Monday, October 14, 2013


Because FanKar(t)
(Version 1.0)

For several years I've been fooling around with fan propelled R/C vehicles - FanKar happens to be the latest incarnation. Stemming from June 2012, FanKar has gone through plenty of modifications and several hilariously terrible accidents.

Probably half the people who frequent RC events have seen or driven some form of FanKar. In the beginning it was a "let's see how fast we can make a fan on wheels go." type of thing, but it turned out much more awesome than I expected, and probably a few others too. 

Fankar is fantastic, there are many reasons why. I'll attempt to list a few in the hopes that some of you may understand what it means to FanKar.

1. It's got a power to weight ratio almost exactly equal to a 2013 Formula 1 car.

2. It's got almost no suspension
3. There is almost no engineering forethought into FanKar.
4. The steering system is made almost entirely of plywood with a few brass tubes as bushings.
5. FanKar has been clocked at 87mph (right before it exploded).
6. There are no brakes.

7. The wheels are held on by zip ties
8. There is almost no protection for any of the components
9. The steering servo is nearly too small, and has no servo screw.
10. The steering system is under-defined.

These are a few of the reasons why FanKar is like that cheap abused plane that should've died many flights ago, but you just keep flying it because you love it, and probably don't care if it explodes (which would just add to the hilarity).

Shown above is version 1.0, or the first version that you could drive in a remotely straight line above half throttle. One of the largest issues with these air propulsion RC vehicles is the thrust line compared to the Center of gravity.

Generally with onroad racing cars you want to have the Center of gravity as low as possible to promote quick directional changes - this is true with fankar, it also helps it stay on the ground when you accidentally sideways (which happens a lot). Low CG is a problem when you introduce a thrust source of some kind because generally it will be above the CG.

this creates a moment arm, making the rear wheels "light" with power input....that's not generally great for stability, so I decided the easiest way to fix this was to add a blown rear wing element.

Stealing pages from the F1 Pagebook, I added this piece of foam behind the fan to create rear traction with thrust.
It worked extremely well, the drivability increased to a level it had not been at before; read (you could go to full power in a straight line and keep it there) You could even make slight left and right turns at full power. Wow, exciting! of course now I saw this as an aero project and started to go crazy with CAD. I turned out a few crazy CAD designs which all utilized the blown rear wing technique. Then I decided that I would ruin the "FanKar-ness" of FanKar if I got too technical about it and added a simple top element and endplates/vertical stabilizers. Also present are new black fiberglass rods to control chassis flex torsionally:

This is the part of the story when FanKar's true potential was realized. I dropped about 10 MPH top speed, but the car had incredible grip and was very stable...until it wasn't. It drove how I thought a fan propelled vehicle should drive. The only problem with this configuration was that the foam actually wasn't strong enough to cope with the high velocity airflow provided by the fan over the double element rear wing...I figured this out when all of a sudden the wing departed in similar fashion to this Kimi Raikkonen accident:

(Pretty much the same thing happens to FanKar when the wing comes off)

here's an after picture of the wing with damage from tumbling after separating from the car.
(also present is a thru-fan receiver.)

At this point I got tired of fixing the foam rear wing and decided to build a stronger and more durable setup.

Enter alternative building materials.

The structure was now comprised of 1/16" plywood endplates with carbon tubes supporting the elements on the underside. You can see the lower tube is also attached to a link which connects the wing to the chassis in a way that I can break the glue joint from the lower wing element to the chassis and adjust the angle if I found that it was needed. This wing worked really well, I actually picked up speed and rear downforce over the Depron version, meaning it was a more efficienct setup. It also didn't fail just driving around, which was a plus.

And now for the tragic end to FanKar 1.0 in the form showed above.
I was showing some friends how awesome the latest FanKar was and forgot how to drive it-
coming off of the throttle means you lose all of your rear downforce with this setup. It behaved like the Raikkonen crash above and swapped ends.....right into a parking block at near top speed.
The car had taken off as soon as it went backwards and landed directly on a parking block without bleeding off much speed at all. It broke nearly everything important.

Components that survived:
the wheels minus a few flat spots from the snap turn, the main chassis rails and rear axle, the fan (I don't  know how) and the ESC. Everything else was broken enough that I didn't really want to deal with it and set the project aside. 
Here's another picture of the car after the crash:

The Fankar chassis still lives in the FanKar box and someday I'll get around the implementing a few more ideas once I become interesting in air propulsion vehicles again (which could be soon, because it's almost that time of the year again)

Anyhow, here's another form that the FanKar chassis has seen since it came into being:

it's a ceiling car...and it sucked, literally.

It worked pretty well until the suction battery voltage would trigger the low voltage cutoff in the ESC,....then you better run and hit throttle hold 'cuz it was coming off the ceiling.

now onto an abbreviated CAD portion of this post -
I'll leave a few of these here for thought.

(above) This was designed for a 70mm fan around a set of rules a few buddies and I had come up with.
(below) Rendered here is a 120mm all out racecar designed around the Formula Fan series rules, maybe it will spur some interest and we can see some truly innovative RC car racing?
time will tell, I'll leave you here with these below.



yup, I did it, I ran out of funds. (start the finger pointing)

actually, I didn't run out of funds building the airplane, or even designing the airplane for that matter - I ran out of funds because some other important things needed to be taken care of. Unfortunately that means the end of the SR-1 racer for this year, however,  it might see a comeback next year in the growing sportsman class.

(end finger pointing. Don't you feel silly.)

The event is scheduled to begin on the 24th of this month (October) and conclude on the 27th. I'll be on site from Friday the 25th until Sunday the 27th, and I'll make sure to take plenty of pictures and do a brief write-up when I return home - hopefully I can grab a few videos and throw them up on Youtube or something.

In other news,
I've already begun preparing for the 2014 AMA Expo. I'll be there flying in the demo area for entertainment and demonstration purposes, come drop by if you'd like! Also, feel free to ask anyone in the demo area about their aircraft or anything else we might have on hand, it's our jobs to promote and explain our great hobby to anyone and everyone in the hopes that we can help people, or even bring new people into the sport.

Quite possibly a week or so before the event I'll compile a list of projects/planes/devices I'll be bringing as a primer for the event.

Skyfighter Updates:

I've been working on perfecting Skyfighters for about 3 years now and I'm really happy with how far they've come. For once I'm nearly satisfied with how something flies and I see no reason to change my 2013 AMA Expo build for this upcoming year, if you'd like to know more about my equipment choice and a few details regarding the model, you can check out the link to an earlier blog post > Here <

I'll do a build log on the 2014 airplane when it comes time to fully prepare for the 2014 Expo.

In the meantime, I've done something a bit silly with a heavily used skyfighter: 

Look, it's a mini-fighter!

This is what a Skyfighter looks like if you cut about 3" out of the center section, add about 5 degrees of sweep,  and splice in a couple new leading edge and nose pieces (the same could be achieved by just cutting part of the wing root out).

Motor: Hacker A05-13S
Servos: Hitec HS-35HD
Battery: Aero-Model 240mAh 2s 30C LiPo
Receiver: Spektrum AR6310 DSMX
Transmitter: Spektrum DX18

The DX18 is currently available as a bonus buy package from Horizon Hobby Currently at this link: 

of course there's been more Skyfighter shenanigans.

I'm not even sure this one needs an explanation.

Notice the two pieces cut off the front of the wing. Remember how I said I "borrowed" some nose pieces for the planes above? well there you go, these are the panels I borrowed them from.

The airplane itself is fairly small. The wingspan is about 18", with the center section consisting of an Estes 24mm ID wrapped cardboard tube made for model rocketry....and I'm using it for such a purpose - the rear of the tube holds a D-sized rocket engine (also Estes)

The plane flies with this equipment:
ESC (used as a regulator) : Hacker X-5 Pro
Servos: E-flite DS60
Battery: Aero-Model 240mAh 2s 30C Lipo
Receiver: Spektrum AR6310 DSMX
Transmitter: Spektrum DX18
Rocket motor: Estes D sized
Igniton Controller: E-flite 10-Amp Micro Brushed ESC

Overall it's a very fun plane to fly. We've only glide tested it so far (dropped from another plane). Soon enough we'll throw in a live engine and light it off...(I figure we should wait and fly it at a legitimate club where rockets are approved in order to keep everyone happy)

Last but not least (for this blog post anyway) is the Thunderbird.
Pictured here after a successful flight.

I built this thing originally about 2 years ago and only flew it once because it requires two people to actually get it into the air and I was having trouble finding people interested in piloting a rocket vehicle.
speaking of which - It's air dropped from a Multiplex FunCub pictured here with the Thunderbird sitting on top in the launch rig:

and a behind shot for good measure:

The plane flies really well and is incredibly stable. It has a fairly low CG, and a high wing mounting position with a slight amount of anhedral for maneuverability purposes and to cup the air a little bit at high angles of attack. The Thunderbird relies on tailerons to maintain control. Tailerons describes a configuration where you use what would normally be the 'elevator' surfaces for roll control as well as pitch control. In the radio (DX18), I have the airplane set up as a delta, enabling delta mixing. It's extremely tame and it self rights, infact we have not been able to get it to roll past 90 degrees yet, it reaches about 70 degrees and just stops rolling. It's certainly interesting and I believe it's due to the low point of control, and high positive roll stability which overcomes the force from the tailerons. Furthermore, I think adverse yaw has a play in it as well, but probably not as much as the other two factors.

A few construction details:
The wing is carved, then finish sanded from three layers of 6mm Depron bonded together with spray adhesive. The airfoil is a 

NACA 2412. Finally it is covered in Orange flavored Japanese tissue paper using 3m Super 77n as the adhesive, then shrunk slightly with  a water mist.
The tail is built from two layers. One layer is 1/8" thick Balsa wood with a fair amount of cross grain, it is the top layer and of course, visible from the top. The bottom layer is 1/16" thick Balsa, it consists of a heavier density wood with large amounts of cross grain with excellent structural properties, it's glued on with Elmers wood glue at a 45 degree angle to the top layer to promote torsional rigidity which is needed due to the rectangular vertical fin shape....and flutter prevention in general. The vertical stabilizers are made in a similar fashion with two layers of wood with the grain structure 45 degrees off of parallel. I then added carved Balsa wood fillets to increase the bond area and provide better load carrying torsionally from the vertical stabilizers to the Horizontal stabilizers. 

the fuselage is constructed primarily of 6mm Depron with 1/4" Balsa wood glued to the corners of the box structure to add longitudinal rigidity as well as ding resistance (foam dings easily, especially sharp corners....) There are several Depron structures inside to hold the wing/engine tube and the forward electronics bay, which is accessible from a door on the underside of the model.

The radio equipment consists of:
ESC (being used as a regulator again): Hacker X-5 Pro
Servos: E-flite DS60
Battery: Aero-model 450mAh 2s 30C LiPo
Rocket motor: Custom ArcherAero 29mm Diameter
Ignition Controller: E-flite 10-Amp Micro Brushed ESC

This concludes tonight's updates, check back soon as I continue to write about my current projects and some cool stuff we have going on soon.