DLE/Walbro Carb Metering Diaphragm Mod

As I read up on gas engines and their problems, I ran across a solution to a common problem my 2-stroke 30cc DLE engine exhibits (we think from a poor break in by the original owner). It already 4-cycles (runs rich) a bit more than it should, running even more rich once at altitude. One of the causes can be high and variable air pressure inside a relatively closed circuit cowl with a running engine at the lower pressures at altitude affecting the fuel metering diaphragm and valve. That solution is a metering vent modification I found online at Flying Giants that effectively moves the vent to a more stable air chamber at the appropriate pressure further aft in the fuse.

The metering diaphragm helps control fuel flow as described in this Walbro Tech Tip.

Use a small nitro muffler pressure fitting. Picked mine up for a couple bucks at Orange Grove Hobby in Gulfport, MS.

Drill out the original metering vent hole to fit the 6-32 fitting. If you can tap it, do it, but I don't have one. It still screwed in nicely.

Obviously the fitting protrudes into the metering chamber and needs to be ground down.

To keep it in place and seal it, I used a torch to heat the metal and solder it in place. I did this before grinding down the inside end (see below) as it made sure the fitting stayed put.

Better living through Dremel!  Nice and smooth, finished off with 220 sandpaper, and a small drill bit to reopen the hole to its full size. Smooth as a baby's bottom.

There are variations on the distal end of the vent tube. I used an extra plastic fuel clunk and a deep plastic top of a bottle. The idea is to have the opening of the vent in a still or laminar stable pressure flow. I drilled the top of the plastic bottle to accept the thick part of the clunk so it rests deep inside the plastic top.

I used Tygon tubing to run from the pressure fitting into the fuselage, and secured the distal "cabinet" inside the fuse next to the gas tank. There is good airflow through here, drawn out by the low pressure louver vent I put in the aft fuse. 

The plastic top opening is open to the air in the fuselage, facing aft.

Looking forward to seeing how this affects the engines performance.

Happy, Happy, Joy, Joy!

"Oh, what a wonderful feeling, oh, what a wonderful day!"

Aidan and I headed out to the field this morning, taking a whole covey of aircraft. The conditions were clear with light variable winds and occasional brisk gusts. It would end as one of my best flying days.

We flew the Alpha 450. Aidan flew it into one of the pilot station fences during one of his take-offs putting a nice dent in the left wing. But he flew much better today than he has, showing nice progress! As we work on his control, he'll refine his ability to fly a pattern and then start making approaches, then landings. Once he gets these skills down, he will be ready to solo! He plans on working on the simulator, which will really sharpen his skills. Still getting a weird stutter from my transmitter when the trainer switch is pressed, with my screen blinking while the alarm tone and vibration go off. Sometimes several times in succession, sometimes 10-15 seconds without. Not sure what that's about yet.

I took up my 30cc Sbach a couple of times. She flew like a gem. Still 4-cycles a bit, more when airborne so I am going to do the metering vent modification to see if I can stabilize that, but wow, she made me so happy! I am getting used to her weight and how she will sink quickly on approaches. I am not sure she is perfectly balanced yet, not sure but I think she's a bit tail heavy and I need to remove a couple of the weights I put in the tail.

Today I was determined to maiden the MX2, and she flew so perfectly, perfect CG, perfect response, perfect stability, just a dream! I was just beside myself I have never flown such an incredible aircraft! We kept hearing a vibrating reed like sound when I put the power one, brought her down a couple of times to check it out, finding nothing. I never thought to look at the cote under the wing, but once again I took off and this time saw a piece of black cote fly off the wing and realized that the cote had probably been worked loose, and that was the reedy sound! I brought her back around and as I came over the threshold down she dropped, loosing lift about two feet off the ground into deep grass. That's when we inspected the underside and saw a wide part of the replaced cote missing. No other damage. I think she is my favorite airplane to fly!

Oops... Piece tore off, the part remaining up to the servo was flapping loose.

All fixed! I made the edges of the replaced cote more generous to ensure it doesn't come off again.

Lastly I took the Align Trex 600e up and she flew wonderfully too! I am still learning heli'sbut took her around in patterns. As I landed when the timer went off, I dropped the tail a touch and the tail blades ground, breaking off. No other damage, but I will have to wait for the new ones to come in. It was an incredible feeling finally getting her into the air!

Can't wait to get out there again!

Dammit, Cat...

My 30cc Sbach became a chew toy for Neko, one of my more mischievous Siberian cats, with a penchant for chewing on horizontal stabs and elevators (its not the first time). Despite my efforts to keep the Sbach, which I could not hang from the wall away from Neko, she found an exposed elevator and chewed on it. This morning, after spending yesterday getting the engine running, I tackled the repair.

Bad kitty.

Right elevator leading edge.

Outside trailing edge.

Both.

Debrided the dead tissue.

Installed, whittled down and sanded the balsa plug.

Spackled.

Only spackled the holes in the training edge.

Sanded down the spackle.

And covered with white cote. Done! Came out rather well.

The Engine War

The 30cc Sbach engine runs, but it doesn't run smoothly, 4-cycling a lot despite multiple attempts to tune it, even resetting the Hi/Lo to factory and starting over. Today I replaced the large admission  valve between the carb and cylinder, and all the gaskets and diaphragms in the DLE/Walbro WTA carb, and then getting the engine to start bone dry. That took f-o-r-e-v-e-r, and once I got it started I had to go back to scratch on the tuning. It still 4-cycles more than it should, but I think I have a reliable idle and max full throttle power. I am tired of fiddling with it, so to make my point I put the cowl back on.

The carb rebuild was easy, and there is a great video here. I didn't mess with the pin under the spring thingy.

Tomorrow, fix the damage one of my darn cats chewed into the right horizontal stab... then fly the thing!

Holy Mother of Dragons! MX2 Power Tested!

I really have to question HobbyKing's motor ratings. The Turnigy Rotomax 1.40 is rated to 10S for 2775W and 120A HV ESC (I went with 100 A, rethinking that now). Today I power tested her...

This thing is going to rip its wings off if I ever give it full throttle.

It drew a peak of 98 amps making a peak 3720 watts on 10S with a 20x11e APC prop in static power testing. She nearly pulled me off my feet. At half throttle she drew 18 amps and 700 watts. Her all up weight is 12.5 lbs, so about 1250 watts for aerobatic flying using the 100 watts/lbs rule-of-thumb. At full throttle thats about 300 watt/lbs! She is a dragon! I may need to pull back to 8S. Time testing she gave me over 10 minutes, so I stopped and set the timer for 8 minutes.

The aft vent louvers in place.

The baffle that generates the low pressure pull behind it. I have since tightened up the cote.

In situ.

All up!

Fly fearless, my ass... she scares the crap out of me!

CG'd tight, so much as a mm of battery movement fore or aft dramatically shifts her. Marked the best placement. Hoping to maiden her tomorrow!

30 size Goldwing MX2 Done!

I finished the MX2 today, well, short of installing the aft vent. It wasn't without its challenges, as we say, there's always something.

The Turnigy Rotomax 1.40 Glow/30cc Gas equivalent motor is the biggest one I have ever put on an aircraft. Capable of 2775 watts, its magnormous! The motor mount is from DuBro via Tower Hobbies and is designed for gas to electric conversions. The Rotomax has 4 screws that hold the back-plate to the motor, and they were off just a smidge from the bolt holes on the mount. So that took some work. The mount is set at its shortest length and the motor fits lengthwise PERFECTLY! There is 1 mm between the cowl and the prop back plate, perfectly centered. I also had to work hard to get the mount centered and drilled new holes to mount it. It overlapped the gas mounting holes a tad as you can see in the pic.

Side view. Its big, I tell you, BIG! I will be flying it 10S with 4500 mAh, (two 5S 4500 in series). She will turn a 20x11e APC prop guided by a FunFly HV 100A ESC, which I programmed today. 

I also did a really cool receiver power setup using a 2S 2200 mAh LiPo battery and a Miracle switch from TroyBuilt. I ran the 2S balance plug through the fuel dot!  To do that I had to cut and extension, run the wires through the dot, and solder them back together.  Now I can charge the LiPo through the JR plug and balance it at the same time. I thought this was pretty clever of me!  I can, of course, do the same thing through the removed canopy, but this was fun to do.

In position just aft of the cowl on the right side where the original ignition/receiver switch set was.

I used a rubber band to hold tension pulling the plug back in the dot. I can push it out for use. I have a 2S JXT extension and a JR extension that will allow me to charge the pack using my LiPo charging station.

A view of the forward compartment showing the main battery bay (Dual Lock Velcro) and the switch set, and in the middle, just aft of the wing tube (and unfortunately then, the CG) the receiver battery. I could have bought a NiMH pack, but I have a couple of 2S 2200 mAh receiver packs for my helis so I just used one of them.

The aft vent, on my carefully chosen styrofoam painting table... Install in the am when its dry, and the plane is done!

Smile!

This has been a major project, from repairing the wing to converting it to electric.

Looking forward to "maiden" flight in a few days! Full up picks soon!