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Author Topic: 1960s Coupe d'Hiver Postal  (Read 158441 times)
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Mark Braunlich
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« Reply #125 on: July 06, 2014, 08:37:50 AM »

Sean,
Yes, September is included in the flying period for those in the Southern Hemisphere.
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« Reply #126 on: July 06, 2014, 05:06:44 PM »

OK, you guys are having way too much fun.

I've started construction of George Batiuk's CdH (see page one of this thread or my CAD Drawing: http://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=6234&mode=search )

So far I went to Kinkos and got two copies printed of the drawing, cut out the rudder and fin, striped the 3/32 square for the fuselage and glued the 1/6th sheet for the forward fuselage.

I don't know that I'll be able to enter in this postal, though, as I will be making a couple of deviations:

1) I will be using a KSB DT clock-work timer.

2) As there is no information about the front-end, I will be using an old FAI Models 'Teeney Torque" Montreal stop mechanism. I am aware that a Montreal Stop is not "period", but building front ends has always been my nemesis.


I'll leave it up to you guys whether to allow me to enter the airplane or not. I'm going to build it no matter what, though...



I wouldn't use a KSB-way too heavy-they're about 20g-which is way way too much weight to put in a Coupe (unless you're deliberately going for the 100g class...;-)  at best you want a Tomy or equivalent electronic timer, unless you like messing about with those pestiferous viscous types

(this should not be taken as any criticism of the KSB itself-they're excellent timers-I have about a dozen of them in use-reliable and easy to set-but in this case just too heavy for the proposed model class......)

 ChrisM
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Mark Braunlich
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« Reply #127 on: July 06, 2014, 09:37:27 PM »

                       Question!     Prop blades, I have the diameter and pitch on the plan, so can I mould the blades on a form or wrap them around a can rather than try to find a suitable block to carve it from?
                                                                                                                                             regards Dave

Yes! 
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« Reply #128 on: July 07, 2014, 03:07:47 AM »

Thanks Mark  Grin
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dputt7
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« Reply #129 on: July 09, 2014, 08:35:57 AM »

OK fuse number 2 completed, this is a new experience for me, being a mostly design as you go scale builder I don't usually rebuild major parts but as this is so limited in power I had to do something to reduce the growing weight. The first fuse used 6lb 3/32" sheet sides and 3/32 square longerons of about 10 lb wood.  I stripped some 7 lb 3/32 but could not bring myself to use such flimsly balsa on such a vital part so I used the same 10 lb wood with diagonals of 1/16th and built a full length structure and sheeted the forward section with 8 lb 1/32, I also saved a bit redesigning the pylon and saved 10 grams. This was a useful exercise but it took the gloss of an otherwise enjoyable build. Its easy to see the advantages of continually building / rebuilding the same model and improving it as you go but there are far to many models on my list for this practice to continue.
regards Dave
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sparkle
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« Reply #130 on: July 09, 2014, 04:32:56 PM »

 Sad I feel your pain!
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ffkiwi
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« Reply #131 on: July 09, 2014, 05:58:22 PM »

Among all the areas where you can save weight-scrimping on the longerons is NOT the place to do it.....you made a wise decision not to use the 7-lb stock.  Spacers....yes, longerons no. I generally use 10 or 12-lb wood for 3/32"  longerons for Coupe and/or small vintage...

 ChrisM
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billdennis747
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« Reply #132 on: July 10, 2014, 01:47:09 PM »

My Baron Knight is about done but I can see no info on the plan as to where to stick the cg. But then I can't see the butter in the fridge either. Can anyone give me a clue before I settle for halfway?
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« Reply #133 on: July 10, 2014, 03:13:49 PM »

Bill, most of the 50s coupes had the CofG in the 60-70% range. The Garter Knight CofG is 73%, but the 'experts' (not me) who fly gadgetless models suggest 60% or slightly further forward plus more decalage to help climb during the cruise. I'd have thought 50% is perhaps a bit far forward, but for me the aim would be to get something in the ballpark without adding noseweight - unless of course you need it to get up to 70g.

Peter
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billdennis747
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« Reply #134 on: July 10, 2014, 03:45:02 PM »

Thanks Peter. Yes, I just spoke with J O'D and he says the same. Somehow I have managed to get this thing down to 58g, so I can ballast away to my heart's content
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DaddyO
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« Reply #135 on: July 10, 2014, 03:50:04 PM »

My Baron Knight is about done but I can see no info on the plan as to where to stick the cg. But then I can't see the butter in the fridge either. Can anyone give me a clue before I settle for halfway?

I'd suggest 50% is a bit far forward Bill, my coupes have CofG's about 10-15% further back. As Peter suggests slightly further forward might help the cruise part of the climb, but too far forward means a big old loop at the start, so lots of downthrust needed which might kill the cruise . . .  Undecided

I'd put it at 60% and take it from there
Paul
ps The butter's behind the dish of salad stuff  Cheesy
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« Reply #136 on: July 10, 2014, 04:01:36 PM »

Found it!
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ffkiwi
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« Reply #137 on: July 10, 2014, 04:48:27 PM »

My Baron Knight is about done but I can see no info on the plan as to where to stick the cg. But then I can't see the butter in the fridge either. Can anyone give me a clue before I settle for halfway?

A rather serious oversight omission from the plan as I discovered with the latest rebuild [it might also explain why I struggled with the original one back in the early 80s...]  The 60-70% suggestions are good-I do recall eventually gluing a piece of sheet lead (~4g) on the nose of the original, towards the end of the time I flew it-so must have started with a fairly aft CG initially. 50% I would consider too far forward for a conventional Coupe layout......mind you there have been the seriously unconventional ones as well.............which I wouldn't presume to comment on as far as CG is concerned...

 ChrisM
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Bingo Fuel
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« Reply #138 on: July 10, 2014, 07:48:11 PM »

Hi all,  I'm going with Brass Monkey from the tiny plan in June '63 Model Airplane News.  I never built a box fuselage with all warren truss so to me putting the two sides together should be a challenge.  Some things seem strange on it like  1/8" sq longerons forward of the wing and 3/32" sq behind the wing.  The truss parts all 1/16" sq?  But with help, I had the plan blown up to full size of which not everything measures out right so I guess I will have to redraw the whole thing.   Anyone out there built Brass Monkey?   Any tips would be welcome.  Regards,   Bingo
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« Reply #139 on: July 10, 2014, 11:23:43 PM »

Thanks Peter. Yes, I just spoke with J O'D and he says the same. Somehow I have managed to get this thing down to 58g, so I can ballast away to my heart's content

58g?/?  Hells teeth- I wish I could manage to build like that-I've never built a Coupe down to weight yet-in 30+ years of trying-my best came in at 74g.............

 ChrisM
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« Reply #140 on: July 11, 2014, 01:46:59 AM »

Bingo,
Brass Monkey is a beautifully designed, ELEGANT model. However, the fuselage thumbnail in MAN has inconsistencies (omissions) that can be corrected. I built as drawn to see if the errors would cause problems, and they don't, but aesthetically fixing the mistakes is worth a small amount of effort. And within the rules.

I enlarged to plan at the copy store and taped the sections together. FIRST, draw a reference line from the prop wire through rubber anchor to the tail of the fuselage so the copies can be perfectly aligned. The longerons seem to be full length sticks, 36 inches long. 

Errors: First, the angled trusses between longerons in the side view should ALSO be shown as reversing, when bulding the second side.   Look at some other plans and you will see this marked with hatched lines in larger scale plans. To correct on the Brass Monkey, simply draw lines from the intersection of the trusses and the longerons, at 90 degrees to the centerline, and connect each to the opposite longeron. These points show where the trusses intersect the longerons of the second side frame. Adding scrap pieces under second set of trusses will keep the trusses aligned with the second pair of longerons.

How to add the cross pieces when the two sies are dry:  Cut two rectangular forms from 1/16 sheet that are longer than the distance between the longerons on the side view. Temporarily glue them at the front and rear where the width is the same. Keep them square and let them dry. Now you can handle the fuselage and begin installing the angled cross pieces in the area between the spacers so they intersect where the vertical trusses meet the longerons. Work in pairs top and bottom. After these have dried, pull the tail together and glue the end so the fuse is straight and true, and then repeat with the nose. Remarkably simple.

If you simply follow the plan as drawn, some trusses will terminate in the empty spaces along a longeron. This is OK because the fuselage does not carry any stresses---they are borne by the motor pod.

Second problem, the angled trusses shown on the top view become too long without enough width between the longerons to be very functional at the tail. I used strong 3/32 x 3/32 for the longerons and 1/16 x 3/32 medium balsa for the trusses. Use thinned white glue and double glue (Titebond 2  and 3 turn orange in sunlight). Trusses were angled as drawn until the width became too tight on the top view and I substituted conventional trusses set at 90 degrees for the last 12 intersections.

In addition, the motor tube does not clearly specify a round or square cross section; I made mine square because it was the easiest to support near the aluminum cross tube to build-in side and down thrust. After building the motor tube you will have to improvise supports underneath to keep the rear of the motor tube from moving around, and to set 2 degrees of down and side thrust without adding friction to the prop shaft. This is a good starting place and smaller trimming adjustments can be made between the motor tube and the nose block in the field.

Don't be scared off. Warren truss fuselages are the EASIEST, LIGHTEST structures to build because small inaccuracies in the length of the trusses will not distort the longerons; essentially the trusses are self-adjusting as you install them if the longerons are well supported by pins set outside. And your trusses do not have to be as accurate as with 90 degree installations of trusses between the longerons. This fuselage is REMARKABLY stiff and strong and does not deal with the torque and compression of the rubber.  VERY smart design that eliminates the complaints aired here about misaligned fuselages. The elegant rudder shape is also strong.

This is as far as I have gotten; a heavy work load (job) prevents working on the prop, wing and stabilizer. 

Hard to explain in words .... but it is really a SIMPLE fuselage to build.

Joe     
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billdennis747
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« Reply #141 on: July 11, 2014, 04:19:19 PM »

Well, I'm ready and shall be trimming on Sunday at Luffenham.
However, somewhere between my 58g yesterday and finishing today (pylon, hooks, peg, snuffer tube, NOSE BALLAST, etc I now have almost a 75g model! I couldn't believe it. But it has been a very interesting process and I intend to carry on in F1G, with wooden models. To save weight, I shall use two blades ( I love these plans that show a very optimistic piece of lead as counterbalance, sometimes referred to as a 'blob'! Mine is not a blob) and take 6 inches off the back end

wing  20g
fuse and tail  30g
prop   16g

total  66g

plus about 8g noseweight
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« Reply #142 on: July 11, 2014, 05:03:02 PM »

Bill

Have you bent the counterbalance weight wire back by about 10-15 degrees in a gentle curve? Also it's normal to bend the wire clockwise by a few degrees - this all helps the balance when the prop is rotating. I apologise if you know this already, it's just that in the photo, the wire looks dead straight Roll Eyes

Happy trimming, shame Sunday looks as though it will be a bit breezy.

Peter
ps the model looks very nice even though I have an aversion to diamond fuselages.
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billdennis747
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« Reply #143 on: July 11, 2014, 05:12:50 PM »

Peter, no I have yet to bend it back. I hadn't heard of the clockwise bend - why does that work? In fact why does the rearward bend work?
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« Reply #144 on: July 11, 2014, 08:19:49 PM »

Hi all,
   Joe,  thanks so much for the description of building the Brass Monkey fuselage.  I will certainly build it to your instructions.  Yes I also believe it to be very elegant and the photo of it in the old MAN certainly got my attention.  I really like the high aspect ratio wing and the polyhedral.  I like the false rib idea and the spar arrangement. Most of all I love the idea of the motor tube that takes the strain and can save the fuselage if it (motor) lets go.  Also like the two blade prop.  I have taped my blown up plan together and started a good redraw.  I shall take to the idea of straight cross members in the far rear fuselage  Thanks again so much.
   Bill, your BK  looks very good.  The idea of black tissue in spots is a great idea in being able to spot it in flight.  Good luck with tests.  Regards, Bingo
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« Reply #145 on: July 12, 2014, 02:51:16 AM »

Bill

It's all to do with dynamic balancing. I do it because those who know better than I advised it and it certainly smooths the motor run. However if you want a detailed and erudite explanation, Martyn Pressnell wrote an article on it in SAM 35 Yearbook 11. It's a bit long for me to precis and contains maths Roll Eyes Suffice to say that I get to a reasonably smooth outcome by trial and error.

Peter
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« Reply #146 on: July 12, 2014, 03:20:44 AM »

The idea I believe Bill is to get the weight balancing the prop whilst rotating (Centrifugal force and old those other pesky forces come into play)  Roll Eyes

Model looks great, and I'm glad it's not just me that finds that the final fettleing adds more can a couple of grammes. I'm tempted to try one of these old coupes to join in the fun (and have even chosen which one), but currently fiddling with 32nd sq. on a pistachio.
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« Reply #147 on: July 12, 2014, 03:47:51 AM »

Here are a bunch of messy sketches of coupe d'hivers (is that the correct plural?) including lots of technical specs/
http://www.prop.at/prop_magazin1961-285-oemv-modellsport-04-1961-pdf.pdf

Notice that this includes Ailbass, qualifying it for this postal. However the airfoil shown here is rather at odds with more detailed plans of Ailbass that I've seen!
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billdennis747
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« Reply #148 on: July 12, 2014, 03:59:42 AM »

Thanks both. I would be interested historically why single blades became popular? They must be heavier, more tricky to balance. Or was it about speed of construction - you read about people churning lightweights out in a few days to lose them at the weekend.
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« Reply #149 on: July 12, 2014, 10:52:21 AM »

Bill

It's all to do with dynamic balancing. I do it because those who know better than I advised it and it certainly smooths the motor run. However if you want a detailed and erudite explanation, Martyn Pressnell wrote an article on it in SAM 35 Yearbook 11. It's a bit long for me to precis and contains maths Roll Eyes Suffice to say that I get to a reasonably smooth outcome by trial and error.

Peter

The article is available at the Builders' Plan Gallery as "Single Blade Propellers".

http://www.hippocketaeronautics.com/hpa_plans/categories.php?cat_id=59

Nice models here. A joy to follow your builds.

Regards
Julio

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