FL180 and above ...

Any DA42 related topics.

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wolfipilot
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FL180 and above ...

Post by wolfipilot »

... I searched the forum but did not find something about the following: I recently watched a video about test flights with the DA42-vi and it climbed up to FL200 easily. So I wonder why the limitation is at FL180 - and I wonder what FL could be reached technically while still being on the safe side.

Any experiences here?
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Diamond13
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Re: FL180 and above ...

Post by Diamond13 »

If the rate-of-climb is less than 125 fpm, you have passed the service ceiling. In some flight testing that is carried out, it requires the aircraft to be at or near aircraft Vne @ the service ceiling, therefore the test is usually start 1 to 2 thousand feet above the service ceiling. There are numerous reasons for making a limitation that is actaully lower than what the aircraft will still comfortably climb at.
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wolfvoador
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Re: FL180 and above ...

Post by wolfvoador »

The Israeli Air Force have tested a DA42 drone up to 30,000 ft, see http://en.wikipedia.org/wiki/Aeronautic ... _Dominator
I have seen Climb performance around 500fpm getting close to 18,000 with my DA42NG. The POH says actually even more, 800-900 fpm at that altitude! I guess the FAA wants to limit number of aircraft flying into Alpha, but somewhere else, I am tempted to exchange my cannula for a mask, and give it a try. It could be a live saver in the tropics, if you have to climb out weather in an amergency....
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wolfipilot
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Re: FL180 and above ...

Post by wolfipilot »

... wow, impressing - FL300 is not what I planned to reach, but I think it is safe to have some climb-options even at FL180. My concerns are that at FL180+ the balance and so on gets out of the limits or something like that?
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Re: FL180 and above ...

Post by cfiguy »

I've flown a DA42 NG at 17,500' on several occasions and found the climb performance up to that altitude to be in excess of 600'/minute. Above 14,500, 92% power results in propeller RPM entering the yellow range so I tend to use 85% power in a climb above that altitude.

Other considerations:

In the flight levels, even if the aircraft is capable of reaching those altitudes, it may become difficult or impossible to keep the fuel, oil, and coolant temperature within limits. And consider an engine failure at those altitudes - a two minute restart limit and a windmilling restart at high altitudes would seem to raise the risks of not being able to get an engine back on-line. Lastly, in one of the other threads. it has been observed that the heater and defroster are barely adequate at lower altitudes in cold temperatures (less of a problem with an unmanned DA42).

This is all speculation, but it would appear that Diamond was trying to control the hazards associated with high-altitude flight, they looked at the aircraft's performance, and decided 18,000' was high enough.

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Re: FL180 and above ...

Post by CFIDave »

I know two pilots (not me!) who have each flown a DA42 NG with Austro engines to altitudes above 30,000 feet. Diamond's 18,000 foot certified operating limit does not reflect the aircraft's actual service ceiling (defined as that altitude where the aircraft can only climb at 100 feet/minute).

The "dash six" Austro-powered DA42-VI is still climbing at 1000 fpm at 18,000 feet with both engines operating, so it can easily exceed 18,000 feet altitude. However one of the benefits of such a strong climb rate up high is that it provides greater safety when picking up ice and climbing out of icing conditions below 18,000 feet. This came in handy a few days ago when we picked up moderate rime icing at 14,000 (in Florida!) and were able to quickly and easily climb to 16,000 feet into the bright sunshine where sublimation quickly melted the ice.

Besides the potential engine cooling issue mention previously, a limitation of exceeding 18,000 feet is that you need to wear an oxygen mask instead of the "rubber hose up your nose" cannula. Interestingly Diamond supplied a nice mask with built-in microphone along with cannulas for our DA42 with a built-in oxygen system.
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TimS
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Re: FL180 and above ...

Post by TimS »

Passing 18k the certification requirements change.
There are descent requirements start to kick in case of loss of O2 or pressurization. There are fuel requirements, testing.... Basically I figure Diamond made the decision no one or not enough would fly high there often enough to be worth the certification effort.

Tim
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Re: FL180 and above ...

Post by wolfipilot »

Interesting so see your inputs. So summarizing up I don't find any real technical concerns here to fly at FL200 for example for a shorter period, for example to avoid weather or so. Good to know.
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Re: FL180 and above ...

Post by Aart »

Ingo,
I have done just that on occasion, climbing to FL200 to remain out of cloud for a while. As commented before, performance-wise no issue, even with my Thielert/Centurion/Continental/Technify engines.
It is an 'operating limitation', not a 'service ceiling' issue, so formally speaking you are not supposed to do it, but I do not hesitate to do it in case weather dictates it.

A discussion on this very topic that you may find interesting:

http://www.euroga.org/forums/flying/155 ... ce-ceiling
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