Fixing the nose heaviness of the DA42-VI

[Antoine]

I am building a spreadsheet to model the influence of various solutions on the forward CG issue of Austro-equipped DA42, and in particular the VI.

I need the following info:
Moment arm of the full aircraft and empty weight for the following configuration:
DA42-VI with TKS, long range tanks and weather radar, no A/C.
Same with factory O2 (where is the factory O2 bottle installed?)

I will post here the following results
1. Present situation (TKS in front)
2. Move the TKS tank to the back (Diamond MäM)
3. Leave TKS where it is (front) install O2 bottle in the back

Any other ideas welcome.

[Tommy]

Quite frankly, excluding the benefits because there are many, the weight, and only the weight is the 800 lbs. gorilla in the room that seems to want to be ignored at all cost. It's a stumbling block I can't get over.
One should not have to try to fix a weight and balance problem on a 1.3 million dollar airplane at the cost of sacrificing an already dismal useful load.

[Gnomad]

Quite frankly, excluding the benefits because there are many, the weight, and only the weight is the 800 lbs. gorilla in the room that seems to want to be ignored at all cost. It's a stumbling block I can't get over.
One should not have to try to fix a weight and balance problem on a 1.3 million dollar airplane at the cost of sacrificing an already dismal useful load.

The -VI is NOT a 1.3 million dollar plane. With the current USD strength over the EURO, unlikely you could even make it to a million fully spec'd out. I'd call it a 900k plane, just saying...

Useful load is definately a bummer, but isn't that the case with most planes? A/C in the back pretty much solves the W/B probs on mine.

Antoine, I can't provide you the numbers you seek, specifically because I have the AC. From what you have listed, I would DEFINATELY move the TKS to the back and add WAAS(US pilot) Oxygen tank is located in the nose, you could always go portable to get more weight out of the front, if necessary.

IMO, the location of the TKS reservoir is the 800lb gorilla!

[Antoine]

Update. Just got a "real" W&B report from Diamond from a recent conversion.

The CG is located at 2.386 m and empty weight is 1439 Kg (with ADF/DME, weather radar, no oxygen, no AC)
This plane was subsequently outfitted with 9.5 Kg of ballast in the tail but I disregarded this here.

So I redid the modeling - conclusions have changed significantly so I edited this post.

Tested 3 loading scenarios and various fuel and TKS tank conditions.

A) 2 PAX = 140 Kg no luggage (that's the two of us with no luggage). Intended as a worst case forward CG
2) Same as above plus 50 Kg luggage (this is my typical mission)
3) 4 PAX, total 280 Kg plus 40 Kg luggage (us and another couple, happens occasionally)

New findings:

1. Aux tanks are very much aft of CG - filling them pushes the CG substantially backwards when filled. Conversely, CG sweeps quite a lot from AFT to FWD limit as the tanks deplete from full to empty. Very different from DA40 and a real headache.
A similarly large movement happens when the TKS tank is depleted. If the TKS tank is forward, the two sweeps somewhat compensate for each other.
This tells us TKS in the back is a bad idea - The CG sweep will be exacerbated so that it will be impossible to use luggage to center CG across a flight leg.

2. Optimum placement is TKS in the nose and oxygen tank (assumed 5 Kg) in the back.

My general conclusion is that each DA42-VI should be carefully designed so that its specific equipment is distributed in such a way as to provide good W&B characteristics. But this alone is not enough.

The position of the extended fuel and TKS tanks dictate that EVERY leg be carefully planned from a W&B perspective and that luggage be shuffled around before each leg to ensure that the CG remains OK as fuel and TKS fluid levels change.

Idea: carry one or two TKS fluid canisters (10 liters or 2.5 USG - 11Kg each) to be used as fwd or aft ballast as required and -obviously- as an "out of jail" TKS refill when on a long trip and no TKS available on the way.

[CFIDave]

Quite frankly, excluding the benefits because there are many, the weight, and only the weight is the 800 lbs. gorilla in the room that seems to want to be ignored at all cost. It's a stumbling block I can't get over.
One should not have to try to fix a weight and balance problem on a 1.3 million dollar airplane at the cost of sacrificing an already dismal useful load.

I don't see where you're getting the 1.3 million dollar figure -- maybe you were thinking of the forthcoming DA62 that's intended to compete with $1.3M G58 Barons or Piper Senecas?

Without radar but with every other option including AC, the "dash six" right now is a $900K airplane -- and getting cheaper by the day as the euro keeps dropping relative to the dollar. If you put a deposit down on a new one now and wait 6 months for it to be built (since there's still a 6 month waiting list), and based on where most financial analysts are predicting the dollar/euro exchange rate will be in 6 months, it's going to become a $750,000 airplane -- cheaper than comparably-optioned Cirrus SR22T G5, Cessna TTx, or Bonanza G36 singles.

The balance "problem" has an easy solution for new DA42-VI aircraft: order air conditioning like Eric and I did, or have the TKS tank installed in the back -- either will shift the CG aft. There is no weight problem, especially with the 99 kg/220 lb recent weight increase for the DA42NG/-VI.

[Tommy]

I just wanted to get everybody excited.

[Chris B]

I just wanted to get everybody excited.

Mission Accomplished!

[Antoine]

FYI just edited my post above based upon real world data. Different conclusions

[CFIDave]

It may be worth sharing what actually happens flying when the DA42 is loaded so that the CG is forward of the published forward limit. This was with a full TKS tank and the rear-mounted air conditioning compressor temporarily removed to fix a refrigerant leak, while still having the weight of a 3rd alternator (to power the AC) up front.

While I can't recommend flying that way, it's not a big deal: The only negative is that after you touch down on the main gear and and airspeed bleeds off, there will come a time when the elevator has insufficient authority to hold the nose up, and then...the nose gear will plop down on the runway. There's still plenty of elevator authority at speeds above stall when you need to flare before touchdown. Exceeding forward CG theoretically also makes the aircraft more stable in pitch, but I couldn't tell any difference.

I'd be much more concerned if *AFT* CG was exceeded, since that's when an aircraft can become unstable in pitch.

[carym]

A) 2 PAX = 140 Kg no luggage (that's the two of us with no luggage). Intended as a worst case forward CG
2) Same as above plus 50 Kg luggage (this is my typical mission)
3) 4 PAX, total 280 Kg plus 40 Kg luggage (us and another couple, happens occasionally)

Antoine,
I don't know about Europe, but the day of the 70 Kg PAX, even if naked, is long gone in the US.
You may have to reconfigure your weight and balance data.