Asymmetric performance for a/c less than 5700kgs
From being an instructor many years ago I must feel sorry for all those new instructors doing multi-eng training. I have now been above 5700kgs for some time and will never go back below that magic number. Guaranteed performance is one thing that any pilot below 5700kgs will never have and only wants too. To them I say get off your arses and get out there. And this is from an engineer with some flight time on above 5700kg machines and they are not those crappy Garett things.
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Your question has been answered but there is a lot to know about twins that isn’t often taught.
Keep in mind that Vmca provided is with 5 degrees of bank towards the operating engine. In Level flight the Vmca will actually increase.
Vmca decreases with altitude (as density decreases). You may reach a point where Vmca is lower than the stall speed of the aircraft if the aircraft is flown high enough. Don’t let the aircraft stall with OEI whilst training.
As a rule of thumb take 1 knot off your Vmca for every 1000 feet increase in DH to ensure the best rate of climb (or more likely a minimum rate of descent). The opposite applies for an increase in Density.
Something else that is very often misunderstood in light twins is the TKOF (and landing). Make sure you properly understand the correct application of Vr, V2 (or Vxse), TOSS (which is published in every POH), Vref and Vyse (and the variations that occur with changes in weight, temperature and configurations). Don’t use the Blue Line as a decision speed - it was never intended as anything other than the Vyse speed.
You will have instructors that try and tell you that Vr and V2 have no place in light twins. I think that no part of your professional flying should be left to an ‘artistic interpretation’. Defining your takeoff with speeds and attitudes will ensure predictable performance and ongoing professional standards.
Know the performance requirements and certification standards from CAO 20.7.4 (for aircraft below 5700kg) and CAO 101.22.
There is lots more to learn...
nig&nog, ???
[ 09 September 2001: Message edited by: Turbine ]
Keep in mind that Vmca provided is with 5 degrees of bank towards the operating engine. In Level flight the Vmca will actually increase.
Vmca decreases with altitude (as density decreases). You may reach a point where Vmca is lower than the stall speed of the aircraft if the aircraft is flown high enough. Don’t let the aircraft stall with OEI whilst training.
As a rule of thumb take 1 knot off your Vmca for every 1000 feet increase in DH to ensure the best rate of climb (or more likely a minimum rate of descent). The opposite applies for an increase in Density.
Something else that is very often misunderstood in light twins is the TKOF (and landing). Make sure you properly understand the correct application of Vr, V2 (or Vxse), TOSS (which is published in every POH), Vref and Vyse (and the variations that occur with changes in weight, temperature and configurations). Don’t use the Blue Line as a decision speed - it was never intended as anything other than the Vyse speed.
You will have instructors that try and tell you that Vr and V2 have no place in light twins. I think that no part of your professional flying should be left to an ‘artistic interpretation’. Defining your takeoff with speeds and attitudes will ensure predictable performance and ongoing professional standards.
Know the performance requirements and certification standards from CAO 20.7.4 (for aircraft below 5700kg) and CAO 101.22.
There is lots more to learn...
nig&nog, ???
[ 09 September 2001: Message edited by: Turbine ]
Moderator
Please don't think me crass and nit-picking, but ...
I Fly
I don't think that things are quite as straightforward as you suggest ...
Achilles
There are more things involved than what a simple reading of the FARs might imply. One has to have a look at the flight test requirements as well, which are in anciliary documents.
nig&nog
It's a brave chap who believes that a heavy has a guarantee of performance - rather a somewhat better and quantified margin with which to play. The real world environment often presents a far more critical situation than what might be envisaged in the certification envelope and seen in routine training exercises, particularly at reduced AUW.
Turbine
The Vmca/Vs crossover on a lightie, in particular, can occur at quite low altitudes - only one of many very good reasons why GA asymmetric training at low speed is ALWAYS hazardous. As you infer, the risk of spinning at this point is near guaranteed.
Maybe I am being a bit boring but, given adequate runway length and for most light twins, I think that blue line is a great initial decision point - to keep going at a lower speed if stopping is a reasonable option unnecessarily invites terribly sweaty palms. Certainly during 25 or so years of renewals I have never had an examiner who was crass enough to challenge that view.
I Fly
I don't think that things are quite as straightforward as you suggest ...
Achilles
There are more things involved than what a simple reading of the FARs might imply. One has to have a look at the flight test requirements as well, which are in anciliary documents.
nig&nog
It's a brave chap who believes that a heavy has a guarantee of performance - rather a somewhat better and quantified margin with which to play. The real world environment often presents a far more critical situation than what might be envisaged in the certification envelope and seen in routine training exercises, particularly at reduced AUW.
Turbine
The Vmca/Vs crossover on a lightie, in particular, can occur at quite low altitudes - only one of many very good reasons why GA asymmetric training at low speed is ALWAYS hazardous. As you infer, the risk of spinning at this point is near guaranteed.
Maybe I am being a bit boring but, given adequate runway length and for most light twins, I think that blue line is a great initial decision point - to keep going at a lower speed if stopping is a reasonable option unnecessarily invites terribly sweaty palms. Certainly during 25 or so years of renewals I have never had an examiner who was crass enough to challenge that view.
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john_tullamarine, certainly very valid points, but worthy of a response none-the-less.
First, your interpretation of my Vmca & Vs statement was correct. If you are flying on a low and cold day in an overweight aircraft, your Vmca will actually DECREASE and your stall speed will INCREASE. The margin closes very quickly and is a recipe for disaster. The Twin Comanche (which was built prior to modern certification) was involved in numerous instances where it fell into a spin based on the conditions I just stated. It is a great touring aeroplane and from personal experience shouldn’t be used for training – but that’s another story…
In regards to the Blue Line decision speed, name me one POH that states that it should be used as a decision speed. Remember that the Blue Line is only applicable as the VYSE in ISA conditions. Any variations from ISA and Blue Line failures to serve a practical purpose, in fact it has absolutely nil significance.
The POH will always specify a decision speed. For example…the Cessna 310 has a VYSE of 106 knots but the POH recommends a ‘Safe Single-Engine Speed’ of 92 knots. The Chieftain also has a VYSE of 106 knots but also recommends a ‘Safe Single-Engine Speed’ of 92 knots. The decision to continue the takeoff above 92knots and below VYSE (in this case 106 knots) will be based upon altitude, temperature, aircraft weight, terrain, weather and pilot proficiency. This should all be factored into a pre-takeoff safety brief. What should be understood that at higher weights you will have negative climb performance until flap and gear is retracted and the calculated VYSE is attained. The manufacturer states, quite clearly, predictable and guaranteed performance from the aeroplane in various circumstances. It’s a wise man that will take the manufacturers recommendation and construct his own expert opinion. Bottom line, I wouldn’t use Blue Line as my decision speed – first because it has no workable significance and second, I have a better chance of saving my aeroplane if I don’t.
The application of flying twins and the aerodynamics is often not understood, even by experienced pilots.
First, your interpretation of my Vmca & Vs statement was correct. If you are flying on a low and cold day in an overweight aircraft, your Vmca will actually DECREASE and your stall speed will INCREASE. The margin closes very quickly and is a recipe for disaster. The Twin Comanche (which was built prior to modern certification) was involved in numerous instances where it fell into a spin based on the conditions I just stated. It is a great touring aeroplane and from personal experience shouldn’t be used for training – but that’s another story…
In regards to the Blue Line decision speed, name me one POH that states that it should be used as a decision speed. Remember that the Blue Line is only applicable as the VYSE in ISA conditions. Any variations from ISA and Blue Line failures to serve a practical purpose, in fact it has absolutely nil significance.
The POH will always specify a decision speed. For example…the Cessna 310 has a VYSE of 106 knots but the POH recommends a ‘Safe Single-Engine Speed’ of 92 knots. The Chieftain also has a VYSE of 106 knots but also recommends a ‘Safe Single-Engine Speed’ of 92 knots. The decision to continue the takeoff above 92knots and below VYSE (in this case 106 knots) will be based upon altitude, temperature, aircraft weight, terrain, weather and pilot proficiency. This should all be factored into a pre-takeoff safety brief. What should be understood that at higher weights you will have negative climb performance until flap and gear is retracted and the calculated VYSE is attained. The manufacturer states, quite clearly, predictable and guaranteed performance from the aeroplane in various circumstances. It’s a wise man that will take the manufacturers recommendation and construct his own expert opinion. Bottom line, I wouldn’t use Blue Line as my decision speed – first because it has no workable significance and second, I have a better chance of saving my aeroplane if I don’t.
The application of flying twins and the aerodynamics is often not understood, even by experienced pilots.
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john_tullamarine, sorry. I just re-read your post and it failed to register in my feeble brain that you were talking about using blue line as an initial decision speed. Obviously if you have miles and miles of runway under the nose common sense prevails.
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JT - The FAR criteria given for reference only. There is always alot of 'Mickey Mouse' going on with published performance figures,I suspect, so the machines could be sold!! If the reality of negative climb performance was made too obvious, it might have turned the buyers off!!!
Turbine - Single Engine Safety Speed (Vsse)applies to a manufacturer recommended minimum intentional one engine inoperative speed (usually a speed 'safely' above Vmca).
Turbine - Single Engine Safety Speed (Vsse)applies to a manufacturer recommended minimum intentional one engine inoperative speed (usually a speed 'safely' above Vmca).
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JT - The FAR criteria given for reference only. There is always alot of 'Mickey Mouse' going on with published performance figures,I suspect, so the machines could be sold!! If the reality of negative climb performance was made too obvious, it might have turned the buyers off!!!
Turbine - Single Engine Safety Speed (Vsse)applies to a manufacturer recommended minimum intentional one engine inoperative speed (usually a speed 'safely' above Vmca).
Turbine - Single Engine Safety Speed (Vsse)applies to a manufacturer recommended minimum intentional one engine inoperative speed (usually a speed 'safely' above Vmca).
Moderator
Turbine,
God, but I do like to stir the pot a bit ...
(a) "If you are flying on a low and cold day in an overweight aircraft...." I don't think that I would concur with your statement. The more general consideration occurs quite innocently and is associated with a reduction in thrust output as height increases which permits a ham fisted chap to play make believe test pilot at progressively lower IAS until Vs arrives whereupon the aircraft departs and the said pilot either gets a big fright or, quite likely, dies. If this sounds like I don't think that the normal GA (static) Vmca demo is a good idea .. then you would be very correct. My experience is that many, if not most, GA ME instructors have absolutely no idea of just how dangerous is the ground upon which they tread.
(b) "In regards to the Blue Line decision speed..." My comments were my opinion only and I would certainly not expect them to be echoed in any POH for reasons of potential liability. As is very obvious from a simple reading of the usual range of POHs, the manufacturers' OEI recommendations are very, very considered for quite reasonable reasons.
In any case, one needs to know the approximate "real" blue line speed regardless of philosophy.
Now, if a pilot wants to continue the takeoff after a failure with 12000 feet remaining ... his/her decision ... ... I will land every time and, I was relieved to read, so would you. I was involved in an accident investigation some years ago on a GA turboprop multi prang where the pilots continued from a lowish speed with, as I recall about 7000 feet left, and subsequently lost the aircraft in a Vmca departure with near total loss of life in the ensuing barbeque .. Is this not food for thought ? My comment stands that a number of very experienced examiners have not seen any need to query my philosophy as stated.
(c) ".... ‘Safe Single-Engine Speed’ ..." mmmmmmmm. I think that your outlook on these matters might benefit (and change somewhat) from a lengthy discussion on OEI flight with an experienced certification test pilot over a beer or twenty. Unfortunately I am not prepared to go down this path in a semi-public forum such as PPRuNE just in case a manufacturer might take offence.
Achilles,
The problems associated with pilots' interpretation of POHs for lighties are legion (unless one has a certification background) and it is not appropriate to discuss them in a semi-public forum.
... one of the reasons that the demise of CAO predicated AFM data in the Oz environment was such a loss to risk management in light aircraft.
God, but I do like to stir the pot a bit ...
(a) "If you are flying on a low and cold day in an overweight aircraft...." I don't think that I would concur with your statement. The more general consideration occurs quite innocently and is associated with a reduction in thrust output as height increases which permits a ham fisted chap to play make believe test pilot at progressively lower IAS until Vs arrives whereupon the aircraft departs and the said pilot either gets a big fright or, quite likely, dies. If this sounds like I don't think that the normal GA (static) Vmca demo is a good idea .. then you would be very correct. My experience is that many, if not most, GA ME instructors have absolutely no idea of just how dangerous is the ground upon which they tread.
(b) "In regards to the Blue Line decision speed..." My comments were my opinion only and I would certainly not expect them to be echoed in any POH for reasons of potential liability. As is very obvious from a simple reading of the usual range of POHs, the manufacturers' OEI recommendations are very, very considered for quite reasonable reasons.
In any case, one needs to know the approximate "real" blue line speed regardless of philosophy.
Now, if a pilot wants to continue the takeoff after a failure with 12000 feet remaining ... his/her decision ... ... I will land every time and, I was relieved to read, so would you. I was involved in an accident investigation some years ago on a GA turboprop multi prang where the pilots continued from a lowish speed with, as I recall about 7000 feet left, and subsequently lost the aircraft in a Vmca departure with near total loss of life in the ensuing barbeque .. Is this not food for thought ? My comment stands that a number of very experienced examiners have not seen any need to query my philosophy as stated.
(c) ".... ‘Safe Single-Engine Speed’ ..." mmmmmmmm. I think that your outlook on these matters might benefit (and change somewhat) from a lengthy discussion on OEI flight with an experienced certification test pilot over a beer or twenty. Unfortunately I am not prepared to go down this path in a semi-public forum such as PPRuNE just in case a manufacturer might take offence.
Achilles,
The problems associated with pilots' interpretation of POHs for lighties are legion (unless one has a certification background) and it is not appropriate to discuss them in a semi-public forum.
... one of the reasons that the demise of CAO predicated AFM data in the Oz environment was such a loss to risk management in light aircraft.
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Reference your point about the reduction in Vmca at altitude, I was actually referring to the practical application of revising Vyse to ensure best performance after takeoff. My point (about the low temp and overweight aircraft) was to exaggerate the effect of the often-misunderstood aerodynamics - it was hardly a practical or everyday working example.
I, like you, am not a big fan of Vmca demonstrations. The number of times, whilst checking META approved pilots with OEI, I have heard patter along the lines of "...and notice we are now well below the Vmca speed...aaahh...because Vmca decreases with altitude... ooh - and there is the stall warning horn...so we better recover...". Sound familiar? Vmca IAS will obviously decrease with height but the Vs IAS will remain the same. The two speeds will cross over at altitude. The certification requirements only apply in ISA conditions. I guess it's the equivalent of a "coffin corner" for a piston - and certainly brings to question the advantages of the reduction in Vyse at significant altitude (or with an increased DH)...but none-the-less it is important to understand the working application in case it can be safely applied. Once again, this is my personal view
To further ramble my point, of course you expect negative performance from an aircraft with flap and gear down with OEI after TKOF, so the Single Engine Safety Speed (Vsse - which may be above or below blue line) will vary given all those variables I mentioned above.
Realistic and book performance are chalk and cheese. We both know that, whilch leads me to believe we're arguing the same point...
I, like you, am not a big fan of Vmca demonstrations. The number of times, whilst checking META approved pilots with OEI, I have heard patter along the lines of "...and notice we are now well below the Vmca speed...aaahh...because Vmca decreases with altitude... ooh - and there is the stall warning horn...so we better recover...". Sound familiar? Vmca IAS will obviously decrease with height but the Vs IAS will remain the same. The two speeds will cross over at altitude. The certification requirements only apply in ISA conditions. I guess it's the equivalent of a "coffin corner" for a piston - and certainly brings to question the advantages of the reduction in Vyse at significant altitude (or with an increased DH)...but none-the-less it is important to understand the working application in case it can be safely applied. Once again, this is my personal view
To further ramble my point, of course you expect negative performance from an aircraft with flap and gear down with OEI after TKOF, so the Single Engine Safety Speed (Vsse - which may be above or below blue line) will vary given all those variables I mentioned above.
Realistic and book performance are chalk and cheese. We both know that, whilch leads me to believe we're arguing the same point...
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After an engine failure, directional control is restored with rudder. The rudder then produces a side force and a moment. When the engine moment and the rudder moment are in balance, the heading remains constant. So far so good, but what about the rudder side force?
If the pilot does nothing about this side force, the aircraft is going to slide sideways at the same time it moves forward.
By sideslipping away from the live donk, you are diminishing the effectiveness of the rudder and eat away at the restoring force that's keeping you from yawing. To prevent this, you bank the aircraft toward the live engine.
Banking has the effect of pointing the lift generated by the wings slightly to one side. The lift is broken into two components - a vertical one that continues to supprot the aircraft's weight and a horizontal one that "pulls" the aeroplane sideways. With a bank angle of 5 degrees, the side component is around 8.75 percent of the lift. This is larger than the rudder side force is likely to be, but it has the effect of sideslipping the aircraft toward the good engine which enhances rudder effectiveness and is good for control.
Now you will see where weight comes into this. If the side force at the limiting 5 degrees of bank is a fixed percentage of the lift, then the greater the lift, the more side force and therefore the more sideslip and rudder authority and the lower the Vmca. Since lift is equal to weight in unaccelerated flight, the heavier the aircraft is the lower its Vmca will be.
If the pilot does nothing about this side force, the aircraft is going to slide sideways at the same time it moves forward.
By sideslipping away from the live donk, you are diminishing the effectiveness of the rudder and eat away at the restoring force that's keeping you from yawing. To prevent this, you bank the aircraft toward the live engine.
Banking has the effect of pointing the lift generated by the wings slightly to one side. The lift is broken into two components - a vertical one that continues to supprot the aircraft's weight and a horizontal one that "pulls" the aeroplane sideways. With a bank angle of 5 degrees, the side component is around 8.75 percent of the lift. This is larger than the rudder side force is likely to be, but it has the effect of sideslipping the aircraft toward the good engine which enhances rudder effectiveness and is good for control.
Now you will see where weight comes into this. If the side force at the limiting 5 degrees of bank is a fixed percentage of the lift, then the greater the lift, the more side force and therefore the more sideslip and rudder authority and the lower the Vmca. Since lift is equal to weight in unaccelerated flight, the heavier the aircraft is the lower its Vmca will be.
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StallSpinCrashBurnDie, very valid point. I made reference to weight in regard to aircraft climb performance and stall speed, not rudder effectiveness or Vmca variations, as did JT, but your point further clarifies my own...
Vmca is calculated with 5 degrees of bank, so flight with more than that reduces Vmca but also reduces your Vertical component of Lift. Approaching Vmca in a dodgy demo requires harsh and possibly full use of aileron control beyond the point that requires full rudder, which illustrates that it reduces the speed at which control is lost. The increased AoA on the outside wing, the decreased lift (due to the bank) and the full rudder condition at a speed that is dangerously close to the stall is a recipe for disaster (remembering that the 'gap' between Vmca and Vs closes very quickly).
I often wondered why 5 degrees was used for certification. It would be nice to know the origin. I may indeed one day bore you all with the mathematics
Interesting point though...
[ 11 September 2001: Message edited by: Turbine ]
Vmca is calculated with 5 degrees of bank, so flight with more than that reduces Vmca but also reduces your Vertical component of Lift. Approaching Vmca in a dodgy demo requires harsh and possibly full use of aileron control beyond the point that requires full rudder, which illustrates that it reduces the speed at which control is lost. The increased AoA on the outside wing, the decreased lift (due to the bank) and the full rudder condition at a speed that is dangerously close to the stall is a recipe for disaster (remembering that the 'gap' between Vmca and Vs closes very quickly).
I often wondered why 5 degrees was used for certification. It would be nice to know the origin. I may indeed one day bore you all with the mathematics
Interesting point though...
[ 11 September 2001: Message edited by: Turbine ]
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Lets look at it practically,
Q) What is the critcal engine on any light piston twin?
A) Either, cause no matter what engine fails I reckon it is critical.
Lets see PA31-350 max Vortex take off weight, 1300m strip, engine failure @80' what are you going to do? Will it fly the book says so - Yeah right!!!
C402B engine goes bang at MTOW 35deg, 90% humidity 500' will it fly - Yeah right!!!
Just my opinion of the ever aging piston fleet. Now what do you reckon, re engine a PA31 with the V8 Orenda engine???
HA.
Q) What is the critcal engine on any light piston twin?
A) Either, cause no matter what engine fails I reckon it is critical.
Lets see PA31-350 max Vortex take off weight, 1300m strip, engine failure @80' what are you going to do? Will it fly the book says so - Yeah right!!!
C402B engine goes bang at MTOW 35deg, 90% humidity 500' will it fly - Yeah right!!!
Just my opinion of the ever aging piston fleet. Now what do you reckon, re engine a PA31 with the V8 Orenda engine???
HA.
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NOTE: there are several deliberate 
mistakes in the following post, at least that's my story, E K G was the first to find them, see below edited by gaunty to ensure his dumbosity is not perpetuated and to demonstrate that in these forums you can run but you can't hide 
John_t and Turbine
I am glad to see you in heated agreement if I may plagiarise our friend 4Dogs.
Please keep stirring the pot and ME pilots and instructors, read carefully and join in.
Here is where the old wives tales and half formed prejudice get sorted out. Not by me I might add
John_t I share your jaundiced attitude in regard to some manufacturers information but have to suggest that the biggest and best of them of them actually provides very comprehensive and IMHO accurate POH information on OEI ROC for different Weights, Temps and PH and the climb penalties for all combinations of gear and flaps up to full flaps other than that certified.
I have found in my experience though that few pilots know where to find it if they were in fact even aware that it existed.
This manufacturers twin Vs was always lower than Vyse by a "good" margin such that a departure was less an issue than keeping upright.
The information on all other take off issues is sufficiently comprehensive and easy to interpret as to enable construction of a "claytons" CAO 20.7.1b scenario.
In another life, I can still see the look on the faces of my ATPL theory students (including highly experienced CPs of large competent GA Charter operators and the odd FOI mind you) when you demonstrate the fallacy of the "twin engine safety" assumptions under which they have been labouring and the dawning that for the most part they weren't ever even close to going where they thought when it turned to poop, up to and including the turboprops.
I agree this is not the place.
As an aside I ran across an operator whose CP had dymoed the speeds and climb and cruise power and FF settings (one size fits all) onto the instrument panel and hid the POHs from the crew in case they got nicked. Ram rise, power computer, OAT what are they??
As a matter of interest.
The last piston twin they designed could be flown through all assy procedures with both feet on the floor, an accelerated stall AEO or OEI would result in the aircraft simply flopping back to straight and level, no matter how aggressively flown and so on. Hands off NO trim change with gear or flap extension right up to full. No fancy gimmicks, just plain old careful design from scratch.
Demo party trick was to sit "hard bitten" CP or such in the LH seat and select full flap and gear at cruise, their hands would fly to the wheel and throttles to find they had nothing to do, disconnect the A/P and the aircraft just started on down.
With a bit of planning it was possible to descend from cruise, circuit entry and land, hands off, using only rudder, gear flaps and power and a touch of elevator trim to flare.
I would have been quite happy, and succesfully simulated the concept, to give the keys to a reasonably experienced C182/C206/C210/A36/Lance driver without any ME experience and a short briefing to go fly it.
WARNING: Do not try any of the above at home folks.
Unfortunately that aircraft type which was to be the start of new generation of GA twins from a safety and design standpoint was basically stillborn due to external issues and sadly only 350 odd were ever built.
It was a close as anyone has ever come to a bullet and idiot-proof FAR23 twin that I've seen.
So it is possible and a salutary lesson on the ways of destiny.
Achilles
Nup no 'Mickey Mouse' with published performance figures in the pursuit of sales at least not for the stuff I was selling. If there was any “Mickey Mouse” it was usually from the resident expert
From the POH "Emergency Procedures" after the check list and the description of the recommended procedure blah blah they follow with "However, it is recommended that in most cases it would be better to discontinue the takeoff" and the warning.
"The propeller on the inoperative engine must be feathered, landing gear retracted and wing flaps up or continued flight may be impossible."
They were VERY honest. Unlike some of the others.
Having said that I have to point out that the "Go faster, shorter, heavier, higher" kits are a real worry in the land of the half understood.
There is not one of them out there, that I am aware of anyway, that doesn’t compromise, bring together or even reverse Vyse/Vs relationships amongst other things.
There is one popular "performance" kit available for B200 which was originally conceived and designed to provide for occasional marginal strip operations and a larger buffer for normal ops the "benefits"
which is used to allow routine ops into strips otherwise unavailable to them. I'll bet most pilots using them are unaware of the compromises and consequences. If my memory serves me correctly Vyse and Vtoss are brought to within a Knot or so of each other and of Vs with absolutely no margin for the usual fumbling when things go pear shaped.
Maybe a risk worth taking for the odd situation, but for the purpose of regular ops?
Disclosure of interest: In a fairly high profile tender process a while ago, which required the highest level of safety blah blah available, the Citation was able to match and or exceed this “enhanced” performance with the bonus of FAR25 protection for a particular application at the same price, but this apparently didn’t suit the political/personal agenda and an ex DCA/CAA “ consultant” (not J_t I hasten to add) hired to advise them was unable to adequately explain the difference to them.
So there they are thundering into and out of a then very marginal strip with a newly endorsed B200 driver. No criticism of the B200 just the process. It took them another 5 or so years to get with the programme but not so unbelievably by accident not design
Turbine
I have Vsse down as the
"Intentional One Engine Inoperative Speed as a minimum speed selected by the manufacturer, for intentionally rendering one engine inoperative, in flight, for pilot training."
I was interested in and concur with your comments regarding the Twin Commanche. In the long ago, we operated VH-WWB as a company hack when it was fairly new, amongst a gaggle of new PA31-300 and C402 and our then CP (later to become an FOI in MEL) found THAT out to his terror, the blue line goalposts were moved thereafter. BTW Modern certification may becoming a little aged methinks, see my comments re the last really "modern" twin.
edited to add "Not by me I might add"
[ 11 September 2001: Message edited by: gaunty ]
[ 13 September 2001: Message edited by: gaunty ]
mistakes in the following post, at least that's my story, E K G was the first to find them, see below edited by gaunty to ensure his dumbosity is not perpetuated and to demonstrate that in these forums you can run but you can't hide John_t and Turbine
I am glad to see you in heated agreement if I may plagiarise our friend 4Dogs.
Please keep stirring the pot and ME pilots and instructors, read carefully and join in.
Here is where the old wives tales and half formed prejudice get sorted out. Not by me I might add
John_t I share your jaundiced attitude in regard to some manufacturers information but have to suggest that the biggest and best of them of them
actually provides very comprehensive and IMHO accurate POH information on OEI ROC for different Weights, Temps and PH and the climb penalties for all combinations of gear and flaps up to full flaps other than that certified.I have found in my experience though that few pilots know where to find it if they were in fact even aware that it existed.
This manufacturers twin Vs was always lower than Vyse by a "good" margin such that a departure was less an issue than keeping upright.
The information on all other take off issues is sufficiently comprehensive and easy to interpret as to enable construction of a "claytons" CAO 20.7.1b scenario.
In another life, I can still see the look on the faces of my ATPL theory students (including highly experienced CPs of large competent GA Charter operators and the odd FOI mind you) when you demonstrate the fallacy of the "twin engine safety" assumptions under which they have been labouring and the dawning that for the most part they weren't ever even close to going where they thought when it turned to poop, up to and including the turboprops.
I agree this is not the place.
As an aside I ran across an operator whose CP had dymoed the speeds and climb and cruise power and FF settings (one size fits all) onto the instrument panel and hid the POHs from the crew in case they got nicked. Ram rise, power computer, OAT what are they??
As a matter of interest.
The last piston twin they designed could be flown through all assy procedures with both feet on the floor, an accelerated stall AEO or OEI would result in the aircraft simply flopping back to straight and level, no matter how aggressively flown and so on. Hands off NO trim change with gear or flap extension right up to full. No fancy gimmicks, just plain old careful design from scratch.
Demo party trick was to sit "hard bitten" CP or such in the LH seat and select full flap and gear at cruise, their hands would fly to the wheel and throttles to find they had nothing to do, disconnect the A/P and the aircraft just started on down.
With a bit of planning it was possible to descend from cruise, circuit entry and land, hands off, using only rudder, gear flaps and power and a touch of elevator trim to flare.
I would have been quite happy, and succesfully simulated the concept, to give the keys to a reasonably experienced C182/C206/C210/A36/Lance driver without any ME experience and a short briefing to go fly it.
WARNING: Do not try any of the above at home folks.
Unfortunately that aircraft type which was to be the start of new generation of GA twins from a safety and design standpoint was basically stillborn due to external issues and sadly only 350 odd were ever built.
It was a close as anyone has ever come to a bullet and idiot-proof FAR23 twin that I've seen.
So it is possible and a salutary lesson on the ways of destiny.
Achilles
Nup no 'Mickey Mouse' with published performance figures in the pursuit of sales at least not for the stuff I was selling. If there was any “Mickey Mouse” it was usually from the resident expert
From the POH "Emergency Procedures" after the check list and the description of the recommended procedure blah blah they follow with "However, it is recommended that in most cases it would be better to discontinue the takeoff" and the warning.
"The propeller on the inoperative engine must be feathered, landing gear retracted and wing flaps up or continued flight may be impossible."
They were VERY honest. Unlike some of the others.
Having said that I have to point out that the "Go faster, shorter, heavier, higher" kits are a real worry in the land of the half understood.
There is not one of them out there, that I am aware of anyway, that doesn’t compromise, bring together or even reverse Vyse/Vs relationships amongst other things.
There is one popular "performance" kit available for B200 which was originally conceived and designed to provide for occasional marginal strip operations and a larger buffer for normal ops the "benefits"
which is used to allow routine ops into strips otherwise unavailable to them. I'll bet most pilots using them are unaware of the compromises and consequences. If my memory serves me correctly Vyse and Vtoss are brought to within a Knot or so of each other and of Vs with absolutely no margin for the usual fumbling when things go pear shaped. Maybe a risk worth taking for the odd situation, but for the purpose of regular ops?
Disclosure of interest: In a fairly high profile tender process a while ago, which required the highest level of safety blah blah available, the Citation was able to match and or exceed this “enhanced” performance with the bonus of FAR25 protection for a particular application at the same price, but this apparently didn’t suit the political/personal agenda and an ex DCA/CAA “ consultant” (not J_t I hasten to add) hired to advise them was unable to adequately explain the difference to them.
So there they are thundering into and out of a then very marginal strip with a newly endorsed B200 driver. No criticism of the B200 just the process. It took them another 5 or so years to get with the programme but not so unbelievably by accident not design
Turbine
I have Vsse down as the
"Intentional One Engine Inoperative Speed as a minimum speed selected by the manufacturer, for intentionally rendering one engine inoperative, in flight, for pilot training."
I was interested in and concur with your comments regarding the Twin Commanche. In the long ago, we operated VH-WWB as a company hack when it was fairly new, amongst a gaggle of new PA31-300 and C402 and our then CP (later to become an FOI in MEL) found THAT out to his terror, the blue line goalposts were moved thereafter. BTW Modern certification may becoming a little aged methinks, see my comments re the last really "modern" twin.
edited to add "Not by me I might add"
[ 11 September 2001: Message edited by: gaunty ]
[ 13 September 2001: Message edited by: gaunty ]
Moderator
StallSpinCrashBurnDie,
"...directional control is restored with rudder".... etc...
The story is part correct.
Banking the aircraft generates a sideslip and subsequent yawing moment (think of weathercocking if you like), either stabilising (helping the pilot) or destabilising (hindering the pilot) depending on whether the bank is toward or away from the live engine(s). The greater the bank angle, the greater the effect one way or the other. At a given airspeed, rudder requirements will vary quite strongly with bank input.
Compared to the "real" Vmcg with wings level, for example, if the aircraft be banked into the operating engine(s) the "real" Vmca will reduce. Conversely, if the aircraft be banked into the failure side, the "real" Vmca will increase. This variation is quite significant and can easily lead to the pilot's losing control of the aircraft if bank is not controlled appropriately and aggressively, especially at low takeoff weights (ie low V2 or VTOSS).
I don't know that I am at all comfortable with your dissertation on weight and lift ....
Turbine,
I suggest that the intent of the 5 degree Design Standard limitation in demonstrating the certification Vmca is quite straightforward.
A manufacturer is in business to sell things, not just design and build them - a subtle but important distinction.
Takeoff distance, for example, is extremely important for marketing. TOD is related to V2 squared. Minimum V2 is limited either by Vs or Vmca considerations. Therefore if Vmca be limiting for a particular aircraft (at light weights, especially for 4 engined aeroplances), the manufacturer would, perchance, desire to reduce Vmca such that Vs considerations become limiting, reducing V2 and TOD etc.
It is reasonable to view the 5 degree bank limit as being a restriction on the determination of Vmca to prevent undesirably innovative test work by a manufacturer in the circumstances indicated above.
Also the performance degradation associated with large bank angles would present routine line operations with a rather hazardous "real" Vmca situation in the immediate post failure manoeuvring phase as precise control of bank in a dynamic engine failure situation is rather difficult. At low weight operations particularly, a Vmca limitation based on a large angle of bank would significantly increase the likelihood of inadvertent Vmca departures - not a good thing.
It is reasonable to presume, in the absence of definitive statements by the manufacturer to the contrary, that Vmca has been demonstrated for the permitted 5 degree bank.
It is relevant to note that the 5 degrees limit has nothing much to do with climb performance - rather handling. Optimum climb performance generally occurs at around 2-3 degrees bank into the operating engine, which is where sideslip is minimised and climb capability maximised - this is not generally appreciated.
High Altitude,
Pass, brother. I can do little other than echo and support your cynicism .....
Gaunty,
I, too, would be interested in knowing the aircraft to which you refer - sounds like a great little machine for old chaps who don't get too much currency practice. If necessary, do email.
I don't know to which contract you refer - Citation versus KingAir - but I think that it is fair to suggest that the two aircraft are somewhat different in their optimum applications.
"...directional control is restored with rudder".... etc...
The story is part correct.
Banking the aircraft generates a sideslip and subsequent yawing moment (think of weathercocking if you like), either stabilising (helping the pilot) or destabilising (hindering the pilot) depending on whether the bank is toward or away from the live engine(s). The greater the bank angle, the greater the effect one way or the other. At a given airspeed, rudder requirements will vary quite strongly with bank input.
Compared to the "real" Vmcg with wings level, for example, if the aircraft be banked into the operating engine(s) the "real" Vmca will reduce. Conversely, if the aircraft be banked into the failure side, the "real" Vmca will increase. This variation is quite significant and can easily lead to the pilot's losing control of the aircraft if bank is not controlled appropriately and aggressively, especially at low takeoff weights (ie low V2 or VTOSS).
I don't know that I am at all comfortable with your dissertation on weight and lift ....
Turbine,
I suggest that the intent of the 5 degree Design Standard limitation in demonstrating the certification Vmca is quite straightforward.
A manufacturer is in business to sell things, not just design and build them - a subtle but important distinction.
Takeoff distance, for example, is extremely important for marketing. TOD is related to V2 squared. Minimum V2 is limited either by Vs or Vmca considerations. Therefore if Vmca be limiting for a particular aircraft (at light weights, especially for 4 engined aeroplances), the manufacturer would, perchance, desire to reduce Vmca such that Vs considerations become limiting, reducing V2 and TOD etc.
It is reasonable to view the 5 degree bank limit as being a restriction on the determination of Vmca to prevent undesirably innovative test work by a manufacturer in the circumstances indicated above.
Also the performance degradation associated with large bank angles would present routine line operations with a rather hazardous "real" Vmca situation in the immediate post failure manoeuvring phase as precise control of bank in a dynamic engine failure situation is rather difficult. At low weight operations particularly, a Vmca limitation based on a large angle of bank would significantly increase the likelihood of inadvertent Vmca departures - not a good thing.
It is reasonable to presume, in the absence of definitive statements by the manufacturer to the contrary, that Vmca has been demonstrated for the permitted 5 degree bank.
It is relevant to note that the 5 degrees limit has nothing much to do with climb performance - rather handling. Optimum climb performance generally occurs at around 2-3 degrees bank into the operating engine, which is where sideslip is minimised and climb capability maximised - this is not generally appreciated.
High Altitude,
Pass, brother. I can do little other than echo and support your cynicism .....
Gaunty,
I, too, would be interested in knowing the aircraft to which you refer - sounds like a great little machine for old chaps who don't get too much currency practice. If necessary, do email.
I don't know to which contract you refer - Citation versus KingAir - but I think that it is fair to suggest that the two aircraft are somewhat different in their optimum applications.
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Gaunty et al, "mickey mouse" as a term was not intended by me to insinuate that manufacturers data on performance was deceptive, but more that some of the worse figures are less than obvious.
This is a good & interesting thread folks, keep it coming!!
This is a good & interesting thread folks, keep it coming!!
Don Quixote Impersonator
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John_T
Cessna 303 Crusader. I didn't identify it as a little test to see if there was any reaction. Not being a smart a ss just that the aircraft only briefly appeared on the radar down here, before the GA piston Manufacturing imploded.
You would be delighted with the aircraft and a walk around would reveal the why and cleverness of the design. The problem for Cessna was that most of their piston line had reached the end of any practical evolution and again you and I would enjoy a walk around say the C310R wherein I could show you how they had run out of places to go wothout compromising sensible standards.
B200 v Citation. The Citation was developed to compete directly with the Kingair. Cessna had the choice to go on from the C400 series with a turbine version as did Beech with the Kingair growing out of the Twin Bonanza/Queen Air. Their reasoning was they could build a multidextrous aircraft that could be operated SP <5700kg FAR23 rules or full FAR25 that would cost no more to operate but with superior performance. They suceeded but kept running into the usual regulatory flak around the world.
Point being, all other things being equal with a mandated 2 crew requirement and the same price/revenue why would you use a FAR23 B200 when you have a FAR 25 Citation available.
I will email you re the contract to which I refer.
HA
I'll follow John_t on that one.
However I gotta say a more powerful engine actually brings as many problems to the OEI argument as it solves insofar as the airframe, empennage/rudder is designed for a given HP ergo the OEI speeds have to go up. This may be mitigated by an increase in acceleration to keep the TO dist down blah blah blah or you limit power used to the design level below a certain airspeed then increase from there.
The C425 (sorta C421C with PT6s) was thrust limited for T/O and up to OEI speeds if you did have to slot one you had to accelerate the aircraft to beyond the appropriate speed (can't recall it just know) then you could go for it. So the extra grunt wasn't all that much use in the context of this discussion.
If you are talking about a more reliable engine that is cheaper than a turbine I dunno. Recips are recips air or water cooled ain't all that much different except in the cooling system which both have their plusses and minus. IMHO turbine is always the way to go for reliability, especially having seen the condition of the insides of Time ex engines still putting out rated power on the frame before removal. Toothless old hags can still put out you know
Achilles
You are correct in that you have to go look for it. As a "salesman" that is the first place I went to when up against anotherys, when you tear their numbers apart you can usually see what they have done to trick up an old design to look like a new one.
In FAR 25 types the second segment climb and WAT charts is where the story is usually told.
M 0.84, FL510, 3200nm 8 pax, yeah right, but not all at the same time out of the same strip, or if you were going to do a multi sector journey of that distance.
BAe used to hate it when we got down to that with the client
One study of this v that revealed our ship couldn't do it non stop against the othery, but we could still beat them point to point by 30 minutes including a tech stop and around a 1000lbs less fuel. We're going GW TO straight to at FL450 M0.84 they're back at LRC M0.7 something struggling to make FL350 end of crz
Fascinating and fun.
Cessna 303 Crusader. I didn't identify it as a little test to see if there was any reaction. Not being a smart a ss just that the aircraft only briefly appeared on the radar down here, before the GA piston Manufacturing imploded.
You would be delighted with the aircraft and a walk around would reveal the why and cleverness of the design. The problem for Cessna was that most of their piston line had reached the end of any practical evolution and again you and I would enjoy a walk around say the C310R wherein I could show you how they had run out of places to go wothout compromising sensible standards.
B200 v Citation. The Citation was developed to compete directly with the Kingair. Cessna had the choice to go on from the C400 series with a turbine version as did Beech with the Kingair growing out of the Twin Bonanza/Queen Air. Their reasoning was they could build a multidextrous aircraft that could be operated SP <5700kg FAR23 rules or full FAR25 that would cost no more to operate but with superior performance. They suceeded but kept running into the usual regulatory flak around the world.
Point being, all other things being equal with a mandated 2 crew requirement and the same price/revenue why would you use a FAR23 B200 when you have a FAR 25 Citation available.
I will email you re the contract to which I refer.
HA
I'll follow John_t on that one.
However I gotta say a more powerful engine actually brings as many problems to the OEI argument as it solves insofar as the airframe, empennage/rudder is designed for a given HP ergo the OEI speeds have to go up. This may be mitigated by an increase in acceleration to keep the TO dist down blah blah blah or you limit power used to the design level below a certain airspeed then increase from there.
The C425 (sorta C421C with PT6s) was thrust limited for T/O and up to OEI speeds if you did have to slot one you had to accelerate the aircraft to beyond the appropriate speed (can't recall it just know) then you could go for it. So the extra grunt wasn't all that much use in the context of this discussion.
If you are talking about a more reliable engine that is cheaper than a turbine I dunno. Recips are recips air or water cooled ain't all that much different except in the cooling system which both have their plusses and minus. IMHO turbine is always the way to go for reliability, especially having seen the condition of the insides of Time ex engines still putting out rated power on the frame before removal. Toothless old hags can still put out you know
Achilles
You are correct in that you have to go look for it. As a "salesman" that is the first place I went to when up against anotherys, when you tear their numbers apart you can usually see what they have done to trick up an old design to look like a new one.
In FAR 25 types the second segment climb and WAT charts is where the story is usually told.
M 0.84, FL510, 3200nm 8 pax, yeah right, but not all at the same time out of the same strip, or if you were going to do a multi sector journey of that distance.
BAe used to hate it when we got down to that with the client
One study of this v that revealed our ship couldn't do it non stop against the othery, but we could still beat them point to point by 30 minutes including a tech stop and around a 1000lbs less fuel. We're going GW TO straight to at FL450 M0.84 they're back at LRC M0.7 something struggling to make FL350 end of crz
Fascinating and fun.
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T303 - good looking, to boot!
One thing that has not been mentioned with regard to Vmca, is the effect of Drag! It's not only climb performance that is affected by excess drag: Any aggravation of the Thrust/Drag vectors will increase Vmca; more drag (induced or parasite) requires more thrust which in turn creates a greater yawing moment, which then requires more rudder force (to maintain direction) which may or may not be available. For example, with the gear down, Vmca goes up. With Flaps at a greater than TKO setting, Vmca goes up; windmilling prop etc etc etc. That's why the AoB into the live engine is important - by tilting Lift and creating a sideways component, it reduces the amount of rudder deflection (and subsequent drag) required to keep the aircraft directionally in control.
One thing that has not been mentioned with regard to Vmca, is the effect of Drag! It's not only climb performance that is affected by excess drag: Any aggravation of the Thrust/Drag vectors will increase Vmca; more drag (induced or parasite) requires more thrust which in turn creates a greater yawing moment, which then requires more rudder force (to maintain direction) which may or may not be available. For example, with the gear down, Vmca goes up. With Flaps at a greater than TKO setting, Vmca goes up; windmilling prop etc etc etc. That's why the AoB into the live engine is important - by tilting Lift and creating a sideways component, it reduces the amount of rudder deflection (and subsequent drag) required to keep the aircraft directionally in control.
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Downwind
How did the Questionaire go ??
Achillies
The use of UC in the drag example is not the best one to use.
In light twin engine ACFT with wing mounted engines, the UC in the down position actualy reduces Vmca.
This is because that the UC leg in the slipstream of the live engine is creating more drag (slipsteam + airspeed)and therfore a drag couple which slightly oposes and reduces the yawing moment toward the live engine.
Once again you are probably aware of this and maybe used a poor example, if you do I apologise for lecturing to you and hope others may learn from this.
How did the Questionaire go ??
Achillies
The use of UC in the drag example is not the best one to use.
In light twin engine ACFT with wing mounted engines, the UC in the down position actualy reduces Vmca.
This is because that the UC leg in the slipstream of the live engine is creating more drag (slipsteam + airspeed)and therfore a drag couple which slightly oposes and reduces the yawing moment toward the live engine.
Once again you are probably aware of this and maybe used a poor example, if you do I apologise for lecturing to you and hope others may learn from this.
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The only common denominator to these replies is that "Asymmetric performance for a/c less than 5700kgs" is like "military intelligence" - AN OXYMORON...