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Author Topic: 30" Dumas DeHavilland Beaver C-2  (Read 2691 times)
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Dan Snow
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« Reply #75 on: September 11, 2018, 04:37:26 PM »

It is starting to resemble an airplane!!  At this stage weight at this stage is 71 grams, including prop, propshaft, wheels, motor and tail wheel wire.
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« Reply #76 on: September 11, 2018, 08:32:41 PM »

Nice work on getting the cowl to fit. Nice set of bones Dan

John
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« Reply #77 on: September 12, 2018, 06:23:37 AM »

You know, that really does look nice!   May I suggest you are no longer entitled to the title “beginner”.  It does have the look that it will fly quite nicely.  Nice to see someone so committed. 
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Dan Snow
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« Reply #78 on: September 12, 2018, 09:14:31 AM »

Thanks David, I appreciate the encouragement.
If I take Don Ross's figures to heart, this build is going to be on the heavy side. He suggests a wing loading of .5 gram/sq. inch, and I estimate that ready to go mine will bearound .8 gram/sq. inch.  I'm not concerned because with the fat fuselage and all the other drag inducing bits this was not an endurance model!  Grin Grin Grin
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Dan Snow
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« Reply #79 on: September 12, 2018, 04:43:56 PM »

This just struck me funny so I had to share. I was shocked to find the supplied wheels weighed in at a whopping 7 grams on my not so super accurate scale. I researched some foam wheels but hadn't found any yet. Then while rummaging for something else  in the shop I came across an antique block of balsa from who knows how long ago. What the heck, says I. About 20 minutes with a scroll saw and then the drill press and some sandpaper blocks and I had what I feel is a reasonable facsimile of a wheel.

Now the funny part is in the second picture.  As you can see, my new wheels, according to the same not so super accurate scale, weigh ZERO!!  Grin Grin Grin And that includes the aluminum axle tube!
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flydean1
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« Reply #80 on: September 12, 2018, 05:49:40 PM »

YOU'VE FOUND IT!!!!  A SUBSTANCE OF INFINITE STRENGTH BUT NEGLIGIBLE WEIGHT!!! Grin Grin Grin Grin Shocked Shocked Shocked Shocked Huh
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Dan Snow
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« Reply #81 on: September 12, 2018, 06:38:56 PM »

Here's another crazy idea, a holdover from my R/C days.  Has anyone ever considered a bolt on wing for some of the larger scale models? I'm thinking of using 3 #4-40 nylon screws into threaded inserts. The photo shows where the blocks would be located, but they aren't glued in yet. I was thinking since I eliminated the weight of the plastic wheels I might get away with it weight wise.

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« Reply #82 on: September 13, 2018, 05:24:41 AM »

In a word Dan, yes - and like you it emerged from my R/C days - so much neater than the hefty rubber bands one needed for a 5 or 6 ft span R.C sport job.  Now some will suggest magnets -which I have also used but they can be heavy.  Other will say that the nylon screws are unforgiving and won't release the wing in the event of a prang. But you cannot have everything!!

My nylon screws weigh nothing - like your wheels.  But I also have to confess that in many cases on models less than 30 inch span I stick the wings on - a few drops of cyano here and there is usually sufficient and in the event that I need to adjust incidence say I drip a little of the solvent on the spot and with the aid of a scalpel things come apart mostly quite well.  Likewise on the tail plane. 

Come to the conclusion  cyano is a bit of a boon!   Wink
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LASTWOODSMAN
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« Reply #83 on: September 13, 2018, 08:32:10 AM »

     Hi Dan.   Your "Jumbo" Beaver looks pretty good.    Cool    I have a couple of questions about the kit if I may.   What does the kit call for in regard to positive incidence degree angle of the wing, and how much dihedral does the kit call for?   How thick is the plastic nose cone?  Is it just glued in place over the nose framework (how much overlap?), and is there any balsa reinforcement for the front of the plastic nose cone? where the thrust bearing sits?  Does the kit also recommend infill planking of the nose?   Thanks.  Also, could you post a pic of the plan sheets?   Thanks.   

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« Reply #84 on: September 13, 2018, 09:55:06 AM »

cyano is a bit of a boon!   Wink

That is a fact!  I discovered CA back when I returned to Free Flight (Always Capitalize) in the late '90's.  I got so enthused that I took a special trip to Miami where it is delivered in super-tankers.  It was called "The Boondocks" Roll Eyes Roll Eyes Roll Eyes

Please forgive the Lower Alabama humor.
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« Reply #85 on: September 13, 2018, 10:34:44 AM »

Here's another crazy idea, a holdover from my R/C days.  Has anyone ever considered a bolt on wing for some of the larger scale models? I'm thinking of using 3 #4-40 nylon screws into threaded inserts. The photo shows where the blocks would be located, but they aren't glued in yet. I was thinking since I eliminated the weight of the plastic wheels I might get away with it weight wise.


Actually, 4-40 bolts are overkill Wink!  A pair of 2-56's will still have more than enough strength and are more likely to give in a prang.
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Dan Snow
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« Reply #86 on: September 13, 2018, 12:02:33 PM »

    Hi Dan.   Your "Jumbo" Beaver looks pretty good.    Cool    I have a couple of questions about the kit if I may.   What does the kit call for in regard to positive incidence degree angle of the wing, and how much dihedral does the kit call for?   How thick is the plastic nose cone?  Is it just glued in place over the nose framework (how much overlap?), and is there any balsa reinforcement for the front of the plastic nose cone? where the thrust bearing sits?  Does the kit also recommend infill planking of the nose?   Thanks.  Also, could you post a pic of the plan sheets?   Thanks.  

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Richard

Nothing in writing on the plans about incidence, but measuring them it looks like ZERO degrees on both wing and stab using the thrust line as a base. There is 1 3/16" dihedral on each panel.
The cowl is .020" thick and made in 2 pieces, the nose is vacu-formed  and the back half or so is a ring glued up from a supplied sheet. Note: As drawn on my plan the pattern for the cowl ring was 5/16" Too Short! I have notified Dumas.
The cowl is glued to a plug that slides into the nose of the fuselage. There is no structure between the thrust bearing surface and the plug but I will be adding some. No, I don't see anything about infill planking.  NOTE: the 1/16" square supplied in my kit for stringers was so light and soft that a sneeze would likely break it. I have made many repairs because I didn't pick up the fuse on a vertical joint.

Hope this helps.

P.S. I moved the rear motor peg forward one bay on mine.
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Dan Snow
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« Reply #87 on: September 13, 2018, 12:11:40 PM »


Actually, 4-40 bolts are overkill Wink!  A pair of 2-56's will still have more than enough strength and are more likely to give in a prang.
[/quote]

The more I look at the model, the less likely it is I'll make the wing removable. There is some rather funky structure going on to blend the top of the wing, the fuselage and the windscreen together. If I put this structure on the wing there is nothing to attach the top of the windscreen to. If I leave it on the fuselage then I don't have anyplace to attach the tissue covering the top of the wing fairing. And then I would need to make the wing struts detachable as well, so I'm thinking it's a lot more weight and work when all I need to do is build a bigger box to put it in.
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LASTWOODSMAN
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« Reply #88 on: September 13, 2018, 01:30:55 PM »

     Hi Dan.  Thanks so much for posting your plan pics.  Smiley  It is really nice to see the plan before one buys the kit.   It seems that Dumas might have had a different designer for each model of my 30" Speedster and your 30" Beaver.  My original rear peg on the Speedster appears to be a full bay further to the rear (see pic), just under the leading edge of the stab,  as compared with your Beaver's original rear peg location.   Maybe the guy who designed the Beaver might have already moved the peg one bay ahead originally.  Huh  I know my Speedster flew better after I moved the rear peg ahead one bay, to about the same position as your original rear peg .    Undecided  

LASTWOODSMAN
Richard
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« Reply #89 on: September 13, 2018, 05:04:07 PM »

Re:  Rear peg location issues.

For many years, designers of Rubber Scale Free Flight models stuck the rear motor anchor as far aft as possible.  They were under the mistaken impression that allowed a "longer" motor.  Indeed, some actually incorporated the rear hook into a combined rear hook and tail skid.  This allowed the rear of the motor be loaded in from below, necessitating leaving one bay on the bottom uncovered.  There was much hue and cry saying a rear anchor that protruded from the side of the airplane was "unrealistic".  I think I remember one UK designer saying, "You never saw a tube stuck through the side of a Spitfire"! 

I think the first time I saw a forward rear peg was on one of the winners of the late lamented MODEL BUILDER magazine International Peanut Scale Postal.  It was a model of a Folkerts SK3 racer.  The model not only graced the cover, but an extended construction article also appeared.  He spent a great deal of effort actually calculating the requirements to score very high using the existing rules.  There were many innovations not seen often in scale models.  First was the "eggshell" construction without any full formers, and also condenser tissue covering.  The rear peg was located very near the trailing edge of the wing!  He said this allowed a motor length of 3X the fuselage length, and allowed a flight potential approaching 2 minutes!

After this, I bought a copy of Bill McCombs book, "Flying and Improving Scale Model Airplanes".  This is an excellent reference, and I think is still available from his daughter.  Location of the rear anchor such that it is about as far aft of the CG as the prop hook is forward is proven mathematically.  In addition, in a related study, he shows the effect of slightly enlarging the stab area, and calculating a new aft limit of the CG, would allow use of a longer motor because the rear anchor could be further aft without exceeding this "balance".

There are many side benefits of this location, not the least of which is allowing testing with a short motor initially, and then a longer one later without upsetting the balance of the airplane. 

I test with a motor cross section of 2X what I plan to fly with.  Using a torque meter, I discover the maximum safe torque the model will handle.  Since the motor is so "fat" it will "torque up" quickly on very few turns.  Then because there are few turns, the model doesn't fly as far.  Shorter chase for these aging legs.  Then, add the flying motor, and stay below 80% of max safe torque.  Fewer busted models.
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« Reply #90 on: September 13, 2018, 05:12:28 PM »

I'm thinking of stuffing a ring of EPO inside the cowl to add stiffness to the circumference and give it compression resistance against the motor.

Good idea or not?  The weight is maybe a gram, and preliminary checking shows I'm going to need nose weight any way.
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Dan Snow
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« Reply #91 on: September 14, 2018, 09:31:07 AM »

Spent about 20-30 minutes working on getting some weight out of the Beavers butt!  I know it doesn't look like much, but every gram I can take out back here is 2.6 grams I Won't need in the nose!

This got me to thinking about the tail wheel. But not sure if there is anything I can do there.
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« Reply #92 on: September 14, 2018, 10:12:03 AM »

Spent about 20-30 minutes working on getting some weight out of the Beavers butt!  I know it doesn't look like much, but every gram I can take out back here is 2.6 grams I Won't need in the nose!

This got me to thinking about the tail wheel. But not sure if there is anything I can do there.
My thoughts, saving weight in the aft end is highly desirable. But one needs to have a structure stiff enough to hold trim settings. I usually don't like holes in balsa. This is because balsa has a strong grain. These holes take far too much strength out of the part for the amount of weight they save. The load path now has to put the grain in shear to go around the hole.  I also don't like the thin the perimeter wood like you did on the rudder. Again with the curved shape of the tail, many areas of the outline has the grain going in the wrong direction.

I often use the supplied parts to make molds for the making of laminations (outline hoops). Ross's book goes into detail about this.

Bolt on wings at this scale offer little or no relief from crash damage as even 2/56 nylon is much stronger than the surrounding 3/32 balsa stringers. The balsa will break before the nylon bolts will. I like removable wings for storage and transport concerns. If looking for knock off wings I think Don Ross's book offers some good work arounds.

From another thread. Flight trim is very dependent of flight speed. If using warps their effect changes by the square of the flight speed (this is from the flight equation).  So if you are using a warp to fly straight in a glide. This same warp will produce 4 time the force should the speed double, like in a dive or under power. You most likely don't need 4 time the force and the model will over react to the warp. This is why often times you will see folks using weight out on the wing tips to trim. This minimizes the speed sensitivity of a trim setting (mass is the same regardless of flight speed).

All the best,
Konrad
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Dan Snow
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« Reply #93 on: September 14, 2018, 07:59:04 PM »

I understand what you're saying Konrad, here's the thing, I considered a removable wing for ease in transporting not for reducing crash damage. The stab and rudder pieces are all laminated so the fibers are glued together and to the other part.
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« Reply #94 on: September 15, 2018, 06:47:56 AM »

I have found the added benefit of removable wings is that an arrival generally causes less damage especially in the trimming stages. The weight penalty is small and would be rapidly overtaken by the weight of repair material. Magnets really earn their keep especially on low wing models and for holding noseblocks in. Generally you need noseweight anyway and this is usefull weight. Again there is a limit to adding lightness at the tail. The ability to hold trim settings is more important.   
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« Reply #95 on: September 15, 2018, 12:38:08 PM »

Strictly speaking you would be right calling the layered  (in plan view) outline  a lamination.

Most folks when talking about laminated out lines are thinking of hoops, where the fiber follows the shape of the outline.

This is a much stronger and much lighter construction method. And with the advent of the radar range oven as fast or faster than conventional pieced outlines.

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=12443.msg87423#msg87423
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« Reply #96 on: September 17, 2018, 04:08:16 PM »

Sorry there hasn't been any real progress on the Beaver for a few days.  I did finish stuffing the cowl and gluing it to the nose plug, pretty happy with how that came out. Still waiting for the plastic putty I ordered for the cowl. I think it's coming by mule train! Sanded the streamlining into the wing struts and pretty much about ready to start covering.

Question: On planes with fixed gear that have fairings on the gear struts, do you glue the fairing to the fuselage and the wire or just to the wire? The planes show the fairings glued to both. I know that stiffens the wire, but as I look at it if I snag some grass or weeds or such on on landing all that load goes into and could take out the bottom longeron.

Another reason for lack of progress is I got distracted with the crazy idea of a sort of No-Cal XB-70 Valkyrie.
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« Reply #97 on: September 17, 2018, 11:03:14 PM »

I'm not much help to you with gear fairings etc.  Check LASTWOODSMAN's posts of his adventures with his Rearwin.  He went through quite a bit to keep it in the air after multiple crashes.  One of his issues is keeping the fairings and wheel pants on such that he did not have to do major repairs after each flight.  The Rearwin is about the same size as your Beaver.  His persistence where most of us would have just binned the model and started over is remarkable.
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Dan Snow
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« Reply #98 on: September 19, 2018, 03:18:39 PM »

Made a little more progress on it, All flying surfaces now covered, but not shrunk yet.

Here's a bit of a quandary. The fuselage width at the wing saddle is 2.66". The width of the wing center section is 2.75" Therefore the wing is only touching the fuselage sides at the leading and trailing edge. Need to think about this for a bit. I know the wing struts will take some of the flying loads, but seems to me they should have matched. That may not be scale, don't know, but structurally seems to make more sense to me.

The 1/16" stringers on the fuse are so soft that the thought of covering the fuselage is giving me the willys!!
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« Reply #99 on: September 19, 2018, 06:09:55 PM »

A strip of 1/16 x 1/16 glued on the inside of the 2 centre ribs flush with the bottom of the rib will do it
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