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Old Feb 17, 2014, 09:12 AM
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Compound Delta wing VTOL

Hi everyone;

I am starting a new project that should span 3-6 months until completion

Project description:

To design and build a compound delta wing VTOL aircraft, using twin counter-rotating props in the rear and a single, fuselage mounted down firing, ducted fan
in the front.
The aircraft should be capable of VTOL and controlled transitions from hover to forward flight and from forward flight to hover.

The rear motors and props will rotate from the down position (for hover) to the full back position for forward flight.

During hover the rear motor control will be a mix of throttle and a gyro to control roll, and the fuselage mounted ducted fan motor will be controlled
by a mix of Throttle-H and a gyro to control pitch. Custom throttle curves will be used for the ducted fan to ease the burden on the gyro control loop.

Moveable vanes under the front ducted fan will be controlled via a gyro to control yaw during hover.

An Eagle A super 3-axis gyro will be used in conjunction with Desert SM2 mixers during hover and a second Eagle A3 Super will be used during forward flight

The FrSky Taranis X9D transmitter will be used due to it's extreme flexibility, and a FrSky X8R 8 ch receiver with 4 Ch SBuss PWM decoder will be used for
a total of 12 airborne channels.

During hover 70% of the lift will be provided by the 2 rear mounted props and 30% by the fuselage mounted ducted fan.
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Old Feb 17, 2014, 09:18 AM
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Control system description and block diagram

Thanks to Ran D. St. Clair's suggestion and all of HappySunday's work on OpenAero2-VTOL firmware for the KK2.1 flight controller board I feel that I was trying to re-invent the wheel with my complicated control system ... please go directly to post #22 to see the revised control system

Hover Mode
3-axis H-Gyro is active
3-axis F-Gyro is inactive
Throttle-H is active with throttle curve (lift ducted fan)
ELE-H is active with full H-Gyro gain
AIL-H is active with full H-Gyro gain
RUD-H is active with full H-Gyro gain
Throttle is active
ELE-F is inactive
AIL-F is inactive
RUD-F is inactive

Transition Hover to forward flight Phase I (rear motors down 0 degrees to back 45 degrees)
3-axis H-Gyro is active with reduced gain
3-axis F-Gyro is active with reduced gain
Throttle-H is active with reduced throttle curve (lift ducted fan)
ELE-H is active
AIL-H is active
RUD-H is active
Throttle is active
ELE-F is active
AIL-F is active
RUD-F is active

Transition Hover to forward flight Phase II (rear motors back 45 degrees to 90 degrees full back)
3-axis H-Gyro is inactive
3-axis F-Gyro is active with full gain
Throttle-H is goes to 0 (maybe slow ramp-down) (lift ducted fan)
ELE-H goes to neutral
AIL-H goes to neutral
RUD-H goes to neutral (or vane closed position)
Throttle is active
ELE-F is active
AIL-F is active
RUD-F is active


Flight mode
3-axis H-Gyro is inactive
3-axis F-Gyro is active
Throttle-H is at 0
ELE-H at neutral
AIL-H at neutral
RUD-H at neutral (or vane closed position)
Throttle is active
ELE-F is active
AIL-F is active
RUD-F is active

Transition forward to hover Phase I (rear motors 90 degrees full back to 45 degrees down)
3-axis H-Gyro is inactive
3-axis F-Gyro is active with reduced gain
Throttle-H becomes active (maybe slow ramp-up) (lift ducted fan)
ELE-H at neutral
AIL-H at neutral
RUD-H at neutral
Throttle is active
ELE-F is active
AIL-F is active
RUD-F is active

Transition forward to hover Phase II (rear motors 45 degrees down to 0 degrees full down )
3-axis H-Gyro is active with reduced gain
3-axis F-Gyro is active with reduced gain
Throttle-H becomes active (maybe slow ramp-up) (lift ducted fan)
ELE-H goes active
AIL-H goes active
RUD-H goes active
Throttle is active
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Last edited by audio98; Feb 19, 2014 at 08:10 AM.
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Old Feb 17, 2014, 09:22 AM
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66% airframe test plane

I am currently in the process of building a 66% version of the airframe (NO VTOL) to verify CG etc for the full sized plane .. photos to follow over the next few days.
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Old Feb 17, 2014, 09:33 AM
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Test thrust of rear motors and lift ducted fan

Over the next few days I will post the results of testing the thrust vs % throttle for both the rear motor and the lift ducted fan.
The rear motor is Turnigy D2826-6 with a 6X4 prop and the Lift Ducted fan is a Hobbyking alloy 64mm
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Old Feb 17, 2014, 09:34 AM
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There's two big problems you will face.
One is that ducted fans are not optimized for static thrust, and that's essentially the only mode of operation for the ducted fan in your design. The second is that for an hover you generally need a fine pitch prop, that will not provide good thrust at flying speeds. So far there's no easy solution to either of these issues, they will always lead to some compromise or greatly increased complexity. I am not saying that what you want to do is not feasible, but probably you won't obtain the performance you expect.
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Old Feb 17, 2014, 09:44 AM
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thanks for the feedback .. I have used the rear motors, and props, in many planes with no problem with performance so I don't think that will be a problem. The ducted fan is another issue .. I won't know how it will perform until I do the thrust tests (hopefully this afternoon. I hope I can keep the weight of the finished plane around 1.5Kg
I am a little worried about the ability of the ducted fan to keep up with the throttle-H / gyro signal ...maybe it will be too slow ... we will see
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Old Feb 17, 2014, 09:57 AM
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I wonder if a thrust augmenter could work to get more static thrust from a standard EDF impeller. The concept was tried in the Rockwell XVF12, but the full size prototype didn't work as well as predicted.
Here's how a thrust augmenter works: http://link.springer.com/static-cont...2-6_10/000.png
Essentially the output end of a pneumatically driven vacuum pump
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Old Feb 17, 2014, 11:00 AM
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Thrust augmenter

If required I could incorporate a thrust augmenter ... I will see after my thrust tests
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Old Feb 17, 2014, 02:22 PM
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Turnigy D2826-6 2200KV 6X4 prop Thrust measurements

I have attached the thrust measurements for the rear motor
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Old Feb 18, 2014, 07:31 AM
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Ducted Fan Thrust Measurements

I have attached the thrust measurements for the ducted fan
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Old Feb 18, 2014, 07:40 AM
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Based on 30% lift for the ducted fan and 35% lift for each of the rear motors; hover will require 13.7 Amps for each of the rear motors and 17 Amps for the ducted fan. A total of 44 Amps.
The above calculations are based on a total weight of 1.5Kg
If possible the ratio could be changed to 20% lift for the ducted fan and 40% for each of the rear motors then the total hover current would drop to 42.5 Amps for hover
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Old Feb 18, 2014, 07:45 AM
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Forward flight pitch speed

During forward flight the rear motors will have a RPM of 20-21K RPM this translates into a pitch speed greater than 128 Km/Hr or 80 Mi/Hr ,,,, this is perfect.
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Old Feb 18, 2014, 09:42 AM
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Thrust Measurement System

Here is the system I use to measure Thrust .... Medusa Power Analyser Pro with a scale .. The data can be logged with a computer . A 58 Amp 11.7V (no load) switching power supple is used to power the system
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Old Feb 18, 2014, 09:48 AM
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CNC Foam Cutter and 66% prototype foam parts

Here is the home-built CNC foam cutter I used to cut the foam parts for the 66% pusher prototype. The vertical stabs will be cut from 6mm Depron.
I plan to glass the fuselage and wings with .5oz fiber-glass and water based poly-urethane.
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Old Feb 18, 2014, 10:22 AM
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Joined Dec 2006
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I don't get the design concept. As has already been mentioned, ducted fans are the opposite of what you want for efficient hovering. Your own data on current and thrust support the idea that propellers are much better for providing raw thrust. Basic disk actuation theory also supports more lift for less power the bigger the prop/rotor disk.

I get EDF's in a scale application, like an F-35 or something, but why would you use one if the mission is about functionality? You are already planning on using two propellers so it's not like you are going to be able to hide them.

I am glad to see you are taking data and using a somewhat engineering based approach. That means you have a chance of succeeding.

At some point you are going to need to give yourself some margin for success. That means a thrust margin of at least 20%. It also means not pushing batteries or other components to their limits. One or more of those limits is going to keep biting you, and the results will be very frustrating.

FYI, using individual gyro's is old school technology. Most modern designs use a flight controller board with 3 axis gyros and accelerometers. Those boards are much more programmable in terms of setting up different flight modes, PID parameters, etc. The KK2 board is very popular, and OpenAero2-VTOL firmware is available for free.

Do you have experience with multi-copters? If not, you would be better off to start with a simple and cheap quad.

I wish you the best of luck.
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Last edited by Ran D. St. Clair; Feb 18, 2014 at 10:33 AM.
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