FTFC23: Build-ruary by Inq: Inq'd F-23 Black Widow

[Inq]

I'd like to attempt a from-scratch design of the F-23 Black Widow. This will be a hybrid model in the same vein as my F-22. I'll use Flite Test design principles for the wing, side rails and tail surfaces. To give it a little better semi-scale look, I'll 3D print the fuselage, motor mount and control horns. I also will go up scale a little in that I'll use the 30" direction of the DTFB for the wingspan.

Specifications
Span: 27.9"
Length: 44.7"
Motor: A2212, 1400kv
ESC: 30A
Prop: 8x6
Battery: 1500 mAh

A very crude survey shows an AUW of about 600 grams before poly and painting. It should have a slightly better than 1:1 thrust to weight ratio. I am interested in any feedback, design strategies, pitfall avoidance you might have. I am particularly interested in the CG. As shown in the drawing below, the CG is almost centered on the wing, yet Flite Test's Mini F-22 Raptor the CG is very near the leading edge. At this scale the discrepancy between the two would be nearly 8".

Here is what I have so far...

Back to Inq's top level Build-ruary...

 

[JetCrafts]

noice

 

[Inq]

Oops! Already screwed up. Got the slot in backwards.
From @Mr NCT - https://forum.flitetest.com/index.php?threads/tight-slot.71581/#post-738167

 

[danskis]

Sorry to hear about the mini as it looked great. I even looked at buying a printer because your design was so slick. I'd say the CG would be in the same place as F22 as the platforms are similar ( this is a guess). The only suggestion I have is reinforce the wing fore/aft at the outer edge of the slot Easily done with BBQ skewers. Maybe move the motor/slot further back too as the battery will be in front causing you to add weight to the tail if my guess of the CG is correct.

Did the mini fly at all?

 

[danskis]

If you're interested in successful flying I would build the bigger F22 before this one as the F22 is a proven design. If you're predominantly interested in a design challenge then I'd love to see you make this one.

 

[Inq]

Sorry to hear about the mini as it looked great. I even looked at buying a printer because your design was so slick. I'd say the CG would be in the same place as F22 as the platforms are similar ( this is a guess). The only suggestion I have is reinforce the wing fore/aft at the outer edge of the slot Easily done with BBQ skewers. Maybe move the motor/slot further back too as the battery will be in front causing you to add weight to the tail if my guess of the CG is correct.

Did the mini fly at all?

No worries at all! I got out of the sport 40 years ago because I spent probably a hundred hours building a Sig Kadet Senior setup for just rudder, elevator and throttle. It lasted about 30 flight minutes. It hit so hard, it cracked the K&N 40 motor. The expense (money and time) to build another was just too much for me to absorb. This time around the F-22 cost about $2 and I spend $10 driving to the field to fly it. Crashing doesn't discourage me anymore as long as all the electric stuff survives.

The F-22 flew fine. I was the weak link in the chain. First flight lasted about 30 seconds and in the first dive, the battery must have come loose and moved into the nose. There wasn't enough stick to get it level and it mushed into the ground. No harm at all to it... plastic or foam. Tightened down the battery, put the nose cover back on and flung it again. It made several circuits (couple of minutes) and I lost orientation at the wrong moment and it did the auger test. I wish I'd gotten a photo of the sod caked nose. The plastic nose buried about 2" in the ground, but was undamaged. However, the shock load cracked the fuselage and bent the wing. Really... the plastic can be re-fused (ABS is good that way) and foam un-bent. But... I like the design, building and the weather doesn't look like I'll another chance for at least a week or two. I hope to finish this one for the next time slot.

Making this bigger and still keeping it light, I'm hoping this one will be even easier to fly.

 

[Inq]

If you're interested in successful flying I would build the bigger F22 before this one as the F22 is a proven design. If you're predominantly interested in a design challenge then I'd love to see you make this one.

Yeah! I like this phase the best... seeing it come alive in CAD is still a thrill and I'm joining the Musk design philosophy. If design says it has a 50% chance of survival, build-it, launch-it, blow it up... rinse and repeat.

 

[Inq]

I'd say the CG would be in the same place as F22 as the platforms are similar ( this is a guess).

I think that seems to be the prudent move. However, it screams crazy in light of the typical 25% of the average cord position. Just hope it has enough elevator on the first flight.

Maybe move the motor/slot further back too as the battery will be in front causing you to add weight to the tail if my guess of the CG is correct.

That was my first thought as well, but I noted on the F-22 they seemed to make sure the longest wing span was un-interrupted by the slot... I'm guessing for strength reasons. Here I've added the skewer as far forward as possible and the slot for the motor mount just behind it. I can even integrate some holes in the 3D printed motor mount to grab the skewers. That way the G-forces on the motor get transferred to the skewers first instead of the foamboard. This looks pretty good and I've got plenty of nose to put the battery as far forward as needed. What do you think?

 

[Inq]

Here's an updated version with the skewers, motor/prop slot, servo locations and the side pieces - main (transparent red) and reinforcement (light blue).

 

[Inq]

Foamboard Assembly (no 3D printing yet)

 

[Inq]

Here is the sum total of the foamboard requirements.

Next up - CAD of the 3D pieces. This will take a lot longer.

There are a couple of changes to make to this. I need to add the tabs to the side pieces and slots on the wing.

I also want to try something. Has anyone tried adding a very slight bit of camber to these type of flat wings? I have a foamboard that I was trying to flatten out. It was arced along the long direction. I stuck a yardstick under it to reverse bend toward flat. Then I had an Ah ha moment!... What if I arc it along the chord direction of the wing. This is not really meant to be wing camber. But as we all have seen in the Master series... once you arc it in one direction, it makes it impossibly stiff to bend in the transverse direction. I'm suggesting this as a wing stiffening exercise. The slight wing camber is a bonus. I'm only talking about a center deflection of 1/4" out of the chord length of 20". But it's enough to keep it from bowing along the 30" span.

What do you think?

 

[Piotrsko]

My experiences: undercamber in place of a flat wing adds stabilization problems and odd low speed performance. Undercamber/warps made into a semi symmetrical wing: baby, oh baby. Warping down the centerline has no noticeable affect except perhaps enhanced dutch roll.

 

[Inq]

I seem to have troubles with the FT hinges delaminating on both my planes. I'm sure it is because of my piloting skills (lack of) or I've not gotten the hot-glue smear technique down.

Although the hinge design I want to use on this F-23 is similar to Flite Test's F-22, the elevons on the F-23 are not horizontal. In the real plane, they not only bend up at 40°, the rotation axes is also at 40°. I've chosen not to model the axis rotation that way as it would take too much structure back there in the prop blast to accomplish that.

As a result, the hinge line is not very large and would exacerbate my delaminating problems. Also, I want to mimic the "flying tail" aspect so that the servos get some load relief by having some area in front of the axis. Therefore, I rationalized I need a stronger hinge and want to add support for the area leading the axis and integrate the control horns.

 

[danskis]

Generally this looks good. I've got no experience with under cambered foam wings so I'd listen to piotrsko. I love the hinge idea and the hinge design.

 

[L Edge]

Suggest you think about adding landing gear to your design to protect motor/prop/plane damage on landing. From your flying video, it looks like you have the Inq and skills to learn takeoff and landing as well as the other flying skills all at the same time.

That way, you eliminate the stage where the prop staying vertical/running usually do damage as the plane touches ground.

 

[Inq]

Forward fuselage exterior is done. It'll need some internal structure, but here's the basic shape.

 

[Inq]

Suggest you think about adding landing gear to your design to protect motor/prop/plane damage on landing. From your flying video, it looks like you have the Inq and skills to learn takeoff and landing as well as the other flying skills all at the same time.

That way, you eliminate the stage where the prop staying vertical/running usually do damage as the plane touches ground.

One of these days, I'll be good enough to fly a plane with EDF. I have two 70's that would go very nicely in this... or a little bigger. When that day happens, I'll go even more scale quality with the whole plane, retracts and the whole bit.

But for me to learn on, I think its important to keep this as light as I can make it. At the moment before actually weighing it, I'm projecting right at the 1:1 thrust : weight ratio with the motor I have.

This plane is only meant to be comparable in cost/cosmetics/quality of Flite Test's F-22, but with a more semi-scale looking fuselage. It's a disposable $3 plane. According to the threads on the FT F-22, most people don't seem to have much issue with the prop. Some said it was worth getting a good quality nylon one, but otherwise, they said they rarely break one. Also... at the field/club I fly, the strip is golf green manicured, but scale wheels still dig in. There is a very good pilot at our field with an F-16 Foam EDF with wheels. I've never seen him crash it, but it regularly noses over on landing and its nose is all bent up. If it didn't have wheels, it'd be able to belly land with a lot less damage. Likewise, if I had wheels on this, I'd trade prop damage for nose damage.

Oh! You saw my (lack of skill) landing... My Storch has 4" wheels.

 

[skymaster]

Nice have checked out ben harbers F-23 black widow maybe it will give you a few idea here check out his videos.Foamboard YF-23 - The Black Widow Flies Again! - YouTube
Foamboard YF-23 - Black Widow Maiden! - YouTube

 

[Inq]

Nice have checked out ben harbers F-23 black widow maybe it will give you a few idea here check out his videos.Foamboard YF-23 - The Black Widow Flies Again! - YouTube
Foamboard YF-23 - Black Widow Maiden! - YouTube

That is a gorgeous plane. He's using Master Series techniques. I also noticed he has the elevator rudder pivoting at the proper 40° angle. I've not see the lights in the exhausts before and liked how the dimmed and brightened with throttle. Sure wish we had paved strip!

 

[Inq]

Exterior Done!