Real Capability

Any DA42 related topics.

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RDGUSLLC
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Real Capability

Post by RDGUSLLC »

Depending on who you read, the full fuel useful load for the DA42 is about around 500 to 600 lbs (depending on how its configured or if you want to carry full TKS or not?

So what is the plane truly capable of? It is claimed that a Cessna 206 can carry anything they can close the doors around. That is not true as some fellows found in Alaska who tried to carry a motor cycle with some fifty gallon fuel drums. We know ferry pilots regularly add 25% over gross weight to ferry some aircraft. If this were the case with the DA42 that would up the max weight to between 625 to 750 lbs. On a standard day, sea level at standard temp I just wondered what what a DA42 would be able to get off the ground?

What is the primary reason(s) of the max weight limitation (landing gear? Structural integrity? Approach stall speed?).

Please no lectures about being a test pilot or sighting the POH. I am just interested in knowing what the aircraft is capable of?
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Rich
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Re: Real Capability

Post by Rich »

RDGUSLLC wrote: Fri Jul 01, 2022 7:12 pm What is the primary reason(s) of the max weight limitation (landing gear? Structural integrity? Approach stall speed?).
All of the above.

-Landing weight has to do with meeting certification requirements with respect to LG and supporting structure strength.
-Heavier means increased stall/approach speeds and you have to guess at both, since the AFM won't go that high. There is also a real question how far extrapolating the CG envelope is meaningful.
-Max Zero fuel weight is really interesting. Among other things this involves the point beyond which bending moment at the wing attachment point(s) exceeds the design capabilities with respect to gust/g loading.

Whether within limits or not, as you load the airplane more heavily you are certainly losing T/O and climb performance. It's also not likely to be linear, and AFM performance numbers are no help. The real trick is that, while a few pounds probably don't matter, at what point is it no longer a few pounds that don't matter to where it's a few too many that do? So how to know how far to go?
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Colin
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Re: Real Capability

Post by Colin »

I checked my LinkedIn and I have no qualifications to be a test pilot.
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Re: Real Capability

Post by CFIDave »

Ever wonder why all light piston twins have about the same single-engine climb rate at max gross weight (or mass on a metric Diamond): only a little more than 200 fpm? (This is pretty terrible, BTW.)

That's not a coincidence. During certification, the maximum gross weight for a light twin is often raised to the maximum weight that will result in about a 200 fpm climb rate when operated by a factory test pilot. Aircraft manufacturers like to be able to advertise the largest max gross weight (and hence largest useful load) in their marketing materials.

So...what this means is that if you overload a light twin beyond its maximum gross weight, one of the major concerns is that it may no longer be able to climb (or even hold altitude) if you lose an engine. For this reason, some manufacturers and CFIs *recommend" that you should always try to fly your light twin at weights below max gross weight in order to achieve a better single-engine (OEI) climb rate.
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RDGUSLLC
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Re: Real Capability

Post by RDGUSLLC »

Two out of three thoughtful replies! Thank you.

It's an interesting discussion. The single engine certification topic changes the picture dramatically. Given it was pro pilots who flew the certification and still only got 200' a minute @ gross weight is sobering. This would mean that a ferry pilot or over loaders at 20%+ over would not be able to climb or perhaps keep the plane in the air on a single engine.

Ok so that is the reason for the limitation. But back to my original question "what could the plane on two good engines really be capable of?" Would a twin over gross perform better than a Cessna 206 over gross for example? Consider the Meridian Jet prop. They strap on a turbo prop and this leaves them about a 300lb full fuel, useful load. Those guys fly nearly every trip well over gross.

I asked one DA 42 instructor about full fuel, useful load and he initially gave me the standard response + the obligatory 'test pilot' quote. Then I asked what is the real world? His response was the plane is highly capable with two engines and can carry a load. He felt it would be comparable to the 206. Of course the plane does not have the interior room of a 206 so its kind of moot issue. He did not comment on the single engine out issue.
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Re: Real Capability

Post by Chris »

I'd expect the fuel fuel useful load on a DA42-VI to be over 600 lbs, maybe 700 lbs if you don't have the A/C installed. My NG gives me a little under 500 lbs unless I have the TKS also filled. One thing that is really nice about the DA42 is that you can go a long way on not very much fuel, so it's extremely rare that I fill up the tanks. I'll often shoot for 65 gals even for longer legs of up to 4 hours when my wife wants to bring more luggage.

Could the 42 carry 20% more load with two working engines? Probably, though I doubt anybody is going to confess to having done so in a public forum.
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RDGUSLLC
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Re: Real Capability

Post by RDGUSLLC »

Chris,
Thanks for your reply.
No one will confess being a few pounds over and that is fair.

Only once in my 20 years of flying I sweating it. I was in Florida, training for a new Meridian 600 I had just bought. A severe hurricane was in the Caribbean and it was time to get out of Dodge. The instructor said he would continue my training in exchange for taking him, his wife and two kids back to the midwest where I am from. Six people in a Meridian 600 (4 adults and 2 kids) are not a big deal. The 300 pounds of luggage, baby buggy, child seat, books and other paraphernalia + your stuff, put us way over gross. Th plane was absolutely loaded. I would guess 300+- lbs over gross.

It was early September and hot in Florida. However, this guy knew the plane and he had instructed in it for over 10 years. He assured me we were good to go. Of course, it handled it but I did notice the pitch response was very sensitive at take off. I am much more conservative and I respect aircraft limitations. I am also curious if the construction of certain planes make it more or less capable. The DA42 has a unique design. The very long wings and narrow fuselage make it obviously efficient. I was just curious if that efficiency extended to its lift capabilities.
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Re: Real Capability

Post by Karl »

The sensitive pitch comment implies that the aircraft was probably outside the CofG envelope.

It's not just about if the wings can lift the weight but also about where the weight is and how it moves during the flight.

For instance, if you are on (or beyond) the fwd end of the CofG and the fuel burn moves it further fwd you may end up without sufficient elevator control to flare the aircraft.

If you are beyond the rear CofG point the aircraft could pitch up during rotation without the elevator control to prevent a stall.
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