Instructions for building plane without kit?

[bernard]

I have finished the wings, horizontal stabilizer, vertical fin, and motor stick. I have made a socket connector to attach the wing and horizontal stabilizer with the vertical fin. I saw that on the Finny 09 plan, the stick that connects that tail, the tail boom, is slanted down. Is there any benefit of this? I was thinking about making the tail boom flat.

If I've been told correctly, a benefit is the stabilizer does not get turbulent air passing from the wing.

[jander14indoor]

That's the common wisdom, not seen much data to see if it is correct.

As a practical matter, not sure it really matters. You see that style tail come and go in indoor plane designs, both very successfully in competition. I suspect the relative success has more to do with the skill of the flyer than the physics of the design.

Jeff Anderson
Livonia, MI

[Kyle_Guo]

I have finished my plane and I am placing the center or gravity is 1/2 above the trailing edge. Here are the weights of my plane:
wing: 1.79 g Tail+tailboom: 0.89 g prop: 0.96 g MS: 3.71 g With a total of 7.35 grams. This leaves me with 0.15 grams of ballast (clay in the FF kit) to play around with for the CG.How do you cut out exactly 0.15 g of clay? I'm planning to move the wing as little as possible, keeping it at 1 1/2 inch behind the prop. Is 0.15 grams enough to alter the CG?

[bernard]

I have finished my plane and I am placing the center or gravity is 1/2 above the trailing edge. Here are the weights of my plane:
wing: 1.79 g Tail+tailboom: 0.89 g prop: 0.96 g MS: 3.75 g With a total of 7.39 grams. This leaves me with 0.11 grams of ballast (clay in the FF kit) to play around with for the CG.How do you cut out exactly 0.11 g of clay? I'm planning to move the wing as little as possible, keeping it at 1 1/2 inch behind the prop. Is 0.11 grams enough to alter the CG?

Great job on recording your masses. It depends on where your CG already is and which direction and how far you want to move it. If your CG is too far forward, very little clay at the tip of the tail will pull the CG backward easily. It's harder the other way because the nose is shorter: the same amount of clay at the tail has a larger moment than that amount at the nose, like an asymmetric seesaw.

Are you using the Freedom Flight kit? If possible, for my own curiosity, I'd like to see a picture.

[Kyle_Guo]

How do you add pictures into the post? I have taken 2

[Unome]

How do you add pictures into the post? I have taken 2

Currently it looks like file uploads are broken. I'd recommend uploading your images to an image-hosting site such as imgur or postimage and using the direct file link (it should have the original file name at the end of the link) inside a set of image tags:

Code: Select all

[img]Put the link here[/img]

[Kyle_Guo]

This is one picture

Link (shared to anyone on internet):https://drive.google.com/file/d/0Bwl5kC ... sp=sharing

[bernard]

Beautiful plane, Kyle. They take a long time to make and you did a great job. Do you have a place to fly it with little air turbulence? Did you use the Freedom Flight kit? Did you try crinkling the mylar before attaching? (The snow!)

[bjt4888]

Kyle,

Excellent job of recording part weights. Your airplane looks very competitive. I have entered into the Bernie Hunt design spreadsheet your supplied part weights and the full size dimensions of the wing and stabilizer from the rules and an estimate of 14" for the motor stick and and estimate of 12" for the tailboom and find that the calculated static stability margin of your airplane is a negative 18% if you intend to keep the nose length at 1.5" and the center of gravity at 0.5" forward of the wing trailing edge.

This is not likely to be a successful starting point for CG. This design spreadsheet does a very good job calculating a starting point for static stability margin and CG and it should be at least slightly positive for a good result.

Please reply with the exact length of your motor stick, the exact length of your tailboom and the dimensions of your stabilizer (width (called the "chord"), length (called the "span") and shape (as it appears semi-elliptical).

If you send this information right away, I can enter into the design spreadsheet and give you a better starting point for nose length and center of gravity.

Brian T.

[Kyle_Guo]

Kyle,

Excellent job of recording part weights. Your airplane looks very competitive. I have entered into the Bernie Hunt design spreadsheet your supplied part weights and the full size dimensions of the wing and stabilizer from the rules and an estimate of 14" for the motor stick and and estimate of 12" for the tailboom and find that the calculated static stability margin of your airplane is a negative 18% if you intend to keep the nose length at 1.5" and the center of gravity at 0.5" forward of the wing trailing edge.

This is not likely to be a successful starting point for CG. This design spreadsheet does a very good job calculating a starting point for static stability margin and CG and it should be at least slightly positive for a good result.

Please reply with the exact length of your motor stick, the exact length of your tailboom and the dimensions of your stabilizer (width (called the "chord"), length (called the "span") and shape (as it appears semi-elliptical).

If you send this information right away, I can enter into the design spreadsheet and give you a better starting point for nose length and center of gravity.

Brian T.

The motor stick is 16" and the tail boom not including the stabilizer, is 3 3/4" and including stabilizer is 7 1/2" Should the tail boom be as long as 12"? The chord of the stabilizer is 3 1/4" and the span is 8 3/4". The shape of it is similar to a rectangle with semicircles on the ends. It has straight front and back edges and curved ends.

"With a wing weight of 1.5 grams and a prop weight of about 1.6 grams, this will give you an all up weight of about 6.3 - 6.5 grams, allowing 1 - 1.2 grams of ballast that you can move around to vary center of gravity.
6. Probably you'll find that a nose length of about 2.5" will be required (instead of the 1.5" shown on the plan) to give the correct center of gravity if the ballast is located about 4" from the nose. This ballast location should be a good compromise to all CG adjustment in both directions."

I changed the nose length to 2.5" like you recommended so if you are to enter the data into the spreadsheet, change the nose length.
I also wonder that if I Offset of the tail boom which direction will it help turn.