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Miss Deeds or 1/4 semi scale Cassutt

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Erfolg11/09/2019 16:16:10
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I was delighted to see the plan of Miss Demeanor Snr, which has morphed into Miss Deeds. There is a PM build thread under that name.

I have previously built the small version. Surprisingly the original Miss Demeanor has proven to be a very nice handling model for such a small model. There has however been some hairy moments with the model, all of my doing. Without the detail of how and why, with the CG at 30% it was unflyable. Put where it was supposed to be at 25% a real pussy cat.

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Without any further ado I cleared my bench and considered how I would build the model.

Living at the end of the Earth or the Motorway, where it stops short of the Irish Sea, there is no longer a LMS, not for 80 miles there. So improvisation is needed if any progress is to be made. On that basis my spars and sheeting are spliced to make long enough.

Another thing I noticed is that being a kit plane, probably not one Cassutt is the same as the next, with respect to build. Just look at on line images. There are two basic fuselages it seems one really narrow about 20" at the shoulder and a wider 3 series. They can be so narrow that the pilots in some instances cross the hand from one side of the cockpit to the other to actuate or adjust a control. They are pretty narrow The wings are apparently skinned with standard size ply sheet, for an economical build. you can just go on about various variations that exist full size.

For my taste the width of the PM model is a little to narrow, I am not into knife edging, just the basic stuff of loops, rolls and inverted flight. So my model will be based on a 20" cockpit at shoulder. The base is to be as drawing, as this width seems pretty much bob on.

I have noticed that the tailplane is larger than scale. I certainly will not be reducing this, as the model has a short moment arm. I like relaxed flying, being a plodder, no interest in absolute scale or proper aerobatics.

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You can see I have short stub spars on the ends, not quite the same as PM has drawn.

Yet again an advantage of a PM design, small changes can be made, for a variety of reasons and still stay true to the design. You have confidence that the basic design will accomodate tweaks, without any compromise to the concept, simplicity is a key word in the concepts and design.

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Splicing sheet to achieve the lengths required.

Nigel R11/09/2019 17:07:07
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Good stuff Erfolg, this looks like being a great bit of kit. As is said, simplicity is the ultimate sophistication and the Cassut has that in spades, as do Pete's designs.

 

"with the CG at 30% it was unflyable. Put where it was supposed to be at 25% a real pussy cat."

At our end of the aerodynamic gene pool a slightly bigger tailplane seems to go a long way, I guess "the rules" are subtly different for full size. I was idly browsing some plan articles on outerzone recently and one thing jumped out from one of them (Gordon Whitehead's Cap 21) - the model, as perfect scale, was quite awkward to fly, but with a slightly enlarged tail it was a very different and more enjoyable beast.

Edited By Nigel R on 11/09/2019 17:07:49

Erfolg11/09/2019 17:28:18
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Nigel

Over a period I have read quite a bit with respect to Cassutt aircraft. In one particular reference, the author stated that the Cassutt is not a touring aircraft. It is cramped, it is unstable in pitch, and roll needing constant flying.

There is somewhere on the internet a reference to a fatal crash involving a Cassutt, where the pilot had minimal head clearance to the canopy. Something along the lines of 1/4" or 1/2", in reality non. Which played a part in the crash, which did not involve anything to unusual.

The PM model on the other hand is very different, the concessions to scale to produce a good handling model are well judged.

Although in many ways generic in design, the wider scale could be scale if modeled on a specific aircraft, as it is surprising that both subtle and significant versions are the norm. From long span narrow chord crescent GRP, as modeled, then there is at least one version all glass panel skinned body, where as the majority are fabric. So many different cowl designs, carb inlet scoops.

Edited By Erfolg on 11/09/2019 17:29:52

Peter Miller11/09/2019 18:18:43
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I have two brilliant books of Hirsch 3 views of formula one racers. The number of assorted Cassutts and look alikes is staggering.

Nigel R12/09/2019 09:04:45
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I can believe that Erfolg, these things are tiny!

I remember reading somewhere about a Cassutt built primarily for show flying and aerobatics, the builder had enlarged the tail surfaces and used a slightly thicker wing section. The original machine is stressed for very high load so the reasoning was that it would not take a lot to turn it into a capable aerobat. So perhaps Pete's mods are not so far from scale anyway smiley

Erfolg12/09/2019 10:24:18
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Nigel

I guess you know that the Cassutt is a Pylon racer. Certainly most of the photographs support the idea, being registered as a midget Formula 1.

The web page claims +600 built, another interesting link suggests the design is based (i suspect very loosely) on Steve Whitman Buster, although I can see some similarities.

I think PM is best placed on the reasons for narrowing the design of the body.

I do believe the strength of the PM design is the amenity to adjust the design to suit your own wishes and whims. One idea I considered was to make the back end of the Fus as a stick build. I discarded the idea this time to reflect accurately, with minor tweaks the PM design. This I have in principle done, it has been after my material restrictions, that I made a few minor changes, after satisfying myself that the Cassutt as PM as designed went together.

Those who have not picked up the modeling knife and plank of balsa are certainly missing out with this one.smiley

 

Edited By Erfolg on 12/09/2019 10:24:56

Edited By Erfolg on 12/09/2019 10:26:56

Erfolg15/09/2019 15:53:13
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Having spliced the sheets together I have sheeted the whole wing. I could say because the full size is fully ply sheeted. It is mainly down to scuff resistance (by clumsy me), easier to film cover and finally a stiffer wing (although on such a low aspect ration wing is hardly an issue).

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Again slightly different to how PM builds, although I guess we all have our favorite ways.

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Just need a body now and a few other things, hmm, it is getting there.

Dad_flyer15/09/2019 16:48:34
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I have been looking at various wing plans with sheeted l.e., t.e. and cap strips and wondered why not fully sheeted. The solid shape held open by the ribs should take away a lot of the need for stiffness in the spar as well?

Denis Watkins15/09/2019 17:03:33
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Solid forms, ie sheeted, DF, can crack right across, with certain materials

" Frame " structures, ie, Bridges etc, are much lighter and stiffer, less cost, etc

So you takes your choice

Fully sheeted can be much stronger but there is a weight penalty to consider

Frames, probably account for most of our models

Ribs and sheet, is possibly built more quickly

Edited By Denis Watkins on 15/09/2019 17:07:37

Erfolg15/09/2019 17:06:47
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My spars are vastly over sized, with respect to the forces you would expect from flying. There is a good reason however, the reason being that is what I have in stock. If there was a LMS, within a 60 mile round trip, I probably would have bought some lighter ones, the size that PM has specified.

What I have neglected to photo are the shear webs, it will have been on the basis of being boring. I probably stuck to whatever PM specified. These are important, doing quite a bit of structural work. To be very boring the parallel axis theorem indicates they are very beneficial.

Erfolg15/09/2019 17:10:18
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Denis what are DF?

Denis Watkins15/09/2019 17:20:03
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Sorry Erfolg

DF is Dad flyer, who posed a question

Nigel R15/09/2019 17:24:33
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Short for dad flyer I expect?

The webs are an integral part of the spar erf. Without them we do not have an I beam or C beam structure of course.

Dad flyer. Fully sheeted is a great method. It can be a little overkill with a built up wing where there are spar elements but with the lightest grade balsa sheeting you still end up with a light structure and it is tremendously rigid. Certainly more rigid than we really need I think as a million and one successful wings have been made using a d box construction. However the smoother surface is indeed a little easier to cover with film. It can be a little quicker to construct in my opinion too.

With a foam core wing then fully sheeted is necessary as the whole entity becomes a composite single structure.

Many ways to skin a cat.

Erfolg15/09/2019 17:40:50
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I think it is worth mentioning that on something such as the Cassutt, the concerns we might have with respect a large glider wing+100" with regard to tip weight, they are far less significant with Low Aspect ratio wings. I will probably expose the wing to greater loads in a less than text book landing (catching a tip, flipping over) than from flying,

Nigel R15/09/2019 17:50:43
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Erf these ultra low aspect ratio wings are real mild mannered animals near the stall. There is a lot of mushing before the break. Very tolerant beasts!

Erfolg15/09/2019 17:54:58
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Nigel

That is certainly the case, but there is no substitute for incompetence.

Whenever I know I have cracked it, I prove that my confidence is misplaced.

Which again points to the benefits of PM designs, robust!

Peter Miller15/09/2019 18:29:46
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The D box leading edge is in fact just as stiff as a fully sheeted wing but A is lighter and B is easier to reapair

kc15/09/2019 18:43:30
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Cheaper too ...sheet balsa is now expensive!

Erfolg16/09/2019 20:26:14
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Just to clarify, the wing still has the equivalent of a "D" box, the spars are separated by shear webs. It is just that the back end of the wing is sheeted, forming a further monocoque type section. The real purpose of fully sheeting is to more closely replicate the finish of the full size, non of that miniscule sagging between cap strips. Although if the full size had been a sown on rib and covering, i would have gone the capstrip route.

Anyway, now i have the Blue Foam (Dow Corning Floormate) wing tips with glass cloth, using Ronseal Hardglase as the adhesive. It makes for very resilient to denting covering. With WBV, my better half never complains, doe not even know what I am up to.

Nigel R17/09/2019 13:34:36
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Interesting technique. I've always used a lump of Ecuador Gold for block tips, but this would seem that it could be lighter and cheaper.

What weight cloth have you used? Is it quite easy to get the tip to blend with the rest of the wing? Does it present any problems at covering time?

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