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Twin performance

I found this very interesting.

A twin needs to demonstrate any SE climb rate if it is either above 6000lb or its Vs is above 60kt.

Also they say the Aztec climbs at just 50fpm at 5000ft, SE.

The first table shows just how marginal the light twins are, on SE.

Administrator
Shoreham EGKA, United Kingdom

This shows very well how much a light airplane suffers aerodynamically from being a twin.

Will digest this article thoroughly on my transatlantic flight tomorrow.

My first thoughts though are that for the "current" twin pilot who regularly practices engine out ops and has properly briefed themselves pre-flight the light twin still offers a better get out of jail card than the single. There's nothing better than a partially blocked fuel injector over mountains or the Atlantic in a single to concentrate the mind!

EGHO Thruxton

Ian, Are you flying yourself over the Atlantic?

I did my multi engine rating on Piper Aztecs in 1971 in Phoenix (AZ). Not at max t/o mass (mostly three persons onboard) the Aztec was still a "good" performer even at ISA+20. The engine failures were induced shortly after lift-off at 50ft - resulting climb rate about 250-400ft/min. What I remember most is that depending on which engine failed you had to bring up the gear with a hydraulic hand pump (about 30 strokes) while trying to hold centerline and not to descend.

EDxx, Germany

Peter, I think you are missing the emphasis here:

A twin needs to demonstrate any SE climb rate if it is either above 6000lb or its Vs is above 60kt.

This is a conclusion based on a Quote from Part 23 (JAR23) which states the opposite:

There is no requirement for continued single-engine takeoff capability for Part 23 twins, nor, in fact, is there a requirement for any positive single-engine climb at all for twins which weigh less than 6,000 pounds and have a stall speed of 61 knots or less in the landing configuration.

So whilst you may try to fly the aircraft at Blue Line (Best SE Climb speed) there is no guarantee that this will be a positive number! Some of the published figures are quite optimistic!

This is like beating a dead horse. Anyway, here's how I look at it.

Most light-light twins and light twins have an envelope where they are vounrable at MTOW and that is just after takeoff when they are low and slow. Denisty altitude, raising terrein etc can leave you with no other option than to shut down both engines and you are basically a little worse off than a single would be due to a little higher stall speed.

A very high percentage of twin accidents happen in this phase where the pilot is trying to fight his way out with one engine.

However, once you've passed that phase (in most cases we're talking less than a minute) having to shut down one of the engines is bascally a non event if you are properly trained.

So, IMHO, I choose to be a little less safe for less than a minute, and after that much safer. I've shut one down at cruise at MTOW minus what we used to get up there, and the plane could actually be trimmed out to fly without any pressure on the pedals, and further had no problem staying at altitude. Actually, I was able to reduce MAP and still keep my altitude.

Some piston twins actullay have very good climb on one engine. A Baron 55 President actually climbs at 600f/minute at max gross on one engine.

Tumbleweed, That comes from the fact that at that speed you are basically no worse off than a single piston should you do a forced landing. With such stall speed, you can just shut the other one down and pretend you are in a single which has lost the engine.

However, most, if not all, piston twins have a Vso of more than 61kts and thus must climb at least 50 feet/minute at MTOW at altitudes lower than single engine service ceiling..

Now, would you care to name a piston twin which does not have a postive rate of climb at MTOW if properly rigged and flown. I do not know of any.

I like where BeechFlyer is coming from. A twin should be safer if flown correctly. Unfortunately many seem unable to fly an asymmetric twin to the necessary standard. Combine that with a built-in aversion to winding down the good engine and doing an off-field forced landing and we end-up with far too many stall/spin occurrences.

The twin I routinely fly (DA42) is an absolute puppy on one engine providing you are not playing around close to Vmca. But then again, if you are doing that...................

Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

Dave, agreed. However one can (and should) commit one self to a shutdown when required as part of the pre-takeoff brief.

The field I used to fly from (ENNM) had a valley with rising terrain east of field. So when using R07 I was trapped until I had climbed out of the valley as I was not able to outclimb the terrain at MTOW on one engine.

So departing at MTOW using R07, throttling back both if I should loose one below 400 feet was part of my departure brief. I think it easier to take the right decision when you have committed up front.

Now, how much time did I spend getting to 400 feet with both engines running. Not long...

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