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Mystic 40/60FS


Martyn K
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This was Hanno's 1993 World Championship design and he was also the world champion that year.

From a UKCAA perspective, this is a bit 'modern', however, we don't really worry about things like that at the Fly-ins.

My original plan was to scale up the Mystic 30 from the OK Model Co plan (available from Outerzone), however after a lot of faffing around I decided to simply start from scratch using the outline - top and sides and then interpolate the formers. It seems to have worked quite well. Need to transfer it into CAD and then add the Profili generated wing - to follow.

The wing section is as per the original.

This results in a nice sized model - about 56" span designed for a piped 40 although I am pretty sure that a standard 46 or 60 sized FS would also be OK.

So.. this is where I am up to..

3d-1.jpg

The black silhouette is what I am working from. Some of the formers will be truncated around the wing root - no easy way of doing this in DevFus. You can also see the outline of the canopy - the formers in this area will be reduced in height slightly.

3d-2.jpg

Now with longerons added.

The rear longerons will be extended forward one more former and will join the 1/2" sheet blocks that will be carved to a nice curved edge. The full length and rear longerons are 1/8 x 1/4 spruce. Wing/Tail/Thrust line are set up to be 0/0/0 with perhaps a couple of degrees right thrust

3d-3.jpg

And a view from the rear. with the (transparent) sheet added. Mainly 1/8" sides, 3/32 upper and lower decking and a 1/8 ply doubler back to behind the wing. May make that 1/16" ply.

The root chord on the wing is 305mm - quite big for a 40 - so to get the best out of it, the target weight will be 2.5kG. Need to keep this light.

I have got a choice of 3 RE 40's I can use - an OS, a ST Blue Head and a rareish Irvine 40RE, bought for spares but has actually never been run. That could be the best £16 I have ever spent.

If there is enough interest, I may get one of my friendly kit producers to put a kit together, available after I have built the first one (get rid of any warts).

More to come.

Martyn

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A couple more evenings work on this and the plan is very nearly completed. This will be the first plan that I am hoping will be good enough to scratch build from. I have now moved from a direct copy/scale up from the Mystic 30 - the only bit that resembles the original is the tailplane - and that will be changed as well - both structure and section.

The fuselage has been redone (again - 4th iteration) - but I think I have got it right now.

plan2.jpg

The original wing section has been scanned and scaled. The built up tailplane will have a symmetrical section - sanded from 3/8 thick balsa - so still quite slim

I still need to draw the top view of the fus but that isn't too difficult and make allowances for the part tunnel for the tuned pipe.

I am quite enjoying this

More to come

Martyn

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Well, I have made a start. The DXF files for the formers and the wing ribs have been sent to Dylan @ LaserCraft and while I am waiting, I can make a start on the tailplane, fin and fuselage

The tailplane is cut from light 3/8 sheet balsa with 3/8 x 1/8 'ribs' and a 3/8 x 1/8 spruce brace. It will be sanded to a symmetrical wing section when lifted from the board. There is no sheeting on the tailplane.

dscn2860.jpg

Last night, the outline was cut to shape and the straight ribs glued into place

dscn2861.jpg

This morning, the diagonals have been added and left to dry.

The tail moment is very long on this model, the nose moment very short so it will be essential to keep the rear components as light as possible

More to come.

Martyn

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A minor update.

Elevators have been added. The observant will have noticed that I am using Kevlar cloth as the hinge material sandwiched between the elevator halves.

dscn2862.jpg

One thing I am also doing on all my models now is adding lite ply caps on elevators and ailerons

dscn2865.jpg

held in place while the glue dries

and

dscn2867.jpg

Voila! - after sanding.

A bit late for this but the ribs have all been cut and sanded to fit. Taking lessons from Simon Feather

dscn2863.jpg

Finished and sanded and now put safe while I carry on with the next bit

dscn2866.jpg

More to come - Fin and Rudder next then I'll make a start on the fuselage

Martyn

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Martyn,

This is looking great! Nice work.

I will be interested in a short kit when ready. At this rate you may well beat me to the Arrow kit! I need to focus on that and get it finished. In any case it looks like you're going to have some nice classics to fly this year.

One of the aspects you might want to consider is a built up stab in the style of the wing design. 1/16" sheeted airfoiled ribs. About the same weight as a sanded 3/8" balsa frame but the laser cut ribs remove the need to introduce airfoil sanding in the 3/8" wood. Generally more reproducible and consistent from build to build.

I've done my stabs like this for a while and lately have added rib spacing built in jigs made of 3/32" balsa. Basically a 3/8" wide strip that is 3/16" notched (by the laser) for the ribs. These are inserted on the LE and TE centrelines. It works particularly well on symmetric non dihedral sections like stabs as the rib/jig intersection is square and level. They also act as a jig of sorts to keep everything symmetric but one can also introduce a couple of 1/8" CF rod holes (front and back) to jig up the ribs on their centerlines during the build. Once skinned, the rods can be pulled much like how a 1/4" rod jig is used for wings. If desired a half span spar top and bottom of 1/8 square balsa to tie the ribs together at the max foil thickness. Just an idea to chew on.

The fuse looks very nice. I would stick to the 1/8" ply doubler to key in the formers but no need for birch ply - light ply is plenty strong and less than half the weight. 1/32" birch ply is equivalent but too thin for keying properly.

Regards, David

 

 

Edited By David Oxilia on 19/02/2016 15:55:09

Edited By David Oxilia on 19/02/2016 15:56:20

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Hi David

Nice to hear from you

The original 30 sized OK kit looked far too cumbersome to be built as light as I wanted - especially at the rear end. That is why I decided to start again. I am sure that with the right wood it could be done.

Tailplane. Swings and Roundabouts. I have just finished a Bubble Dancer glider and the tailplane construction was similar to this. I was surprised on how I light (16g) I could make it using this technique - although I admit that was only 6mm thick. I haven't weighed this one yet, I'll do that later and report back. It doesn't feel that light TBH. When I built my 25 sized Curare about 4 years ago, I used a built up tailplane as you suggested - no sheeting and it was too light - ended up putting half a church roof of lead at the rear to get the CG right. I wished that I had sheeted it. I had forgotten that scaling down a model by 20% for an engine half the size doesn't give an equal proportion reduction in mass. It still flies very well though

OK on the birch formers. Only the Firewall is birch now - the rest are all light ply except for a small strip of 3mm ply for the LE dowel and another piece for the wing bolts. I agree - they should be ample strong enough.

In hindsight, 3mm lite ply doublers would have been a really good idea - I wish I had thought of that (or you had told me) sooner - especially the opportunity for keying.. However, the formers are now with the laser cutter so I am stuck with 1/16 birch ply doublers at the front and a short length of 1/32 ply around the tailplane.

I'll email you the plan - would appreciate your expert eye on this if you don't mind.

Martyn

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  • 2 months later...

There has been progress, but by my standards, it has been a bit slow. I wanted to get the Aurora completed and a new wing built for the Magic, both of which have now been done so back to the Mystic

Work on the fuselage has been ongoing. Not much of a written blog - more of a photo blog..

dscn2903.jpg

Problem no 1. I forgot to include the fuel tank base on the cut parts so had to cut one from scratch. Here is the engine crutch assembly

dscn2904.jpg

I have never built a model with a jigsaw type assembly like this before. Nice joints are confidence inspiring

dscn2905.jpg

1/16 ply doublers and one fuselage side and longerons added. The rear formers are cry fitted at this stage. The upper longeron is dry fitted and adds stability to the forward formers while the glue dries

dscn2906.jpg

The angled formers delimit the cockpit boundaries and the wing seat rear

dscn2919.jpg

There are 2 sub formers that limit the fuel tank bay. I have had to cut out the recesses to allow the former to sit around the captive star nuts

dscn2920.jpg

Error no 2. This is an error on the plan. The tailplane is about 15mm too far forward so I have had to rework the tailplane seat so that it sits level with the datum

There are a few other minor errors which I am listing around the fit of the formers on the lower longerons - nothing to stop this build though and I'll correct the DXFs

dscn2921.jpg

Fuselage sides joined and rear formers fitted - ready for the upper sheeting

dscn2922.jpg

Like this. 1/16 balsa used - was 3/32 on the plan and blended in.

More to come

Martyn

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Hi Martyn

Just a word on your cowl moulding. I am in the process of planning out another HP design and wondered about the mould for the cowl as well, moving towards a one piece mould. I was fortunate to borrow an original cowl for this design as per those that were sold in Japan (different to the UK supplied kit, they were made of ABS). This one is epoxy glass and was constructed from a two part mould. That answered my question and the mould I am taking from it will also be in two parts. Makes releasing the final artefact a lot easier, even with having to attend to the join line, it's worth it

Hope that helps

Steve

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Cheers Steve

I was wondering how to do the cowl. Apart from making the plug - which shouldn't be too difficult, there is very little taper on this cowl so I guess I'll have to make a 2 piece mould. That will be a first for me

I'll have a closer look when the plug gets done.

Martyn

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A bit of progress this weekend. Started work on the wings. All very straightforward as the parts were laser cut.

dscn2923.jpg

Building tabs ensure that the ribs are at the correct angle and no twists built in. I use a mix of steel tubes and heavy dowel to make sure the ribs are located firmly on the building board while the glue dries

wing1.jpg

After a while it looked like this. All very straightforward. 3 days of workshop activities to get this far.

dscn2926.jpg

Once again using Kevlar cloth for the hinge material.

Mechanical retracts - these look like e-flite copies from HK

wing2.jpg

Still need to work out the best way of fitting the retract servo though

Martyn

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Martyn,

good to see your progress on the Mystic. I have been swamped with design projects as well as work but do intend on finishing up that Arrow 40 in the not too distant future.

One thing I thought might be worth mentioning is that the retracts on the 25 & 30 size OK Model versions are setup such that the retract body is closer to the spars where the foil is a little flatter and there is more space for the body. This is probably more important on the smaller models due to the proportionately smaller airfoil thickness but it does provide a little additional strength. The caveat with doing this however is that it puts the strut over the spars where the wheel can't retract. In order to take care of this problem, the struts are bent forward so that the wheel retracts in the rib bay forward of the spars.

It worked out well on the pair of Mystic 30's I built so I kept it on my Supra Fly 25 re-design as well. Otherwise, the wing was re-designed more along the lines of how the 60 size wings were designed and built by Hanno.

Looking forward to seeing it come together!

David

supra_fly_25_02_wing_cad.jpg

supra_fly_25_03_2view_cads.jpg

Edited By David Oxilia on 04/05/2016 00:13:40

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Cheers both

Steve - I have gone right off electric retracts, I found them heavy and unreliable. I have actually removed them from the Magic and gone back to fixed. With the new wing, I have saved over 0.5kg in model weight of which the majority was the retracts - aka ballast

David

That is basically what I am doing. I looked carefully at the OK Mystic 30 plans for inspiration.The wheel just clips the main spar - about 5 degrees of forward rake will be required. with the retract down, this will put the spindle just under the LE - which should be about right. I am using a standard cheap Turnigy MG servo for the retract servo, probably OTT, but its what I have available and currently on a very tight budget due to huge drop in combined income.

I have 'fitted' the bearers so that the retract plates stay flat by carefully removing a little of the bearer material at each side. I think they will be OK.

Not sure whether the retract servo should be mounted vertical or horizontal. Opting for horizontal at the moment

Progress in the the last day has been a bit limited. The wing is now in one piece - joined with spruce joiners - 1/2 x 1/4 top and bottom and tapered over 2 bays each side. When webbed, these should be more than strong enough for this sized aeroplane.

More to come

Martyn

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Last night was spend mainly doing retracts. I eventually settled on putting the servo vertically but as low as possible and then used piano wire links to connect to the retract actuation arms

dscn2927.jpg

Lots of bends to clear the undercarriage, I am not sure if this is correct but I couldn't think of another way of doing it.

dscn2928.jpg

And a video to show that it does actually work!

 
(sorry about the Planet Rock soundtrack off the radio. I should have waited for some music..)
 
This morning, I went back into the shed and redid the linkage to make them more permanent - soldering small brass nuts over the piano wire push rods at the servo arm. I have also moved the linkages into a more inner hole on the servo arm to try and keep the push/pull mechanism travel more linear
 
Finally, last night, I added the TE section at the root up t the ailerons and this morning I have started to sheet the wing.
 
dscn2931.jpg
 
and
 
dscn2930.jpg
 
More to come.
 
Martyn

Edited By Martyn K on 05/05/2016 09:14:38

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