Performance for light twins

[Contacttower]

You are probably right bookworm, 1300m was only a very rough calculation. The more runway the better....

What would your estimation be though of the Comanche's to climb away between 90mph (Vmc) and 105mph (Vyse)?

Piper seem to think that you'd be OK at 97mph (described as the 'take off safety speed' in the POH) but I've yet to meet someone who has had a very low level failure who can 'tell it how it is'.

[Tinstaafl]

Unless I've the wrong end of the stick, you have misapprehended Vtoss. It's the IAS to be achieved by 50' to conform to the take-off performance charts while providing an adequate margin above Vmc, not to provide asymmetric performance.

There is no requirement for the PA30/39 to be able to climb away between Vr & Vyse although once cleaned up, feathered etc it would be reasonable to expect to see some amount of climb performance if speed has accelerated towards Vxse. Can't remember if a Twin Comanche's stalls below 61kts though. If it's below then there's no requirement for positive climb performance no matter what you do. The best that its certification offers you is that its climb performance "...be determined." I'd bet a pound to a penny that unless you've reached at least Vxse with the wheels & flap up and prop feathered then downhill is the most likely outcome.

All at MTOW, of course. Given particularly favourable WAT conditions then it may well limp skywards. *Accelerating* to Vxse or Vyse would be problematic though.

[bookworm]

What would your estimation be though of the Comanche's to climb away between 90mph (Vmc) and 105mph (Vyse)?

The only person who could tell you that would be one who has suffered a catastrophic engine failure in that speed range. It's hard to suggest a realistic test at altitude, and it's nuts to suggest a realistic test at runway level. I would also agree with Tinstaafl that the 97 mph quoted is not an indication of the ability to climb.

[SNS3Guppy]

Unfortunately, many pilots think that, with two engines, you have redundancy. Truth is: maybe yes, maybe not....

A multi engine airplane which can't sustain flight, or maintain altitude with one engine failed, is still a redundant aircraft; engine failure is only one form of failure. More common is a vacum pump failure, and a light twin with two vacum pumps has far more chance of not suffering an insidious decay into partial panel than a single...or an electrical failure or a hydraulic failure.

A single, by comparison, is absolutey bound for mother earth after failure of it's one and only engine. The light twin may be headed the same direction, but with more options, a decreased descent rate, etc. Further, for IFR operations, the light twin is generally far more redundant and safer in terms of handling potential systems failures.

The second engine was never there to prevent a descent with one failed. The second engine is there for added performance when both are operating.

That the aircraft may not be able to maintain level flight with an engine failed is really irrelevant, making it no different than the single in that respect. Certainly it's redundant.

Any pilot which has received adequate instruction will certainly not believe the airplane will fly with an engine failed under all conditions. If a pilot has not received adequate preparation and doesn't take the time to calculate performance, then no amount of repeating the obvious will help him or her.

[BelArgUSA]

Probabilities and simple math...

Thinking about the "extreme" reliability of reciprocating engines...
And the excessive power of engines fitted on light aircraft...
xxx
Looks like many people still do not "get it" in their head... yet...
With a light twin, you have twice (double) the odds of getting into deep troubles...
That is, compared to single engine airplanes. This is known, in math, as "probability"...
Exactly like "Roulette" in Macao, Monte Carlo or Mar del Plata...
If an engine fails as average every 5,000 hrs (???), a twin will have one engine failing every 2500 hrs...
Are you well trained, and fully proficient... ? Will that propeller feather as it is supposed to...?
Will your remaining engine run ok at max continuous power, for the longest minutes of your flight...?
xxx
I recall this doctor (or was he a dentist, or a lawyer)...?
Like many of these brilliant professionals, was not too knowledgeable when playing pilot.
He had an old Bonanza, which he sold to buy a PA-23 Apache...
Two motors, he told me... so much safer...! - Correct.
I was told, that if 1 engine is out, an Apache has vertical speed of about 200 FPM descent...
In English, a powered glider... Just increases your options of crash sites...
xxx
Unverified statistic I was told, by an experienced worldwide lightplane ferry pilot...
Toby was his name... "Shark-bait" was his nickname... Did numerous California to Hawaii crossings... 2300 NM...
There are more oceanic ditchings of light twins, than there are ditchings of single engine lightplanes, per flight time hours.
He told me that it was based on insurance company statistics... These are experts, are they...?
I have to say I believe him more, than doctors, dentists and lawyers knowledge of planes...
xxx

Happy contrails