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Old Jan 14, 2007, 07:44 PM
Fly Big, Fly Hard!
Royster's Avatar
Brisbane, Australia
Joined Jan 2007
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GWS Piper Cub Build Tips & Hints?

Being our first build (we are still in training on the Electrafun XP), my son and I are about to build a GWS Piper Cub (non painted version) but are unsure of a few things. The instructions are pretty good but basic terms or techniques are what we dont know about.

We have built a few plastics models but these are a bit different as they meant to FLY!

So I am calling out to any people who have built this model or are experts in GWS kits to lend a hand when we get stuck.

Our local guy we bought this off is helpful (thanks Neil) but dont wanna bug him all time.


My first question is the instructions require the wings to be set at 10% angle.

How do you do that?
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Old Jan 15, 2007, 03:26 AM
Next time I'll ARTF...
glydr's Avatar
Canberra, Australia (Southside)
Joined Feb 2004
4,634 Posts
They probably mean dihedral - that is when the plane is viewed from front or behind the wings are a shallow "V" rather than flat. When you don't have ailerons dihedral is your friend!

My GWS slow stick wings were folded up and glued in place in order to achieve the dihedral. I also used some fibreglass tape across the top (probably about 1/3 along the wing - maybe more) to hold the dihedral in place.

I assume the piper cub is similar? If you get into trouble take a photo and show us

Enjoy!

Graham
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Old Jan 15, 2007, 05:19 AM
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Joined Apr 2006
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You should be able to find PLENTY of build threads and pics on the GWS forum.
They are great value planes in my opinion,just have some foam safe c.a glue at hand for when you begin flying.Zap Odourless is my favourite,you can use epoxy too-but it gets heavy.Keep it as light as you can.A light plane crashes lighter!
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Old Jan 15, 2007, 05:35 AM
Fly Big, Fly Hard!
Royster's Avatar
Brisbane, Australia
Joined Jan 2007
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OK thanks, but how do I adjust and measure the 10% GWS are on about?

Wheres the GWS forum?
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Old Jan 15, 2007, 06:05 AM
Volta was revolting
old man emu's Avatar
Mount Annan, Sydney
Joined May 2006
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Royster,

Please read the instructions again and see if they say 10 degrees, not 10 per cent, which is an odd way to express the value of the diehdral.

If the instuctions say 10 degrees, then this means that the wing tip will be 5 degrees above the horizontal compared to the wing root which is on the horizontal. (5 degrees left wing + 5 degrees right wing = 10 degrees dihedral)

Think of a right angled triangle with the long side (hypotenuse) formed by the wing. The wing root is held flat on your workbench, and the wing tip is raised until there is an angle of 5 degrees between the bottom side of the wing, and the workbench.

Another way to find out high high you have to lift the wing tip up off the workbench is to calculate it using the following formula:

Height = length of wing (from root to tip) x sin 5 degrees
= length of wing x 0.09

Now isn't that strange. 0.09 is close enough to 10% for government work.

Old Man Emu
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Last edited by old man emu; Jan 16, 2007 at 03:20 AM.
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Old Jan 15, 2007, 08:39 AM
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Ok,I don't know how to post a link STILL,but if you have a look in the topics toolbar,the very last item is "vendors"-GWS is in there.
I reckon a flat surface and a protractor in one of those $2 maths sets would do the trick.10* surely would just be a guide,whether you had 8*or 12* I wouldn't imagine to have a detrimental effect?
Dihedral angle basically is what allows the wings to SELF-LEVEL WITHOUT THE USE OF AILERONS,so typically any 3ch with throttle,elevator and rudder has to have Dihedral.
I used to find my Slow Stick hard to fly inverted,and put it down to dihedral wanting to level the wing.
I will confess to NOT being an aero expert,as I also devote a lot of time to LIQUID RC.
When boats glitch,they generally don't careen into the dirt at 50mph!
Though they can make you go canoeing occasionally-LOL.
There are PLENTY of guys here who can help steer you in the right direction.
Just keep asking !

Fleetmaster.
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Old Jan 15, 2007, 10:17 AM
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Dittmer, MO. U.S.A.
Joined Dec 2000
16 Posts
I didn't measure mine but just used the 2 sided tape shaped like an airfoil to join the 2 sides together, the angle built in the wing sections are pretty close to 10 degrees, it's a little over but over is better than under in my book.
If you follow the instructions be careful, where it shows installing the battery hatch it doesn't say anything about installing the landing gear first and it can't be installed after putting the battery hatch in.........just my 2 cents........good luck........ Larry
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Old Jan 16, 2007, 12:57 AM
Fly Big, Fly Hard!
Royster's Avatar
Brisbane, Australia
Joined Jan 2007
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Quote:
Originally Posted by old man emu
Royster,

Please read the instructions again and see if they say 10 degrees, not 10 per cent, which is an odd way to express the value of the diehdral.

If the instuctions say 10 degrees, then this means that the wing tip will be 5 degrees above the horizontal compared to the wing root which is on the horizontal. (5 degrees left wing + 5 degrees right wing = 10 degrees dihedral)

Think of a right angled triangle with the long side (hypotenuse) formed by the wing. The wing root is held flat on your workbench, and the wing tip is raised until there is an angle of 5 degrees between the bottom side of the wing, and the workbench.

Another way to find out high high you have to lift the wing tip up off the workbench is to calculate it using the following formula:

Height = lenght of wing (from root to tip) x sin 5 degrees
= length of wing x 0.09

Now isn't that strange. 0.09 is close enough to 10% for government work.

Old Man Emu
Yep youre right its 10 degrees! I'll try and line it up with a small protractor (unless someone knows of a better way)

Also whats with the thrust angle and how is it adjusted, which I think is too late for me as I glued it in as per the GWS instructions!
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Old Jan 16, 2007, 01:21 AM
Beginner with a Vector
Sutho, Southern Sydney
Joined May 2006
182 Posts
my suggestion to adjust the dihedral is to plonk one wing on your flat build table, then lift the other wing tip up until that wing is at a 10 degree angle. The best way to figure out how much to lift is to do some maths.

My highschool memories say SOHCAHTOA - the SIN of an angle in a rightangle triangle is equal to the Opposite side divided by the hypotenuse (the side away from the right angle). So in your case, SIN (10) = X (the height we want to raise the wing tip) divided by the length of the wing. SIN (10) is roughly .17365, and that means to find X, you multiply this with the length of your wing. So for instance if your wing is 800mm long, then X would be 138.9mm, so raising the wing to that distance would be approx 10 degrees. 900mm is 156.3mm.

HTH

(and if anyone cares, SOHCAHTOA is Sin=Opposite/Hypotenuse, Cos=Adjacent/hypotenuse, Tan=Opposite/Adjacent)
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Old Jan 16, 2007, 01:59 AM
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Royster's Avatar
Brisbane, Australia
Joined Jan 2007
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Wing Pic

Heres the pic of the manual with the wing spec.

Someone mentioned not to use the GWS glue but 5 Min Epoxy?

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Old Jan 16, 2007, 03:35 AM
Volta was revolting
old man emu's Avatar
Mount Annan, Sydney
Joined May 2006
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Quote:
Originally Posted by auspoundy
my suggestion to adjust the dihedral is to plonk one wing on your flat build table, then lift the other wing tip up until that wing is at a 10 degree angle. The best way to figure out how much to lift is to do some maths.

(and if anyone cares, SOHCAHTOA is Sin=Opposite/Hypotenuse, Cos=Adjacent/hypotenuse, Tan=Opposite/Adjacent)
Auspoundy,

I agrre with you.

The dihedral angle is the angle between the arms of the V, where the point of the V is along the midline of the a/c.

When you build the wing, you take, say the port (left) wing and plonk the wing root on the workbench. Then you raise the wing tip until the bottom forms an angle whose value is half the dihedral angle. I call this angle the 'build angle'. However, in this model, the maker has given you the build angle, which is 10 degrees.

When the two wings come together, they will make the required dihedral angle.

I suggest that it's easier to calculate the height the wing tip has to be raised, using the formula:

Height = half wing span x sine (build angle)

If the wing span was 1000mm, sine 10 degrees (build angle) is 0.17, htere for you would have to raise the tip 173mm. (175mm would be OK in practice)

[Note to self: If someone has the decency to post a photo or scan relating to their enquiry, be sure to read it before you answer.]

Old Man Emu
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Old Jan 16, 2007, 03:51 AM
Next time I'll ARTF...
glydr's Avatar
Canberra, Australia (Southside)
Joined Feb 2004
4,634 Posts
As long as it is at least 10 degrees you should be fine! My slow stick wing has more diherdral than the instructions say - as I used the dihedral that came about when the halves were glued together - like Larry did (post above).

Epoxy used sparingly is more reliable than the GWS glue.
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Old Jan 16, 2007, 03:59 AM
Next time I'll ARTF...
glydr's Avatar
Canberra, Australia (Southside)
Joined Feb 2004
4,634 Posts
Thrust Angle

A plane which is designed to spend most of its time flying right way up (like your cub) does well to have the motor mounted such that it points slightly more down and slightly to the right.

The slightly down is to help airflow hit the wing at an angle of attack when the throttle is opened - also prevents a sudden zoom up under power.

The slightly right is to counteract a tendency to roll left when the throttle is opened. Many pilots are taught that this is due to opposite torque of the prop... I read an interesting article about how this roll comes about due to airflow hitting the vert stab - anyways - however it happens the slight right-thrust (sidethrust) overcomes this (or helps to do so).

By the looks of the manual the down thrust is already built in. The slight angle to the right (as viewed from behind) of the mounting stick is the way that the sidethrust is achieved.

If you glued it in straight - no great dramas - it will still fly. I have a cub inspired balsa model whose proto has no sidethrust and flies fine.
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Old Jan 16, 2007, 04:01 AM
Next time I'll ARTF...
glydr's Avatar
Canberra, Australia (Southside)
Joined Feb 2004
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If you glued as per the manual (with epoxy - sparingly) your sidethrust should be sweet.
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Old Jan 16, 2007, 04:13 AM
Beginner with a Vector
Sutho, Southern Sydney
Joined May 2006
182 Posts
ok, so a terminology issue has come up. I'll revert to OME's definition, you do this stuff all the time.

But given the actual picture from the manual, to get the 10 degrees indicated, I believe you have to use the SIN(10) = 0.17365 factor with one wing placed flat on the table and raising the other.
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