RobertL18C wrote:
They are blessed with two red lines, Vmca and Vne :)
:)))
RobertL18C wrote:
Vmca with both engines windmilling would be interesting as it is quite high up the back end of the drag curve and not too far from V
I think one of the most demanding situations would be to arrive at Vmca with engines at low power and initiating a go around where both engines initially respond but one quits just as you reach go around power. If I am not mistaken, failures happening during that phase have resulted in loss of control on occasion.
Doing Vmca testing for the DA42-L360, I found that there was a control problem. I did not have enough rudder to overcome the more powerful engine with one feathered. I ended up blocking the rudder pedal full displacement with a cut to size piece of wood. The I moved the rudder by hand, and it would move back toward the trail position when the blocked pedal should have held it over. What I found was the the rudder cable loads were very high (though still design acceptable) because of the very small rudder bellcrank. The eye and thimble arrangement on the rudder cables was inadequate, as under great load, the thimbles would stretch. I measured across them with calipers while various loads were applied to the rudder for me. Diamond should have used proper swaged terminal ends on the rudder cables, rather than cheap and needlessly complex eye/thimble/nicopress. Thimbles and eye ends are not designed to be used that way together, I don’t know how that was approved!
For an excellent discussion on the lack luster performance of light twins on one engine, search out an article called: “Always Leave Yourself an Out” by Richard Abrams, it explains it all well, and it eye opening as to what multi engine planes cannot be expected to do on one engine!
Am I seeing this right – you are diving at 225kts way past redline ? That’s not Vmca, LOL !
PS: interesting article, thanks for sharing @Pilot_DAR! It can be found here.
Pilot_DAR wrote:
What I found was the the rudder cable loads were very high (though still design acceptable) because of the very small rudder bellcrank. The eye and thimble arrangement on the rudder cables was inadequate, as under great load, the thimbles would stretch. I measured across them with calipers while various loads were applied to the rudder for me. Diamond should have used proper swaged terminal ends on the rudder cables, rather than cheap and needlessly complex eye/thimble/nicopress.
That’s very interesting development history. It looks like the intent was to inexpensively couple cables from both sets of rudder pedals, instead of doing it with a mechanical linkage? That would be an odd design.
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IMO one should get to know the aircraft and accept its limitations. I don’t think anyone expects any light twin to go up like a rocket OEI.
The fact that one climbs at all is IMO what makes it different from a single if an engine quits.
In a single you learn to look for somewhere to land constantly in case the engine quits. In a glider or TMG you can look for a landing spot further afield.
It’s the same in a twin you constantly think and plan for the " what if " situations.
If I planning to fly over the Alps in an Apache with a OEI service ceiling of 4200’ IIRC I would planfor what I would do if an engine failed. I would have choices
1) Choose a route which I could fly at 4000ft.
That could mean going round the high parts of the Alps
2) I could take a bit more of a risk and choose a route and an altitude which would allow me to always be within slow descent of an enroute airfield.
3) I could get high enough so that I would be over the highest part of the Alps by the time I drifted slowly down to 4200ft.
This is exactly as I would do in a single except in the SEP I would have to keep descending below 4200ft and make a landing.
There are moments in flying a light twin where the risks are at their greatest. One works out how you would try and avoid those risks turning into disasters.
I tried simulated EFATO in DA42 yesterday at 500 ft with gear down and flaps at APP position in climb, like it would be when performing go around. Even in DA42 the yaw and roll are significant and require pretty fast reaction to continue uninterrupted climb at Vyse. It’s very different from OEI in cruise flight.
@Emir this is something I practice regularly on a DA42. Did you go OEI at 500ft or were you OEI before 500ft?
I agree you need a pretty strong leg for control, until you can either get some rudder trim in or reduce the power on the live engine.
The old maxim
Control (yaw, roll and speed)
Power (cram fully forward)
Drag (clean up starting with landing flaps if down, then gear then approach flaps)
Identify (dead engine, the leg that isn’t hurting, Verify ( look at rpm (da42) others might be pull dead throttle slowly back while monitoring yo see you are not cutting the wrong engine
Feather ( prop makes a lot of difference to drag.)
You can now set about tidying up, such things as alternator on dead engine, crossfeed if needed, decide what you are going to do and tell ATS.
There’s always a debate between instructors about whether this is a " panne panne" or not.
Simple really, the biggest problems when it happens for real is not to go brain dead or to rush at everything in panic, you do have a little time but (not a lot).
This is where currency helps as does regularly walking up hills. I’ve lost count of the number of times after a heavy session in a DA42 I’ve walked away with one leg trembling for an hour or so after.😁😁😁
So true, happened to me also, the last CPL flight lesson was 2h35, we did 6 different terrain with all an OEI GA exercise… at the end I was protecting the power lever from the action of my CRI because i knew it would happen.
Btw the alsim fnpt simulator needs stronger reaction as the real da42. And I would say the same for c525, but it’s a very different exercise…
Did you go OEI at 500ft or were you OEI before 500ft?
I was exactly at 500ft AGL when OEI, full throttle on right engine and idle left:
- right leg, right bank, nose down
- gear up, flaps up
- left engine to 12% instead of feathering
- climb on blue line
I didn’t like how rusty I was doing this 
