitude.

[john_tullamarine]

Centaurus highlights very nicely the problems associated with decision making in the grey area of the early airborne phase of a takeoff in a light twin.

At the end of the day, unless the aircraft is reasonably light and at a lowish density height, then, until one is cleaned up and at a suitable height with respect to obstacles, and at a useful speed, there will always be a sweaty area associated with a significant risk in the event of a failure.

He poses a quite reasonable question which might be paraphrased to read "why the variety" ?

While Centaurus' view must be respected due to his vast experience (20,000 hours plus) both as a pilot and instructor, I see the main problem being one of trying to simplify the decision making process .. especially for comparatively inexperienced pilots.

Ideally one would like to transform this process to the programmed decision which applies generally for the FAR 25 cousin.

While this latter stategy is rarely achievable for a FAR 23 aircraft, some of the alternative approaches seek to reduce the period of time during which the pilot is faced with that sweaty problem of will it go or will it not ? The inexperienced pilot who perseveres with the continued takeoff in a clearly deteriorating situation sets him/herself up for an eventual Vmca departure.

I echo his concerns regarding ground effect acceleration. While I loved to watch a revered bearded elder do this in the Mustang out of Essendon from time to time, it is not a technique which is appropriate for the routine GA takeoff.

The concerns regarding blue line lift off are valid but I would propose that that situation still remains considerably simplified for the less experienced pilot when compared to a "normal" liftoff speed. It is an underlying principle that this technique is inappropriate for a short runway.

The question of overspeed and the potential for overrun is valid but can be addressed by comparatively simple calculations or a rescheduling of the AFM data.

The manufacturer generally will be constrained to schedule minimum speed data for all the normal commercial reasons. There is nothing sacrosanct about the normal takeoff speed and a higher speed can be scheduled if desired and appropriate for the Type's handling characteristics .. but perhaps not for the lovely Twin Commanche. Such overspeed scheduling was not uncommon in Australian charts produced to the old CAO 101.22 rules.

Perhaps Centaurus' concern is directed more to the endorsement training scenario. If this be the case, then I am totally in agreement with him. As the more generally applicable technique will remain the minimum speed takeoff, it is essential that the new twin pilot be very competent with the problems associated with such a takeoff. The other techniques canvassed in this thread ought only to be addressed in the endorsement situation as discussion items. After all, they are intended to be simplifying considerations, not basic technique.

As to which is the best approach ? How long is a piece of string ?

[ 07 January 2002: Message edited by: john_tullamarine ]</p>

[big pistons forever]

I think John Tulamarine has summed up the debate quite nicely and we do seem to have beat this one to death, but I am very impressed by the quality of the posts. It has definitely given me some things to think about especially with respect to prop overspeeds. It is nice to be part of a truly professional forum <img src="smile.gif" border="0">

[Chuck Ellsworth]

I agree this has been a good discussion and quite on track.

In closing may I suggest that there are many, many different aircraft out there so the most important consideration is learn and use the best technique for the make and model you fly.

Another little thought, there are still a lot of W.W.2 aircraft flying and their P.O.H's can be very sketchy at best.

Most important item on the emergency check list is " Think before you act. "

................
:) The hardest thing about flying is knowing when to say no. :)

[Like This - Do That]

Points made earlier by BPF and OzExpat about use of the tachometer made me think .... many light twins use a combined tacho. In the case of the Partenavia, the engine instruments are way over the other side of the cockpit, and making out which is which in the heat of battle can be tricky. Even worse if it's a black **** night!

I had to abort a take off in a P68 several months ago due to one engine not making full revs (run ups were OK). All the signs were there, nose started swinging and acceleration not as brisk as usual, but my first thought was weathercocking into the right crosswind (I think it was about 15kts all XW). The right tacho was only showing 2350 - 2400 revs, but the only way I could see this was to take my eyes OFF the runway, the ASI and AI in order to look at and interpret the tachometer. Nobody in the right seat to help.

Most working light twins are single pilot, and many are flown around the back end of the clock, light freight etc. Most also have poorly lit cockpits. This stuff isn't easy - I think I agree with OzExpat; time for another drink then I'm going back to bed.

By the way, re Scramjet's opening post about climb attitude - do any of you who have flown the P68 agree that its standard climb attitude destroys over the nose visibility?

Cheers

LTDT

[compressor stall]

I asked a not dissimilar question here about 18 months ago, more with respect to my short field bush operations in a 401/402A/B <img src="eek.gif" border="0"> rather than operations with the luxury of 3km+ tarmac.

From it I use the following procedure:

1. Full power prior to Brakes Release (if surface permits).

2. Rotate at recommended flight manual speed

3. When airborne and in ground effect, retract the gear.

4. Accelerate towards best RATE of climb Multi Engine.

5. Retract flap as soon as a positive rate of climb is identified.

6. Climb to a safe height (Circuit height in VMC or LSALT in IMC) at Multi Engine Best RATE of climb.

7. Reduce to cruise climb power/settings speeds.

8. Release sphincter muscles. <img src="smile.gif" border="0">

*****

For NORMAL operations there is absolutely no reason to fly any particular speed with relation to blue line - that comes in to play if you have an engine failure, and as you still have 2 engines, what's the point?

The idea behind the above technique is to get AS HIGH AS FAST AS YOU CAN.

Flying any other speed than MEROC will introduce excess parasite/induced drag which can never be recovered should you lose a donk and you want as much altitude between you and the ground. In other words, you can NEVER recover turn excess speed into height.

For the proponents of climbing at blue line +10 knots, reread the previous paragraph. If you have the altitude, you can make allowances for the "sh!t f*&k factor" in attaining blue line speed as you are cleaning her up. Remember you will not die if your airspeed falls a little below blue line. Remember Best ANGLE single engine is in most aircraft less than Best RATE single engine.

Also, when you have the aircraft cleaned up, feathered, 5 deg to live engine yadda yadda yadda, and flying blue line, remember that blue line on your ASI may not be the environmental blue line for your aircraft on that day. Blue line speed decreases with an increase in pressure altitude (on my current aircraft by 3 kts over 4000'). You may require a little bit of tweaking to find the real best rate of climb single engine speed.

ALso beware of non standard ASI's on your aircraft - it may be a replacement, or a spare with a blue line painted on it that is a few knots out from the actual one for your aircraft!

Personally, I am VERY reluctant to advocate anything other than what is in the flight manual wrt aircraft operations for take off (ie taking off with nil flap on long runways). Should something go very wrong and not to plan, then you leave yourself wide open to litigation... Consider non standard operations VERY VERY carfefully.

Good to see you are thinking about things Scramjet! Many light twin pilots give it nary a second thought!

CS

[ 13 January 2002: Message edited by: compressor stall ]

[ 13 January 2002: Message edited by: compressor stall ]</p>

[john_tullamarine]

compressor stall,

We probably are talking about two scenarios and decision processes, I suspect.

If the runway is of minimal length (or we are looking at an initial twin endorsement saga), then I'm with you.

If there is excess distance, however, then the pilot has the luxury of considering some choices, the reasonable extremes being ..

(a) If he/she chooses to go with the minimum distance scenario, fine, there is no argument with the proposition that AEO energy management is better addressed by going for height rather than speed.

However, if there is an engine problem during the grey area prior to cleaning up and achieving a suitable height/speed, then the speed range for which the aircraft (at decent weights and density heights) will climb is quite marginal, if it exists. This then leaves the pilot with the problem of doing all that which needs to be done, accelerating, and eventually climbing if the aircraft capability so permits. This takes time and distance at low level (perhaps well beyond the runway confines), and involves a sweaty period during which the inexpert pilot can easily find him/herself in a deteriorating performance situation bounded by a Vmca and/or stall/spin departure on the lowspeed end.

(b) If he/she elects to use the spare runway to get a bit faster before climbing significantly (ie puts the go/no go decision speed a little higher), then the AEO energy management is inferior but the OEI handling decision making is simpler. For pilots without the opportunity to do lots of asymmetric training practice this possibly offers an overall lower risk outcome.

The pragmatic upper speed limit is at or around the anticipated blue line for the day and many pilots appear to like a 10 knot pad.

I don't really think that this philosophical technique in any way contadicts anything in the AFM requirements. Normally, AFM performance data for this class of aircraft merely provides some guidance. The pilot is left to determine a number of practical applications of that guidance material ... consider terrain avoidance for instance.


The concern is not a failure at height, rather during the early post liftoff grey area.

No argument that the decal blue line may not be the most appropriate speed, but it is certainly going to be within the climb capable speed range for the day. If the pilot doesn't know the "correct" optimum value, blue line is probably the next best choice.

For final OEI climb, climb performance at a bank angle of around 2-3 degrees will be a little better than that for 5 degrees. In general, 5 degree bank approximates the climb performance for wings level under these conditions. For initial control of a failure at LOW speed (where Vmca becomes more of a concern), then a bank of 5 degrees (perhaps even a little more in some circumstances) may be quite critically important.

If the aircraft ASI is marked incorrectly then that is a different problem altogether and one would be advised to shop around for a more ethical and procedurally competent maintainer.

As I am sure you would agree, each takeoff ought to be assessed by the pilot prior to commencement and a specific decision made as to the intended handling procedure and tracking intentions to be adopted for that particular takeoff. The next takeoff may well be approached in a different manner.


At the end of the day, you pays your money ... you takes your chances. I would far rather improve my chances, if circumstances permit, and then argue about the niceties afterwards.

[ 13 January 2002: Message edited by: john_tullamarine ]</p>

[yxcapt]

Compressor Stall-

Most "short field" procedures call for a climb at Vx untill obstacles are cleared then Vy. Am I to assume your short field has no obstacles since your climbing at Vy? In a Vx climb your betting your rear end that both engine keep working. A position I would rather not be in!!

Why are you raising the flaps with a positive rate of climb? Bringing up the flaps produces a pitch down moment which must be countered with a nose up elevator doesn't the airplane tend to sink slightly if you don't time the pitch correction correctly. If your retracting the flaps with a positive rate of climb wouldn't you be leaving ground effect at the same time? As you retract the flaps you are dumping some lift as well. As you leave ground effect you loss lift and increase drag. What performance and handling qualities are you experancing at this point? Where is the airspeed at this point? Some where between rotation and Vx (or Vy if thats what your using). It seems to me you might be setting your self up for something.

I highly recommend avoiding situations that require the use of a true short field procedure. The spacing between Vx and Vmc is small*, you are low to the ground, and high pitch angle if an engine fails in this position, it's all over but the crying. (*some twins Vx is below Vmc)

Here the FAA recommends using the manufacturers procedures, speeds and configurations. They read pretty much like this:

Positions the airplane for maximum utilization of available runway... Hold brakes... Add takeoff power... release brakes... Rotate at recommended Vr... Gear up with positive rate... Climbs at recommend speed and configuration or, in their absence, at Vx until obstacle is cleared or until 50 feet AGL... Establish pitch attitude to accelerate to Vy... Flaps up after clearing obstacle.

I agree you want to obtain as much altitude as quickly and as safely as possable. In normal takeoff climbs I use Vy or Vyse +10 (max) which ever is greater. The reasons are: (1) the pitch attitude at this point close to that of a single engine climb at Vyse (2) It allows for the swimming in glue affect (reaction & configuration time) (3) The amount of altitude differance between the two speeds is small and (4) If you do need to push the nose down to get to Vyse, you will lose less altitude becouse you didn't get very far from Vyse in the first place.

Fortunatly in most twins, Vy is above Vyse by about ten knots or so. Some one talked about the relation ship between Vyse and Vmc. Some twins Vmc is very close to Vyse and in others there is a wide spread. There is however a relationship between Vmc and stall speed. The certifcation requirement as I recall is that Vmc can not be greater that 1.2 Vs1.

I use to debate these techniques all the time with and old friend many years ago. We both had many engine failures and had flight tested many different techniques. In the end, we agreed to disagree. We continue to use what is best for ourselves. But it is fun defending our positions!!

By the way, I think Bob Hoover does the best conversion of altitude to airspeed and back again (on one and two engines) I have ever seen! To bad he retired the shrike.

[compressor stall]

YXCapt,

Some very astute observations from you.

To clarify your queries, I was using Vy as there were no significant obstacles in the area in which I was operating...the oz outback. Trees were fairly insignificant too.

I agree with you 100% to try and limit the operations into such strips. Fortunately the medics I used to fly were aware of the fact that whilst it would have been legal to operate into there at max weight, it was downright scary, and they were happy to limit payloads to 4 adult pob max.

The idea of retracting the flaps at the earliest safe opportunity is to reduce drag to allow a maximum Vy. The performance of said aircraft from which I can recall had minimal sink with flap retraction when it was retracted approaching Vy, which was about when positive rate of climb could be established and identified with said technique.

I agree with your penultimate paragraph, but having said that, discussions such as this serve to have a better understanding of things and better understand the physics behind our ideas.

As for your final paragraph, I have had the privilege of watching the Bob Hoover display no less than 4 times, and now that I fly 900+ hours a year in them, I have an even greater appreciation for the man's abilities.

[yxcapt]

John you make some good points. Some where around here I have formula for the optimum bank angle (optimum for control and climb). Rather than play with numbers, I found a yaw string worked best for finding this angle.

The only reason 5 degrees of bank exist is becouse of the FAA. You can continue to reduce Vmc by banking steeper. The FAA wanted establish a level playing field amoung the manufactures, thus the limit. You can however, continue to bank into the operating engine right up to the point you stall the rudder (yes, stall the rudder) then the airplane spins like a top!!! (you will be well beyond 5 degrees of bank but at what bank angle this rudder stall occurs at is anybodys guess)

An accidnet investagator friend of mine pointed out something from his experiance. Most loss of control accidents resulting from a engine failure on take off occured at a speed above Vmc. He beleaves the pilots where attempting to steer the airplane with the ailirons and very little rudder and one wing stalled before the other.

Two other points on Vyse. Vyse also varies with weight as well as with altitude. At sea level "blue line" might be close enough but at high altitude it will not. Same with weight Blue line is at gross weight. The indicated airspeed for Vyse decreases with a decrease in weight. This improves the rate of climb as well as the climb ratio. I know that if a take off is attmepted with a high and heavy condition, climb performance will be minimal to begin with, so flying the proper airspeed may make the differance of making it or not. (Again, I try to avoid this situation)

Another place to use Vyse is in a single engine drift down situation. Flying the proper speed here will increase the "glide" ratio and you will level off at a higher altitude.

I'm always thinking that damn engine is going to go south on me. The odds are 50/50.

No airplane has enough power unless it can accelerate going vertical!!!

[john_tullamarine]

Piece of string along the nose works real well ... the aim is to eliminate sideslip. Used to great effect on sailplanes.

And there is certainly an advantage to be gained by knowing the speeds for one's aeroplane in detail .. but, in so many cases, either the pilot doesn't, or the full range of speeds of interest is not readily available from published data...