A scratch build twin.;)
I have seen these flying out of Liverpool Airport and at any altitude the wings look like pencils!
It seems like a good subject for a really lightweight design and with that tiny wing area it would have to be as a park flyer. :D
Apart from the challenge of building the long fuselage it has some features that would help the build.
The wing is mounted completely above the fuselage 'tube' so structurally easier to do.
The engine nacelles are huge so no problem fitting the ESC and flight battery in each side.
Although a 6 blade prop is really too difficult however even a 3 blade would be huge.
So a hand launch, belly land all Depron twin.
That's about as far as I have got. The real question is could I possibly finish it by 15th Sept?
We shall see
Should be awesome. Good luck! Can't wait to see it.(Amazing those little wings carry all that! )
A little bit further.
On of the problem starting from a small 3 view is the lines get very blurred when printed out at the intended size.
So after a few hours redrawing the small 3 view line by line on my computer but at a much larger scale the lines remain sharp even when printed out big.
This is a small size version of the file that can be downloaded.
The big file is 9600 pixels wide. The same bit now looks like this. :D
I have also done the side and front views.
Now I have to work out how on earth to actually make something this big in sheet Depron.
It is just over 6' 6" (2000mm) long. :eek:
Yes, my Concorde is a bit longer but that had a wing built along most of its fuselage length. This fuselage will be supported just in the middle. :concern:
Why this particular size?
It is set by the only 'handed' pair of 3 bladed props I could find. 9x5x3.
Find the props and build the plane to match! ;)
At this stage any amount of thinking things out can save a lot of time in the long run.
For a really lightweight build the real problem is the fuselage (its by far the biggest bit!) rather than the wings. The lightest construction method is a stressed skin over closely spaced 'ring' formers much as is done in full size.
A 3mm Depron skin needs to be supported at least every 2" (50mm) which means there would be 23 identical formers in just the parallel portion of the fuselage. :concern:
I did consider making these 5.75" (150mm) diam formers complete in one piece but it would use up a huge amount of Depron.
I eventually chose to build the fuselage as a 'half shell' over the plan from top and bottom keels and to save Depron each former ring would be made up of quarters.
Two quarters joined to make the half circle formers being added to the keels. The keels are joined by thin 'jury' struts that will be removed once the other side is added
When all the formers are in place a start can be made with the planking.
I had not intended to use grey Depron but this portion of the fuselage is over 43" (1100mm) long so the planks have to be cut from the big 1250mm sheets that are only available in grey.
Having proposed this for the $100 twin contest there must be a real possibility that such a complex build will not be completed in time but I will keep plugging away just in case.
This should be a pretty amazing build. Best of luck with it!
With the half shell almost fully planked it can be lifted from the plan.
A start on the other half of the formers.
It occurred to me that the fuselage would need local reinforcing under the wing mount to resist the weight of the wing in a belly landing so extra formers with full internal sheeting.
It is also where the plane will be held for launching.
At this stage the fuselage has little torsional rigidity so the planks will have to added alternate sides to avoid building in a twist or a banana!:concern:
Completing the fuselage formers is a slow process.
This shows the sequence.
First the remaining half of the former ring is glued on and the jury strut removed.
Then the one piece inner flange is added to turn the former into an "I" beam. A tricky operation as it has to be cut to exactly the right length to ensure it makes contact all the way round the inside of the ring.
A flange is added to the lower keel to also turn that into an "I" beam.
Finally another jury strut is added to keep the former square.
Access limitations mean that each former has to be completed before work can start on the rest one and there are 23 to do!
Eventually it looks like this.
Now there just 17 more planks to add! ;)
And it definitely wont be complete by the 15th so it is no longer an competition entry.
I suppose I could submit my Hamilcar X. It was first built nearly 5 years ago but has only recently had its true maiden flight! (All the previous attempts were only seconds long and ended in a crash!)
The last plank, or rather the space where it is has to fit!
always the most difficult as it has to fit both sides all along it length.
The engine nacelles are huge (16" long!) and would not look out of place as the fuselage of a small park flyer. :eek:
There should be masses of room to fit the motor, ESC and battery in each.
With the radio in the wing and the rudder & elevator servos in the T tail (their cables will run in the dorsal spine) it means the fuselage will have absolutely nothing in it! :D
The nacelle has a substantial air intake and exhaust so the intention is to use it to cool the ESC.
The drum mount is fixed on to the bulkhead using self tapping screws. The particle board is locally 'hardened' with cyano.
The 1200kV Emax test mounted in the nacelle.
It looks rather 'lost' behind the huge spinner.
The nacelle and intake complete.
Technically the spinner is the wrong shape (too pointed) but it fairs in well with the nacelle. Quite a bit of fine sanding still to do.
The exhaust duct at the rear.
All the formers have large holes in them.
This is about as far as the nacelle can go until the wing is built.
Now I have just got to make another exactly the same!
Thigs move on slowly.
The nose section under construction built the same way as a half shell over the plan.
Obviously the planking is very much more complicated that the constant section of the fuselage.
The half shell off the plan
The nose complete.
And added to the main part of the fuselage.
The engine nacelles are in about the correct position to give an idea of the overall size.
I had a small trick to get a smooth joint. The cockpit was actually built very slightly under the fuselage diameter. The cockpit skin was then slit several times for about 5cm. This allowed the skin to 'petal out' to exactly match the diameter of the fuselage. The slits were only 0.1mm wide so could easily be filled once the nose was glued on.
Impressive work, sir.
As this is not in the twin build contest any more things have slowed down a bit coupled with a long period of very good flying weather!
With the rear part built the fuselage is now at its full length.
Near enough 6'6". Quite a bit of sanding and filling to do.
The planking has been left off the top at the rear to allow its enormous fin to be 'built in' to the fuselage.
Having finished the cascade ducted Harrier work can start again on this.
Being a T tail the fin needs to be fairly stiff but on such a long fuselage it is also a long way back. Weight is critical so I decided to use a substantial 'flush with the surface' balsa/Depron/balsa spar like this.
The fin spar will extend right through the fuselage.
Lifted from the plan the 3mm Depron skin can be added.
The missing section of skin is to allow the rudder servo to be added.
The fin installed on the fuselage.
The fin spar as actually inserted into the fuselage lower skin as shown by the red circle.
The tailplane is next.
Slowly creeping on. The tailplane.
All 3mm Depron with the tapered balsa spar flanges as part of the skin to give the maximum depth. The Q400 tailplane uses a conventional air-foil section but it is upside down.
The elevator halves are joined by a short glass fibre tube.
The horn is glued to the mid point of the tube so it will be hidden inside the fairing on the top of the fin.
The elevator servo is almost completely buried in the tailplane.
The substantial fairing on top of the fin completely hides the elevator linkage - just!
The rudder servo is built into the lower part of the fin with just part of the servo arm protruding.
The rudder is centre pin hinged top and bottom.
To reach the radio, which will be in the wing centre section, the servo extension leads have to be nearly 1000 mm long. :eek:
This picture does rather show how 'spindly' the wing is compared to the fuselage.
The span is quite a bit less than the fuselage length and the wing chord even at the root is less than the fuselage diameter! :D
The Q400 has a surprisingly thick (18%) wing at the root for a fast plane and it is almost a 'sail plane' type section with the maximum thickness well aft and a slight under camber at the trailing edge. It reduces to 13% at the tip.
The centre section and outer panel ribs.
With the motors way out in front of the wing and the elevator and rudder servos right at the back whilst they should more or less cancel out it does mean the wing centre section will have to withstand a substantial torque as well as any bending loads.
As a result it has a substantial balsa/Depron/balsa box spar.
It has internal webs corresponding to the rib positions.
By comparison the wing outer panels only need a much more modest "I" beam spar.
The centre section complete.
The upper rear skin is left off to give access to install the radio within the wing.
The wing mount on the fuselage.
The dorsal spine is hollow and carries the elevator and rudder servo wires within it.
The wing is held on by 4 nylon bolts that fix into plastic captive nuts in the wing mount.
The completed mount with its substantial leading and trail fairings.
With the wing mounting complete the nacelles can be glued on.
The ESC and servo wires are lead to the tiny 'Lemon' 6ch radio in the wing.
For the first time it is possible to get an idea of what it really looks like when all the bits are put together.
With the fuselage substantially complete the painting can start based on the new Flybe colour scheme.
The rest of the fuselage is purple!
Next problem is to mount a 1500mAh 3s in each nacelle. A quick CofG check showed they would have to be mounted well forward so it was easier to have a hatch on the under side and to push the battery forward on the 'floor' of the nacelle.
Done this way meant the hatch itself carried no load. Front hinged it could be held shut with just tiny magnets.
The battery is positioned about 6mm under the ESC so allowing cooling air to be directed at the ESC heat sink.
The shrink wrap was partially cut away to improve heat transfer.
The purple acrylic paint is quite heavy so in a departure from the scale scheme the wings are painted white althouth the nacelles are purple.
Again for contrast the spinners are also left white.
It weighs 30 oz (850g) ready to go.
As the batteries and radio are the wing it can be run 'stand alone'.
Its thrust exceeds its weigh quite a bit below full power.;)
Wow, that is a great looking build!
Another outstanding build. It just doesn't look like it should fly with all that fuselage to haul up in the air on those spindly little wings... But with your super light building i've no doubt it will fly like a bird.
The extraordinary fuselage to wing ratio was really the reason I set off building it.
My main worry is not the weight of the fuselage (its only 12% of the total weight) but its aerodynamics.
As long as it is 'normal' to the airflow all should be fine (except for the skin friction) but at high angles of attack there must be possibility that the fuselage lift (and where ever its centre of pressure acts!) might 'swamp' the not very generous elevator.
About the only saving grace of the long fuselage is that it also puts the tailplane a long way back as well.
Yeah, you just have to trust that the designers of the real thing got it right... and the fact that the real one flies kinda proves they did... pluds of course hope that it all scales down!
It flies - but I also broke it a bit!
The problem was it was rather tail heavy. Just a simple circuit and set up a long approach keeping from flying too slowly but a foot off the ground it slowed too much and dropped the right wing cracking it just out board of the nacelle.
Easy enough to fix.
After the wing repairs I taped 1/3 oz to the nose. Doesn't sound much but remember it is acting a whole yard, yes 36", ahead of the CofG. This modest weight moved the CofG forward by nearly 1/2". On a wing that has an average chord of just 5" that is quite significant.
An edited video of the second flight although again nothing spectacular.
The main reason I kept it steady was it needed full right trim to keep the wings level even with the elevator extensions in place. I did not want to get anywhere near the aerodynamic limits. :eek:
On inspection there is a slight twist in the RH wing which I should be able to 'massage out' easily enough.
Despite the apparently small wing it flies remarkably slowly (or rather the very long fuselage tends to make it appear to be flying more slowly that it is) and it has plenty of power being capable of a very steep climb.
It glides well enough but those big 3 blade props don't half create a lot of drag when they wind mill so the power off sink rate is ....er....positive!
A bit of an untidy landing but so far so good.
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