"Closing Up" a gas engine opening on the MX2

The MX2 was first built and flown with a DLE 35cc gas engine. While the model is advertised as gas or electric, Kenny's experience was that it couldn't handle the vibration and stresses a gas engine creates. As I reworked the airframe there was clear evidence that the previous owner also had issues flying it gas. With this is mind I am rebuilding it as a very powerful 10S electric with a Rotomax 1.40 electric engine.

This left the large opening in the bottom of the cowl that used to allow the DLE cylinder head and Pitts muffler exit the airframe. I had an idea to close the opening, with some residual low airflow, but opted instead to set it up with an air dam system to direct high flow air through the airframe. I will have to also make a louver opening aft to allow the high flows to exit. That's for tomorrow.

Yeah... go ahead, say it. That's one Johnson of a hole underneath the cowl.

From the inside.

First I mapped out the hole and created a template. The drawing underneath is the first design. These are tongue depressor craft wood.

Allowing CA to dry. Since the wood tends to be acidic, the CA can have a problem drying. Using CA activator can speed the drying. I don't have any, so used some isopropyl alcohol.

I created a jog out of triangle wood. It keeps the angles and spacing consistent.

And does a nice job!

Build finished. Inside...

Outside.

Test fit. 

I decided to turn it around. This is after painting.

Finished!

Clean lines. Each louver will create a low pressure behind it drawing air in.

This motor will draw a low of power and create a lot of watts, so this extra airflow will be critical. Tomorrow I will work on the exit louvers. The electronics should be here as the week ends. This plane is really looking great, and is going to fly like a madman; they system should create 2800 watts!

A Main Hobbies is coming to our fly-in!

The MCRCC fly-in in Gulfport is this weekend. As a special treat the A Main Hobbies flying team will be there! Join us!

A Main's Traveling Flight Team
The A Main Hobbies' Traveling Flight Team will be on the road May through August visiting over 75 flying fields and several of the hottest fun flies; we hope to see you at your local flying field.

What We're Giving Away

When Will We Be In Your Neighborhood? Here are some of the flying fields we'll be attending in your area. June 12, 2014 - Middle Tennessee RC Society (Nashville, TN) June 14, 2014 - Birmingham Helicopter Modelers (Birmingham, AL) June 15, 2014 - Mississippi Coast RC Club (Gulf Coast, MS) June 18, 2014 - Heli Jam (Tallahassee, FL) June 19, 2014 - Stone Mountain R/C Flyers (Stone Mountain, GA) June 20, 2014 - BCMA Club (Cartersville, GA) June 21, 2014 - Georgia Model Aviators (Ball Ground, GA) June 22, 2014 - Hill Top Flyers (Loganville, GA) Check our full schedule to see when we will be in your neighborhood

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TIdbits

I decided to build the MX2 that Kenny gave me, and last night ordered all the electronics. They should be here by the end of the week.

Kenny had described that the plane rolls out at low speeds and can catch one unwary, especially on landing. Since I could, and I think they look kinda cool, I made side force generators for it (the wings are drilled for them, the model comes with them, but this one didn't). I didn't photo the build, but I epoxied two 3" wide pieces of wood end to end to make a 6" tall SFG for each side.

The left wing is on the left, the right wing is on the right. After gluing I sanded, then coted them.

Oh... wait... that damn flag is upside down... WTF.

In the process my elderly Dremel Stylus, since discontinued by Dremel, failed... so Wally-World let me buy a Dremel 3000. Decided to go corded for the power; now need to watch my fingers even more carefully.

I also designed a baffle for the cut-out for the DLE 35 that used to be in the cowl, and decided instead to create a louver system to drive intake air up through the electric motor. I will need to build another set aft to draw the air out. Getting kinda tired of building louver systems... I finished the build and painting. Tomorrow when I install it I'll post photos!

Okay, calm down citizens... here's a preview!

Wasted day...

It was another Africa Hot day here in Biloxi-Gulfport. Swimming throughout the air is exhausting. It was a wasted day as I did more time futzing with the engine on the 30cc than flying.

Aidan and I got an earlyish start, getting to the field around 10-10:30 this morning. There were already four stalls filled. I brought Aidan's Alpha Sport 450, my Sbach 70 and my 30cc Sbach.

The 450 hates grass, being a tricycle gear plane the front wheel gets caught up and bends and/or the plane rolls head over heels left or right. The new wheel kept bending until bending it back snapped it off. Then the cog & control horn that steers the wheel cracked (the original did too, this was a MacGyver replacement). We did get a couple of flights, but the heat melted Aidan and he was done for the day.

I took the Sbach 70 up a couple of times, flew great, not much to say.

I also tried tuning the 4-cycle out of the 30cc Sbach. No one has managed to do that, and there have been some pretty savvy people who tried. One was Jason, who offered after watching me fuss with it today, that I need to examine the carb's petal valves... We (Kenny and Jason) feel whoever owned this engine when it was new might not have broken it in correctly. Jason wonders if the petal valves in the carb have warped. He's ordering me another one, will be here Wed. I could look, but having to got through removing the engine and then the carb then dis-assembling it, why not just replace it. This could be the answer to why it persistently won't tune out of 4-cycling. Well, today she dead-sticked on me. I didn't trust her and would not go to full idle during that particular test flight. I finally did when I had her positioned on a downwind leg, and she quit as I thought she might. Easy landing.

In tuning her Jason gave me the advice about the petal valves, but Jim had me increase the trim on the throttle on the DX8 from zero, where I was tuning her, to 50%. This allowed me to increase the endpoint on the throttle servo low end to 70%, and tune in a more reliable idle! Thanks guys!

As promised, pic of the vent system. I ended up with 4 oz in the tail to balance her! I finished the vent louvers with the baffle to generate low pressure over the louvers, covering the opening where the weights went in.

Sorry about the backlighting ruining the contrast, but you get the idea of how it looks from the side. I tightened up that cote.

After tightening up the cote and laying down some electric tape to clean up the edges. I used Dual-Lock velcro at the from end, and a tab under a shaped piece of ply under the Pirate sticker, held in place with Dual-Lock. It ain't going nowhere.

Put my AMA number on the baffle. Because I could. The baffle causes low pressure to form behind it, drawing in air through the fuse and louvers out of the plane, increasing air flow from the cowl openings all the way back. They are a PITA to make, but they are a quick manufacture.

You can see the near 45 deg angle of the louvers.

Tomorrow I may go fly again, maybe take a day off... Going to fly the 30cc as is until I get the replacement pump for the carb and replace that Wed night. I think I finally got her CG's out, but she may still be a smidge nose heavy.

A most excellent day!

Today I maddened the electric Sbach 70, and she flew perfectly. Put 4 batteries through her as I figured out what she could do.

Skyline Sbach 70 electric.

Electric Sbach 70 taking a break

I also got the nerve up to start up and fly the new-to-me 30cc Sbach (gasoline) for four flights! She remained a bit nose heavy, and a bit rich. I think this is why she can be difficult to start. That and I haven't quite figured out how to work with the Quikfire...  No pics, dammit. Tonight I took the cowl off and removed the last weights from the nose. I also added about 3 oz to the tail, but that's what it took. I decided to open the bottom and create a louvered vent hole aft; I am making the louver thingy now. This allows me to create a low pressure zone that will pull air through the fuselage from the cowl. It also allowed me to create a shelf to put the weight in. With the cowl off she is a tad tail heavy, with the cowl on she is still nose heavy but only a bit. I think she will be nicely balanced all told. I'll have some pics of the mod tomorrow.

May fly again tomorrow!

I got gas...

Well, its happened. And its about time it did! Why didn't I do this sooner?

I bought a 30cc gasoline powered Goldwing Sbach from Kenny Chandler last week on a deal we made. I made some mods, adding a Quikfire filter/primer, changes to the throttle linkage, tightened the rudder wires, fixed the receiver charge plug alignment, and set the plane up on my DX8. I had never setup dual elevator servos, but it was a cinch.  The cowl is good, but thin, and may need replacing soon. The most, and still problematic issue, is the gas can: the top is designed to be punched out so there is a pre-cut line all the way around the cap. This already tried to separate. I used JB Weld as it is gas resistant, and it provided a great seal. But yesterday I noticed it was already coming loose intact on the top...

Setting up the DX8 required I setup and tune the engine trying to find my idle and servo limits. For my first time I did alright. I still get a little four-cycle action at full throttle but just at first (I believe this means she is still a little rich at full throttle).  Flying electric I am used to a lot finer resolution: this throttle has idle, medium fast and full throttle, more or less.  Its a DLE 30cc with a Pitts muffler (bought a silencer for her not knowing someone had upgraded her to a Pitts...), turning a 19x8 Xoar laminated prop. She gives me a reliable 6700 rpm with an idle around 1670. This produces nice full power thrust and at idle no thrust. The manual says a generic (i.e. no prop noted) max of 8500 rpm, and some with less prop are getting pretty close to that, and idle at 1700. Kenny says the 6700 rpm is plenty, so we'll see. I think she will still need some fine tuning. My fear is the engine quitting at idle... this is my only beef with gas, and I think its only a problem during setup, is losing the engine in flight for an immediate dead stick landing.

Here are her specs from my log:

Goldwing Sbach 30cc Gas

• Battery: Rcvr 6V NiMh 2700,  Ign 4.8V NiMh 2000
• Engine: DLE 30 with Pitts, NGK CM6 at 0.02 gap
• Prop: 19x8 Xoar or Bambula
• Optical Ignition Lock
• Servos: 
• • Throttle: Hitec 5985
  • Elevator (x2): Hitec 5645MG
  • Rudder: Hitec 7955TG
  • Aileron (x2): Hitec 5645MG
• Receiver: Spektrum AR7210 with Satellite
• Comments: My first gas plane!  72” wingspan.  Miracle Ign/Rcvr Switch, Quickfire

Ginormous...

The JL Products Quikfire installed (the blue aluminum thingy). This acts as a filling/fuel delivery hub, gas filter and primer. It holds about 1/4 oz of gas once primed so that after the first start of the day all of the following starts should be quick.

It requires one port to the fuel tank and the vent/siphon preventer, and that's it. Had to MacGyver a cap for the extra tube. Otherwise nothing different. I did modify the firewall routing of the Tygon tubing, but that was it.

No sharp angles.

Top line going into the QUikfire is from the fueling button, the bottom one to/from the tank. 

Those weights are gone. Kenny noted the plane was already nose heavy and in my prelim CG tests that was the case. I took off about 3 oz of added weights, the Quikfire adding back a smidge. She seems well balanced now, certainly not tail heavy.

The plan is to take her out to the field today. Its not really a maiden as she has been flown before, but it will be my first gas flight. I am so used to the reliability of electric, and I have see so many people farting around trying to get their engines to run (and my tuning was not without its moments), that I don't yet trust. I hope to get her running as smooth I have seen others achieve.

Not to be forgotten, I will also be taking the 70 sized electric Sbach #2 out for her maiden today! More to follow.

MX2 Wing Repairs Completed

Finishing out the MX2 I got form Kenny that I will be converting to electric.

Last night I put the cross bars in to provide more flex support beyond the wing tube, and this morning I finished with top with some spackle then coted everything. It came out much better than I had hoped, perfectly true!

On the left a single 4x4mm balsa post between ribs, and to the right the popsicle stick X up against the main rib where the wing tube ends.

Another view.

A little spackle on top of the sheeted wood after repairing the cracked sheet balsa and putting a rectangle of tongue depressor under the sheet (used a push rod attached to a small post I CA'd to the rectangle to get it into place, with 5 Min Epoxy).  Tailored a piece of white cote. Can you tell where the repair is? Remember this wing had been repaired before (as I worked with the cote I can see patches).

I think this was ingenious of me, but I doubt I am the first to do it. I needed to segue a small piece of black cote at the corner. In the photo below you can't see it, but I wanted to continue the curve of the trim cote as I carried the black panel out to the end of the wing. I used a pencil to trace out the existing shape and used it as a template.

The finished wing on the bottom! I didn't continue the checkerboard as I don't have any of that green. You can't tell but the outer edge has the green of the original checkerboard and the white trim curving down, the black intercepts it. I an considering continuing the white trim down the inner side of the wing just for giggles.

Poifect!