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A down spout glider design

Hi all,

I designed this glider using the aluminium down spout as the fuselage. I like to post it here for your review and suggestion on how to improve on it.

The reason that I have chosen the aluminium down spout is because it gives me a lot of room for my battery and electronics so that if I would like to add a flight computer for autonomous flying or an additional Rasberry Pi for some AI target recognition then that is possible. The aluminium is also quite rugged and light so that if there is some accident on landing then it wouldn't break up.

The good news is that it flies but seems a bit under power in a windy day. Here is a video of its maiden flight

At the end I think it may be a little bit too heavy to be a glider (1377g) and its motor is a little bit too weak to be a plane (340W). So I would like to hear from flitetest members on how it could be improved upon. This is my first build so I would like to learn how to be a better builder.

The good thing is that it is very easy to build and you can find most of the building materials around the home.

Solar Seeker Glider Design
Solar Seeker is the name that my daughter gave to the plane. :)

The design goals for Solar seeker:
  1. Easy to build, easy to maintain, can withstand landing accident without breaking up
  2. Has a lot of room for electronics and battery to allow for computer control automated flying.

Some practical design guideline:

  1. Wing area: A good aspect ratio for a wing is 5 to 1, that's span to chord.
  2. The balance point is 25% to 33% of wing chord from the leading edge.
  3. Fuselage is 75% of the wing span.
  4. Nose length is from back of prop to wing leading edge, should be 20% fuselage length.
  5. Tail length is from wing trailing edge to leading edge of horizontal stab, should be 40% of fuselage length.
  6. Horizontal Stab area is 22% of wing area.
  7. Horizontal Stab aspect ratio should be 3 to 1.
  8. Elevator is 20% of the area of the horizontal stabilizer.
  9. Verticle Stabilizer area is 1/3 Horizontal Stabilizer area.
  10. Verticle Stab is about as tall as it is wide.
  11. Rudder is 1/3 to 1/2 of the vertical stabilizer area.
Wing Design Calculation:
The wing is perhaps the most important component of the plane. I used the following calculation and guide line.
  1. Calculate wing cube load C:
    C = (plane weight in gram) / (lifting area in dm square) ^ (1.5)
  2. C values should be less than or equal to 12 to make it easier for take off, slow flying and landing. Good value of C is between 8 to 12. C value less than 8 will make the plane float.
  3. Gliders tend to have small C value around 5 to 8. Acrobatic plane tends to have C value around 8-12

Our glider has a wing cube load C of about 6:
1377g / (2.5*15)^1.5 = 5.9

Plane Dimension:
Wing: length 1500mm, chord: 200mm, control surface (aileron/flap width): 50mm
Horizontal stabilizer: 330x80 mm, elevator control surface: 330x50mm
Horizontal stabilizer support: 70x30x10mm
Vertical stabilizer: 240x80mm, rudder control surface: 240x50mm
Overall length from propeller to rudder: 1200mm, fuselage: 510mm, tail boom including elevator and rudder: 530mm
Carbon fiber for tail boom length: 81mm
Landing gear: 240x100mm
Landing wheel diameter: 55mm
Fuselage measuring from the back: 60x20mm-200mm, 45x250-410mm
Motor plastic cap mount (from Castro motor oil 1 gallon can): diameter - 60mm, cap depth: 20mm

Plane dimension with pictures:
Top View

Tail Side View

Plane Side View

Motor Mount View

Fuselage Top View

Fuselage Bottom View

Motor Power Calculation:
Here I calculate the motor power needed for the Glider. For glider it is recommended that the thrust to weight ratio to be between .35-.55. Where as for faster airplane, the thrust to weight ratio could be much higher like .8 to 1 or higher.
Choosing thrust to weight ratio
Glider: .35-.55
Find thrust based on how heavy the plane is.
For 1.5kg plane, the thrust is .35*1500=525g
Choose KV based on desired airspeed:
1000KV: 70km/h
2000KV: 140km/h
3000KV: 210km/h
Calculate power to thrust ratio (Watt/g) = .17*KV/1000+.09
For 2200KV, Watt/g = .464

The needed motor power is
For 525g thrust: .464*525 = 243.6 Watt

Given the power requirement, the following motor/ESC combination is chosen where the max power is 342w which should work:
abcGoodefg RC 2200KV Brushless Motor 2212-6+ with 30A ESC Set

Airplane weight:
  1. Landing gear: 70g
  2. Motor: 92g
  3. Fuselage (just aluminium tube): 110g
  4. Battery 3000mAh:202g
  5. Fuselage + Motor + Receiver: 305g
  6. Tail+boom: 146g
  7. Wing: 530g

    Total plane weight : 1377g

There are a total of 6 servos were used:
  • 2 for controlling the flaps
  • 2 for controlling the ailerons
  • 1 for controlling the rudder
  • 1 for controlling the elevator

The part that was used was: YoungRC MG90D 9g Digital Micro Servo Motor Metal Gear.

Transmitter and Receiver:
The transmitter and receiver used were from Radiolink. These tx/rx support 12 channels. 6 channels are used to control the servos, there are still 6 channels left for various mode setting and configuration.
  • Radiolink AT10II 12 Channels RC Transmitter and
  • Radiolink Receiver R12DS
Note: the prevalent Transmitter/Receiver used in RC plane are from Spektrum. There is also a huge price difference. For example the Radiolink 12 channels costs only $158.99 whereas the Spektrum 8 channel DX8 is already $379.99. So far I have not seen any performance difference yet.

Wing build:
The wing is built from Dollar Tree Readi foam boards. The wing design is the well known ARMIN wing. A youtube video can be seen here.

Flight control system and AI:
TODO: the plan is to use the Matek F765 to implement the flight control system for the automated glider. The Flight Control system will be connected to a Rasberry Pi 4 where additional computing power for AI and target recognition can take place.

Matek F765: https://www.rcgroups.com/forums/showthread.php?3391649-Matek-F765-Wing-Flight-Controller-w-Ardupilot-(ChiBiOS)
Raberry Pi 4: https://www.raspberrypi.org/products/

Some Build and Design Remarks:
I began to build Solar Seeker on May 10, 2020. The built was done on a part time basis and there was time idle waiting for the parts to arrive. So it took me about 14 days to complete it on May 24, 2020. In reality if all the parts are available then it may only take about 3 days to complete.

Solar Seeker had it maiden flight on May 31, 2020. It was a very windy day with wind blowing at about 15mph. Although it wasn’t recommended to do a maiden flight in such a condition, I went ahead and did it anyway to see if it works. The plane did fly but it was clearly under power. The motor power was chosen to be 340W, I think a 1000W motor would fit it better. Also the motor KV was chosen to be 2200KV which was supposedly for a faster plane of speed around 140km/h. Perhaps a motor with 1000KV that has a speed of 70km/h would had been more appropriate for a glider.
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Well-known member
Ingenious idea using the downspout. You could drill some holes in it and cover them with packaging tape to make it lighter. If you haven't already take a look at Experimental Airlines for some basic fuselages. Basically he uses a foam downspout. I've found if you reinforce the foam square/rectangular fuselage with full length bamboo skewers and use a solid plywood firewall it is virtually indestructible. If your interested let me know and I'll send some pics. oops, it looks like you're well aware of Ed's great work.
Hi and thank you for your suggestion. Yes I have seen Ed's work. I have not tried the foam tube fuselage before but I think its wall might be much thicker than that of the down spout. The advantage of the down spout is that it is very light and rugged, and it only take a few cuts to build. It has a strong rib line where you can attach the tail boom securely to the plane. I also like to watch real airplane landing so I have attached a landing gear to it and the strong structure allow it to take some bad landing. The heaviest part of the plane is the wing. I built it with a heavier wooden spar instead of a lighter carbon fiber tube. May be if there is a way to build a much lighter wing then it could make a good glider.


Well-known member
Change the incidence from +4 to maybe 1 or 2 or even 0 using an upswept leading edge and appropriate horizontal stab shimming or up trim. Weight isn't all that much for a 4ft span slope soarer, a bit heavy for thermal but I bet it flies like my simple stick. I don't see a problem with a wood spar, a bit over kill and even more so with carbon tube.

How does if fly on a calm day?
Change the incidence from +4 to maybe 1 or 2 or even 0 using an upswept leading edge and appropriate horizontal stab shimming or up trim. Weight isn't all that much for a 4ft span slope soarer, a bit heavy for thermal but I bet it flies like my simple stick. I don't see a problem with a wood spar, a bit over kill and even more so with carbon tube.

How does if fly on a calm day?
Thank you for your suggestion. I was reading some where and it was suggested to me that it is good for a high wing have a small incident angle. So that was why I have built it that way. I can test it again without the incident angle to see what'll happen. Since its maiden flight I have not flown it again. The reason is I don't know how to fly RC yet and I had to go to a fairly distance air field (about 1.5 hours from home) to have a friend fly it for me. I am trying to learn RC flying with computer simulation and joining a local club. I found that flying RC plane is not easy at all. There are many times where I just lost my orientation on left and right turn. Or lost sight of the plane altogether. It is funny but I found that flying a real plane is easier. At least I don't lose my sense of left and right and I always have a bird eye view of where I am flying to.