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Sep 17, 2015, 06:52 AM
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Taking on foam: Electric SPAD’s for flying in the park

It’s time to change direction a bit. I recently bought an 80W HXT “Blue Wonder” motor with the intention of making some small depron planes. However, it has proven to have more than enough power for carefully designed correx planes. Given that the matching Lipos weigh between 30g and 70g, AUWs of between 300g and 400g become possible.
So I think that it is time for a thread that has links and plans for those who ask the question “Can I build an electric SPAD that I can fly at my local park?”
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Sep 17, 2015, 06:58 AM
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Design criteria

I’d like to make this an open thread where anyone can post designs that fit the criteria.

So what are the criteria? Obviously construction must be primarily from correx or other cheap materials. However, I have no aversion to the use of the odd bit of foam here and there, or to CF. Just as long as the planes remain low cost and reasonably simple to build. I’d also like to keep most of the designs focused on the beginner and early intermediate. Why? Because the more experienced folks are quite capable of designing their own planes, while it’s the beginners that SPAD currently does not cater for very well. Also, I believe it takes more skill to design a light plane with predictable handling than it does to design one that only an experienced pilot can fly.

But the key criteria is that they must be genuine park flyers. That means that the average pilot can fly them SAFELY in a park or from a school sports field. In practice (IMHO) that dictates planes with an AUW of between 250g and 750g and which fly reasonably slowly, or which are very predictable fliers. Just because you fly your 1.5kg SPAD in the park, does not make it a park flying SPAD.

The motors I have in mind are the following:Obviously, this list is not prescriptive, but let's try to keep the power plants relatively standardized and within the range of these ones. These more or less correspond to the old '1/2A' category, and there is no reason why the designs I have in mind could not be converted to the equivalent glow power.

One final note. I’d like to categorise the designs to make it easy for a beginner to choose what to build. This is what I have in mind:
Absolute beginner: Must be suitable for a first time pilot who does not have access to any experienced ‘buddy’. This means a totally forgiving flier, that is very simple to build and requires only a very basic knowledge of the principles of flight to set up. So far the only plane I know of in this category is the Correx Pusher Trainer. In the foam world, there are several designs that would qualify (BlueBaby, SuperSlow etc)
Assisted Beginner: Must be suitable as a first plane, but the pilot will probably crash and need repairs if s/he does not have help from a more experienced modeler. So the construction and set up can be a bit more complex, and flight speeds can be a bit higher. My correx Q-Tee would fit in this category.
All The Rest: This is the category for everything else – the MUGI, my funjets, the Bloody Wonder and its derivatives, the eMig7 and the powered versions of all the slopers on Flying Beagle’s sloper thread. Correx parkjets (profile and full fuse) will also fit here.

I hope that is all clear and makes sense. Now start designing!!
Last edited by Extreme Sports; Sep 17, 2015 at 07:06 AM.
Sep 17, 2015, 06:59 AM
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Links and plans

Here are some other correx planes suitable for flying in the park:

Absolute beginner:
The Corro-pusher-trainer:
Correx Drenalyn (flying disk style aileron trainer): Starts at post #28 in this thread

Assisted Beginner:
Correx S-Tee (aileron trainer): Starts at post #5 in this thread
Correx Q-Tee (Rudder trainer): Starts at post #21 in this thread

All the rest:
George's profile mini-jets:

Mugi delta wing: (The original mugi website seems to be inoperative)
Correx funjets:
Correx MIG7: and see post #37
Correx warbirds (slopers that can be e-powered):
George's profile Draken:

More to come....
Last edited by Extreme Sports; Oct 26, 2016 at 02:26 AM.
Sep 17, 2015, 01:53 PM
Allways the hard way!
georgy's Avatar
As a huge foam fan you definately have my attention talking light weight parkfly.. very keen to explore the Spad world!

Just maybe i can contribute one day..

Sep 18, 2015, 02:49 PM
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Correx S-Tee

OK, so I have decided to base the first build on the Airtronics S-Tee from the late '70's. For those unfamiliar with this plane, it's a shoulder wing version of the very popular Q-Tee trainer. Both were powered with a Cox 049 or .051 glow motors.

This version will have a few changes:
  • It will be larger - scaled up about 25% to have a wingspan of 1150mm
  • It will have ailerons and rudder - the intent is for this to be an aileron trainer
  • The nose will be slightly lengthened to enable it to balance with an E-Max CF2822 motor and 1300mAh Lipo
  • Most of the fuselage curves will be replaced with straight lines to simplify the build.
I'm hoping to keep the AUW below 650g. This will put it at the upper end of the target size and weight range. It should be suitable as a second plane, or as a first plane if you have a 'buddy box'.

My intent is to also post plans for the original size, which will match with a Blue Wonder motor and should weigh in at around 450g.

I'll start the build once I've completed drawing templates in Sketchup.

Pictures are of the balsa original (920mm span).
Sep 20, 2015, 07:33 AM
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Do you think any of the flite test builds could be adapted?
Sep 20, 2015, 09:00 AM
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Not only adapted, improved upon!

2mm Correx is lighter than the foamboard we get in SA, and is better at forming curves. So you should end up with a lighter model that has better aerodynamics. Just resist the temptation of 'add strength'. At this scale building light is stronger.

Please post the results of anything that you build.
Sep 20, 2015, 09:11 AM
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Originally Posted by WaynejG
Do you think any of the flite test builds could be adapted?
I've been eying the FT Storch!!
Sep 22, 2015, 12:26 PM
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S-Tee wing

I changed the scaling to just ~110% of the original size, but then increased the wing span by 50mm each side to give me a total span of 1100mm. The original wing was on the short side as the designer kept it at 3' so that it could be built from single lengths of balsa and spruce.

The wing is very standard for a correx wing and is relatively simple, being constant chord. Anyone wanting a lighter build should consider building the wing from 3mm depron - the templates and techniques would be almost identical (just remember to tape the outside of the LE before scoring and bending. Here are the basic steps:
  1. Trace or measure out each wing half onto the correx or depron. Be sure to make sure that the correx flutes run perpendicular to the LE. If your sheet of correx is large enough, the full wing can be cut as a single piece. Note that the top skin is slightly wider than the bottom (since the top will be curved)
  2. Mark and cut out the cutouts for the ailerons
  3. Mark the position of the spar, and glue the top anti-crease strip about 10mm behind the spar line on the top skin using contact adhesive
  4. Cut the ailerons, deflute the appropriate flute to form the hinge and glue to the bottom skin, with the hinge facing downwards.
  5. Score and fold the LE. Use a straight edge. Note that my photos show a rounded LE. This is not essential for this design and not recommended unless you have worked with correx before.
  6. Add the toque rods to the ailerons. I plan to mount my servo inside the fuse, so the torque rods protrude through the wing bottom skin. This makes closing the wing a little harder, but is not an insurmountable issue.
  7. Make the spar. The easiest method is to cut some 6mm depron the right length and width, and glue this to the bottom skin. Then glue a 6mm CF or GRP rod to the bottom skin (use hot glue) just in front or behind of the spar . The dihedral joiner can be made from correx and GRP rods (as in the photos) or from thin ply. Resist the temptation to build a heavy spar. Mine weighed 25g. Try to keep below 35g.
  8. Glue the wing closed using the normal techniques. I highly recommend using a jig to hold the wing LE to the table.
  9. Add the center doubler. Set the one wingtip up on some books as this step will lock in the dihedral and permanently 'lock in' any twists - so take the appropriate care.
My wing weighs 204g. A depron one should be almost 100g lighter.
Last edited by Extreme Sports; Feb 13, 2016 at 06:36 AM.
Sep 25, 2015, 02:32 PM
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Have made some progress on the fuselage. The basic steps so far are as follows:
  1. Mark out the fuselage sides from the templates. To ensure that the wing and horizontal stabilizer (HS) are properly aligned, make sure that they both lie on the same flute line - mark the flute with a pen and then pin the template to the correx with the wing saddle and HS saddle along the line.
  2. Cut out (combination of scissors and sharp knife works best), then score and bend all the folds. Slit the inside of every second flute along the length of the turtledeck (the rounded part on the top of the fuselage behind the wing)
  3. Cut the various joiners (note the flute directions) and join the fuselage halves along the bottom with the bottom joiner. Glue the remaining joiners in place - they will also assist in aligning the formers.
  4. Cut out the firewall and formers. The prototype's firewall (F1) is 1mm ply laminated to 2mm correx, F2 is 2 slabs of 2mm correx with the flutes perpendicular, while F3 and F4 are 6mm depron. I may add an F5 later (this will be at the LE of the HS). I usually drill the motor mounting holes etc now. I use the 2mm screws that come with new servos to mount my motors. They are plenty strong enough and weigh nothing.
  5. Fold the fuselage up around F2 and glue it in using hot glue, and taking care to make everything is square.
  6. Fold the bottom of the fuse into place and fix with sellotape. If the fuse has been cut accurately, it will be as straight as an arrow. If not, trim and re-stick.
  7. Glue in the Firewall and the remaining formers.
  8. Glue in the doublers for the remaining bottom joints and remove the sellotape
  9. Cut the holes for the wing dowels. I typically heat up a scrap of piano wire and melt the holes.
  10. Bend the LG and bind with sewing thread. Now poke a hole down the appropriate flute in each front side doubler and insert the LG up the flutes. When you are happy with the position of the LG, withdraw it slightly and smear the thread liberally with wood glue. Once dry, push it back in - friction will hold it in. This is more than strong enough at this size.
Now is the time to make the tail feathers and add the servos and other odds and ends - will post details when done.
Sep 26, 2015, 12:39 AM
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A few questions please...

Looking at the arrow i placed on your pic:

(A) is a folded joint, angled across the "grain"... how do you get that straight instead of zig-zaggy?

(B) is a flute-to-flute joint, how do you join? (as there is very little surface area.. (i see you mention tape, to hold while glueing or is that the permanent joint?)

(C) Much the same question as (B)...

Sep 26, 2015, 01:57 AM
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A: Score and fold, similar to making the LE of a conventional folded correx wing. Line up a straight edge along the desired fold line, score the inside of the fold with a blunt instrument (my 3mm screwdriver works well), then fold up the correx against the straight edge. If you try to fold it without keeping the straight edge in place you will get a wavy line, and the flutes can crease. Takes some practice to get neat, but easy on 2mm correx, and progressively harder and less neat as the correx gets thicker.

B & C: That is what the doublers are for. Look at the picture taken from the top of the fuselage - you will see that I glue scraps of correx on the inside of the fuselage running along the joint line. So in practice I sellotape the bottom together (sometimes I need to do some trimming first), check alignment, apply contact adhesive to the inside of the fuse joint and the doubler, and, when ready, I press the doubler in from the top. I push the bottom of the fuselage against the table top, so that the two bottom 'tabs' are forced absolutely flat. Thin fingers and a bit of dexterity help on the smaller builds

This 'fold and doubler' method gives me a neater. lighter and stronger joint than trying to hot glue a separate bottom piece to the fuselage.

I'll add some pictures later with the doublers marked more clearly. While on white is hard to see.
Sep 26, 2015, 02:43 AM
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OK, here are some pictures.

The black lines are the doublers that cover joints (and add some strength). You could also use strapping tape, but I find that correx generally gives a better result.

The red lines are doublers that simply add strength. These can be omitted on smaller (~300-400g) builds. They only add about 10g - 20g to a typical build but increase strength significantly. I put them ahead of the LE, and sometimes between the LE and TE - in this position they make it easier to cut the wing profile into the fuselage (since their flutes are at 90 degrees to the fuselage flutes, so it is easier to control the cut. If you are not sure what I mean, try cutting an airfoil shape along the flutes lines vs perpendicular to the flute lines.
Sep 26, 2015, 03:15 PM
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Made good progress today and even managed to fit in a quick maiden this afternoon. AUW is 600g on the button with a 1300mAh Lipo, but I am using a heavier motor and ESC than envisaged - this would be 580g with the Emax 2822 and 20A ESC. So either way, it has come in well ahead of the weight target.

Maiden flight was exactly as I had intended - very well behaved and light on the controls.

Here is a quick summary of the last build steps:
  1. Cut out the tail feathers and deflute the hinges
  2. Insert the wire joiner in the HS, and the tail skid in the VS.
  3. Glue the VS to the HS using hot glue. Ensure a 90 degree angle between the two
  4. Temporarily attach the tail feathers (I use pins), place all electronic components in their planned locations and test for balance. Position the servos to achieve balance slightly ahead of the CG (still some weight to come on the tail). Check that the servos do not interfere with each other and that you can slip the Lipo through F2 into the front compartment. Build a servo tray and install the servos.
  5. Add the pushrods. I use 3mm wood dowel and piano wire - weight of both pushrods was a whopping 3g. Use a heated rod to melt holes for the pushrods through F3 and F4, and cut out a section of flute at the tail for each of the pushrod exits
  6. Add doublers to one side of the fuse top and close the turtledeck - photos will make this clearer. Do not be tempted to close this joint before the pushrods have been installed.
  7. Check that the wing is horizontal, align the HS and hot glue the tail feathers in place
  8. Add control horns and connect up the pushrods to the horns and the servos.
This got me to first flight status; more to follow on trimmings.
Sep 26, 2015, 03:31 PM
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You sure don't mess around when it comes to building.

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