Tee Bee

She's finished! Glued the canopy on with Pacer Formula 560 Canopy Glue. After it dried, I applied a bead of clear silicone around the edge for good measure to keep fuel creep out. The local sign/graphics shop made the lettering for me from vinyl. Russian translation = "Sliver". I spent a lot of time on this one getting the little mechanical details sorted out and working in such a limited space. I'm tickled that it all worked out in the end. I still need to run the engine and set up the throttle linkage/servo throws before taking it out to the field. Can't wait to see how she flies!

The specs:
Designed by Steve "skaliwag" Adams of Select Hobbies fame. Deviated mildly from the plans here and there.
Wingspan is 24".
Weight is 7.45oz.
Engine: Cox TD .020 with cylinder and throttle sleeve robbed from a new Pee Wee .020RC. Cox tank removed and replaced with firewall mount plate.
1/2oz fuel tank in fuselage
Spektrum 4 channel rx
Dymond 4.7 servos on all 3 control surfaces. Dymond 3.7 servo for throttle
400mah NiMH battery pack
Dubro Micro Pushrods and hardware
Mylar floppy disc control hinges
Ultracote Lite Scale White covering with Monokote graphics

Tee Bee

Good news and not-so-good news. Engine testing was lackluster. I had gone through this engine beforehand and used the best of all my TD .020 parts. I found it difficult to start but finally got it running and breaking in on the rich side for a while. After several temp cycles, it just never came up to the performance level of the other TD .020s I've played with. It did run fairly reliably, just at low power output than desired. With the sun setting and darkness imminent, I hurriedly went to the field across the road, refueled, cranked it, and tossed the little plane into the air, thinking it would fly decently enough. It was a real handful at first, severely out of roll trim. After a couple of circuits, I had it trimmed. The airplane was very slow, wallowing around somewhat, hunting back and forth in yaw. Reminded me of the way a Gee Bee handles at low power settings. It climbed, but not with gusto. It required high rates to roll it in a sloppy slow manner. This bird just wanted to go faster! After a few minutes, it was out of fuel and landed without any drama. She survived the maiden! I felt that i could tame the handling given some tweaking and practice but the engine needed way more motivation to get her up on the step. I walked back home and continued tinkering with the little Cox, unable to get it to spin up properly. The venturi fuel passages were clear but i swapped it out anyway. No dice. The head glowed great but i installed a new one anyway. No dice. The needle valve was already sealed from air leaks. There were no air bubbles in the fuel line. Compression felt perfect with no resistance while turning it over. I replaced the standard 4.5x2 prop with a 4x 2.5 ti see if it would turn it up. Nope. It got too dark to continue. Tomorrow, I will install another engine that I fly regularly that runs great. I'll have to remove it from it's tank and install the backplate mount on it and forfeit the throttle function. When I get home from work, I might have just enough time to try it again. This little plane deserves a proper running engine in order to evaluate it properly. Stay tuned...

Pond Skipper

Use a Pee Wee gasket in conjunction with the flexible plastic back plate, if the glow element looks good perhaps add a
fresh shim to seal the top, I use some oil on the plug threads (all threads) to help seal leaks. I like using the aluminum
cnc carb bodies can tighten them down leak free providing full seating and tight collar during assembly. Flush the NV
body with fuel, (needle removed) I use a squeeze bulb to pressure wash out any FOD. Reset tool on the socket with
oil in the socket before setting, a reset tends to avoid any issues with the head reaching past the first gasket at TDC.

The TD will spin up great with a E-flite 3.75x3 if you don't mind flying with them makes the most lame TD .020 come alive.
I like to bench test engines and then use them for projects based on their inspiring performance. The engine can be ran on
the bench to access and tinker with until you removed any air leaks, FOD and gremlins. Sucker should run it's always trash
or a leak fuel draw is everything along with high nitro.

Pond Skipper

Here is what you get with a E-flite 3.75x3 (thrust and some speed)



AmpAbuser
Published on Feb 28, 2016

TD .020 Static test per prop calc: Best read: 3.75x3 / 22,790 rpm / 65 mph / 5.3oz thrust / 37w
Plane with engine 142.4g / 5oz dry weight. 35% nitro. With fuel at full throttle it pulled out of my hand straight up.
The engine prop combo is actually making over 5.3oz of thrust.


After bench testing the plane was flown to confirm static results:

TD .020 / 3.75 x 3E Prop / Best Level Pass- 29,554 RPM / 84 MPH / Throttle Sleeve / 35% nitro.
Engine unloaded well down wind do to small size of plane and low weight. Up wind low 70's.

Your plane would still do nice 70ish mph passes down wind with the 3.75x3
Throttle response and thrust is what you are more after and this prop delivers.
Have not had a prop fail yet under engine load. Have lost a few with bad landings.

Pond Skipper

One last thing read this again the master TD .020 whisperer:
Under charges he will sell you the aluminum back plate and custom aluminum spinners.
Bob Mattes, [email protected] , 636-447-9580

Of course a TD .010 spinner will yield more rpm / shorter bolt is a big help too keep the mass
off the engine. The config you use now looks cool I have been there, vibration control, balanced mass
is more important for top end rpm all frills removed for the big thrill.


http://www.flyfreeflight.com/Site/Cox_020_Rework.html



And his .pdf file on operation has more good thoughts and findings.

Tee Bee

Yep. I am suspecting air leakage somewhere. I had very limited time to troubleshoot it due to my work schedule and end of daylight. I hadn't really planned to fly it so soon. It was all on a whim. My other TDs have run really well but they have always utilized the stock tank. I'll get it sorted one way or another. I used mostly new parts on the engine and everything seemed to fit snuggly on assembly. We'll see. Those alum backolates look nice! I NEED some of those.

Tee Bee

Well, I spent some time tinkering wih the .020. Replaced or swapped most every part. Added a backplate gasket. When compared to my strong runners, the only noticeable difference was that this one made less compression. That's a shame since the piston/cylinder/throttle sleeve combo was from a "new" Pee Wee RC. I replaced the piston from another TD and had the same problem. The new throttled cylinder seems to fit too loosely. I've got another new Pee Wee RC sealed in a blister pack. It may or may not have a tighter fit if I try it. Otherwise, it's back to flying without a throttle like most of my other Cox planes. That was a feature I looked forward to but I want this plane to fly well even if it means no throttle for now. Those fleabay deals aren't always that great. It's not the first weak engine I've bought "new" on there. I'll probably have to remove the lip around the base of one of the older thin walled cylinders to get it working right. Machining it is not an option for me, so I'd have to file it down by hand. I sure hate to ruin one of those old cylinders since I only have a couple of them. I hope to try another test flight this weekend if time allows.

Tee Bee

Another update: While on a break from work, I installed the throttled cylinder on a different engine with the same lackluster results. I then removed the throttle sleeve and tried it again. Bingo! That beautiful TD .020 wail rang out. RPMs, power, testosterone! The Cox throttle sleeve exhaust port is too small and restrictive. And yes, it was aligned properly at WFO during my tests. The sleeve port is about half the size of the cylinder port and evidently small enough to be a performance bottleneck.

During testing, my wood threads stripped out of one the firewall holes. I will drill them out and install nutplates inside but that leads to other issues that will delay further testing for now. I'll have to pry open the silicone-sealed hatch, remove the guts, drill out the holes, seal them with resin, redrill them, install the nutplates, and so on...

Meanwhile, I'm off work on Monday and plan to do some flying, so other models will take priority for now. Gotta break in a hotrod reedie .049 I just assembled so I can fly it then.

​​​​​​​Stay tuned..,

Tee Bee

I know the throttle sleeve port is supposed to be smaller but...this much smaller?

skaliwag

My Feedback: (1)

Answer is no. We made ours the same height but a tad shorter.. A Dremel should fix this..

Tee Bee

"same height but a tad shorter" ? same width?

The ports match at the bottom but the cylinder port is taller than the sleeve port. They look the same width to the my questionable naked eye. I've never seen a Dremel attachment small enough to fit. Will try to find some kind of thin file that will slide in there. In the meantime, i will make the needed mods to the plane and set it up without a throttle so test flying can resume soon.

skaliwag

My Feedback: (1)

Height ... Width...
OEM. probably skinnier because getting close to the "C" clip.
My Confusion... To much Turkey with adult beverage.
Should be .... 'We made ours to match the Cylinder in Height but a tad shorter in length.

Next worry is the "Hunting"

Tee Bee

Gotcha. Definitely close to c-clip but there is room to remove some material if i can find the right tool to get in there.

Not gonna worry too much about the handling until I can fly it again with full power available. Possibly reacting to gusts? We'll dig in more once it's up on the step. When I get home, I'll dig thru my hardware to see if I have any more 2-56 blind nuts for the firewall.

Next engine test is on the Skydrill I just brought out of retirement.

Pond Skipper

Yes width must be less to insure low idle as there is some leaking.

Here is a comparison of to two of my throttle sleeves to yours both have performed well with no issue with power loss.
I do make sure full throttle has the sleeves opening in the center of the exhaust ports / centering has tach out the most rpm.

Also if there is some up and down play in the sleeve and some have it (one out of the 4 I have does) if
allowed to rest in the down position the piston top barely drops bellow the lip line of the sleeve's exhaust port
BDC severally hindering breathing performance as it increases heat to sag mode. See pic it's a power killer.

Simple fix is get a tie rap off a bread bag strip the paper off it to bare wire rap and twist secure around the base
of the cylinder to keep the throttle sleeve elevated.

There should be no notable power loss after that as long as the exhaust port is center on the sleeve port.
Just have to never give up you deserve to enjoy some throttle with this one, it works I can confirm with many vids.

Tee Bee

Due to the previously mentioned issues with the engine not developing full power with the throttle sleeve attached, a handful of test flights were conducted on Monday morning without the sleeve. After some tweaking between each round, the airplane started to fly pretty well. Agile, quick handling and lots of fun. I like the way she looks covered in castor oil goo.

Tee Bee

I went back out for more test flying this morning after working the night shift. After the previous flights, the engine seemed to be running stronger today and more consistent with some break-in. I decided to re-attach the throttle sleeve and experiment a bit. This time, she ran just fine from idle to full power! Once the throttle ring position and servo throws were sorted, I resumed the test flights starting with a Cox 4.5x2 prop. She ran, flew, and throttled great. On the 2nd flight, I conned a clubmember into capturing some video footage on my iphone. I didn't have a camcorder with me. The linked video is not very good quality but it does show the versatility of the engine's performance well and captures what the little plane is like to fly. For some reason, the engine flamed out early on this flight. Murphy's Law, I guess. She ran through the entire 1/2oz tank on all the other flights. After my videographer left the field, I experimented with a Cox 4x2.5 prop combined with an OEM alum spinner. Bingo! That was the ticket and the airplane flew and ran even better. It's unfortunate that I wasn't able to capture it on video in this configuration. Will try again later.

The yawing instability I experienced on the first test flight last weekend is gone for some reason and no longer concerns me. I think it must have been responding to the gusty conditions at the time. On the last flight of the day, I lost control of the model while handlaunching in a gusty wind. It smacked the sidewalk causing some minor but repairable damage. I look forward to getting her repaired and back on the flightline soon. A little glue here and patching there and she'll be good to go.

Nice airplane, skaliwag!!! A bit of a challenging build but a ton of fun to fly. I look forward to seeing how/if this design evolves beyond this prototype stage. Meanwhile, it's pretty cool to have the only model like it in the world.

Pond Skipper

Congrats Troy!!
Your first throttled TD .020 fun stuff fo shizzle, now your spoiled!

Specs from audio tach app: Cox 4.5x2
- Best idle pass 5,248 rpm / many 7,028 rpm
- Static In the hand at launch 16,795 rpm
- Static 4.93oz thrust / 32 mph / .027hp / 20.14w
- Best pass 20,495 rpm / 39 mph
- 3:15 mins run time / tad bit rich

Tee Bee

Thanks for the data. Yep, a bit rich on that run. Ended up snuffing it out with low throttle. Following runs were better.

Pond Skipper

Here is my TD .010 Nano with an upgraded TD .020
RTF less fuel 3.43oz
Need to add a throttle servo next.
3.75x 4 prop / Static 24,188 rpm / 4.93 oz thrust / 92 mph

skaliwag

My Feedback: (1)

That's "PANZER BLOOD"

skaliwag

My Feedback: (1)

Happy news that you have the trims dialed in, throttle working and she does what a "Tiny Toy" is supposed to be good at.

Tee Bee

Thanks Steve! I'm sorry it took so many years to get done. I got a little frustrated/intimidated with it back in 2012, wondering how to make it all fit together, look like the drawings, and actually fly in a controlled manner. I found a renewed sense of enthusiasm for 1/2A stuff this year for some reason. Ended up aquiring some new-to-me Cox engines of various sizes and styles and restored some older ones back to running status. With each style of engine I worked on, I began imagining model airplanes I'd like to fly with it. When I started working on the TD .020s, I dug this one back out of mothballs and had a strong urge to see it through to completion. Funny how that happens. I think I sat on that Shark XV kit for at least 8 years before building it earlier this year.

I hope to repair the minor crash damage this coming week.