mikekuepper

LIGHTNING experts, please help to proper balance CG!

have built C-ARF Lightning and need to finish now the RC-gear installation.
I use P-160 turbine, JR-radio ( Graupner MC-24 EMCOTEC dual frequency + 2 x SMC 20 DSYN ) Emcotec DPSI-Twin with 35 + 40 MHZ receivers.
Same configuration as in my Strikemaster (Jetwelt Peter Mayer and very sorry to say, was used in my Eurosport which catched fire in air last season)
The 40 MHZ antenna is installed in the left wing, 35MHZ wip antenna as shown in the manual, center top of fuselage.
All servos are Graupner-8811, nose gear Hitec

the lightning is my first Jet equipped with FUEL-WATCH telemetries, great technology, always online with the fuel quantity on board.
Transmitter and air unit not yet fixed in the fuselage, will be in the front of the canopy section, need to make field test to ensure not having and interference with the RC gear
I hope Markus will finish the design of the "radio fail-safe" module soon, so I will have also information which transmission is operating ( 35 or 40MHZ ) on my radio.
Landing Gear original C-ARF Behotec based set
BVM UAT installed in the position of the hopper tank which comes with the kit.

I have provision fixed batteries and air tank on piece of 3mm plywood, bolted on top to the BEHOTEC front landing gear mechanic with M4 spacers.

I am a bit confused about the way to balance CG.
Manual 1.1 asks to balance the plane - wings off! - on the wing tube, which I did. Batteries are fixed front of the plywood piece which reaches into the nose cone, no extra lead necessary to achieve the plane balanced.
So far so good!
The manual specifies CG -wings on!- 5cm ( 2inch ) IN FRONT of the centre of wing tube! The wings no doubt create a back force moment, as the landing gear is behind the wing tube, so the CG never can move forward wings off!

Could someone who already operates a Lightning please assist me how to balance the plane, maybe the CG wings on is 5 cm behind the wing tube, then the procedure to balance wings off on the wing tube seems more logic to me.

Mike

Robrow

Mike, you are correct on both counts, you should use the wing tube as a rolling fulcrum pivot(this is what is meant by 'on the wing tube') and balance the fuselage (minus wings) at the 2" position, that is 2" in front of the fuselage wing tube hole.

Hope thats clear enough, I found this position is in a safe forward position which requires around 2mm of up elevator trim for straight/level flight.

There are a lot of other experienced Lightning pilots here and some have some more complex methods of cg calculation using weight on each wheel.

Rob.

SAP_2000

Now I got confused.

How can the plane be balanced on the wingtube if the CG is suposed to be 2 inches in front of the wing tube hole (or app. 3 inches in front of the center of the tube)
Wouldn't the plane just tip forward?

I'm also building mine, but haven't gotten as far as balancing yet...
My understanding was that it was suposed to be balanced on the wing tube minus the wings, making the CG at the wing tube minus the wings. Now I'm unsure??

Robrow

OK, I thought there might be some confusion. First of all take the fuz (minus the wings) and sit it on top of the removed metal wing tube so that the tube acts as a roller and you can freely push the fuz backwards and forwards. This should be done on a flat surface.

The fuz should now balance at a point 2" in front of the empty tube hole and not 2" in front of the actual tube which is currently acting as the rolling fulcrum balance point.

Hope that's clearer.

Rob.

harpoonlightning

Hello Mike,
I have flown for 4 months with a lightning equipped Simjet Nexus 16,3kg. The centering of the note is the good and the method is very practical. My lightning is centered to 4,5 cm in front the hole of wingtube.
I have to put 400 G of lead in front of the nose gear with two accumulators lipo 7,4v 4800 my for the radio reception and 1 lipo 11,1 v 3200 my for the turbine in the nose of the lightning.
best regards Michel

mikekuepper

Dear colleges

Thanks for your help!
I have ballenced the plane on the wing tube installed and was wondering why most people I read in various articles add lead to the nose, now I understand the procedure and will use standard batteries for RC and turbine, fixed to the plywood spacer which reaches into the nose cone.
Would have loved to use LIPO´s and get the plane a bit less heavy then with standard ones.
Not worth to spend a lot of money for new generation batteries if you finally need to compensate with lead to get correct CG.

Anyway I look forward to my first flight, normally this will not happen before March in our aerea, but weather this "winter" is funny so might be I can start earlier.
Will keep you posted, hope to have great fun with the plane!

Mike

mikekuepper

hello, guess this to be the way it should be done, thanks again for your help

Mike

Robrow

You got it

Rob.

SAP_2000

Ok. Got it now. Thanks Rob and Mike!

As I understand it: When you put the wings back on, the CG moves aft. How much more aft does it move?
Does it move far enough back so you could balance it with the wing tube installed and wings on?

Would be an easy way to do it if you could leave a litlle gap between the fuse and wings and hang the airplane from the roof with a string tied to the tube....

pilott28

My Feedback: (27)

The balance point with wings on, residual fuel in the tanks and gear down is 53.75 inches from the tip of the nose.

If you have access to a baby scale, I have a spreadsheet that allows you to balance big planes like this very quickly. I actually bought three for less than $100. The procedure calls for a few measurements to be put in the spreadsheet, the plane is put on the three scales ... one for each wheel .... and the weights are put into the spreadsheet. The formulas compute the CG and tell you how much nose weight is needed to get to the factory specified CG. Very nifty and simple way to do W&B on large planes.

If you only have one scale, you can block up the other two wheels to keep the plane level and just take one weight at a time.

Good luck with the Lightning, I think you will like it.