diamondaviators.net

Fact or fiction...? I guess we will find out during Oshkosh.

Apparently all NEW DA40 Lycomings are going to be supplied with a 200lb useful load enhancement vs current, and there will be an STC available to retrofit / do something to older DA40's to provide the same enhancement.

If true... this is significant and kudos to the management and leadership of Diamond.

My understanding of the reason why DA40NGs can have a higher useful load is because Diamond changed the internal structure of the wing stubs (actually part of the fuselage) to accommodate more weight. If they apply this same strengthening to Lycoming DA40s, it would "standardize" production and permit a higher useful load for all new DA40s.

But it's unclear to me how (or if) this change to the internal structure of the wing stubs could easily be retrofitted to existing Lycoming DA40s.

Interesting.

During my conversation years ago with Christian Dries at the Katana Kafe in Austria, I had asked about a useful load increase (and changing to an IO-390, as Cirrus did with the SR-20).

Aside from his contention that the Avgas market was dead to him, he indicated that even with an IO-390, the DA40 would not have adequate performance to support the increased gross weight. I certainly didn't agree with him at the time (and still don't), but glad to see Diamond is at least making an attempt to improve their best airplane (Lycoming powered DA40).

I can only say I'll believe it when I see it. I've analyzed this in quite a bit of detail recently (even though my ancient bird has no real problem with this factor). I'm assuming this will largely be accomplished by increasing MTWO/MLW (that's how the entire industry operates). Three things need to happen to make this added useful load, well, useful:

- Structural beef up somewhere. At least where Dave has said, but possibly elsewhere.
- Empty CG needs to be moved forward somehow. Antoine has suggested building a lighter horizontal stabilizer. This would help, but I believe probably not enough by itself.
- CG envelope needs expansion. Especially for the 50-gallon option.

In particular, retrofit seems impractical. Reworking new airframes seems feasible.

For grins I fiddled with my basic loading (1705 lb, CG 95.5 in., 102 in. aft limit), assumed I could load 50 gallons in it. Long before getting to (the presumed target of) 2850 lb, I would run out of aft CG unless I make sure I have 400+ lb. in the font seats. And I wouldn't want any further forward empty CG than I have now. Those 400 lbs of load in the front seats can't fly alone as it is.

I would think a 200lb MTOW increase without additional power or significant drag reductions would hurt the take off performance enough to make it problematical in many areas during summer. From what I recall 1000fpm in ISA conditions at sea level?
I often see a density altitude of 3-4K in the my local airports which are only 3-5 hundred MSL. Adding 4000 ft of altitude will really reduce the climb margin.

Tim

TimS wrote: ↑Sat Jun 01, 2019 11:41 pm I would think a 200lb MTOW increase without additional power or significant drag reductions would hurt the take off performance enough to make it problematical in many areas during summer. From what I recall 1000fpm in ISA conditions at sea level?
I often see a density altitude of 3-4K in the my local airports which are only 3-5 hundred MSL. Adding 4000 ft of altitude will really reduce the climb margin.

Tim

Arbitrarily increasing MTOW (and using it) no doubt compromises takeoff/climb performance, absent a power increase. This is true for every normally-aspirated airplane you're talking about. And even turbocharged aircraft have their limitations in this regard. Even with the existing DA40 limits this is true. It's always been prudent at higher DA's to think about whether you really need to top off the tanks when you've got a lot of cabin load. Or whether you really need all those people and stuff. In numerous types of aircraft I've done many, many takeoffs at DA's of 8,000 ft. and above (including my Cherokee 140 that had a POH that indicated this was impossible) and this is second nature. My current home airport is at ~3250 ft. and often has DA's of 6,000 ft. in the summer. FWIW, I have no desire to further increase my MTOW, as I'd have a hard time even using it. 940 lb UL is sufficient for me. But for the folks with the newer, heavier, CG challenged ones, it would be very helpful to have some more capacity for situations where performance would be acceptable. Right now they don't have that option (legally, anyway).

Rich,

I agree. Just pointing out in the current market; increasing the MTOW without other changes will mean the plane will not have sufficient performance. Both from a practical standpoint in large portions of the country; and also from a market comparison to other aircraft.

Tim

TimS wrote: ↑Sun Jun 02, 2019 12:55 am Rich,

I agree. Just pointing out in the current market; increasing the MTOW without other changes will mean the plane will not have sufficient performance. Both from a practical standpoint in large portions of the country; and also from a market comparison to other aircraft.

Tim

Note we've assumed no powerplant changes. Lots of unknowns here.

Rich wrote: ↑Sat Jun 01, 2019 11:31 pm I can only say I'll believe it when I see it. I've analyzed this in quite a bit of detail recently (even though my ancient bird has no real problem with this factor). I'm assuming this will largely be accomplished by increasing MTWO/MLW (that's how the entire industry operates). Three things need to happen to make this added useful load, well, useful:

- Structural beef up somewhere. At least where Dave has said, but possibly elsewhere.
- Empty CG needs to be moved forward somehow. Antoine has suggested building a lighter horizontal stabilizer. This would help, but I believe probably not enough by itself.
- CG envelope needs expansion. Especially for the 50-gallon option.

Actually, I have a 2012 DA-40 with the extended range and the various options and a MTWO / MLW increase would work great. The CG envelope is just fine for my (and most) DA-40s (though I admit that replacing some weights in the front with a supercharger would be a nice exchange of useless weight with useful weight).

A 200# increase would be greatly appreciated.

Andrew this sounds like great news. I hope they do!
Rich: I did some calculations back then on the carbon tailplane. It is fairly easy to replicate:
- take a standard W&B sheet, add a station which is the middle of the tailplane and load it with minus 5 or 10 lbs - the result is quite impressive IIRC - keep in mind there is a HUGE moment arm.
- While you are at it, you may want to use the aft CG limit from the 40 USG version, not the 50 USG restriction.
I CANNOT imagine that DAI re-certify the aircraft WITHOUT fixing this "50 Gal aft CG" mistake.
As Jeff Owen once wrote, a check valve between the outboard auxiliary tanks and the main tank would do the trick...
When the outboard tanks are empty, the aircraft's CG envelope is back to normal. and when you are fully loaded with passengers, you probably don't have more than 40 USG on board...