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Mystic 40/60FS

Hanno Prettner's World Champion Model - scaled down

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Martyn K07/02/2016 21:09:44
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4234 forum posts
2959 photos

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

Martyn K07/02/2016 21:31:12
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4234 forum posts
2959 photos

And here are the formers

formers.jpg

Definitely one for a laser cutter or router.

F1 - 6mm birch ply, F2, 3mm birch ply - the rest 3mm lite ply with additional local reinforcement

Martyn

David Foley08/02/2016 00:56:39
49 forum posts

Looks great , well done. Interested for sure.

extra slim08/02/2016 10:37:21
329 forum posts
29 photos

yeah man, into it...smiley...YS63s would be sweet!...pretty model

Martyn K08/02/2016 15:19:44
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4234 forum posts
2959 photos

I agree - a YS63 with a nice big prop would be great.

Here is the plan so far...

mystic_40_plan_v1.jpg

I may well go for retracts on this one.

More to come

Martyn

David perry 108/02/2016 16:09:23
931 forum posts
10 photos

Is Hanno still flying?

Martyn K08/02/2016 16:34:18
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4234 forum posts
2959 photos

I don't believe that he is flying competitively, but there are still images on the internet of him flying as recently as 2012

Martyn

Martyn K11/02/2016 22:53:50
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4234 forum posts
2959 photos

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

Martyn K13/02/2016 18:48:35
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4234 forum posts
2959 photos

Just about there now. Ready to send the files to Lasercraft

plan3.jpg

Martyn

Martyn K18/02/2016 08:57:12
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4234 forum posts
2959 photos

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

Jon Laughton19/02/2016 05:54:31
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985 forum posts
74 photos

Looking good Martyn and I will be watching with interest. Can you advise what your plans are for making the cowl please as I have a specific non related interest in that?

Thanks

Jon

Martyn K19/02/2016 08:02:23
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4234 forum posts
2959 photos

Thanks John

I was going to make a plug for a one piece glass mould. Ditto for the canopy except that this will be vac formed

Martyn

Jon Laughton19/02/2016 08:18:57
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985 forum posts
74 photos

Hi Martyn - per the cowl I need to do the same (for the first time) so I will PM you for some advice if ok?

Jon

Martyn K19/02/2016 09:01:40
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4234 forum posts
2959 photos

Sure. No problems. I am no expert though. I did my own cowl on the Magic build and that came out pretty good although it was a struggle to release the cowl from the mould.

I'll follow a similar process again. It was quite straightforward

Martyn

Martyn K19/02/2016 13:11:02
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4234 forum posts
2959 photos

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

David Oxilia19/02/2016 15:53:46
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24 forum posts
6 photos

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

Martyn K19/02/2016 16:11:24
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4234 forum posts
2959 photos

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

Martyn K29/04/2016 15:02:34
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4234 forum posts
2959 photos

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

Steve Dunning29/04/2016 17:33:18
321 forum posts
186 photos

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

Martyn K29/04/2016 17:52:13
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4234 forum posts
2959 photos

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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