JH Sharknado - a ridiculous foamboard speed machine

[FAI-F1D]

A quick recap for those who haven't been following: #blameBen is the name of the game. @Mid7night started this ridiculous arms race, and I aim to catch up. First there was his Angry Bee, then my Speed Deamon, then his Yellow Jacket, and I've built umpteen things since then trying to catch up by throwing absurd amounts of money at the problem.

And to review further, Speed Deamon:

Hot Deamon (a confirmed absurdly fast airplane):

I now present to you a breaking of the mold, the JH Sharknado!

Planned power is a 3674-2650 inrunner driving an APC 6.5x6.5 prop. This is the same setup that was used to push a Strix Goblin to over 250 mph!

Per my usual pattern, the plans and such will be posted subsequently once things are fully worked out.

 

[FAI-F1D]

Alpha plans added 3 August 2019.

Do not attempt to build this airplane if you have not flown high performance (>100 mph) before. It is a very stable, forgiving airplane, but with a roll rate of over 720 deg/sec in glide and a power system running twice the recommended watt limits, it is extremely demanding of pilot skill in both orientation and throttle management. Quality batteries can result in power draws of over 240A at WOT.

Specs:
Wing Span 40 inches
Length 40 inches
Center of Gravity 1.5 inches aft of wing root LE
Wing Area 356 square inches
All Up Weight 54.6 ounces
Wing Loading 22.1 oz / sq. ft.

Skill required
Build skill level: 4 - Able to taper wings for smooth closures, comfortable using a covering iron to seal the edges
Pilot skill level: 5 - Expert level; it's stable, but it's also VERY fast and requires extensive throttle management

Electronics
6 channel rx
150A esc minimum, rated for cell count desired (3-6s) - requires 200A continuous rating for 6s operation
External UBEC, 5A minimum
2s 400-500 20C lipo for rx/servo power
Leopard 3674-2650 or equivalent such as Neu/Castle 1515 up to GoolRC 4074-2250
APC 6.5x6.5 prop (7x10 for 40mm inrunner)
5x Towerpro MG90 metal gear servos
Transmitter capable of dual aileron mixing/crow
4s 2200 30C - 6s 2500 70C lipo for motor, 2s 500 for RX power

Recommended throws:
Ailerons: +/- 15 @ 50% expo
Elevator: +/- 20̊ @ 50% expo
Flaps: +15/-50

WARNING!!!
This is a an extremely fast airplane that pushes the structural limitations of foamboard. It is capable of speeds well in excess of 100 mph, and foam wing spars cannot take the flight loads imposed by those speeds. Do not attempt to substitute a material for the specified 3/16" CF spars and plywood inserts. Failure to comply with these warnings could have lethal consequences!

Additionally, this power system is extremely overpowered and intended specifically for speed records. Operating at WOT for more than 5 seconds WILL result in destruction of the power system.

Known setups and performance:
GoolRC 3670-2850, Red Brick 200 Opto, APC 6.5x6.5, 2x Turnigy 3s2200 25C series (6s 2200): 143 mph
GoolRC 4074-2250, Red Brick 200 Opto, APC 6.5x6.5, 2x Xilo 6s1250 70C parallel (6s 2200): 120 mph
GoolRC 4074-2250, Red Brick 200 Opto, APC 7x10, 2x Xilo 6s1250 70C parallel (6s 2200): 165 mph *World's fastest foamboard airplane as of 8/31/2019
GoolRC 4074-2250, Red Brick 200 Opto, APC 7x10, 2x Xilo 6s1250 70C parallel (6s 2200), Graupner 42mm Precision Spinner: 152.9 kts/175.8 mph *World's fastest foamboard airplane as of 9/14/2019

Price breakdown:
FrSky X8R, $30
Red Brick 200A Opto, $23.87
Turnigy UBEC, $5.87
Zippy 350 mAh 2s, $3.49
GoolRC 4074-2250, $36.73
APC 7x10, $2.45
MG90s servos, $1.55x5 = $7.75
Xilo 6s 1250, $29.99x2 = $59.98
3/16" CF tube, $10.30
.050 CF rod, $4.99
1/32" plywood, $2.85
1/8" plywood, $3.29
_______________________
Total, $191.57

 

[FAI-F1D]

Reserved for build videos

 

[cranialrectosis]

Anticipatin'....

 

[FAI-F1D]

So let's proceed with the build photos. Until (and if) I get around to making build videos, these will serve to explain some of the less clear parts of how this thing is to be built.

Parts; note that there's more plywood in this than usual. The wing is designed to attach with four Dubro 4-40 bolts into blind nuts. This reduces drag considerably over my previous designs.

A look at the power system: 200A Red Brick opto ESC, and a cheap UBEC for a separate rx battery, along with a GoolRC 3670-2800 motor. Dirt cheap stuff, but the separate UBEC gives a decent chance of keeping things under control in the event of an esc failure. I've burned out a lot of internal BECs and the probability of having one fail rises drastically above 1000W. We're leaving that threshold in the dust here!

The nose section is built separately. For durablity, I sunk a piece of .050" cf rod into each crease, for a total of 8 cf rods in the nose. This may not be necessary, but speed planes lead short, abusive lives, and this reinforcement will hopefully extend that a little so I can get more flight data. I recommend leaving the firewall off until mounting the motor to it, then glue in the firewall and reinforce everything.

Don't skimp on reinforcing. This motor is capable of over 4 kw with the right battery and esc. That's a huge amount of thrust to restrain. You will need to cut cooling holes later and cut off the ends of plastic spoons for the airscoops. The power system CANNOT function without these. Even 10 seconds at half throttle without proper cooling could lead to a fire. As such, static runups to full throttle are an absolute no-no!

Here we see the nose held up to the rest of the fuselage. Note that the top decking is not attached, but the elevator servo has to be installed during that process since it sits just ahead of the stab leading edge. Review the build video for the Hot Deamon for details on that. The center area has several doublers that are necessary for compression resistance. Also the battery access top deck CANNOT be attached yet!

Here are a few photos of the sandwich of the center section top deck. Use 1/16" ply for this; it's going to see a lot of load!

There are some refinements required to the plans here...the center decking is really critical in how it has to be installed. Lots of fiberglass tape is warranted here. I cannot overemphasize just how much load this area sees on even a light pullout from a 120+ mph dive.

Here's the nose attached. Note that this is actually a mockup since the nose didn't have strapping tape in this photo, so there's no motor in there. The nose-fuselage join needs heavy reinforcing with strapping tape. Note that I've attached the tail surfaces at this point, too, since that servo and its pushrod are already in place.

I use a covering iron to round off all the edges. This makes them more durable and noticeably increases the performance of the plane.

 

[FAI-F1D]

Moving on to the wing...

This is a NerdNic style speed wing. It's built in right and left panels. Tape them together and build things out. Two 3/16" carbon tube spars go in there. There's a bottom and top plate for the screw mounts for maximum strength. I used 1/32" ply for the bottom and 1/16" ply for the top. That makes things a little challenging to fold over, but it's worth it. Servos get installed later.

There's plenty out there on NerdNic wings, so I won't repeat it here. Mine is slightly different just for ease of assembly. The finished result does look pretty nice.

Before installing the servos, hog out some of the foam on the bottom of the top surface. That lets you sink the servos in flush with the bottom of the wing.

Wing installed. Note that I made little fairings to streamline it in after everything was fitted out.

 

[Mid7night]

Well you're certainly faster and better at getting build threads and pics up than me! I had no idea about that Strix Goblin run, that was pretty insane...however he was in a bit of a dive, so I'm not buyin' it.

Stay tuned for Redline updates!

 

[FAI-F1D]

And it's finished:

I have full crow mixing and some camber settings, plus about 1/8" elevator up trim on a momentary switch for launch. You probably don't need any of that, but I put it in for safety's sake, plus I really like hotliners and you need crow and camber to make them fly to their full capabilities.

CG is currently at 10% chord with a 4s 2200. Yeah, that far forward. It's ridiculous. And yes, I have flown the plane. It's very locked in and flies quite nicely. There are a lot of cooling issues...the battery, ESC, motor were all very hot after 4 minutes of flying (and that's how much you get from the full capacity of the battery; I never even got past half throttle either!).

Video will be forthcoming with a couple of ~100 mph passes. The airframe is definitely good. Power system still needs tweaks obviously.

 

[Air-headed Aviator]

This is basically the plane equivalent of a muscle car. You're juicing this thing with irresponsible power! I like it!

 

[jross]

This may not be necessary, but speed planes lead short, abusive lives,

Outa my league for now but I believe it.

Love what's going on with you and Ben. You're both talented designers and it's fun to watch. If you look back at some of the most innovative designs and improvements for almost anything, there was competition involved. No doubt you do a nicer job of documenting the process which has taught me a lot. Thanks!

 

[FAI-F1D]

It's time for some color!

Really, these photos hide a lot of imperfections from paint peeling off when I was removing the masking. Still, it's a very strong color scheme which will help with orientation, and therefore this is one of those rare cases when pretty paint makes the plane actually go faster, if only because I can fly it better.

I want to thank everyone who has complimented this build. I stand on the shoulders of giants in my pursuits and just hope I'm able to give back 1/10th of what they gave me.

 

[DamoRC]

Looking forward to seeing the flight results. That STRIX Goblin vid is insane!

 

[rockyboy]

Yeah, this is completely nuts. Bravo good sir!

 

[Air-headed Aviator]

Hey Josh what kinda weight were you running?

 

[FAI-F1D]

Well guys, she's in sick bay for a bit. It was soooo worth it though. Launched on two 3s2200 in series, and on the fourth speed pass I let it go a full 4 seconds before cutting the throttle. When I when to pull out, there was a horrific noise as the left flap and aileron when into flutter and separated from the airframe. Somehow managed to circle around and make a safe landing in tall grass. After I got it down, I looked at the GPS log and saw a new personal best foamboard speed of 125 kts!

Batteries were at a little over 3.8v/cell after the light motoring around I did and four WOT passes. Mind you "light motoring" has a different meaning here--This thing has nearly unlimited vertical at 1/4 throttle.

I'll get it fixed up soon enough. For the time being I'm pretty happy overall and want to take some time to digest the outcome before embarking full speed again on this.

 

[Air-headed Aviator]

Well guys, she's in sick bay for a bit. It was soooo worth it though. Launched on two 3s2200 in series, and on the fourth speed pass I let it go a full 4 seconds before cutting the throttle. When I when to pull out, there was a horrific noise as the left flap and aileron when into flutter and separated from the airframe. Somehow managed to circle around and make a safe landing in tall grass. After I got it down, I looked at the GPS log and saw a new personal best foamboard speed of 125 kts!

View attachment 138262

View attachment 138264

Batteries were at a little over 3.8v/cell after the light motoring around I did and four WOT passes. Mind you "light motoring" has a different meaning here--This thing has nearly unlimited vertical at 1/4 throttle.

I'll get it fixed up soon enough. For the time being I'm pretty happy overall and want to take some time to digest the outcome before embarking full speed again on this.

Nice, looks like you're on the verge of success! It seems like perhaps though tape and paper hinges have their limits at 3000W

 

[DamoRC]

Congrats!

 

[FAI-F1D]

Here's some footage of the craziness here, along with several other foamboard speed planes (sorry, the flutter fest wasn't caught on video):

 

[FAI-F1D]

I got a few more Xilo 6s packs recently so I could fly this plane on good batteries. Going from a pair of Turnigy batteries to a pair of Xilo batteries drastically upped the power, but I burned out the 3670 inrunner on my second pass, recording another 140 mph pass. Ooops.

After taking some measurements, I concluded that I could still get the plane to balance with a 40mm inrunner, so I ordered a GoolRC 4074-2250. That is an absolute beast of a motor. Balance was...interesting...

With a 6.5x6.5, the speeds were predictably lower, around 120 mph, so I upped it to a 7x10. Ceilings were low and visibility unexceptional on Saturday, but I still got in a flight with it. First pass was 130 kts (my transmitter readout is in kts and haven't figured out how to make it convert on screen))! With the batteries warmed up, entered another pass, starting around 300', diving to 200 and then holding level after I hit the throttle. Less than 5 seconds of power and then she coasted for a long while. 144 kts!!! I landed after that; She's a happy bird and needs a spinner before I do anymore flying.

So I'm officially in the 150 mph foamboard club, which is a fantastic feeling, and she's a good 10 mph faster than Ben Harber's Yellow Jacket. Since these were GPS runs, the speeds are of course somewhat questionable, however having seen 150 mph planes on many occasions, I have no doubt she's doing every bit of that and more.

Video will be forthcoming.

One other thing: She's 54.6 oz all up with two 6s1250 Xilo in parallel. Pretty hefty for a 40" span, but there's enough wing area to slow down nicely for landing with crow braking.

 

[FAI-F1D]

New speed record! The Sharknado gained another 10 mph to achieve 175 mph today (GPS indicated 152.9 kts). The new Graupner 42mm spinner definitely played a major role in achieving this speed. There's much more to come, but I stripped a flap servo somewhere along the way and that made the model start getting rather unhappy. Probably time to stop using cheap servos in these planes now that we're pushing FAR beyond the realm of normal toy airplane speeds.

At this point I'm going to have to start doing research on ways to beef up the power system. I'm running a Red Brick 200A esc which has hopelessly undersized wire for the 230A+ that I believe this plane is drawing. Cooling inside the fuse is terribly inadequate and I need to open things up to provide more cooling (or cut a hole in the top of the fuse so that I can surface mount the esc to expose its heat sink to the airflow). Also I've gotten away so far with XT60 connectors, but that just isn't safe and I'm surprised I haven't killed them yet. I'll probably just go up to an XT90 feeding into the ESC for now, but eventually it needs bullets.

Anyone who's got some wisdom on this, please provide input because this is far outside my knowledge base. The goal is to stay cheap, so a Castle esc or something like that is kinda outside the realm of what I want to do, if at all possible. It looks like cleaning up the airframe a little more will get the desired speed (stab is double layered foam, for example, GPS is mounted externally, etc, etc. Plus if we cut down on the internal resistance of the power system by upping the wire gages, it should be able to dump more power into the motor.

Plans and parts list are all up to date in post #2. Please consider supporting this project, not by sending money or anything like that, but by downloading the plans and trying this plane out. I'd love to see several of these planes at Flite Fest 2020!

Oh one other thing--those cheap Chinese inrunners are AMAZING.