Red Bull Rat Racer

by mrjdstewart | August 7, 2018 | (2) Posted in Challenges

2018 Red Bull Air Challenge


Team Introduction

For over 30 years Red Bull has been encouraging people to engage in competitions as a way of maximizing performance and having fun. On June 18, 2018, Flite Test announced “The Red Bull Air Race Challenge”. Feeling energized and inspired, we formed a three -man team to compete in the challenge. The team members of Sonoran Sky are:


Jason -  Tucson, AZ.  Jason was the team leader. His duties included directing the work -flow, evaluating and completing prototype #1, checking working drawings, converting full size plans to Vector, laser cutting parts, 3D printing, plane assembly, and flight testing. 


Stephen - Tucson, AZ.  Stephen was in charge of graphics. Stephen is well known for his beautiful graphics and wing skins for Flite Test planes.


David - Shell Beach, Ca.  Dave was in charge of building prototype #2, drafting up full size plans and flight-testing. Dave was in daily contact with Jason to share ideas, discuss and work through any design issues.


Design Overview

Many of the activities that Red Bull sponsors revolve around speed. With the need for speed in mind, we decided to design a speed plane: a Red Bull Vee -Tail Pylon Racer!  We wanted the plane to have the looks of a vintage 1930’s Golden Age Racer and a sleek design that looks fast even when still. We believed designing the plane with a vee-tail, elliptical wing tips, and a faired in low-profile canopy would achieve the desired aesthetics.  Also keeping within the spirit of past Flite Test planes the racer is built using foam board and poster board from Dollar Tree. The standard Flite Test build techniques, including the folds, bevels, score cuts, and hot glue, were used in building the plane. If a modeler has experience building any of the  Flite Test planes, they have all of the necessary skills to assemble the Vee-Tail Racer with ease. To sweeten the deal even more, most high end composite pylon airframes cost anywhere from $200-$600 each. The cost for this airframe is three dollars!


Other Design Criteria included:

  • The use of 3s to 4s 1000mah to 1800mah lipo batteries
  • 36-inch wing span, large enough to see while flying at high speeds
  • Power provided by a Brother Hobby 25071850kv/2450kv motor or an NTM prop drive 28-36-1800kv/2200kv. Good for 600 watts


Deliverables:

  • A pdf of full size plans
  • .SVG files for laser cutting
  • Red Bull Graphics, including detailed wing and fuselage skins
  • .STL files for 3D printed materials
  • Multiple prototypes for testing
  • Completed airframe, with graphics for pictures
  • Flight video of maiden flight

Design & Methodology:

Preliminary construction began with some sketches and mockups using foam board, poster board, and lots of masking tape.

 

Figure 1: mockup of the Red Bull V-Tail Pylon Racer


The full size plans were converted to a PDF format from hand drawn plans. They were then sent to Jason to assist him in the building of protoype #1, as well as the productions of the .svg laser cut files. 


Figure 2: Overview of the initial plans for the plane before conversion to a PD

Figure 3: conversion to Vector files

                      

Prototype  #1 partially built by Dave in California, and then was shipped to Jason for evaluation, design changes, completion of the initial build, and flight  testing.

 Figure 4: prototype #1 arriving to Jason's house


Jason designed and 3D printed a firewall, motor mount, control horns, and a canopy for prototype #1. Changes were also made with the front cowl to wing-canopy fairing, as well as the turtle deck. Photos below show a lay out of the power system, servos, and rx. A piece was constructed to close the bottom of the fuselage.  Jason wanted to improve the size and motor offset of the power pod, so he designed a new version in CAD and 3D printed it.


Figure 5: Tinkercad designed, 3D printed parts

 

 Figure 6: prototype #1 completed by Jason

Assembly of the aircraft was very straight forward, even though we were communicating and building with 500 miles between us. Dave did an incredible job laying out prototype #1, and with the additional 3D printed parts, the plane was looking good! Jason prepped the airplane for it's maiden flight, and crossed his fingers that everything was right.  The center of gravity of the plane was a major concern going into the maiden flight, specifically that and the plane might be too tail heavy. As they say, "A nose heavy airplane will fly poorly, a tail heavy will fly once.". With the due date quickly approaching, we needed a clean launch and flight so we could turn our attention to the finalization.  Regrettably we were not that lucky...    

     

  Figure 7: Photos of  test flight of prototype #1


Jason like to blame it on a poor launch (of course it's never our fault   ), but the plane stalled out during the first test flight launch and had a semi-hard landing. It looked good in the air right up to the crash landing!  As a result, we decided to move the center of gravity from 30mm to 25mm. Jason felt the plane wanted to pitch up, so Dave decided to shim up the trailing edge of the wing 1/32 of  an inch, add 1 degree of right thrust, and 1 degree of down thrust when building prototype #2.

While Jason transitioned to building the final prototype, Dave was busy building prototype #2.


Figure 8: Proto #2 with colored packing tape


One of the big changes from prototype #1 was the movement of the servos from the bottom of the craft to the top.

 

Figure 9: Spar and aileron servos glued in place for prototype #2


Dave built a motor box with 4-40 blind nuts and 4-40 allen head bolts to hold the motor X-support in place. The motor is a NTM Prop Drive V2 28-36-1800kv, which can also be interchanged with the NTM Prop Drive V2  2200kv and 3000kv versions. Later, this motor box will be 3D printed.


 Figure 10: the motor box with blind nuts and the 28-36 motor mounted to the motor box


   Figure 11:  Final assembly of Prototype #2     


Maiden Flight  of prototype #2

 The maiden flight of pototype #2 took place at Laguna Park, San Luis Obispo, Ca on July 31, 2018 at 8:30am. Ambient temperature was 70oF, sunny, with a wind of 1mph. Dave was a bit nervous about the maiden flight; high speed pylon planes are challenging to launch, and often have a violent torque roll to the left that results in devastating crashes. As if the stakes weren't already high enough, the pilot only has milliseconds to launch and then regain control of the TX to resume flight of the plane to avoid a crash. With those thoughts racing through Dave’s mind, he launched the plane...it was off to the races! The plane had a slight torque roll/stall, easily fixed by 3 clicks of right aileron trim. Dave thought it was one of the easiest pylon planes he has ever launched and flown. Dave flew the plane for about 90 seconds before successfully landing the plane at his feet. The maiden flight was flown with a 1000mah 40C lipo. The 90 second flight drained 250ma from the battery. The video tells it all, enjoy!


Laser Cutting

The parts fit for  prototypes #1 and #2 passed quality control, so Jason went ahead and laser cut a kit for prototype. 





Final Skins & Assembly


Figure 12: Final Skins done by Stephen

 

Jason first cut out all the foam board parts and then glued the skins to the foam and poster board parts with 3M77 spray. Jason likes to weigh the parts down while the glue is setting up to insure a strong bond of the skins to the foam and poster board parts.

Figure 13: skins glued to foam board and poster board parts

   

 Once the glue set up, Jason began to assemble the wing. The wing goes together in 2 parts, like your typical FT wing. Servo pockets required foam removal on both the top and bottom of the wing. The paper was reinforced with poster board and tape. 

Figure 14: assembly of wing

      

Figure 15: Dave's servo pocket


Figure 16: Full wing assembly


One of the advantages we felt we had was the access to a 3D printer. Jason, over the last few months, had spent enough time at Tinkercad that we were able to create 1-off parts specifically made for our craft. The ability to take an idea, create and manipulate it in a digital format, then export to a 3D printer was invaluable. Jason designed and printed six different motor pods before we were happy. 

            

Figure 17: Final 3D printed motor box for NTM Motor  

                                                     

Figure 18: Motor box inside fuselage

 

As Jason was building the final prototype, he realized he had made a few errors when tracing in the .svg files. The new fuselage did not match the scratch built measurements of Dave's. Thankfully, this did not have a major affect upon the aircraft. The skins had been made to the erroneous .svg files so they still fit, but it explained why our fifth design of the motor box was so off, requiring the creation of design six. Duh, measure twice, cut once. Jason also chose to not use the turtle deck formers that were used on the prototypes, instead choosing a simpler, maybe stronger approach. With the addition of the skins, he felt the the turtle deck did not need all that additional support.

                                 

Figure 19: pre-assembly photo

                             

Jason also had to modify the the trailing end of the upper turtle deck, due to the movement of the servos from the top to the bottom. The skins were designed off the origional .svg files, which still had the control lines running underneath. This was as simple as cutting off the trailing end and placing it under the control wires.

                  

Figure 20: Prototype#1 servo and control line arrangement


Figure 21: Final Prototype v-tail arrangement

 

Finally prototype # 3 was finished and I hope you agree, we definitely achieved the, "it looks fast sitting still" goal we had set!  


 


 

Figure 22 (a,b,c,d): final assembly photos    

The skins make the plane look like an expensive high end composite model. As a team we agreed, this was pretty cool! Now we just had to get it in the air. The airplane was completed on August 3, 2018 with the hope of a maiden the next day. The clock was ticking and we were feeling the pressure; we still needed video of the "glamor flight", plus finishing the article! This is when mother nature decided to make it even more interesting. The Saturday maiden flight was canceled due to and "extreme heat warning." When Jason woke up at 4:00am the ambient temp was still 84oF and heading straight back back up to a high of 113oF. If the heat didn't make things challenging enough, we were facing high humidity due to summer monsoon rains. A quick flurry of texts later, it was obvious that NO ONE was going to the field. This meant no possibility for video and another day lost. Hopes were high for Sunday, but once again, 4:00am rolled around and a flurry of texts lit up the dark. Flights were canceled again. 

So, now it is Sunday, the plan was to submit Monday. We decided that we were just going to have to live with it, if Jason could arrange a flight with video before submission great, if not oh well. We already had met most of our goals, we had proof of fight with prototype #2, so although not tickled, we had what we really needed. We to add an additional video of a 4S spin up test and call it good. In this video, you can tell Jason had been working way to long, his mental abilities and his throttle cut switch abilities did not match.





Final Evaluation of Model

  • Great flying model. Easy to build, fly and land.  With the addition of the skins, people at the flying field will be surprised that this is a plane made from Dollar Tree foam board and poster board. TIf you have been thinking about going fast but have been too nervous, this plane is for you. It can be your "entry into speed" and at a fraction of the cost of a typical pylon racer. The basic model is set to fly off a 3S or 4S battery, allowing you the opportunity to start slower, and progress. If you choose to use the Brother Hobby motor option you even have the ability to go as high as 6S!    

              

  Flying Set up

  • CG @25mm
  • AUW 21oz with a 1000mah 40C lipo  (proto#3 with skins-  550g w/o battery)
  • Aileron high rate 5mm up and down, low rate 3mm up and down
  • Elevator high rate 5mm up and down, low rate 3mm up and down
  • Mild set up: NTM prop drive 1800kv motor, 6x4 apc prop 4s 1000 40c lipo. 
  • Faster set up: NtM propdrive 2200kv motor, 6x5.5 apc prop, 1600 4s 40c lipo
  • 40amp esc
  •  51mm Turnigy Turbo Spinner, spinner is  well balanced.

                                       

   Recommended Parts and Materials (if you don't have 3D printer)

  •     2 sheets of Dollar Tree foam board  
  •    * 1 sheet of poster board from Dollar Tree
  •    * 5mm x 800mm hollow carbon fiber tube from Hobby King.
  •    * 4” x 4” piece of 3/16” plywood to build the motor box and firewall
  •    * 4-40 allen head screws (x4) for fastening the motor cross mount to the fire wall                 
  •    * 4-40 blind nuts (x4) for the firewall
  •    * 1 pkg of dubro control rods and guide tubes for the vee –tail linkage
  •    * 1 pkg of dubro micro control horns for the ailerons
  •    * 1 pkg of small vee-tail control horns from Art Hobby
  •    * 9 gm servos (x4) for the ailerons and vee-tail
  •    * NTM-Prop Drive V2 28-36 1800 -kv motor,

              or the NTM Prop Drive V2 28-36-2200kv motor

  •    * 30-40 amp esc with bec
  •    * 3s-4s 1000-1800mah 40C lipo battery
  •    * 6 x4, 6 x 5.5 apc prop
  •    * Turnigy Turbo prop 51mm spinner
  •    * 6 channel receiver

Basic cost of for the Red Bull V-Tail Racer was $100, including an airframe cost of just $3.


3D Printed Parts

Motor Box - propdrive 2826

https://www.thingiverse.com/thing:3033486

V-tail Horn

https://www.thingiverse.com/thing:3033535

Skids

https://www.thingiverse.com/thing:3034860

Canopy

https://www.thingiverse.com/thing:3039447


Aircraft Skins



In Closing...                              

Although Dave has been building models for over half a century, he had never worked with foam board or hot glue. After watching several hours of Flite Test build videos and practicing doing the various folds, score cuts and bevels with a utility knife, he was ready to take on the Red Bull Challenge. Dave also learned to download plans to a flash drive and send them via e-mail, as well as how to write a document using Microsoft Word with photos and videos. Dave designed and hand drew the original plans for the racer.

Jason, although new to the hobby in comparison, had spent the majority of it building FT foamies, along with multiple custom designs. Over the last 1 1/2 he had also learned to 3D print, design custom parts in Tinkercad, create .svg files in Inkscape, use a Co2 laser to cut designs, and the beginnings of graphics design for skins. When he fist saw the Red Bull Challenge, he knew exactly the 2 guys he needed to call to get on his team.

Stephen (Rasterize) is a super star with the graphic design of airplane skins. Hopefully, he already knew that! He did a superb job designing the skins for the Red Bull V-Tail racer. 

Our goals at the beginning were;

Deliverables:

  • A pdf of full size plans (check)
  • .SVG files for laser cutting
  • Red Bull Graphics, including detailed wing and fuselage skins (Check)
  • .STL files for 3D printed materials (check)
  • Multiple prototypes for testing (check)
  • Completed final airframe, with graphics for pictures (check)
  • Flight video of maiden flight (check)

The only area we feel we did not achieve our final goal was the .svg files. As mentioned above the conversion (tracing) of the .pdf plans into vector format (.svg), a mistake was made somewhere. Although this does not affect much as far as aesthetics, it did require a good amount of mods for the final model. So, with this in mind we will not submit the .svg files at this time. We frankly ran out of time, and need more before we release a final product. For those who can read, Dave's hand drawn plans are a piece of art, that can easily be turned into a racer.

To say that we learned an incredible amount of information over the last few weeks from participating in this challenge would be a slight understatement. I think the biggest thing we took away from it was; It takes a LOT of work to take an idea from your mind, and turn it into a "ready for release" model. Even with all the precision and attention to detail we took, there is always something to fix. Granted we only had a few weeks, but this definitely gives us new found appreciation for the effort FT must put forward to bring a new model to life and ready for sale.

Thank you Flite Test and Red Bull for sponsoring the challenge and pushing us to learn more.  

“Red Bull Giving Wings to People and Ideas”  

Team Sonoran Sky 

*Another attempt was made to maiden the final prototype on 8/8/18 but due to a broke solder joint the flight was canceled. Unfortunately time is up and we will not have time to get video before we submit. Hopefully I can get some Saturday and post it later.

COMMENTS

Damorc on August 10, 2018
She's a beaut! Well done.

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CptCrazyFingers on August 10, 2018
Great job! The plane is simple, yet elegant and you put together a fantastic article with all the information I could possibly need to build this. I love it!
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shhhhh! on August 10, 2018
Jason, Fantastic job ! You were a super team member and should be very proud of the final result.
Plane flies as well as it looks!
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Red Bull Rat Racer