I said nothing about "balanced field length" (which, according to def'n rarely exists anyway.) What I was referencing was a takeoff where a pilot found himself at/near Vmc with insufficient runway remaining to either abort, or sufficient clear-way to continue the takeoff. The regulatory basis to which I referred earlier is found in FARs 91.3 "Careless or reckless operation" and 91.103 "Preflight action". Those regs together work to require the pilot to utilize Approved Data to confirm the safety of the flight as it pertains to runway length requirements, ...and since no mfr publishes the aforementioned near-Vmc-transition-to-climb, single-engine data,...any failure to successfully complete the manuever places the onus directly upon the pilot. (The accident report will read: Pilot failed...to adequately pre-flight plan...to assess req'd runway length...to determine aircraft performance...etc. etc. etc.) He will also run the risk of serious injury or death if my family was onboard.Doherty wrote: Your response that you have to have a balanced field length to take-off per the FARs is not accurate. ... This will be achieved by horsing the twin off the runway sooner than any best performance climb, but after VMC. If your VMC is at a slower speed, you can lift off (safely) at a point before the runway ends, and fly into a non-obstacle departure route, waiting for best rates. ...
So upper wing contamination can be a problem, even if you are conforming to all of the FAA regs.
"...you can lift off (safely) {NOT!-gahorn} at a point before the runway ends, and fly into a non-obstacle departure route, waiting for best rates..."
The example you gave was one which most light, multi-engine airplanes will not accomplish with the loss of an engine, and which their mfr's have not documented for that very reason. "...waiting for best rates...??" There is no certification requirement for an aircraft to demonstrate the ability to accelerate on one engine in the takeoff configuration from Vmc to a climb. (In fact, I cannot think of a single general aviation airplane that, without the loss of altitude or the reduction of remaining-engine power, can acceleratre from Vmc to a climb conditon. Not even the re-heater equipped simulations I've flown when training at BAe in the test pilot program could perform that feat.) "...you can lift off (safely)..." ?? There's very little safety in that procedure, in my opinon, and therefore the idea that VG's will somehow increase safety is pure imagination.
But I know what you're saying: That if in some self-created scenario wherein one is willing to take the risk of crashing the airplane in case of imminent failure of an engine at/near Vmc then the crash sequence can begin at a lower airspeed with VG's than without.
Mr. Doherty, let me ask a question: Why does one pay any attention to Vmc whatsoever if one intends to operate out of such short strips? (Why indeed? If mud is a problem, wouldn't it be far better to apply full power, raise the nose and fly out of the mud even sooner,...well below Vmc? The all-engine best climb angle is near/below Vmc in most twin airplanes anyway! I think that if confronted with such a choice the later is what I'd do. Any sudden loss of an engine would simply be a foregone conclusion that I'd chop the power on the operating engine and land straight ahead right back down in the mud which would help me slow down and stop! ...rather than attempt to continue to build speed to smack the obstacles at 80 kts and still trying to accelerate!)
A lowered Vmc is no particular advantage in my view, if I've decided to toss away single-engined climb capability anyway. (Yes, I've done the drill: I've applied full-power to a ME airplane, and performed a "soft-field/short-field" takeoff similar to the single-engine airplane technique, and yes, a ME airplane will do it quite spectacularly....IF...one is willing to accept the loss of control that will result if one is below Vmc....and IF...one is willing to accept the crash that will result if one is below the minimum climb speed the airplane will acheive on one engine. (Don't attempt to assure us that there's some happy airplane will still climb at Vmc and the sudden complete loss of the critical engine. Re-read what I just said:..." if one is below the minimum climb speed the airplane will acheive on one engine. " Flight a/below Vmc with or without VG's most assuredly is below the single engine climb capability of general aviation airplanes unless it involves a loss of altitude or JATO bottles.
OK, so VG's will reduce Vmc. I grant that. But why did one need to reduce Vmc if the airplane still won't climb? VG's were a waste of time and money since the stock airplane will perform the same feat.....namely a takeoff well below safe single-engine climb speeds.
As for the gross wt increase: If one has already decided the regs are not relevant to this particular takeoff (with regard to field length)...then why are any regs pertaining to aircraft wt's of any importance? Are we going to assign greater import to the ramp check at the destination than we do to the takeoff risk?
Icing: I have to admit that I'm slightly incredulous about the icing experience you metnioned. I've ferried airplanes across Greenland, the N. Atlantic, Iceland, and regions beyond, and while I've never been to Alaska, I've seen icing condiitons that have far exceeded those experienced by most pilots. Supercooled rain will form ice upon impact, ...and flying through temperature inversions will re-melt/re-freeze precip while inflight causing some run-back, but....freezing rain is not a validation of the merit of VG's. Not even the VG mfr's make that claim. (In actual icing conditions I discovered to my dismay that VG's became a prime location of ice build-up (an ice-magnet if you will) and in icing conditions very quickly lose their charm, even on a TKS equipped Hawker Siddely.)
"...even if you are conforming to all of the FAA regs. ..." If one accepts the various definitions of icing found in the AIM, then what you have described would meet/exceed the definitions of "severe" icing. No airplane is certificated for continued flight in "severe icing" ....so one may be assured one is not..."conforming to all of the FAA regs."
Great, challenging, discussion. I hope we're not boring our 170 friends.
