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Planning an FT Spear build!

#1
But it's gonna be nitro, because I'm that much of a gearhead. What I'm going to do is, instead of using a single powerplant swinging a 9" prop like they intend, I'm going to run twin throttled 0.049s in pusher config, counter-rotating, with 5x3 3-blade props on them. I'm also going to give it fixed(for now) tricycle landing gear so I don't have to handlaunch the thing every time. I don't expect it to take off from grass under its own power, but hard pavement should pose no issue.

I'm not concerned about power at all. I've found a video on Youtube of someone running a comparably sized flying wing off just one 0.049 that lacked a throttle, and it flew fine. I've got two engines in this build, so it should be reasonably fast and certainly have no problem staying aloft.


Planning on using two fuel tanks, 30cc each, for this thing, and I'm going to mount them where they're right on the CoG so that won't shift during flight. Differential thrust is also planned, though I am somewhat concerned about how well it will fly on a one-engine-out scenario.

And yes, FPV is in the future as well. And perhaps more fuel reserves, retracts, other cool things like that. But to start off with itt'l be line of sight, fixed gear, 60cc total fuel reserve.

Would make a nice hangarmate to my Hobbico NexSTAR 46, don'tchya think?(And yes I'll FPV that too eventually).
 

Headbang

Active member
#2
Do your 049's have throttle? That is the tricky part of twins in glow, getting the throttles and tunes synchronized. It is easier on gas motors, but small glow engines are tricky.

I totaly support it tho!
 
#3
Yeah, the engines I'm going to buy will be throttled. I'm planning on being able to use differential thrust to help with yaw control as well, so I should be able to trim out if one engine's pulling harder than the other that day. They also won't be too far apart from one another(Maybe a quarter inch clearance between prop tips) so the yaw effects of one engine running slightly stronger than the other won't be as strong as in a normal twin.

https://coxengines.ca/cox-.049-rc-ranger-engine.html <-- the engine I'm going to be using.

I also got an email back from that outfit, they say I can position the backplate wherever I want to, so I'm going to have both of the throttles facing each other while the cylinders stand up straight. They also say the engines are good for 8 minutes at wide open throttle on a 1oz tank, so unless I'm trying to race other wings I should have a good 12-14 minutes in the air. Maybe 15 if I keep 'em at half throttle for the majority of the flight.

Here's hoping, with my tax return's arrival, I'll be able to get everything gathered up and get to building!

Oh, you know if that foam armor in the FT store would work to seal the foamboard from fuel spills/exhaust residue? Could pick a bottle or two up when I buy the airframe itself if that stuff will work.
 

Headbang

Active member
#4
I do not have any experience with the foam armor product. So can not say, but thinned epoxy or rustoleum paint should work. Paint needs 4 or 5 days to cure tho before it can be considered fuel proof. (Lesson learned on painting a motorcycle gas tank)
 
#5
Project update: Parts are on order now! Should be most everything I need, airframe, engines, fuel tanks, the works. If I forgot anything itt'l be something minor. For now it will fly on fixed steerable tricycle gear, as I didn't feel like waiting another two weeks to begin the build and FT's store(AKA Amain Hobbies <3) won't ship in-stock stuff now and ship the rest later. I'll upgrade to retracts in the future, though.

Will be using the Rustoleum paint trick on it, but I haven't yet decided on a color. Part of me wants to use a pretty metallic blue to colormatch it to my SC10GT and B4.2(Tamiya PS-16 x2 layers backed by PS-1 x2 layers), but I'm also half tempted to do a Half Life themed paintjob on it. Or at least try to. Haven't yet decided. Will need to see what's on the store shelves, gonna buy that in person rather than screw around with trying to ship such large aerosol cans.

Also need to track down a supply of 1/2a fuel for the engines. I'll be in my local-ish hobby shops on Wednesday anyway(One of them has the carpet track I race my B4.2 on and the other one's just down the street and where I buy my normal glow fuel) so I'll see if they can get me some. If not I'll have to try to find an online source. Happily, these engines are so small that even one quart will last an eon and a half.

And I think for now I'll have to steal the FPV system out of my CA-10. Itt'l get a dedicated system of its own soon enough, once the parts roll in, but they're slowboating in from Shanghai and I don't have a tracking number so that might not be till March. Banggood had a killer sale on for Eachine 1000tvl microcams and Eachine TX805 VTX's. 9.59 per camera, 11.99 per VTX, and the VTX has an on-board mic! So of course I bought two of each. Between now and then I should be able to get my hands on some goggles(I currently use a 32" widescreen SD CRT TV as a monitor, works great for driving an electric farm truck RC, not even remotely practical for a glow aircraft) and some cloverleaf antennae. Push comes to shove, I have one in the CA-10 now, and it uses the same connector, so I can just steal its antenna.
 
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#6
I have the airframe built! Few things to note:

* In my inexperience...this was my first airplane kit that isn't a static model...I might or might not have put the spars on the wrong side of the wings. But they folded in and glued in just fine, so I'm not concerned about it.

* Had to deviate a bit from plans in a couple places. The hole FT put in the hatch I patched up, since I won't be needing it. It has tricycle landing gear with a steerable nosewheel. The FPV gear mount was modified, there'll never be a gopro in the nose of this thing as the nose gear mounts to that board. But there's still room for a boardcam and a VTx, which I will be flying it with. And I'm going to have to notch for prop clearance at some point, but I don't yet know where because I don't have my engines in yet.


Without any more ado, some pics!


Not too bad if I do say so myself. Looks the part, and the landing gear are growing on me so quickly that I've pretty much given up on putting retracts on this one. I just love the look of those wheel pants on it!


I will have to do some tinkering, though. It's sitting a bit nose down, needs to sit nose-up. I might take it down to the racetrack wednesday night because they have a tire truer there and I can use that to massage the wheels on the main gear until it sits right. The adjustment needed isn't very large but I can't really move the nose gear further out and have it remain reasonably sturdy. I'm thinking if I buzz a quarter inch or so off of the main wheels she'll sit with 2-4 degrees nose up attitude, which is just about perfect.

I could dremel them down but there's no guarantee they'd be round. I....don't have the steadiest hand in the world, which can be seen by those bevels on the leading edges...


How I got the nose gear mounted in. I don't own, nor do I have access to, a gopro, so I don't much mind that I can no longer fit one in this aircraft. I still have plenty of room to mount a boardcam, though, albiet with a slight offset to one side. I'll probably bias it left with the VTx on the right side. Either that or I'll put the VTx behind the bulkhead and mount the nosegear servo on the starboard side of the FPV pod. Haven't yet decided, will be determined by how I set up the linkage for the nose wheel.

I also want to come up with a canopy/windshield that's transparent, but sturdy enough to keep the wind at bay, to cover the nose portion. Any suggestions on how to make something like that?


Main gear's in nice and solid. Itt'l tear the firewall before it falls out.


Not the prettiest patch in the world, but I didn't leave the slot open under here. Plenty of hot glue in there too. Looks kinda gnarly, strong as can be, and once I've done the sealing/painting steps it won't even be noticeable.


The receiver, receiver battery I'll be running in this thing. Fuel tanks will be mounted inside the main spar, stressed members as well. I want them to be right on CG so the thing doesn't start flying worse as the fuel drains off.


I haven't done much about engine mounts yet. I don't want to get too committed to something only to find it doesn't work when the engines arrive, so I'm waiting until they're in before I work on the motor mounts. I'm thinking I'll sandwich some 3mm thick balsa wood across the firewall and bolt the engines to that, rather than trying to mount them directly to the foam.
 
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Arcfyre

Well-known member
#7
I love the look of that landing gear! I've been trying to brainstorm a good idea for gear on a wing, and I'm digging your setup.

Couple things: you may want to take a sanding block to your beveled leading edges to even them up, then reinforce with a strip of heavy duty packing tape. Usually the bevels are on the inside of the wing fold and hot glue bonds foam to foam. Your wing built the way it is without reinforcement is vulnerable to delamination.

As for a clear canopy, I've had really good luck recycling plastic bottles. Careful with the hot glue though as sometimes the glue will melt and deform the plastic if its too hot.

Good luck! I can't wait to see your motor setup.
 
#8
If you want the part numbers for the gear I bought, I can dig through my order history and find 'em. They're for a small cessna-like trainer...10 size electric I think. I was going to grab some retracts from a 70mm Red Arrows EDF jet but, as I said earlier, I'm not all that keen on doing so anymore because the fixed gear with the wheel pants looks awesome. A lot of my inspiration for the gear on this is from Kerbal Space Program, funnily enough. I'm highly prone to building very similar aircraft in KSP and, more often than not, they have very similar gear setups.

Ideally, the main gear would be another inch farther forward, but there's nothing there substantial enough to hold it. I may have to rely mostly on it just naturally having a nose-up attitude on the ground to actually lift off, we will see.

It also helps for prop strikes. I can't tilt it too far before the wheel pants hit the ground, and they hit just slightly before the vertical stabs at the wingtips. I'm not concerned about propstrikes on rotation like I was before I got it put together. If you want to put landing gear on a Spear I highly suggest also going with twin pusher...perhaps BLDC as I'm pretty far out in left field running mine nitro, but you're gonna need some long and spindly gear if you want to land it and take it off with the 10" prop they intend it to fly on. But twin pushers on 4" or 5" props...I'm running 5x3...will come out nice.

On the wing leading edges, I will definitely do something about it, had been pondering options on how to sort that. I have a roll of flex tape on hand, might use that instead of packing tape. I've found that stuff is boss for repairing lexan bodies on cars, it should be strong yet flexible here as well. Woulda been nice if I put the spars on the correct side of the wings when I was building it. Oh well. It should still fly, I'll just have to do some extra work to the leading edges.

On the power system, I do wish they weren't having to percolate through US/Canadian customs. I ordered them the same day I ordered the airframe. Hopefully they show up this week and I can get them mounted, start running them in, taxiing it around in the driveway. I won't attempt a flight until I'm sure both engines are reliable and the FPV system is working properly.


Edit: The landing gear I used on the plane: https://www.amainhobbies.com/hobbyzone-landing-gear-set-hbz7606/p249832
 
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#9


These engines are TINY! Truth be told, my first time working with them. Been playing with glow cars for >15 years and I had zero trouble getting a 46AX to sing a happy song, but I've never worked with engines this bloomin' tiny. They're gonna look boss back here, though.

Slight change of plans. The more I thought about it...and I'll apply some credit to a redditor for jogging my memory in the first place...the more I thought that running two tanks would just cause issues. Either I'd suck air on a climb, suck air on a bank, or the fuel draw would be too long for these engines to run properly. That percolated through my mind for a few days, then I saw a 4oz slant tank at one of the two LHS's I have. Turns out it was almost like FT designed the spar around fitting it! That gap they put in there for batteries was the exact width I needed, I just had to enlarge it, flatten out the floor, and glue the snot out of it. Also means I'll probably have something like 20-30 minutes of flight time unless I firewall it(even then 16 minutes of constant WFO flight). Might experiment one day, brim the tank, fire it up, set a stopwatch timer, and fly normally until it shuts off.

I don't have any structural concerns. Yes, I did have to cut about 85% of the spar strength out to get that fuel tank installed, but the tank itself is a stressed member replacing that missing structure and I'm not exactly going to be ripping the skies apart with this thing anyway. I'm expecting somewhere around 40-50 watts out of each engine(Running 24%N 1/2a fuel from Fitz Fuels in them), so best case scenario I'll be pushing about 100w equivalent at full blast. She'll fly nicely, but she ain't gonna be very fast, and that means high-G maneuvers aren't gonna be in the flight plan.

The tank I bought supports 3-line operation, which worked out nicely. I have it set up for 2-line, but I'm using all three holes, with each engine having its own clunk inside the tank to draw from. As far as each engine knows, it has its own dedicated fuel reserve. No T-fittings to leak, no crazy plumbing, just straight to the mixers.

They're not mounted on yet, but I do have them configured, the plumbing is squared away, prop clearance notches are cut(Will hotglue and tape them after posting this). I just need to find the right standoffs to bolt them down with, then get a couple pieces of plywood involved to sandwitch the foamboard and give them something firm to hang off of!

Expect a ground runup video of both engines in the coming days, assuming the weather holds out.
 
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#10
I hope you have the spings for starting them! 049's are finicky beasts until broken in. Get at least a few tanks of fuel through them before trying to dial them in. Same as any glow motor, run it rich on break in. With a twin you want to always be a bit rich, less chance of engine failure in flight. The real trick is how touchy the needles are, to sync them is going to take a bit of patience! Make sure you have good way of accurately measuring rpm, dialing in twins by sound is difficult to say the least.
Looks awesome so far!
 
#11
Edit: Ran some numbers. Quick and dirty napkin math tells me that, if I'm getting ~15,000RPM out of these engines(which is what I should be getting per Cox Intl) I'll have a top speed of somewhere around 40MPH and it should have a cruise speed somewhere between 25 and 30 with the engines turning a happy 10k or so.

I don't expect to be able to balance it on the props, but those numbers are lookin' quite good for my goal of having a relaxing, fun to fly 1/2a powered wing that can take off and land from a paved strip!

I hope you have the spings for starting them! 049's are finicky beasts until broken in.
I do have spring starters, but I don't have any way of getting them installed. I have to pull the cranks to get the drive washers off and then get the plastic part of the spring starter in. GG. Might try to get it primed up nice, then bounce each engine backwards against compression while glow heat's applied in the hope itt'l kick itself around in the correct direction. I'll have a shop rag on hand if they want to start backwards, chuck that in the prop to stall it and try again. Will run them in one at a time, won't worry too much about synchronizing them until I have them attached to the radio system. Gonna use a couple of linear 1.9g servos hotglued right to the sides of the fuel tank for throttle, and I'll connect them on a Y-harness for now. Later on if I do want to experiment with differential thrust I can just omit the Y-harness.

At some point I'll get the spring starters installed. Whole reason I bought them was to make it easy as can be to start these things. But I'm not gonna go trying to pull the drive washer off the crank without the proper tools, done some reasearch, real easy to destroy the crankcase, crankshaft, and/or washer if you try other methods. Not like a larger engine where the drive washer tends to just flop off, or if it's stuck, just needs a whap or two.


I'm an idiot. The plastic bits that mate with the drive washers install from the prop side and I just didn't realize that earlier. I have now, props off, spring starters on, props back in, confirmed that the RH starter is on the RH turning prop and vice versa. Also, they spin these things with some authority, I can actually feel a breeze off the prop just from the spring starter!

Get at least a few tanks of fuel through them before trying to dial them in. Same as any glow motor, run it rich on break in.



I hear tell these things also take a fair bit longer to wear in than a typical ABC or Ringed engine, too. Given the tank is 4oz/118cc, each engine running through the entire thing...mm, 5 tanks maybe? 6? It's a LOT more fuel than they usually had available back in the day, that's for sure. I won't be running both engines at the same time until run-in is complete, what I'll do is heat-cycle them in alternation. Port engine runs through a tank, then while it cools down I'll refill the tank and run the starboard engine, then repeat until they're suitably ready.

With a twin you want to always be a bit rich, less chance of engine failure in flight.
You don't have to tell me twice about runnin' 'em fat! My glow cars, my NexSTAR's engine, all smoke like crazy. In fact, I actually managed to smoke myself out in my own front yard running the SC10GT one day. The wind was dead still and the smoke just wasn't going anywhere, after about 30 minutes it had gotten so thick I couldn't really see the truck anymore.

Way I see it, if it ain't smokin' blue under load, it ain't rich enough. I don't expect to see any smoke out of these things, though...they're so small and the exhaust is so diffuse relative to the size that itt'l be nigh impossible to spot...but I do expect to see a lot of castor schmoo accumulating near the exhaust ports if the mix is on the right side of peak.

The real trick is how touchy the needles are, to sync them is going to take a bit of patience! Make sure you have good way of accurately measuring rpm, dialing in twins by sound is difficult to say the least.
Difficult, but so is getting a cantankerous 33 year old Ford I6 to pass emissions, but I manage. I'm a gearhead right down to the core, I'm sure I'll be able to get these little guys to play nice with each other. I don't expect OS dependability out of a mixer that small but it should still prove reasonably easy for me to wrap my head around.

I'm also not overly concerned about it going into a flat spin if one engine fails mid-air. Between the relatively low output and how close to the centerline/CG the engines are the yaw moment created should be fairly minimal and countered well enough by the winglet stabilizers FT put on the Spear. I can't imagine it's gonna be climbing if it loses an engine, but I do expect to be able to semi-glide it back to the runway if that happens. Will certainly be an emergency landing situation but I don't expect it to be a crash situation.

Looks awesome so far!
Thanks!
 
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#12
ITS ALIVE! Or, well, one of the two engines is. I couldn't get the port engine to take a prime for nothin', but the starboard engine kicked to life without much fuss. Ran about 3oz or so of fuel through it with it rich enough to fourstroke some of the time, plenty of castor schmoo dripping out the bottom.


I'm thinking my issue with the port engine isn't with the engine itself, rather, with the fuel line. I think it may be kinked where it passes through the firewall. It's a bit on the short side(Well both are but I made an extension from some brass tubing left from buying the 4oz tank for that side) and when I use my car's pit bottle on the vent line to prime it I can force fuel to dribble out of the starboard engine's choke tube yet the port engine's choke tube is dry as can be.

Gonna try to sort that out and run that engine tomorrow. ~3oz or so went through the starboard engine today.

I also had no choice but to swap to the plug adapters. My DuBro Kwik-Start won't heat the glow heads. Contact with the body is fine, but the pip that the center contact needs to meet is nowhere near long enough to reach into the recess of that ignitor, so no chance of it working. Gonna have to buy a clip for them, I do want to run it with the glow heads since they'll give me a bit more top end.
 
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#14
First time I've ever heard it outside of Youtube. Never even seen a 0.049 in person before now. They're so damn adorable I almost want to buy another one just to bolt to my computer desk as an ornament!

Starboard engine seemed to run quite nicely, too. Only time it stalled is when I did something to cause it to stall. Kinda had to guess on the needles, one thing Bernie @ Cox Intl could improve would be bundling some instructions with the engines, but my experience with other glow engines got me to where it came to life without too much trouble.

I've since googled up some instructions on them, found an original Cox set in pdf form for the Surestart engines. They say three tanks is good for break-in, and they're assuming the typical 8-15cc worth. Not 3oz, which is what mine burned. So I'm gonna fire it back up tomorrow and lean 'er out, then try to get the port engine running.

Put another order in with Cox Intl. Crank install/removal tools, a piston reset tool, some better mounting hardware, and a proper glow clip so I can swap the glow heads back onto them.

I'm also already thinking about my next FT 0.049 build. Long EZ is an easy target, another pusher that's small enough for just one engine, but perhaps mounting one of these engines inverted in the nose of the SE.5 might prove fun? Or the Dr.1? They'll swing a 6x4 prop which is what FT recommends on those birds anyway.

I also did some testing. Turns out FT Foamboard doesn't really care about glow fuel. I soaked a piece of scrap foam in some and the only result was the paper came off a little easier. This stuff's more resilient to the fuel than previously thought so I'm not overly concerned about exhaust residue harming a tractor plane. I think, as long as I put a deflector in the nose to keep the schmoo out of the interior, they'd be fine. Hopefully someday I'll have one of every FT speedbuild kit in my hangar, built, flying, on glow power. Bigger ones'll get OS power, these smaller ones'll get Cox power.
 
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