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Old May 22, 2016, 03:08 PM
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Build Log
Restoration/Rebuild of a 1.8m Richmodel Lightning Dart

Let's start with a bit of history.

This all started with my frieand Giannis aggressively trying to give me a pair of wings. "Take them! Make them fly fast!" he said with passion. I carefully tried to explain to him that I had enough airplanes as is. That I can barely find time to fly (and crash) the ones I have. The wings also sounded bigger than anything I had ever built before. I told him that I found great comfort in my foam building. I had no knowledge in balsa construction. But Giannis would not listen! "Take them anyway! It will be fun! It only needs a fuselage!". "Maybe another time" I told him.

Time went on. I happily continued flying my foam airplanes.

A few weeks later I was at the field. Giannis arrives out of nowhere. He bolted out of his matte-black car. "HEY! I'VE GOT YOUR WINGS!". I was not sure what he meant. Surely I had respectfully declined his kind offer a few weeks earlier. "What wings?" I said. "These!" He shows me a pair of huge yellow balsa wings. Turns out. Giannis will not take "no" for an answer. Say "no" and he hears "yes".

So here I am. The wings are beautiful. I can no longer say no. And what I say does not matter anyway. Giannis wants to see the wings fly. I have to build something.

So this is the first post in this log. The log will cover research, planning, testing, building and, hopefully, the maiden flight of a large wing.

Lets start by looking at the wings.



They where originally part of a flying wing kit called "Lightning Dart" made by Richmodel.

Here is a video of a gentleman flying his Lightning Dart.

Richmodel Lightning Dart Flight (3 min 50 sec)


As you can see the original model had a small simple fuselage between the wings. The original fuselage for my set of wings got destroyed in a crash.



The wings feature elevons and flaps.



A fixed gear with a wheel can be found under each wing. A third steerable wheel will have to be placed in the nose of the fuselage to make a tricycle-style landing gear.



The wings have two slots for 14mm spars. My plan is to use a carbon fibre spar that passes through the fuselage.

Which leads me on to my next piece. The fuselage! I have studied the old fuselage in different pictures online. The best picture I can find is the one below.



The fuselage is very simple. A key thing to note is that the motor mount is elevated a few cm above the chord line of the airfoil. It looks like there is no thrust angle. When I asked Giannis about this he was pretty sure that the thrust line was completely neutral, parallel to the chord.

The fuselage is pretty much the only thing that needs to be scratch built for this project. Since I have very little knowledge in balsa building, which would otherwise be a good choice, I have decided to try to use 3D-printing for building the fuselage and other parts that I might need. I've been looking for an excuse to get a 3D-printer for some time anyway. I've designed and 3D-printed small parts for other models by going to 3dhubs.com before. But since this will be a much larger piece the total cost of printing on 3dhubs.com would probably be close to buying a small DIY printer.

This is the end of the first post. Next time I will go through details of the power plant and do a prototype fuselage to test proper placement of components for balance.

I would like to take this opportunity to thank Giannis for generously giving me the wings, answering questions and giving guidance along the way. Also Angelos for guidance and lending me his wattmeter that I managed to destroy... Dimitris for troubleshooting a motor setup.

Thanks for reading!
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Old May 25, 2016, 08:57 AM
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Back again!

As promised it’s time to look at the power and electronics setup.

The brushless motor I will be using is a large Scorpion 4020 1390KV helicopter engine. The motor will swing a 10x6 inch carbon fibre propeller. It will be powered by a 4S 5000 mAh battery. A complete calculation can be found here http://www.pdf-archive.com/2016/05/2...tning-dart.pdf. In short it should produce around 4.5kg of static thrust. It should pull around 100A adding up to about 1350W of electrical power. Calculated rpm is around 17000 at full throttle.

Since this setup will run at very high RPM, at least compared to what I have worked with before, I will make sure to take every safety precaution necessary. Everything will be thoroughly tested on the ground and supervised by more experienced builders. The project will only be completed if reviewed and judged as safe to fly. As an extra precaution I will probably put in a throttle limiting mix into my transmitter. The plane should easily be able to fly with half the power anyway. The setup will definitely be way over powered and I am aware of the dangers associated with high RPM but I believe that it can be safe with the right precautions in place.

For the elevons and flaps I will use large Blue Bird servos (High Speed Digital Metal Gear 7.2kg / .10sec / 46.5g).

For the front wheel steering I will use a generic Turnigy servo (Metal Gear 3.0kg / 0.14sec / 26g).

Power to the motor will be provided by a RotorStar 150A ESC

Power to servos and receiver will be provided by a Hobbyking YEP 20A BEC.

For remote control I will use my trusty Turnigy 9XR. The radio link will be a FrSky-module and receiver setup.

With that out of the way it is time to determine placement of components for correct center of gravity. I do this now, before designing the fuselage so that I can take the component placement into account in the design. Instead of going back later and moving stuff to fix balance issues.

To conduct this experiment I need a simple placeholder fuselage holding the wings together. I did a quick design and printed it. Just like the final fuselage this has to be printed in at least 3 pieces due to my 3D-printers maximum print dimensions: 200x200x200mm.



In the back of the piece there is a sliding motor mount that makes it possible for me to try different motor positions for balance. An exciting highlight is the printed screw threads and nut that is used to hold the motor slide in place. It came out straight from the printer and worked great. This is amazing to me. Printed screw threads! In the video below you can see me cleaning up and assembling the pieces with CA glue.

MogWing Mock Fuselage Assembly (3 min 3 sec)


I also prepared each wing for balancing by mounting the necessary servos.



The elevon servo mounts directly to the balsa frame of the wing.



The flap servo needs a mount. I designed and printed two prototype ones.



In the video below you can see me measuring the wing to calculate the center of gravity. I then put the components in different positions in the fuselage until it balances correctly.

MogWing Balancing (1 min 52 sec)


Calculation:


During this video I developed a highly technologically advanced and precise method for balancing a model. It is a great advancement in model building. Remember where you saw it first! The method depends on 3 crucial tools…

The big secret:

3 large bottles of beer. Take two of the bottles and place them under the model. Move weight around on the model until the balance is perfect. The great technological advancement lies in the third bottle. This bottle has to be drunk during balancing to help the process. If you cannot manage to get the model straight on the center of gravity simply drink beer from the third bottle until it looks straight.

I have now reached the end of this second log post. I now know approximate positions of components in the fuselage.

In the next post I will go through the fuselage design, printing and assembly. Thanks for reading!

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Old May 25, 2016, 04:01 PM
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Wow sparks your thinking and planing are right on . Can't wait to see your results . i'll be watching and following just do me one favor and take on this project with a determination to completion. I have never used a C G calculator I just use the that looks about right formula and in reality C G is for sissies. Some of my most exciting flights were horribly tail heavy aircraft that were way outside the envelope of control-ability but memorable as hell. And now that I know large bottles of beer are a tool for testing C G I might try it more offten
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Old Jun 22, 2016, 01:11 AM
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Quote:
Originally Posted by alpea 41 View Post
Wow sparks your thinking and planing are right on . Can't wait to see your results . i'll be watching and following just do me one favor and take on this project with a determination to completion. I have never used a C G calculator I just use the that looks about right formula and in reality C G is for sissies. Some of my most exciting flights were horribly tail heavy aircraft that were way outside the envelope of control-ability but memorable as hell. And now that I know large bottles of beer are a tool for testing C G I might try it more offten
Glad you like it!
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Old Jun 22, 2016, 01:14 AM
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Finally done with lots of 3D drawing and modeling.

I now have a design for the fuselage ready. This took longer than I expected. The most complex model I have worked on.

I did the design in Fusion 360 from Autodesk.

Here is a rendering of the design together with wings.



Without wings you can see the profile and where the carbon fibre spars will pass through



The fuselage features two scoops in the front for air intake.



The air is then transferred to the ESC and engine using internal air channels.



In the nose an internal servo is placed to enable steering with the nose wheel.



A large battery hatch.



A compartment for the receiver, accessible from the belly.



The ESC compartment



That is it for now. I will start printing the fuselage next week.
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