HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 26, 2006, 09:50 AM
Registered User
Singapore
Joined Nov 2001
802 Posts
Build Log
Little Duo Discus

We were flying EPPs at this particular slope, since there isn't any nice place to land a plane other than into the bushes. Glass ships are too expensive to take such a beatings but I always wanted to fly a scale sailplane there.

So, I started to design my own 2 meter version of the Duo Discus from the 3 views. This project will serve as an experiment and it'll test the survivability of the design on this kind of landings. If successful, it'll open the door for me to design more scale gliders for such slope or if not, it'll serve as a sacrificial model for me to have some quick time fun there.

I broadened the chord a little and use the Selig 3010 to compensate for the low Reynolds number. The stab is enlarged by 10% and all these deviations are hardly noticeable anyway. Construction is fo blue foam for the fuselage and balsa sheeted sandwich wing structure with blue foam core. Stab and rudder are balsa.

The entire fuselage is laminated with 2 layers of medium grade glasscloth with Z-poxy resin. After priming, sandings, fillings, the fuselage is given a few coats of automotive white paint. The wings,stab and rudder are covered with Oracover light-scale white. The canopy is moulded from PVC sheet and given a coat of 'smoke' paint. All up weight tips at 21 oz.
Joe Yap is offline Find More Posts by Joe Yap
Last edited by Joe Yap; Mar 28, 2006 at 02:58 AM.
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 26, 2006, 09:56 AM
Registered User
Singapore
Joined Nov 2001
802 Posts
The result is very satisfactory. The plane is smooth and easy to fly. It picks up lift readily and will soar even in light slope winds. In fact, it's so much easier to fly than my 3m HF version. The finishing is also very desireable as one can easily mistake it for a moulded model. I even flew it to the base of the slope after a dive and easily climb back to height.

The model turns out quite durable for such beatings and bad landings usually result in only minor damages, which can be easily repaired on the field and fully restored with considerably little effort. I had smashed the nose into concrete walls but all it takes is just some body filler,primer and top coat to restore it's glory.
Joe Yap is offline Find More Posts by Joe Yap
Last edited by Joe Yap; Mar 26, 2006 at 12:18 PM.
Reply With Quote
Old Mar 26, 2006, 10:24 AM
Registered User
The Far East
Joined Jan 2006
853 Posts
Nice JOB!!

Impressive accomplishemt. A 2m Discus must be a real treat to fly on the slope!!
suirendoujin is offline Find More Posts by suirendoujin
Reply With Quote
Old Mar 26, 2006, 02:22 PM
I failed linkage geometry
salisbug's Avatar
Melbourne, Australia
Joined Jun 2002
4,240 Posts
G'day Joe,

Fantastic looking model.

Congratulations.

Glenn
salisbug is offline Find More Posts by salisbug
Reply With Quote
Old Mar 26, 2006, 02:39 PM
daveosoar
hampshire
Joined Mar 2006
607 Posts
Soooo Good.
Please give us all a full rundown on plan/materials/build so we can all have one!
daveosoar is offline Find More Posts by daveosoar
Reply With Quote
Old Mar 26, 2006, 06:37 PM
Registered User
Singapore
Joined Nov 2001
802 Posts
Of course. I drew the plan using Autocad R14. If interested, just drop me your email. However, it's just more like a draft, but should be sufficient.

Here's how I did it.

The fuselage profiles are printed in A4 sheets and joined. The patterns are rough cut, pasted on cardboard with 3M77, and cut out as templates. The fuselage consists of 2 pieces of 2" blue foam on each side. The half plan profile is hotwire cut on each side. After that, the waste foam pieces are lightly tacked back to the cut profile with a very thin coat of 3M77. This will provide a flat surface to pin the side profile templates in place. Next the side profile is then hotwire cut out.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 26, 2006, 06:42 PM
Registered User
Singapore
Joined Nov 2001
802 Posts
After removing the side profile templates, the canopy profile templates are pinned in position. the canopy block is then hotwire cut out. Only now, all the watse foam will be removed.

The canopy block is then tacked into it's position again and the entire fuselage is then hand carved and sanded to shape. Once done, the canopy block is removed and te 2 halves were split. On each half, the fuselage is sectioned off at a few stations with a PENKNIFE. Hotwire cutting here will cause some shrinkage and since the joints will be glued back later on, a less than perfect penknife cut will still match.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 26, 2006, 06:53 PM
Registered User
Singapore
Joined Nov 2001
802 Posts
The cross sections are traced on a piece of cardboard, and the inner profile is being estimated and drawn on it. Do this for all stations to make a set of templates for hollowing the fuselage block.

The sectional templates are pinned in thier respective positions, followed by hotwire cutting the internal profiles. After that, the pieces are then epoxied back to thier original positions. Before joining the 2 halves, the outer sheath of the nyrods have to be glued in positions, or else you find some hard time doing so later on. A small hole is also made at the tail end with a round needle file for the antenna exit. I use the smallest Sullivan flexible push-pull cable for the elevator control and Sullivan push-pull wire for the rudder. Ensure that the movements are free.

The 2 halves are finally epoxied together and the assembly has shed quite some weight.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 26, 2006, 06:58 PM
Registered User
Singapore
Joined Nov 2001
802 Posts
Next comes the fin construction. The fin is hotwire cut with a symmetrical profile. I discarded the rudder after cutting out and replaced it with a balsa one later. A small hole is drilled within the fin from the root to the tip to recieve the nyrod outer sheath. The fin is then dry fitted to the fuselage and check for the control cable freedom of movement before glueing it down with epoxy. The joint is blended with somelight sandings.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 26, 2006, 07:00 PM
Registered User
The Far East
Joined Jan 2006
853 Posts
Now I know how you were able to make such clean inner surfaces. Ingeneous. I had thought that you went for the lost foam method, but was wrong.
suirendoujin is offline Find More Posts by suirendoujin
Reply With Quote
Old Mar 27, 2006, 03:54 AM
Registered User
Singapore
Joined Nov 2001
802 Posts
I discovered that if you want to achieve sufficient strength and rigidity with glass alone, you'll need to build up several layers of cloth to achieve it, or else the structure will not be rigid enough. The layers of cloth built up like this will weigh down the structure. However, if you combine the foam with just a few layers of cloth, you can achieve desired strength and rigidity at just a fraction of the weight. Compared to a fully moulded fuselage, this one weighs much lesser.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 27, 2006, 04:03 AM
Registered User
Singapore
Joined Nov 2001
802 Posts
The fuselage now receives it's first layer of medium glasscloth, applied with finishing epoxy resin. I did one half before another.

After curing, the excess cloth is trimmed and light sanding is done before the 2nd layer of cloth is being laid. When cured, the excess is again trimmed off and the entire surface is given some light sandings. Imperfections are filled with automotive putty and sanded to shape before a thick coat of primer is being applied.

When cured, most of the primer is sanded away, leaving only traces behind that fill imperfections.

Some balsa sheets are laminated to make a block, and tacked down to the cockpit with 3M77 before being carved into the canopy plug. Theplug is removed and the bottom, front and aft faces are lined with scrap balsa. A frame assembly is made out of plywood and hardwood rails.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 27, 2006, 04:07 AM
Registered User
Singapore
Joined Nov 2001
802 Posts
A PVC sheet is clamped between the frame and heated before forming. Once formed, the clear canopy is trimmed and given some coat of 'smoke' paint. The canopy base is made out of scrap balsa and plywood. The inner surface is lined with thin foam sheets as trims. The canopy is then glued down to the base.
Joe Yap is offline Find More Posts by Joe Yap
Reply With Quote
Old Mar 27, 2006, 12:35 PM
Registered User
White Rock, BC
Joined Sep 2004
44 Posts
Great thread. Joe, did you consider a light layer of glass inside before joining the sides? While a monocouqe structure is very a strong, a monocouqe with a sandwich would be even better.

Phil in Vancouver
Sleeper1 is offline Find More Posts by Sleeper1
Reply With Quote
Old Mar 27, 2006, 03:00 PM
Less Whinning, More Flying
Sailhigh's Avatar
SF Bay Area, USA
Joined Feb 2003
1,764 Posts
I think someone already said it, Ingenious!
Sailhigh is offline Find More Posts by Sailhigh
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Anyone have info on HF Model or Lenger Duo Discus??? Magna Electric Sailplanes 0 Apr 29, 2003 07:37 PM
Icare RC Duo Discus w/ SLS Fly4Fun2 Scale Sailplanes 4 Apr 09, 2003 11:48 AM
Need translation for the Lenger Duo Discus Joe Yap Slope 21 Jan 06, 2003 03:30 AM
ICARE's new Duo-Discus T Daniel Mc Crae Electric Sailplanes 5 Sep 12, 2002 02:37 PM
NSP Duo Discus Comments? jf ryan Slope 4 May 20, 2002 09:46 AM