Ok, got wood, plans and well a questiion or two.

[jim gilmore]

Ok, I'm building a mini-magician. It's just a scaled down magician and NOt from the magician 15 plans. My question is basically  when yu scale a plane up or down. How do you decided if the nose is too long or short. Before your complete it. I'm thinking the nose looks long but definitely do not want it to be short. Engine is going to be an .09.

[Leester]

The nose is long on a Magician, if you had the plans scaled down at say Kinkos or some place similar I wouldn't worry about it.

[jim gilmore]

Tile print

[Kim Doherty]

Jim,

The length of a planes nose is only governed by the need to achieve the correct CofG. While the Magician has what may look like a long nose, you should adjust that length so that you do not have to add any lead to balance the model when completely finished. Start by using full length motor mounts that extend all the way back to the wing. This will serve two purposes. One, the nose will be much stronger and resistant to vibration. Two, you can now cut the nose off at any length and mount the motor to achieve the correct CofG. Before you committ to mounting anything in a particular place and prior to starting the finish, attach all the components with masking tape or rubber bands and balance the model just a hair on the nose heavy side of the Cof G. Since there is more dope applied aft of the CofG, the model should come out right on the correct CofG without needing any balance weight.

Hope this helps.

Kim.

[John Miller]

Kim gives a good method to use for determining these relationships. At the risk of being scewered for using math outside of the engineering thread, there's a simple mathematical way to determine a close approximation.

First, consider that the nose has to be long enough to mount the engine, and tank comfortably.
Second, determine the wings CG at the MAC.
Third, measure the distance from the CG forward to the approximate center of mass of the engine,prop, and spinner.

Get the accurate weight of the engine, prop, and spinner.

Do the same for the tank, and also the landing gear.

Estimate the total weight of the fuselage itself, and figure that about 25% of that weight will be forward of the CG.

This now means that 75% of the fuselage weight will be aft of the CG.

Figure the approximate center of masses for the portions of the fuse, on either side of the CG, and this will be your length.

Estimate the weight of the stabs,, rudder, and elevators.

The formula looks like this.

(A*L1)sq'd +(B*L2)sq'd +(C*L3)sq'd + (D*L4)sq'd = (E*L5)sq'd - (F*L6)sq'd

Plug in the weights, and lengths that are associated with each other. Work the simple algebra, and you'll be left solving for L6, the legnth to the centerr of mass for the stabs and elevators. Your tail moment. Be sure and remove the sq by using the sq root function.

This will get you very close to a balanced condition, as long as your actual weights are close to what you estimated.

You can work even closer by inserting more component weights if you want to, but the above will usually be good enough when all conditions are considered.

Since I've always been math challenged, I may have made an inadvertant error. If so, I'm sure that someone will correct me.

[Jim Thomerson]

Which 09 are you thinking about? A TD 09 will fly the Magician 15 just fine.

[jim gilmore]

I have the AP .09 but I'm considering the thunder tiger for $49 from Randy. Which is most likely what I'm going to go with. While there is a magician 15 I'm using MY wing build and a fuselage from scaled down a scaled up magician 3-view I have. My wing is basically a "d" tube I think but I use arrow shafts for keeping it straight while building and my ribs all get cap strips from the l.e. to trailing edge.