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Old Apr 08, 2015, 02:55 PM
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How long fuselage does a 3m glider wing need?

The situation is simple:

I have a home-built wing. Details:
wingspan: 3 meters
airfloil: RG15
chord: 22 cm (in the mid 2 meters, and 15 cm at the end of the wing)

I have a Phoenix 2000 fuselage and I'm wondering wheter it's enough for the 3 meters long wing or not. (the chord of the original wing is 20 cm long. I've aready built a 2 m RG15 with 22 cm chord and it works fine with the original fuselage)

put it another way around:

How much should be the minimum distance between the trailing edge of the wing and the leading edge of the horizontal stabiliser if you have a 3 meters wingspan glider wing.

+ infos:
- the wingload will be about 28 gramm/dm2 with the longer wing
- horizontal stabiliser: symmetrical
- the wing area of the horizontal stabiliser is about 540 cm2
- the original distance between the trailing edge of the wing (chord 20 cm) and the leading edge of the horizontal stabiliser is 49 cm
- the distance between the trailing edge of the home-built 2m rg15 wing (chord 22 cm) and the leading edge of the horizontal stabiliser is 47 cm
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Old Apr 08, 2015, 03:10 PM
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one more important thing: I don't want the long wing acrobat flight just for thermaling.

as I know the factory sells the original fuselage with a 2,6 m wing (maybe tha stabilisers are bigger)

If you thing the 3m is too long, what do you thing how is the maximum wingspan what I could built on the original fuselage?
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Old Apr 08, 2015, 03:12 PM
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I don't have the actual numbers in front of me, but from memory...
Nose to wing LE = ~1-1.5 x wing chord
Wing TE to Horiz LE = ~1.5-2.5 x wing chord.

Overall the fuse to wing ratio = ~ 0.5 to 0.7.
There is a little more to it than that , but that is the basics. There is no ser exact figure. Tail sizing is a never ending thing. There are a lot of variables at work that must be looked at. Horiz. Stab Volume, Vert. Stab Volume, Effective Dihedral angle, overall wing planform.
There are a could of pretty good spreadsheets out there on the interwebs that will point you in the right direction.
Tailwinggliders.com i know for sure has a good spreadsheet to use. I use it all rhe time during initial concept development. I'm not at my desktop to get access to the others I have saved but I can post the links later if needed.
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Old Apr 08, 2015, 03:29 PM
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"...Wing TE to Horiz LE = ~1.5-2.5 x wing chord. ...."

It sounds good. It'seems my plan might work.

But I don't understand why important the "nose to wing LE" distance.
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Old Apr 08, 2015, 04:00 PM
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Balance
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Old Apr 09, 2015, 01:35 AM
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You can get the Phoenix with a 2,6 meter wing and it fly very nice, so why not also with a 3 meter wing.
I would give a go.


Regards
Soren
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Old Apr 09, 2015, 05:26 AM
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the simplest way

if you watch sailplanes, in most of them the fuselage is half wingspan.
that could give you a plane that behaves for thermal flying.
then of course you have to make room for the components that sit ahead of the wing, and to balance the whole thing.
but if you start with 1.5 meters in your case, trying the finished wing and tail and placing all the components on a stick at the front, that may give you a close point for the wing to sit.
of course there are more scientific ways...
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Old Apr 09, 2015, 08:47 PM
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See PDF

A very incomplete list I have started where I am compiling data from aircraft to see if how different aircraft compare just by numbers.
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Old Apr 09, 2015, 11:00 PM
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Phil's suggestion isn't a bad one for models in our size class. There are better ways.
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Old Apr 09, 2015, 11:13 PM
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thanks for everybody, now I start to built and
"I'll be back" in a month
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Old Apr 10, 2015, 06:30 AM
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you should check some numbers according Prof. Drela
http://www.homebuiltairplanes.com/fo...-stability.pdf
For a given length of a fuselage you might have to increase the size of your horizontal and vertical tailplanes when increasing wingspan.
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Old Apr 10, 2015, 10:41 AM
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also

agree.
he was asking about the fuse, but your advice is sound. that is the next step.
from my experience, 10% of horizontal tail is the minimum (meaning area of the stabilizer and the elevator together).
but i think better provide the guy figures instead of getting into hi-science.
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Old Apr 10, 2015, 10:46 AM
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easy does it

Quote:
Originally Posted by Avaldes View Post
Phil's suggestion isn't a bad one for models in our size class. There are better ways.
i suggested the easiest way-in any size- and said that there are more scientific ways.
and of course there are other things that have to be considered too.
but let's try to make his life easy.
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Old Apr 10, 2015, 12:03 PM
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Sizing fuselage is a real issue.
This has to be defined in conjonction to The fin area. this conduct to think yaw stability.

The length depends also upon what you want to do.
As you expect to have a TD plane, the idear is also to know whether or not you want to circle tight at very low altitude as for F5J.
In this condition, you cazn compute length of fuselage and fin area in order that you have an amortisation factor of 0.7 at low speed.
This represent an optimum that is wordwide used in any other mecanical topics...
I expect you don't want to compute it. So I will provide you with a sort of recepe:
Total length of fuselage from front to far end should be 1.25 half span. And fin fuselage should be between 10 and 12% of wing area. With those data, you will not have any problem and circling tight will be far more easy than with any F3J planes...

Try and you will appreciate.

Marc
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Old Apr 10, 2015, 11:39 PM
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Try the Sailplane Calc at http://www.tailwindgliders.com/Tips.html
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