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FT Edge 1080

Pieliker96

Active member
#1
540 * 2 = 1080.

This is an idea I've had kicking around ever since seeing the Yak-110 at OSHKOSH - two Yak-55's transformed into a single twin-fuselage craft. The goal is to basically do the same thing with Andres' Edge: join two of them together at the wing and (maybe) sling a EDF underneath. This should be relatively simple, involving no more than a custom wing and elevator - everything else will be completely stock. I've not done any really detailed planning (ex. weight, battery requirements, wing loading, etc.) beyond just entertaining the concept. I'm interested to see how it'll fly.

UlxIYEJ.jpg
 

Pieliker96

Active member
#5
I've done a decent preliminary estimation of the performance of this aircraft.

Expected maximum AUW is 1.7kg, or 2kg with the EDF (Stock is ~850g). That's with two 1800mah 4s batteries. I would go with more capacity given the high current draw of the motors & edf, but I don't want to make this bird too heavy - I'll have anywhere from 30% (no EDF) to 55% (With EDF) more mass per unit wing area than the stock plane.

This translates into a ~15-25% increase in stall speed over baseline given that v ∝ √ (mass/wing area) - not insignificant, but very manageable with the already low stall speed (or at least maneuvering speed), propwash over the massive control surfaces, and high thrust-to-weight ratio that the craft has.

I'll be using counter-rotating propellers to eliminate torque, as well as differential thrust, just for kicks. I'm debating whether to have the fan on all the time while in-flight. I think I could have three modes, all on a switch:

-Off (For battery saving)
-Tied to throttle with a ~50% dual rate (For general flying/maneuvering)
-Directly tied to throttle (For high speed passes)

which would allow me to potentially extend battery life a bit by disabling the less-efficient EDF when it is not needed.

I'm playing with the idea of making the EDF removable by means of a pod that would slot into the wing and horizontal stabilizer. That would allow me to have the best of both worlds in terms of raw thrust versus aerobatic performance and flight time, but would add extra complexity and potentially wear out over time.
 
#7
That sounds real difficult in figuring out how to balance the power between the two systems. Not an expert but I would think that too much thrust from the EDF will cause the propellers to drag and waste power and the opposite on the other end. Would be interested in seeing the results.
 

Pieliker96

Active member
#8
...EDF will cause the propellers to drag and waste power and the opposite on the other end.
This is a great point which I've been thinking about for a while. I guess it's time to do some calculations:

The 9x4.7 propellers I'm planning to use, along with 1100kv motors on 4s (Max 16.8v), give a maximum theoretical pitch speed of about 80MPH (Plenty fast for me). As speed increases to this magnitude (assuming it is attainable), most of the thrust will be coming from the higher-pitched EDF with the propellers producing negligible amounts of thrust (and therefore little drag).

Increasing the pitch to a 9x6 yeilds a theoretical maximum pitch speed of 105MPH. Realistically it'll be a lot less, taking into account drag, voltage droop under load, and the fact that battery voltage decreases throughout the flight. I'll also probably stick to the 9x4.7's for the snappier throttle response and lower amp draw.

Either way, this seems to be a fantastic top speed before the props become detrimental. This plane is designed and built for 3D flight, which is arguably more fun when "low & slow". I'm not really concerned about the drag caused by the fan (even when stopped) because it's quite a small area when compared to the cowling on the plane itself. Sure, it'll be inefficient. But if I wanted efficiency I wouldn't be strapping an EDF to it anyways. :)
 

Pieliker96

Active member
#9
Made some progress on the right-side fuselage. The double-wide elevator was too large to fit on a single sheet of foam so I just removed the counterbalance from one side. I figure I can basically make both fuselages sans the wing, tape them together at the H-stab, then figure out the wing from there.

20190317_223515.jpg
 
#10
And then there were two!

20190319_001721.jpg

An advantage of not using the waterproof foam is being able to simply make the canopy out of black foam. One disadvantage (from buying the laser-cut kits) is that the more complex geometry is more prone to error / small misalignments.

20190319_001635.jpg

I also made a little tail wheel wire holder with some sheet balsa. It's sort of grafted under the skin of the foam to give a cleaner look.
The tail wheel is also protected by the little ventral skid. Not that I intend to fly off of grass, but it couldn't hurt.

20190319_002025.jpg

Custom motor mounts without thrust angle for counterrotation purposes.