Lead weight in tail fin bulletin

[Kekstrom]

Has anyone done the OSB40-021/2 bulletin for shifting CG rearwards? This includes installing a lead weihght in the tail fin (up to 7,5kg). I am thinking about this as my plane has a very forward CG and causes all sort of troubles with w&b management. At the moment if 2 big guys (above 90kg or so) occupy the pilot and copilot seats, the baggage comp has to be fully loaded + some additional weight on the backseats and then the fuel capacity becomes an issue as the max T/O weight becomes the limiting factor.

[Karl]

Have done it a few times.
Largely depends on where the CG is now.
Its easy to do the SB but I would recommend doing a new CG so you know exactly where it is now. Then run up a spreadsheet so that you can change things around and work out what is the best adjustment and how much weight to add.

[Kekstrom]

Do you know what the moment arm is for the lead weight? Would help in estimation of new cg.. Thanks!

[Rich]

What DA40 variant do you have now? Where is the CG and what is the empty weight?

Mine is somewhat forward CG and gets marginal with two 90kg dudes up front. With the Hartzell Al prop this would be a big problem. I'd be loathe to correct a problem induced by the extra 16 lb. prop weight by adding even more weight in the rear.

Later DA40s generally have a more rearward CG and can handle the Hartzell Al prop wright challenge.

[Rich]

You can get an approximate lever arm with a tape measure

:

Measure from the root rib to an appropriate point on the fin and add 2194 mm (86.4 in.). It won't be exact but the number for the arm will be large enough that you'll be fairly close. It might even be close enough to scale it off this drawing from the POH. Doing so I come up with 6980 mm(275 in.)

I put together a spreadsheet that allows me to play "what if" calculations like this. Given my plane + Hartzell AL it looks like 7.5 kg would handle two 100 kg front seat passengers.

Note that the OSB expects you to reweigh the plane.

[Kekstrom]

Yep 7 meters is about what i figured it would be from the drawings also. I have a Hartzell prop + a bunch of avionics and the plane is quite nose heavy. Two 90-100kg guys in front requires maximum weight in standard baggage compartment (btw the 30kg limit is not really realistic as you can really only but 15-20kg there as otherwise youll exceed the surface load limitation stated in the manual..). And then you run into problems with total weight and have to sacrifice fuel.

Why would you not compensate with the tail weight? As far as I understand that.is the most weight-economical way to shift the cg backwards (longer arm, less weight needed). My mission are always max 2. people (pilot & copilot) basically, also.

[Rich]

Why would you not compensate with the tail weight? As far as I understand that.is the most weight-economical way to shift the cg backwards (longer arm, less weight needed). My mission are always max 2. people (pilot & copilot) basically, also.

If I were foolish enough to put the heavier Hartzell on the plane it would pretty much require the additional weight. So instead of the extra 16-ish pounds of empty weight it'd be over 32 lb.

What avionics do you have that aggravate the forward CG problem? My panel is full of avionics with no room for anything additional.