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Twin Engine Speed Scratch build (W.I.P.) - C.2 Flying Scorpion

#1
Greetings Flite Test community! To encourage more building and more use of the forums by me, I'm gonna start posting on here daily of my next build, logging the steps and development.

What I am dreaming up this time is a vicious approach to the favorite question - SPEED

What is planned is a twin engine park flyer sized sport plane with a semi-conventional tail. Most twins that are popular are slow, or cruisers, or cargo planes, or, just plain tiny!
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I want a BIG ("big") twin engine where extra motors are for the sake of POWER (tho I understand that the advantage of multiple motors for electric aircraft aren't the same as on full scale types with petrol, I just think they're cool!)

Current planned plane dimensions are that of a 48" wing span, 38" inches in length. Two motors, as swappables, to encourage testing on like C-pack equivalents, then pushing it on mightier motors, like the NTM Propdrive 35-36

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(if you recall this is the famous HUUUUUGE motor from Viewer Requested Speed Challenge. Obviously I would need two but recently the motor has been updated, so I might need to own 3?? this one pictured I had for a whiiiiiiile)

As far as speed goals I'm shooting for sustainable 90+ on 4 cell. If I hit it easy, great! If I exceed it even better, but if I'm short than it doesn't seem to inescapable to attain.

My progress so far has me planning out the layout and working on the wings. You can see two things here, one is that I intend for the motors to be ahead of the nose of the fuse and preeeetttty close to each other; about an inch clearance for 10 inch props. The design would probably push balancing for a 2200 battery, but wanted to do it like this to really squeeze together the weight in close. Just cause its a twin doesn't mean it can't roll like a top ;)

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nothing particularly crazy about the wings, in fact I'm trying to keep it very simple with their construction. The most crazy thing about it is the monster chord of 12 inches at the root, and the raked wingtips, where the wing sweeps back. This should work like a winglet in giving me more effective aspect ratio but I keep the wing relatively short (about the size of a cruizer while the plane is the weight of a guinea :LOL:)

The true fancy thing I'm doing is setting up the wing to hold the motors on pylons. You may know of him, but Ramy RC did something with a build a while ago that gave the idea. using some large paint sticks, the pods for the motors will exist relatively far away from the wing, leaving much of it free past the pod. Aerodynamically I suspect that will simply improve the efficiency of the wing, less drag with the corners of the pod touching the flat of the wing.

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the sticks will, uh stick 8 inches ahead of the wing LE, allowing for my 6 inch long pods to be nicely held away. I have little concern that twist will be an issue, but we'll see. Other than that I'm cheating with using the sturdy yard sticks from Lowe's as a ready cut spar, and the two parts of the a wing half will be married to each other through glue, tape, and paper.

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I'm excited for this build! I've been wanting to do a twin for a long time, and if I'm diligent, I should be able to get it done before school starts in August. Lets see where this will take us!


DAY 2

Okay so second day of work, and not much done admittedly. I did do something! I intend to work on this bird daily, between the gaps of time! but for now its really just more brain storming. Today's efforts explored what I'd like to do for the ailerons. I looked at some of my favorite fast twins for some inspiration, like the Me-410, while keeping in mind the kind of things i wanted the aircraft to do different.

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the Ailerons I wanted to begin within the prop arc, taking advantage of some of that propwash, but I avoided drawing them to the tips of the wing. Since the planform tapers sharply to the tips a stall begin aggressively there. Although I loose some authority with the ailerons closer in, They will at least maintain control longer in stalls, plus any wing flex will likely be resisted more with them at this position.

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the other thing I'm considering is adding a barbecue stick within the aileron to keep it super stiff, since it is being built to approach 90.

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Other than that I drew in the prospective positions for the wing servos.

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with that, thats all my progress today! Nothing really exciting but, what cha gonna do?

DAY 3

The days progress! Despite having all day to do things, I was a bit sick so couldn't do much.... but regardless progress progress trudges on!
Today, more progress on the wing is done - I decided to mate the wing halves and then the half halves together.

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The halves are halves because the large chords wouldn't fit on one board as a single connected sheet (though ironically both can be cut on one board as separate). To Fuse them together a bit of paper was set to be glued to the section that was the top fold. It was first attached with tape, then of course glued afterwards.

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the two true halves had a bit of separation, but that was easily fixed. and thus, they were glued.

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After that I dug out the reliefs for the servos, whom I planned to have embedded in the wings. Here I shall talk about a peculiar thing that I'm trying with this build. On the inside, I'm lining the bottom of the wing with poster board. The wing is being built to sustain 90+; on other builds that would involve carbon fiber or metal spars; I, I'm using just wood.... so any other basic strengthening, like this heavy card stock, should help loads.

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After these additions I glued in the Yard Stick, which is my spar, and called it a night. It's gonna be piece mail work the next coming days, but I'm determined to do a little something every time!
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#4
Soooo, the past two days I was sick....

I ended up getting tanked in energy and vitality and couldn't really do anything for school, work, or planes. However I'm ready to get back into getting some good progress! however this night will be very little progress... again.

What I've done today is get prepared to complete the wing. If you are familiar with the nerdnic speed wing, it is a completely closed wing with a zero tapered edge. This wing will be the same way; the paper around the edges of either wing half was removed, revealing one sides soft foam. That soon will be sanded down on both wing halves so that they will fold and glue closely together. the other thing done was that paper was removed on the top half of the wing to allow it to curve over the spar-once again, it mirrors the style used in the FT Master Series, doing away with score lines to allow for a super smooth fold. smooth becomes speed

Next post will have more work, and more pictures! but until then that concludes day 6!
 
#5
Day 7 (non-consecutive)

The biggest, baddest part of the build is coming near to an end. After doing more measurements and double checks, I decided to move onto finally finishing the wing. Making use of my new $18 rotary tool (really speeds up the building!) I sanded the edges of the wing planform so that every where other than the leading edge I would have a razor thin meet.


with the double bevels beveled and the edges tapering, a bit of paper on the top wing was removed, up to half the chord, to allow it to fold smoothly over my spar. Placing in the servos, I formed the wing to make sure every thing met well, and trimmed any overhang that wasn't needed.
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Every thing fitted good so I went ahead and did the real kicker of the build - the pylons! sizing and cutting two large paint sticks from Lowe's, I glued them onto the bottom wing, poking out of the bevel area. Liberal amounts of glue were made, and every feels very secure. That set, servos were glued in, and given an access hole for the wire extensions. The Power split (without the Y harness :rolleyes:) was also installed and everything was carfully set so I could fold everything together permanently.

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almost forgot to glue the servos in! but every folded together fine

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Now that the major wing structure (without the y harness for the motors :whistle:) was complete, I went on to building the motor nacelles

Quite simply it was a gutted box with the foam removed and replaced with the paint stick.

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sanding and trimming made everything flush afterwards. The sides of the box introduces some drilled Popsicle sticks to help reinforce what would be powerpod holes. This area always gets worn the quickest, so I wanted to reduce that as a chance. They are at an angle, causing down thrust. Nothing specifically designed but something to help with the inevitable pitch up from high speed and flat bottom airfoils.

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with the two nacelle boxes done it really started to look like a twin engine wing

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the next work began with finalizing the intakes with the pods (since I wanted intakes). Nothing more than just a box with an angled front, but in addition to that is an attempt to add some aerodynamic trickery, that would improve the cooling of my esc's (maybe) and boost efficiency. A small hump was glued into the throat of the intake. The idea is that just like a wing the throat will force the incoming air to accelerate and flow faster into the pod chamber. This wind will thus help improve uses of the motor at prolonged speeds and allow me to pin the sticks for longer and more often. Honestly, this is all theoretical, but it is a prototype! So as long as additions are within reason, whats the harm!

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as always, when you start to get close to finishing, you get really excited! So I might end up doing a BIG push to complete the model. Here's hoping to a well designed initial attempt. End of Day 7!
 

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#6
Day ??????????

I ugh, did that thing were you keep working up til an irresponsible time of day (4:00AM I think?) and, well finished my build! As far as the progress from when I last posted, I believe I got started on the fuselage. As far Hundo planes, or in this case those near too, You want an aircraft to have a sleek aerodynamic fuse. at the same time tho, This plane is very short coupled, or short in nose. I was concerned that even with two motors up front the plane could still be tail heavy. The thought was, if the fuselage was too narrow to fit a wider battery, or product, I would be boned, but if it was just wide enough for something extreme, like maybe a 6 Cell battery :unsure:, I would have higher play room. Only after I finish building would I know if this would be necessary, but for now, Big Block! 2019-07-31 23.05.18.jpg
This piece became the forward nose section and the main fuse area under the wings, this would act as well as an interior sleeve for a nose hatch, so on the outside a fuse "skin" is applied, with which also added more to the fuselage shape sing I used that Andres style geodesic style forming. 2019-08-01 18.36.31.jpg 2019-08-01 00.06.48.jpg
In addition I trimmed the nose down in its height so that It'll be prepared for a tapering nose hatch. For this iteration, the fuse was straight glued and taped to the wing. Future iterations, only after the plane flies well, will introduce removable wing setups via bolts. I will say, I had some issues and despite my best efforts, the fuselage does have a small angle. This is ironed out with the tail ( later attached) so little issue should be experienced. (PS, excuse my sock) 2019-08-01 20.36.50.jpg

A major driving force for this aircraft was that I wanted it to be STRONG. I've only built one aircraft with the intent of 100 mph so I'm just not sure whats necessary and whats not, so again, airing on the side of caution was my motto. The concept for the tail was to create kind of a T form that acted as a skeleton, while a foam skin continued the contours of the fuselage. In addition a paint stick was added to the tail of the T to act as reinforcement for the central v stab.
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the photo above shoes the transition in the taper that goes into the upper fuse, and that which forms the lower tail

Test fits as always to make sure things are snug, and angles stay true. In the Future I might completely build the tail before adding it, just to ensure a completely accurate angle. In addition, two right angle pieces of foam were added to either side of the bottom of the T to really, REALLY make the joint strong.

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Pausing on Tail work, I began on the stabilizing surfaces. All of the surfaces were of the Nerdnic style by @nerdnic; double thickness foam that tapers on the edges. The Horizontal stabilizer I made quite large - 20 inches! and reinforced with a barbecue skewer and popsicle sticks for the elevator.
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For my build, I wanted to have a tri tailplane - 3 vertical Stabs! So The finished H stab would include three slots on the elevator to allow for movement past the vertical stabilizers. 2019-08-02 22.33.27.jpg

The vertical Stabs have two types, the central stab and the side stabs. They were reinforced Just like the H stab but with a Paint stir trimmed and cut

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as well, they were nerd nic style, and fitted into their slots. And thus the tail is installed and secured to my sub structure!

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Above you see the paint stir reinforcement, and below the fit of the v stab

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Below all of the stabs together
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The sizing of the v Stabs was mathmatically determined, and supposedly only one stab would of been necessary, but since I'm pushing to extremes and really really REALLY wanted the plane to be locked in, All three I go!
 
#7
Day: WHAT EVEN IS TIME ANYMORE

I got tired last night trying to finish the "final" post for this log, so here I am again with the remaining data! 2 things though.

1. I've realized that I installed a y lead into the motor instead of two extra extensions for the purpose of differential thrust ( dummy :rolleyes:)
2. The canopy of this build is a long work in progress so I'll end up having many different ones until I'm happy with the fit.

Now! where were we last?


Additional topics on the tail. I actually glued the H stab on first on to the tale, and not construct the tail in one go. As seen by this preliminary photo here
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reason for this of course is because with everything being deigned by hand the fit of product obviously won't always be right, so as I attempt to join things it becomes easier to adjust smaller single pieces instead of whole structures.

I might as well say that I'm not immediately happy with the fit of H stab to V's, the triple split stab obviously not being as stiff as I'd like. Future versions will probably offset the elevator behind the rear of the verticals, simplifying construction.

Moving on to building things! After all the tail brewhaha has been settled I traced by hand the bottom "skin" of the fuse
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cut and free, dry fits were done and tapering was made made at the section that approached the tail to make a smooth transition to the V stab. 2019-08-03 21.29.42.jpg 2019-08-06 09.19.17.jpg

A technique I used while forming this skin was to glue within the central score lines and fold it over the tail without gluing it to make sure it held its shape.

With that set up I installed the elevator servo on the top deck of the T, and installed the control rod supports. The support I made from a cocktail stirrer and some foam. 2019-08-03 22.39.22.jpg 2019-08-03 22.29.30.jpg

The top skin of the fuselage was next to be added, having things like tapering and reliefs at the rear to the tail for the control rod. Unlike the the bottom skin, the top skin was taped to to the fuse, giving the convenience of access to the elevator servo at all times. Past the tail decking a decking for the upper fuse was also installed, this being glued

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The next bits of work involved were to design the canopy! I will only show parts off this build since It is gonna change, buuuut I will at least show how I got the major part, and explain a little more on how I made it.

Having none rectangular edges meet with rectangular edges I had to introduce contours that tapered the shape smartly in the angles needed. The common tapering shape used were triangles, which produced a width and tapered it to zero. The angles and positions of the triangles are thus determined by which direction the hatch needs to droop. Now, this being the first time I designed anything with a geodesic design, I crafted the hatch in steps, cutting out sides early to test fit and see if they fitted and contoured appropriately.

below the Hatch that incorporated the sides and bottom was drawn first.
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You can see clearly that the tapering triangles have an angle to the center trapezoid. When the sections taper up towards the front of the nose a "up taper" is caused if the long leg of the triangles are horizontal. Precisely what I'm wanting. The trapezoidal sides are perpendicular to the triangle side, causing the proper edging for the hatch so that the rear is flush. Having a good base to work off I added additional pieces to the hatch with tape and again fitted it dry to see how everything was looking. Now, I did end up tracing the hatch before I glued it complete, but like I said, I don't completely like how it looks, so some changes are coming.
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This was how the aircraft looked after I finished the finished the prelim canopy and cut free the ailerons.

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And at least to my eyes, it looked wicked!
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It definitely become way more "built" then I originally envisioned it. While it has clean (*clean*) lines its no pencil, and feels very rigid!
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Now after i connected all control surfaces (and lamented at my oversight for motor connectivity) I tool the plane and expected gear for sport flying (consisting of two powerpods with GT22/15's and a 4 cell battery) I weighed it to see how heavy the Flying Scorpion prototype would be.
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The diagnostic showed that this plane is, well, HEAVY
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3.33 lbs or 1511 grams..... In comparison an aircraft like the Guinea Pig form Flite Test, with a wingspan 10 inches longer and fuselage WAY geometrically wider is 2.2 lbs sans battery....

Now its not like I don't understand why the plane is heavier, the model is heavily reinforced for the sake of SPEEED, and additionally I'm not actually concerned with power. a GT22/15 apparently produces 1250 grams of thrust max, plenty to fly the model normal, and i have *two*. The shakey thing I'm concerned with is if the wing will be sufficient. The Flying Scorps wing is quite broad and decent in span, but the two planes in at least FT's rep that come close to my planes weight have thicker and wider wings. The concern becomes whether or not the plane will handle well. I think it will fly, but if it flies poorly that's not exactly a win. Regardless, I will of course still attempt to fly this and see how it does. the most immediate changes planned for new iterations include simplifying the tail, perhaps lightening the tail construction, or even slimming down the whole fuselage. Adjustments on the wing of course if it is insufficient would also be made.

Well, at that the Plane is completed! (at least until I get the proper leads for the motors) The plane is flight worthy, but I do intend to paint it before I fly, if for no other reason cause I want ta. Idc if its a maiden disaster its a prototype anyhow, so whatever crashes and troubles are had it will be fixed and adjusted until it results into a complete replacement of the frame in entirety.

To any of those that have insight on building park flyers above 3 lbs in weight, and especially those who are well versed in the domain of SPEEEEEEEEED, feel free to leave inputs, criticisms, or praise!