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New Fixed Wing Design Project

#1
I am looking to try my hand at foam board aircraft design so I can fly it over the summer and gain some experience. I have built a few of the FliteTest aircraft in the past so have some experience in building, but have never designed one myself, and am looking for interesting project ideas.

Ideally I would like to try something new, unique, and interesting, maybe with a challenge to work towards (flight time, or speed etc.) , or to fulfill a role (such as search and rescue, an FPV aircraft, etc.).

My current challenge ideas are:
- Endurance build: some sort of glider
- Top speed build: try to attain the highest speed possible
- Water balloon drop: this would be a mix of endurance/lift/accuracy/aiming method
- Long range build
- Aircraft recovery build: a of system to "rescue" a plane in case of component failure in mid air
- Aircraft in-flight launcher system: launch on aircraft from another in flight

My current "role fulfilling" ideas are:
- Stable FPV platform: smooth and stable flight
- Search and rescue: similar to FPV platform, but with more payload for extra equipment
- Package delivery aircraft: similar to water balloon drop, but with an actual purpose

Does anyone have any more idea to add to my list, or possible roles to fill as mentioned above?
 

quorneng

Well-known member
#2
JakesProjects
I can advise on a powered endurance build.
There are 3 fairly obvious elements.
1. Reduce the power required to fly. The power to fly is a function of weight and speed so it becomes a compromise between aerodynamics and the structural weight required to achieve an efficient but light air frame. The overall size of the plane can influence the materials used for its construction.
2. Carry the biggest capacity battery as proportion of the rest of the aircraft's weight. This is fairly obvious but it does have an impact on structural compromise used in 1.
3. Use the electricity from the battery as efficiently as possible. Brushless motors are already pretty efficient but their efficiency does fall away a very low power outputs. The size of the motor thus has to be chosen so it is running not too far from its efficiency 'sweet spot' when at its endurance cruise power. Propeller efficiency is a function of its RPM and diameter, the bigger and slower the better, so the motor kV and the battery voltage has to be selected to achieve this. It also makes sense for the plane to be designed to fly with the minimum of control inputs to limit the battery drain from the servos.

You can set an arbitrary weight and size limit to reduce the number of variables and along with some intelligent guesses your plane will fly for a long time. To achieve the absolute maximum possible for a given set of limits you will likely need quite a bit of experimentation.
I hope this helps.

For my endurance quest I set myself a wing span limit of 48" (1200 mm) and a 5000mAh 2s battery that matched a specific small 80 W brushless motor.
 
#3
quorneng
Thanks for the advice! I am thinking of doing something similar to your project.

I have had some long-ish flights back in the day with a Horizon Hobby Super Cub LP (3-channel training aircraft), and I could get maybe 30 minutes if flying conservatively. So I feel like a good start goal for an endurance flight would be 60 minutes or maybe a bit longer.

If I end up deciding on an endurance build I will likely model the aircraft similarly to a glider (high aspect ratio wing, probably a simple Clark-Y airfoil, slim fuselage just large enough for the battery/electronics). A slight wing dihedral (or maybe wing sweep to simulate dihedral) would be good to limit control inputs. I like the idea of setting a wingspan/weight limit.

What kind of flight times do you get out of your endurance build?

I will definitely update this post as I go forward into design, and I am open to design suggestions.
 

BATTLEAXE

Well-known member
#4
If you are looking for a stable FPV platform i would suggest the FT Goblin. I built mine at 130%. Used a 3536 1200 Kv on a 9x6 prop. It would need at least a 5500mah 3s just for the weight to balance but that means you will get at least a 15 minute flight time running at a constant 70% throttle. It will fly at about 50% easily and glides forever. If you are light on the left stick and even shut down for some gliding you may get up to a half hour or more. The link to my YT channel is in my signature and there are a couple vids of it there. Check it out for kicks
 

quorneng

Well-known member
#5
JakesProjects
This is what I ended up with after nearly 2 years and several major re designs along the way.
06Feb19.JPG

It looks like a simple pusher, which it is, but I realised it was likely to have to be test flown for many hours during development so it had to be robust enough for that yet light enough to use as little power as possible. Ready to go it weighs 15.3 oz (434 g) of which the battery alone accounts for 48%.
It is made of 2 & 3 mm Depron foam with just a small amount of balsa and a glass fibre tail boom.
Under the right conditions it can maintain height using just under 1 A in total. It has a 5 Ah battery so its maximum duration is 5 hours.
Not actually done it as after a full 2 hours of slowly flying round and round I realised I had reached the limit of my endurance rather than the plane's.
I still fly it but the battery is now 5 years old so has lost about half its capacity but even so it can still fly for a long time. ;)
 
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#6
quorneng

That is a really cool project, a theoretical 5 hour flight time is pretty amazing. I can definitely understand the 2 hr limit while being piloted by a human, maybe it's time for an autopilot.

Thanks for the information and inspiration!