1/20 Scale U-2R (3D Printed)

[Phantom]

Yep listening to his bird, is the same thing I'm dealing with wide open throttle just to maintain flight. 2/3 to 3/4 throttle is a poorly powered edf, even for a glider like the U-2, but I'm at full throttle unless I want to lose altitude. An edf adequately powered can maintain level flight at 50% throttle, obviously a better power to weight ratio is gravy. But the phase 3 U-2, is very under powered.

[Dirty Dee]

True, but their U-2 isn't modified with 3 extra servos, flaps and rudder, and two centerline wheels.

One guy with flaps, retracts, and rudder. 35 oz AUW.

https://www.rcgroups.com/forums/showpost.php?p=17648477&postcount=443

[Phantom]

Take a look at some videos online, doesn't seem the plane suffers from lack of thrust and departs a hand toss fairly nicely. But, regaining 10-15% thrust would be a good bonus to flight time and performance.

True, but their U-2 isn't modified with 3 extra servos, flaps and rudder, and two centerline wheels. I've been trying to find something to stuff in her to get some more static thrust. I just installed a 70mm FW 6s setup in my FA-50 but I can't do anything like that with my U-2 because there is no room for any bigger batteries than stock.

[Dirty Dee]

That settles it, in putting cheater holes in my hobby people U-2.

Take a look at some videos online, doesn't seem the plane suffers from lack of thrust and departs a hand toss fairly nicely. But, regaining 10-15% thrust would be a good bonus to flight time and performance.

[Dirty Dee]

Thanks Alpha.

Im having some trouble visualizing this arrangement. Is there an example of another design doing this, or a napkin sketch?

The wings are removable and mimic the designs of the 70mm F16 and YAK130 with attachment. The failure happened at the interface of the wing to the fuselage, so the wings im thinking might be ok seeing how little flex happened during the test. I did however retest with wrapped carbon spars, and the failure then moved into the fuselage where the 6mm spar slips in. I'll be needing to beef that area up with more wall thickness.

[Phantom]

Lead time on some 1mm piano wire and printer issues slowed me down a bit. But still moving along. I was curious about how the glide slope would be, so I made a downsized 1/50 scale chuck glider at 88g balanced to 25% MAC

Did some thrust tests and found that the long intakes and exhaust create 25% thrust losses.

FSA: 1,338 mm^2
Tail Exhaust Area: 1,306mm^2
97.6% FSA

Baseline:
With the EDF mounted in the single section
Grams of Thrust: 500g
Max Amps: 26.4A
Max Watts: 297.5W

Full Exhaust:
Full tail section
Grams of Thrust: 440g
Max Amps: 25A
Max Watts: 283W

12% losses

Complete Intake and Exhaust:
Full inlet and exhaust
Grams of Thrust: 375g
Max Amps: 25.3A
Max Watts: 288W

25% losses

That settles it, in putting cheater holes in my hobby people U-2.

[Alpha]

Inspiring work as always, Dirty Dee!

Just a thought about the load testing you've mentioned... I noticed the photo of your wing sections shows joints that are perpendicular to the typical wing load. If your wrapped carbon tube doesn't do the trick (I happen to think it will be fine), then perhaps consider using a staggered system where each joint overlaps its neighbor in a layout opposing the Gs. This would help further distribute the load across the wing at the joint positions. I could see an arrangement where, nearer the wing root, the overlapping section opposes the downward force (that snaps wings), and outward toward the tips the overlapping section opposes the upward force (that flexes wings to failure). Of course, this would greatly complicate the 3D printing process because the base of the section is no longer completely flush to the bed.

And again, I think it's overkill. But I thought I'd mention it nonetheless.

[Dirty Dee]

Lead time on some 1mm piano wire and printer issues slowed me down a bit. But still moving along. I was curious about how the glide slope would be, so I made a downsized 1/50 scale chuck glider at 88g balanced to 25% MAC

Did some thrust tests and found that the long intakes and exhaust create 25% thrust losses.

FSA: 1,338 mm^2
Tail Exhaust Area: 1,306mm^2
97.6% FSA

Baseline:
With the EDF mounted in the single section
Grams of Thrust: 500g
Max Amps: 26.4A
Max Watts: 297.5W

Full Exhaust:
Full tail section
Grams of Thrust: 440g
Max Amps: 25A
Max Watts: 283W

12% losses

Complete Intake and Exhaust:
Full inlet and exhaust
Grams of Thrust: 375g
Max Amps: 25.3A
Max Watts: 288W

25% losses

[TiredIronGRB]

Thanks Guys. Hoping to have everything finished in the next 2 weeks, and get it flying before it gets too cold. Probably will strap a mobius cam for some inflight footage.

Anticipation

[Dirty Dee]

Thanks Guys. Hoping to have everything finished in the next 2 weeks, and get it flying before it gets too cold. Probably will strap a mobius cam for some inflight footage.

[MikeT]

Ya know the really cool thing about Dee is his stuff actually fly's. I've seen many really cool builds that never leave the ground or even get completed. I have to really admire the guy.

Mike

[vduniec]

So cool and glad to see you efforts into this interesting airframe. I have the Hobby People U-2 that I plan on modifying some day but would like to buy these files from you when they're complete just to support those who improve the hobby.

[MikeT]

WOW Dee, you never cease to amaze me.

Mike

[fhhuber]

It is surprisingly easy to exceed 9G

Many years ago someone put a G meter in a Pattern Competition model and exceeded the meter's 38 G max reading, just doing the AMA Pattern Master's sequence.

Dynamic soaring models have been calculated to exceed 120 G.

[Dirty Dee]

Did a destructive test to make sure the wings and annular spar former can survive high G maneuvers. Plane was balanced on the MAC points, and handled 9.25kg of load.

At 9.85kG, the port spar started to break and the wing folded in. Assuming 1100g AUW without super pods installed, the plane could handle 8.4G loops. I think if I use wrapped CF tubes instead of pultruded it would be stronger.

[Dirty Dee]

Thanks

[Elbee]

DD, You are a bloody genius. Amazing work. Best, LB

[Dirty Dee]

Here is a whole wing with detachable super pods. Some printer setting tweaks and minor design changes and I will be printing the first set of wings.

[Dirty Dee]

Here is a test print of the tail section. I'm using 3mm square CF tubes to operate the elevators and rudders.

[Dirty Dee]

Design is close to being finished. Wings just need some tweaks for attachments of the removable super pods. Fuselage tail section is mostly done and I am moving to the EDF and battery bays.

To avoid having to add nose ballast, I am designing a torque tube for the rudder and elevators so the servos can sit in the battery hatch ahead of the CG.

wings will have 4mmx2mm carbon tubes to strengthen them, as well as help with aligning the sections together. The vertical stab goes on pretty nicely, but I am still adding a small 40mm CF tube mostly for alignment during assembly.