Mistake with fuselage cutting - RC Groups
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Nov 09, 2017, 06:00 AM
Registered User
Question

Mistake with fuselage cutting


Hello
I'm building a balsa trainer.I tried to cut the fuselage by copy the plan and attach it to the balsa with glue stick.
Probably the copy wasn't accurate so the fuselage didn't become exact.The place of the wing and stabilizer are still the same ratio but it's a bit narrower.Is it so bad?In model airplanes aerodynamics book that I have it says about the figure of the body that it's almost rectangle so it seems that it's not so critic.
It's a balsa trainer with 60 inch wingspan, similar to pt-40 or tower trainer.what do you say?
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Nov 09, 2017, 10:10 AM
An itch?. Scratch build.
eflightray's Avatar
The main things to aim for are --

the wing and horizontal stab are level with each other, when looked at from the front or rear,

the incidence angle, (the angle between the wing chord line and the horizontal stab) are as the plan shows),

the fuselage is straight, (not banana shape), so that the vertical stab is inline,

the horizontal stab is flat, no twist or warp,

the wing has no twist or warp, (except where specified, e.g. wash-out).

Get those right, and the rest of the plane will follow where ever they go.

Ray.
Nov 09, 2017, 11:03 AM
Registered User

Thanks a lot!


thanks
Nov 14, 2017, 03:37 PM
Registered User
Kardanas's Avatar
Oooor...
I might get slapped for this post, but actaully if you dont have anything drastic, your machine will fly anyway. Might be slightly weird, but you can trim it out to have something half decent. Better focus on having air time to learn flying and only then try perfecting models.
Nov 15, 2017, 10:27 PM
Registered User
All true.

That said, NO plane is trimmed right sitting on the ground before the first flight, no matter how micrometer-measured perfect it looks.

The hardest thing for a newbie to learn is to simply fly. Learning how to do that with a badly trimmed plane is recipe for disaster.

Doing a first flight on a VERY badly trimmed plane is difficult even for an experienced pilot. With balsa you have only -one- chance to fly it and 100 ways to crash it. (Been there, done that, ALMOST went home with a bag of toothpicks. LOL!)

Do you have an experience friend that can do the first flight? You will have 1000x better chance of successful first experiences if the plane is trimmed IN FLIGHT at least vaguely properly.
Nov 16, 2017, 07:15 AM
Registered User

sure I'm not going to do the test flight alone


But do I need to be worry about this mistake and cut the fuselage again or it's not so bad?
Quote:
Originally Posted by jbarchuk
All true.

That said, NO plane is trimmed right sitting on the ground before the first flight, no matter how micrometer-measured perfect it looks.

The hardest thing for a newbie to learn is to simply fly. Learning how to do that with a badly trimmed plane is recipe for disaster.

Doing a first flight on a VERY badly trimmed plane is difficult even for an experienced pilot. With balsa you have only -one- chance to fly it and 100 ways to crash it. (Been there, done that, ALMOST went home with a bag of toothpicks. LOL!)

Do you have an experience friend that can do the first flight? You will have 1000x better chance of successful first experiences if the plane is trimmed IN FLIGHT at least vaguely properly.
Nov 16, 2017, 09:11 AM
An itch?. Scratch build.
eflightray's Avatar
Post #2 explains the basic requirements.

You just need something to attach the wing, tail, and motor to at the correct angles, it doesn't matter what the fuselage shape is, (though really ugly ones may get criticized ).

The accurate parts are the wing and tail, and even then just about any shape will work, just try to minimize any twists and warps, or at least try to match them each side.

Models don't have to be perfect, they don't have to follow the exact lines of a plan, or be critical regarding dimensions. Adding or losing an extra 1" to a fuselage width or length wont really make much difference.

In the scratch builders forum people often make up a design without even the need for a plan, and they work, generally.

Please don't worry so much, it's a hobby, it's meant to be fun and enjoyable . If you worry at this stage, you will probably never fly the model.

Relax, if you have any problems you feel are of major concern, post them, and include some pictures, pictures always help.

Ray.
Nov 16, 2017, 09:48 AM
Registered User

wing-horizontal stab angle


There is any easy way to measure the angle on the cutted fuselage?
thanks to all the answers
Nov 16, 2017, 09:57 AM
An itch?. Scratch build.
eflightray's Avatar
What model name/plans are you working on ?

The more information you can give the easier it is to answer.

Ray.
Nov 16, 2017, 11:07 AM
Registered User

It's an self designed plan that i copied from someone


Quote:
Originally Posted by eflightray
What model name/plans are you working on ?

The more information you can give the easier it is to answer.

Ray.
15 years ago
Nov 16, 2017, 02:23 PM
An itch?. Scratch build.
eflightray's Avatar
Oh dear .......


.
Nov 16, 2017, 02:49 PM
Registered User

It's not so "Oh dear"


Quote:
Originally Posted by eflightray
Oh dear .......


.
I flied one like that before 15 years,but then i was little and the men who taught me was there to fix my mistakes..
Nov 16, 2017, 04:21 PM
B for Bruce
BMatthews's Avatar
Do you have a plan you are working from? Or some pictures you can post? So far you have not given any measurements or good description of how large or small of a mistake you made. So we cannot say if it is a minor thing you can ignore or if it will result in an instant failure.
Nov 16, 2017, 05:49 PM
Registered User
Shoot some 3-view pics that we can see.

One from the front along the thrustline of the motor. The tail should be visible behind the wing.

One from the top, pointed as squarely down as possible, on the centerline of the fuse, centered about halfway between the nose and tail.

One side view. Set the plane on a table. Prop the tail up a little till the fuse looka level. The h-stab should be very level at that point too. The wings should be pointed slightly upward. It's the angles between fuse, wings and stab that will 'look right' or not. Propping the tail up makes it easier to see those angles, as if the plane is in flight.

Opinions will most likely be 'go with it,' though there's a possibility of 'that doesn't look right.'

When I do weird/wacky stuff, asking a lot of questions about this/that/the other, the pros usually answer with 'put it up in the air and see what happens.' BUT I'm doing 99% foam which if tragedy happens is far easier to repair than balsa, so yeah you do want the best chance possible to start with.
Nov 18, 2017, 03:35 PM
Registered User

some pictures


I draw a line from the wing string crossing the horizontal stab line,if it can say something about the decalage


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