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Old Oct 17, 2012, 02:15 AM
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Contest Kits Inchworm Fuselage

Any you guys out there got experience of this model?

I built one years ago (50 or so) and it flew very well indeed.

Am about to build another as an off the wall RC project for histart but the plan has got me stumped even though I got a laser kit from Belair.

There is no actual fuselage cross section shown on the plan although it appears to be a T section with triangular fillets and the nose/fuselage layout/shape makes no sense at all.

Having said that I seem to remember the original was a mystery as well.

Anyone got any ideas or an image of a finished nose/fuselage?
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Old Oct 17, 2012, 04:35 AM
RFJ
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I faced the same dilemma fifty years ago when I built my Contest Kits Inchworm. Not knowing what to do I left the rear fuselage as a T section and just filled and painted the bare wood.

Recently I mentioned this to a club old timer who told me that back then the usual way was to cover the T with tissue to produce a triangular cross section.

Here are some scans from Martin Pressnell's redraw of the kit plan which may help. If building it today as an r/c conversion I would be tempted to extend the 1/16" angled front side sheeting the full fuselage length.

Ray
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Last edited by RFJ; Oct 17, 2012 at 07:36 AM.
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Old Oct 17, 2012, 07:38 AM
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Wow that's great thanks a bunch................. this internet thingy is a wonderful resource.
I reckon if I had thought of it when I were a lad, I would be ruling the known world by now............

On that second image there is a measurement of 19.5inches.

Is that right to the fuselage end?

AndyC
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Old Oct 17, 2012, 08:09 AM
RFJ
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Andy,

That is the distance from the trailing edge of the wing to the leading edge of the tailplane.

On earlier kits this was 17.75". Later kits used 19.5".

Ray
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Old Oct 17, 2012, 09:20 AM
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Thanks Ray

The laser cut bits I have give 19.5 inches.

I just worked up a trial fit with my chosen radio gear and I reckon I need to move the wing back 20mm to make room and to reduce that massive nose weight (I hate carrying lead about) and then I can keep the triangular lower sections too.

I'm thinking 1mm ply doublers and 1/32 balsa sheet on the vertical spine back to behind the wing and Oracover overall.

I might also replace the centre section spruce main spar with square carbon tube as well.

AndyC
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Old Oct 17, 2012, 01:57 PM
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Inchworm eh - another memory jolt! The photo below is the model "storage" corner of my tiny workshop (boxroom) in about 1960 or maybe a bit later and the black fuselage hanging down diagonally from the top left is an Inchworm. I can indeed confirm that it was a "T" shaped structure tissue covered to make it triangular. I can also confirm that it needed a LARGE amount of nose weight, more than would fit in the available space. I only had one Inchworm but did have several of Contest Kits later A/2 glider, the Empress, one of which I actually converted to radio later with single channel pulse rudder (fly-ball actuator and McGregor Minimac Rx). IMO the Empress was a better model than the Inchworm.
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Old Oct 18, 2012, 03:33 AM
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Thanks Sundancer - I dont remember the Empress - but then where I put the car keys this morning is a problem too.

Could only get the Inchworm plan and kit.

You confirm what I recalled though - the nose weight is substantial - so I will definitely move the wing mount back - never did see the point of building a 250gr airframe only to add 50gr of lead to the nose.

be lucky
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Old Oct 18, 2012, 09:14 AM
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Can I pick your collective brains just one more time?

For RC would you go with the FF models flat bottomed tailplane section or go symmetrical?

And if symmetrical can the balance point still be around 50percent chord?

I was planning on staying simple with a front hinged/sprung all flying job pulled down at the rear with a kevlar thread.

be lucky
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Old Oct 18, 2012, 12:21 PM
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I can't see any reason for changing the tail plane section, but if you did change it to a "non lifting" section - i.e. symet or flat - then very likely the CG would need to be a bit further forward - me, I'd stick with the original.

An all moving tailplane (AMT) is a good way to do it. I have flown many models with AMTs, but normally these are pivotted with 20-25% of the area ahead of the pivot point, the rest behind. I have flown ONE with it pivotted at the leading edge, an APS Bicki glider, this worked fine, but needed a surprising amount of movement to produce significant pitch changes, which surprised me as I was thinking in terms of the 1/32" or 1/16" packing that I was accustomed to adding under the tail on free-flight models. Another good way, which I have used on converted F/F models, is to make a rocking platform pivotted at 20-25% and strap an entirely as per plan tailplane to it.
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Old Oct 18, 2012, 01:33 PM
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>On earlier kits this was 17.75". Later kits used 19.5".

The Inchworm is an extremely good A/2 - Open Glider, albeit keeping the tail surfaces light is a pre-requisite.

With its immediate success after the kit was released I have to wonder why Contest would change the design at all, not only necessitating yet more noseweight but also changing kit contents and redrawing a plan.

Could it be that the plan redrawn by Pressnell (the Inchworm copy I have in files) which gives the shorter 17.75" moment arm be representative of 'amendments' that sometimes are incorporated in his works? It would be interesting to hear if anyone has an authentic kit plan showing this measurement.
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Old Oct 18, 2012, 03:09 PM
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Thanks yet again.

Simple enough to use the original section tail pivoted at 25percent.

It will have to be raised slightly anyway to incorporate the 'down' movement.

Just been casting a lead nose weight using the original plan and its nearly 100grams.

No way am I strapping that weight onto the nose ................ so probably a lighter tail called for so maybe look at the structure rather than section.

Ordered the strip and stuff so will get building proper next week.

be lucky
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Old Oct 30, 2012, 04:45 AM
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Inchworm updated

So here it it all ready for test flights.

Nose weight is temporarily taped on as the balance point on the plan appears a long way back at 50percent.

Its now 40percent (even then )

Tail is all flying with 12 percent symmetrical section pull for down rubber band return.

Rudder enlarged a bit with closed loop kevlar thread.

Wing tips modified as experts say standard tip design prone to tip stalling due too short a taper on the trailing edge and severe washout.

Radio is Jeti 2.4, 2 x SD100 servos and 2cell 180 lipo (no regualtor as both Rx and servos are ok up to 9v)

Weight came out at 345gr /12 oz but that's with loads of lead up front (70gr plus) but my local experts say is good as this type of undercambered wing section needs a bit of loading to keep it flying.

Covering is Hobbyking clear yellow and opaque black.

Looking for light winds and a bit less rain and mud ..............
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Last edited by Motobiman; Oct 30, 2012 at 05:06 AM. Reason: expand description
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Old Oct 30, 2012, 05:04 AM
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Looks great. 12 ounces is light, as a F/F A/2 class model it had to weight over 14 ounces to comply with the A/2 (now F1A) rules.

You should be ultra safe at 40% CG, in fact I am prepared to bet it would be OK at 50% due to the powerful tailplane and longish tail moment.

Good luck with the flights, it should go nicely.
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Old Oct 30, 2012, 05:14 AM
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Oh right, I didnt realise the 14oz was a limit thing.

That probably explains why there is so much wood in the wing.

The mottling on the main spare is because we are using bungee so I used a 6mm sq tube spare and the rib cutouts are 6.3 mm sq so light balsa on top sanded down.

I was going to go further with the lightening with every other rib cut back to the main spare at the rear and composite balsa/carbon spares.

Same with the fuselage balsa/carbon composite.

The weight would likely come down to about 250 gr.

Anyway lets see......................
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Old Oct 30, 2012, 05:56 AM
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It probably wouldn't fly any better if it was lighter since it was designed to the A/2 limit. It's possible for a model, especially one with a "draggy" section, to be TOO light!
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