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Old Feb 15, 2015, 10:53 AM
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Bombardier Q-400 in Depron

The first time I saw one of these flying overhead it looked like the wings were just 'pencils' quite incapable of supporting that long. long fuselage!
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The originals for most of my scale Depron builds have been chosen to make best use of its lightness so the Q400 looked a suitable subject. To fly at a reasonable speed using modest power it was going to have to be light!
A six blade prop was not really an option but it would look acceptable with a 3 blade and to avoid any torque problems they would be 'handed' although on the full size they are not.
As I fly from a rough field hand launch and belly land is the only option. It means I save the weight of undercarriage and even more important on a Q400 the prop tips will just remain clear of the ground.
Hunting around I found a handed pair of electric 3 blade 9x5s - so it is a case of find the prop and then size the plane around them.
I had a pair of 2822 motors that would drive them ok on a 3s.
The nacelles of the Q400 are huge (well long anyway!) so it should be possible to put the ESC and a dedicated battery in there as well. By not having the battery in the fuselage it would also off load the wing at the root.
The 3 blade prop against a scale front view.
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It would require a 2.25" (57mm) diameter spinner.
This would give a fairly modest span of 61" (1550mm). The length on the other hand would be 76" (1930mm)!
The prop and spinner on my test stand.
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The motor looks rather 'lost' but it produces about 20oz (560g) thrust drawing 15A. This suggested a pair of small 1500mAh 3s could be used (each would still only be loaded to 10C at full power) and if I really made best use of the Depron I estimate there is a good chance of keeping the whole plane to less than 40oz (1100g) all up.
On paper at least it looks viable. As far a weight goes the biggest unknown is that huge fuselage so it is first.
The 3 view tile printed.
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The easiest bit to make is the centre part as it is just a 6" diam parallel 'tube'.
To keep it really light I have chosen to build it as a planked 'half shell' using top and bottom keel strips and closely spaced half formers.
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The half shell planked.
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Each plank is glued to the formers with UHU POR but the planks are glued to its neighbour by 'wicking' in foam safe CA which dries hard and can be sanded whereas POR although very tough remains 'rubbery' and is almost impossible to sand without damaging the Depron.
At this point you begin to appreciate a) How much effort is involved and b) How much more there will be to do!
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Last edited by Quorneng; Feb 19, 2015 at 07:11 PM.
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Old Feb 15, 2015, 05:49 PM
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Very, Extremely cool Q400 build Sir! Love the work on your fuselage so far!

Sub-me-Up!
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Old Feb 15, 2015, 06:41 PM
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I'm signed up. Looks great!
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Old Feb 16, 2015, 11:31 AM
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With the 'half shell' complete it is lifted from the plan. Note the small jury struts.
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At the wing mounting the formers are even closer spaced and it is locally 'lined' with an inner Depron skin for extra strength.
Adding the formers is quite complex process as first the jury strut is removed, the former glued on and then a 'flange' is added all around the inside of the former to create in effect a circular I beam. A new jury strut is added to hold the former square.
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All the formers added.
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Then its back to planking again.
There is considerable relief when there is only one plank left to do!
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As a fuselage it already looks pretty 'long and thin' but it is only just over half its total length!
But it is very light - just under an ounce (25g).
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Old Feb 16, 2015, 09:19 PM
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Cool! Never seen it done this way in depron, usually it's a "woody" in this method.

Watching with much interest!

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Old Feb 17, 2015, 06:10 PM
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I try to think of Depron as balsa except the sheets are bigger and much cheaper. With some modifications for the high stress areas there is no reason why the construction methods cannot be exactly the same.

Next is the nose section. It is built in exactly the same way but with double curves the planking is rather more complicated.
Formers over the plan
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Planking
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As this is a stressed skin structure and weight is critical the cockpit glazing is 'solid'.
The half shell lifted from the plan
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The nose section complete with a solid Depron nose block, some lightweight filler and a bit of sanding.
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There really isn't much inside!
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The key issue is will it match the centre section?
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Old Feb 17, 2015, 06:16 PM
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Quote:
Originally Posted by Quorneng View Post
cwrr5
I try to think of Depron as balsa except the sheets are bigger and much cheaper. With some modifications for the high stress areas there is no reason why the construction methods cannot be exactly the same.
Agreed. I'm familiar with it, just hadn't seen it used this way. (or didn't take note till now)

Another advantage is that it doesn't have a grain, which enables it to be curved in any direction as needed.
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Old Feb 18, 2015, 07:06 AM
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Actually Depron is a bit more flexible one way than the other. Not really a grain as such but It certainly helps to detect which to prevent (or delay) it splitting on a tight radius bend.

Grey Depron seems to be a bit softer and more flexible than white.

'Aero' quality Depron (but I think it may have been discontinued) is 20% lighter still and is softer and more flexible.
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Old Feb 19, 2015, 07:16 AM
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Ploughing on.
The fuselage tail section is made in the same way.
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As it is more or less a constant taper the planking is not quite so complicated as the double curves in the nose section.
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As it is a pure stressed skin structure it s important that the skin joints are as strong as the skin itself. Although UHU POR is good even in a butt joint each section has an additional full circle internal flange covering the joint.
When joined you have one very long fuselage.
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Actually it will be a tiny bit longer still when the APU tail cone is added!
The planking omitted from the tail is to allow the fin to be installed.
It weighs just under 2oz (55g)
It looks almost unreal but then so does this picture of the inside of a full size one!
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Old Feb 21, 2015, 08:45 AM
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The next job will be the engine nacelles as I really need to have them available to work out how they are going to be fixed to the wings.
Not only are they quite heavy in their own right with the flight battery in them but they will also have to be distinctly 'nose heavy' to counter the weight of the tail assembly. The joint with the wing is thus going to have to carry quite a bit of 'torque' as well'.
This gives an idea of its size compared to the motor and 1500mAh 3s.
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Fortunately quite a bit of the side of the nacelle is flat so it can be built rather like a conventional fuselage. As the Q400 promo literature points out each of its nacelles is longer than DHC's first plane, the Chipmunk!
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The underside is planked and a bulkhead added to carry the motor.
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So far so good but the hard bit will be creating the complex shapes leading to the spinner and the sharp edged inlet duct
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However with that huge inlet and the turbine exhaust right at the back it should not be too difficult to provide adequate cooling air.
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Old Feb 21, 2015, 09:21 AM
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Quote:
Originally Posted by Quorneng View Post
The next job will be the engine nacelles as I really need to have them available to work out how they are going to be fixed to the wings.
Not only are they quite heavy in their own right with the flight battery in them but they will also have to be distinctly 'nose heavy' to counter the weight of the tail assembly. The joint with the wing is thus going to have to carry quite a bit of 'torque' as well'.
This gives an idea of its size compared to the motor and 1500mAh 3s.
Attachment 7594208
Fortunately quite a bit of the side of the nacelle is flat so it can be built rather like a conventional fuselage. As the Q400 promo literature points out each of its nacelles is longer than DHC's first plane, the Chipmunk!
Attachment 7594212
The underside is planked and a bulkhead added to carry the motor.
Attachment 7594214
So far so good but the hard bit will be creating the complex shapes leading to the spinner and the sharp edged inlet duct
Attachment 7594224.
However with that huge inlet and the turbine exhaust right at the back it should not be too difficult to provide adequate cooling air.
Beautiful Work Q! are you adding retracts to your Bird?
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Old Feb 21, 2015, 04:07 PM
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Those look great! Nice work.
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Old Feb 22, 2015, 06:06 AM
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As the field I fly from is very rough it has to be hand launch and belly land so no retracts.

As this construction is rather 'make it up as you go along' it seems logical to concentrate on one nacelle to see how it turns out and only bring the second on to the same state when the first looks right.
The first former with the shape of the spinner and the air intake.
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The motor mounted with the spinner temporarily in place.
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Note on the Q400 the spinner is the same width as the nacelle.
All the formers have large holes in them for cooling air.
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The turbine exhaust.
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The inlet planked and the nacelle built up close to the back plate of the spinner.
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The top of the nacelle is left open to install the ESC which will be low down behind the motor bulkhead in the intake airflow.
The CofG position of the complete nacelle (including ESC but less battery) does rather show just how light Depron is.
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Now I have just got make another one exactly the same!
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Old Feb 22, 2015, 07:47 AM
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Very skillful work with your depron Q-400 Nacells Q, I find the darker Type to be more flexible and easier to curve than white depron, must be a chemical difference between the two.
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Old Feb 22, 2015, 09:03 AM
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One of the more innovative depron builds for some time...

Looking very good

Ben_E
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