Another Ozzie Extreme Composites 40% Extra 260 Build

[b0Bro's dad]

After all the noise about the tank location, I needed to do a proper aircraft weight and balance before I located the rudder tray and batteries to make sure the CG came out exactly where I wanted it. The procedure was pretty easy, requiring only video/cd cases to level the aircraft, a square to make sure it was level, a tape to measure distances from the datum point, and a sensitive set of scales (max weight 35 kg accurate to 2 g).

I started by removing the engine and cone and, after cutting the new carbon wing and tail joiners to size, fitting the wings, stabilisers and rudder (complete with servos and cabling). I levelled the aircraft by placing a stack of video and CD cases under each wheel until the square showed that I had the firewall perpendicular. I then substituted the sensative scales for part of the stack under each wheel, and measured the weight of each wheel in turn. Using the firewall as the datum, I measured the longitudinal distance to each wheel and recorded the mass and arm for each wheel in an Excel spreadsheet. I then measured the mass of each of the other parts to be fitted (engine, cowling, batteries, rudder tray etc) and the distance between the centre of mass for each component and the datum point (firewall). The weight and arm for each component were added to the spreadsheet.

The moment for each component was calculated by multiplying it's weight by it's arm. Then all of the weights and all of the moments are summed. The total mass is the sum of all of the component weights and the CG relative to the datum is calculated by dividing the sum of moments by the total mass.
Then it was simply a matter of moving (changing the arm) of the rudder tray and batteries until the CG came out exactly where I wanted it (25 mm in front of the centre of the wing tube. Fortunately, this showed that could add the additional 2 tail servos as long as I was 'generous' with the engine baffling. The method can also be used to calculate how much ballast is required at what location to move the CG to any desired location.

Although I'll redo the weight and balance when everything is properly installed, according to my interim weight and balance calculations, Byrons Extra should end up:
Empty weight 21.717 kg with CG at -280.0mm relative to the firewall, and
Loaded weight 23.184 kg with the CG at - 278.2 mm relative to the firewall.

I've attached some photos and the CG calculation spreadsheet for those that are interested.

[b0Bro's dad]

Having worked out exactly where I wanted the rudder tray, I now needed to construct the support structure for the SWB 3 Servo Self Adjusting tray. I had planned to construct this with aluminium angle 'beams' but Byron and a few others suggested the metal to metal might create RF interferance, even if I insulated the joint. Ah well, I won on the fuel tank location so now it was time for Byron to get his way on the rudder tray.

I started by marking the locations for two tranverse part frames in the bottom of the fuselage and using some scrap ply as a template to work out the exact shape required at each location. That done, it was easy work with a tenon saw and face sander to cut the frames from 2mm birch ply. I glued 8mm square section spruce along the top edge and used another short piece as a doubler under the attachment point. I reinforced the attachment point with a top plate of 2mm birch ply before drilling each former and fitting 2 x 3mm blind nuts for the attachment.

I assembled the formers to the SWB Rudder Tray with 3mm cap head bolts and fitted 2 x 3.5mm carbon thrust braces before I glued the whole assembly into the aircraft with epoxy. Next morning, I undid the bolts to remove the SWB rudder tray and used a thick paste of epoxy and micro-ballons to fillet all the sub-frame joints and add a small thrust brace behind the rear sub-frame.

While that dried, I assembled the 3 x Hitec 5955TG servos into the SWB Servo Tray as per the instructions and used the Hitec servo programmer to centre all of the servos before I bolted the completed assembly back into the aircraft. Pretty fiddly but very satisfying to see it all fitted in place. It's starting to look like a proper model now.

[b0Bro']

Now where talking my kinda language with that rudder tray! So glad you decided to ditch the aluminum strut idea... I'll have to find time next week to come up and help with the rest of the wiring and programing. Just need to also fit in time to practice for pdarcs as well. But i really like that tray, good stuff dad!

[DesertHucker]

This is the one i use

CofG.zip

	Quote: Originally Posted by b0Bro's dad
	After all the noise about the tank location, I needed to do a proper aircraft weight and balance before I located the rudder tray and batteries to make sure the CG came out exactly where I wanted it. The procedure was pretty easy, requiring only video/cd cases to level the aircraft, a square to make sure it was level, a tape to measure distances from the datum point, and a sensitive set of scales (max weight 35 kg accurate to 2 g). I started by removing the engine and cone and, after cutting the new carbon wing and tail joiners to size, fitting the wings, stabilisers and rudder (complete with servos and cabling). I levelled the aircraft by placing a stack of video and CD cases under each wheel until the square showed that I had the firewall perpendicular. I then substituted the sensative scales for part of the stack under each wheel, and measured the weight of each wheel in turn. Using the firewall as the datum, I measured the longitudinal distance to each wheel and recorded the mass and arm for each wheel in an Excel spreadsheet. I then measured the mass of each of the other parts to be fitted (engine, cowling, batteries, rudder tray etc) and the distance between the centre of mass for each component and the datum point (firewall). The weight and arm for each component were added to the spreadsheet. The moment for each component was calculated by multiplying it's weight by it's arm. Then all of the weights and all of the moments are summed. The total mass is the sum of all of the component weights and the CG relative to the datum is calculated by dividing the sum of moments by the total mass. Then it was simply a matter of moving (changing the arm) of the rudder tray and batteries until the CG came out exactly where I wanted it (25 mm in front of the centre of the wing tube. Fortunately, this showed that could add the additional 2 tail servos as long as I was 'generous' with the engine baffling. The method can also be used to calculate how much ballast is required at what location to move the CG to any desired location. Although I'll redo the weight and balance when everything is properly installed, according to my interim weight and balance calculations, Byrons Extra should end up: Empty weight 21.717 kg with CG at -280.0mm relative to the firewall, and Loaded weight 23.184 kg with the CG at - 278.2 mm relative to the firewall. I've attached some photos and the CG calculation spreadsheet for those that are interested.

[DesertHucker]

I keep trying to upload this ZIP file but seems to become corrupt when downloading it.
If anyone would like a coppy of it PM me and i will email it to you.

[RH1N0]

	Quote: Originally Posted by DesertHucker
	I keep trying to upload this ZIP file but seems to become corrupt when downloading it. If anyone would like a coppy of it PM me and i will email it to you.

The file works Lozza but there is some sort of WinZip incompatibility with this site. If you "save as" and then unzip it with WinRar it works fine.

BTW, we use the arm/station method on the full size planes at work but I've never had the need (or patience) to use it on model planes. But I can understandand how it must be good reassurance when the calculations allign with what looks about right.

[DesertHucker]

	Quote: Originally Posted by RH1N0
	The file works Lozza but there is some sort of WinZip incompatibility with this site. If you "save as" and then unzip it with WinRar it works fine. BTW, we use the arm/station method on the full size planes at work but I've never had the need (or patience) to use it on model planes. But I can understandand how it must be good reassurance when the calculations allign with what looks about right.

Thanks mate,
Just tried total comander unzipped it fine.
Strange.

I use 3 scales only takes a minute with laptop at my side

[DesertHucker]

That rudder tray looks good. it aint going no were.
Good job Ian

[Stu_D]

Time to put her in the air now boys . I see no more than two more nights work there . I know your not stalling for time so as the saying goes "JUST DO IT" . Your flying so well now Byron its a pitty the plane is the only thing holding you back .

Stu

[3dubya]

	Quote: Originally Posted by b0Bro's dad
	CG calculation spreadsheet for those that are interested.

Far out thats full on calcs,

[b0Bro']

lol thanks stu, i am a little keen to get her in the air now...

[b0Bro's dad]

Dear Byron,

If there is one thing I hope to have taught you (apart from never buy cheap tools), it is to do your best in all things. I was proud of your first place in your last competition, and prouder still that you have been bumped up a class where the trophies will be harder to earn. Your new plane will be finished when I'm satisfied that I have done the best job I can....and hopefully that will be before Bendigo.

Things still to do:
- fit the canopy
- complete the wiring
- fit two more cooling baffles under the canisters
- install the fuel plumbing
- build up the diameter of, and fit the tail tubes and locking nuts
- fit all the control horns
- locate and drill holes for, and fit the rudder cables
- fit the nylon bushes and carbon hinges on all surfaces
- fit the control linkages and program servos for desired control throws
- fit baffling into the cowling
- do a final CG calc and adjust CG as necessary
- wet sand and polish out all of the paint 'masking ridges'
- run in the engine
- get a CofA
- and last but not least, talk Tony into doing the test flying

Sadly Stu, I suspect that list might take more than a couple of days to complete.

Cheers,
Ian