Bush Baby weigh/balance advise needed

[flykr]

I did the WB on my BB this weekend and after entering all the relevant weights into the WB spreadsheet (got this from Monty) found that in all conditions the CG falls in front of the CG range….so the BB is too nose heavy
Here are the weights:
- Empty weight = 260.9kg (is this weight heavy for a BB)

- Empty (zero fuel): Left 126 Right 130 Tail wheel 4.9 (cg 173.3)
- Pilot: Left 175 Right 159 Tail wheel 8.5 (cg 196.9)
- Pilot + Pass: Left 208 Right 212 Tail wheel 12 (cg 208.5)

(CG range 268-373)

- Standard tail dragger BB fitted with a Rotax 582 (P Prop)
- I used the bottom longeron between the gear attachment points as a horizontal reference (is this the best point of ref)
- Three electronic scales used, readings where checked for accuracy and found to be okay.

Before I start moving the battery around can the BB x-perts check if I’ve not overlooked something.

Thanks guys

[Morph]

you need to get the plane into flying attitude, i.e. the wingtips parallel with the ground

then drop a plumb line from the leading edge, (this is the datum)

now measure the distances from this line to the mainwheels and the tail wheel

then we can work it out for you

260kg is spot on, in fact, shave off .9 kg so you can fly it on a standard MPL and not a Sport Pilot licence

I have attached a COG calculation based on the front wheels being 100mm behind the datum and the tail wheel 3952mm. These I got from Boet and are typical values

Yes empty I read 172.34 mm, with a pilot 261mm (minimum should be 268) and full 327mm

By moving the battery to the luggage shelf, 850mm back, the pilot only becomes 271mm and 333 full. Perfect.

Alternatively by adding 700grams to the tail, you are perfect

[flykr]

Thanks Morph. I’ll re-check my calculations again this weekend. I’m sure the elastic under-carriage has something to do with the weight moving forward when it flexes, I didn’t check the levels again when I was sitting inside the plane.
All I need is an extra 1kg on the tail and I’m okay.

Thanks for the info and spreadsheet

Cheers

[Morph]

When I built my BB I put a round inpection hatch in the farbic at the tail, (incase I decided to go tailie later) Apart from making it easy to add the little wheel it also makes it easy to add a little weight. Wheel weights, or shotgun pellets in a bag and cable tied to the fuse, viola

[Boet]

Fly KR, contact me before starting major modifications. Boet 082 8041896

[KFA]

Hi flykr. There is a set procedure to follow for the weight and balance.
1. Empty all the fuel out of the maintanks and header to determine the BEW(Basic empty weight). Engine fluids up to level.
2. Secure the legs to the bungee trusses with rope to prevent the suspension from flexing.
3. Set the aircraft level in the flying attitude. Use the bungee trusses as the datum or the roof.
4. Hang a plumb line from the leading edge (in line with the spar bolt) to the floor and mark this position on the floor. Do the same on the other side. It's a good idea to mark this position on the door entrance for future reference.
5. Hang a plumb line fom the centre of the wheel axle to the ground and mark on the floor ( both wheels). Do the same with the tailwheel and mark it on the floor.
6. Connect the leading edge mark lines on the floor with a a straight edge and measure the shortest distance from this line to each wheel marked on the floor and record them.
7. If the aircraft has to be moved on to a scale use blocks or other device that is of same height as the scale and role the aircraft slowly on and of the scale taking the weight readings of each wheel and recording them. Remember to zero the scale after each reading.
These calculations will give you your BEW.

Step 2 ( Calculating the Extreme forward COG or minimum flying config)
Fill the header tank ( approx 5l)
The unusable fuel will be in the region of 1.5l per side
Get a very light pilot (50kg) and weigh the aircraft again. Recording all the weights.

Step 3
Now Do the same but fill up with fuel and two heavy pilots in the seat and you can also add luggage to get up to gross weight.

Step 4
Measure all arms, every aircraft is different. Measure the MAC from wing leading edge to the trailing edge of the flapperon. can be from 1290-1315mm.
Calculate the COG range by taking the MAC and muliplying it by the % (20.5 and 28.5%) This will give you the range in millimeters from the leading edge.
eg an MAC of 1290 will be 264mm-368mm

Step 5
PHONE US ON
082 601 8970 and I will send you the correct C of G spreadsheet.
Regards
Stefan

[flykr]

Hi Guys,
Thanks for all the support. I’ve spoken to Stefan and Monty who have given me the correct procedures to WB the BB. I’ll let you guys know what the outcome is next week

Cheers

[flykr]

I redid the WB this weekend and found that my measurements to the main gear and tail wheel where different to what was recorded on the WB spreadsheet. After correcting these measurements my CG is now within limits.

A simple error but I'm glad I rechecked it before moving things around

Now I must fix the leaking fuel tank and she will be ready for her first test flight

Cheers

[grostek]

I redid the WB this weekend and found that my measurements to the main gear and tail wheel where different to what was recorded on the WB spreadsheet. After correcting these measurements my CG is now within limits.

A simple error but I'm glad I rechecked it before moving things around

Now I must fix the leaking fuel tank and she will be ready for her first test flight

Cheers

Hi flykr,

Must be a big relief that the W&B is OK.

Good luck with the leaking tank.

Kind regards,

Gunter Rostek.