Introducing the MX-Bach!

You will recall that a couple of weeks ago it ended badly for my giant sized MX2 when I underestimated the trees....

I got the idea to take the wings off the 30cc SBach that died in a fuel deprivation crash a year ago back in Mississippi on Trash Day.

Fitting the SBach wings to the MX2 works in theory as they are the same scale. The wings are about the same length, but the SBach wing is much longer in the chord, and runs a good length down the MX2 fuse. The SBach fuse also is wider, and does not taper as quickly as the MX2, so the wing required extensive modifications.

 

The fresh uncovered wood is the finished wing wedge I created to fill the gap that the unmodified wing had. I built them on both sides to follow the airfoil, the wing, and the fuse, allowing me to use the original wing tube on the MX2 and the SBach wing. I had to move the aft anti-movement pin into the new built up section so it fit the fuse and added it's required fixation for the wing.

 

 

 

These are the new wedges drying. To add strength I coated them with alcohol diluted epoxy. The ribs sopprt the wider aft of the chord. I super glued them to the original wing and drilled pass thru holes for wires, wing tub and wing screws.

 

 

 

Tailored to fit!

 

 

 

This is what the original MX2 wing looked like.

 

 

Yeah... The landing gear hard point is tilted to starboard. I will fix that... The wheel pants were demolished in the crash, but I rebuilt them. Had the struts from the SBach and just modified them to fit. Had to epoxy the SBach hard points to keep strength with the new holes drilled to fit the MX2.

 

All in all I am quite pleased! I gave no idea where the real CG is, but plan to use the wing tube when I balance her. That first flight will have some kinda pucker factor!

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Sbach Tip Stall and Vortex Generators

The Sbach and I have a long rich history of tears, pulling of hair and gnashing of teeth, mostly due to its unstable wing at low speeds and its strong tendency to severly tip stall into an unrecoverable death spin.

When I took the old 30cc Sbach wing and adapted it to the MX2 fuse creating the MX-Bach, it was necessity, not a love for the Sbach wing, despite its sexy shape, that made me do it. To address the tip stall, I sought a way to keep the lifties under the wing tips for as long as possible and to allow a more gentle stall. And voila, I discovered Vortex Generators.  Here is a great presentation on the concept, a video of experiments by an RC engineer.

I didn't, and don't, have the data nor the gumption to do all that math, so I just made some using L-shaped styrene strips, and installed then where I thought they should go, about 5-8cm back from the leading edge.  It's all described here.  I knew they would be tall enough, just picked a length, decided a V shape was nice looking, and stuck the buggers on. It actually worked! The MX-Bach has only flown a couple of times with the VGs, but she no longer shows the stall tendencies she used to. I think flying her at 10S made her a bit underpowered, so am very excited to be converting her to 30cc gas!

So as I prepare to build yet another Sbach, I am considering putting the vortex generators on her too. I will use the same guess work and install them similarly. I still have the L styrene strips. I think she is going to be an amazing flier!

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.

What is it with me and landing gear?

BEAUTIFUL DAY today. Took the Sbach and the Pulse XT60 out this afternoon. The Pulse started, ran fine, flew well, but discovered a small problem. The Sbach started but wouldn't run right. I removed the cowl, tuned her and she ran fine, but lacked something. I was flying her with the 12x8x3 blade, and she didn't seem to like it. I put the 2 blade 13x8 back on, small tweaks to the needles and she found her somethin'-somethin'! She wants the two blade. Sweet.

After the third flight, the first with the two blade, she rolled out after a nice landing and her gear just came right off. Right. The. Frick. Off.

Reset the crash clock...

The fore and aft tabs on the hard plate, and glue on those two longitudinal stringers was it. Thin balsa held the tabs in front. This was just begging to fail.

I did manage to find a muffler extension length and position to keep most of the exhaust oil off the fuselage.

The Pulse flew well. Her engine still sputters in the mid ranges, sweet at WOT. But her elevator servo will twitch once or twice up when the vibrations hit on WOT. I saw this is I gunned it, both in flight and on takeoff. It does it once, pitching the nose up then goes back, aa quick up flick. I bet this is what happened  when she flipped over her wing and threw the fuse cover. Need to replace that servo I guess.

So, the gang is all here. The Sbach is already fixed, strengthened the attachments. Still looking for a used 30cc gas engine for the MX-Bach. Here's hoping the Sbach and the Pulse become dependable.

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!

Sbach 60" versus Pulse 25XTe 52"

For comparison. The Sbach 60" wingspan next to the Pulse 25XT 52" wingspan. The Sbach flies 6S to 8S and the Pulse flies 4S. The Pulse is my best flying aircraft to date. Can't wait for the spinner to arrive so I can set the CG and call the Sbach build done.

 

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I flew the Sbach, so of course it...

It was a beautiful day to fly, no winds, no clouds, coolish temp, and only a handful of regulars at Bob Miller Field. I went straight from work having loaded the Three Musketeers into the car, the Pulse, the Ultimate and the Sbach!
 
I flew the snot out of them! I was practicing aerobatics, basic maneuvers, landings including short field landing and cross winds when a breeze came up. Great time to get my fingers flying again, much needed practice after such a long dry spell.
 
I even figured out that what the Sbach wants is a 3S 2200 to 2650 mAh battery with that 12x6 prop. Great performance, vertical, aerobatics, and with the improved wing loading, sound stable slow flight. She likes no more than 40% flaps, which slows her down nicely. I flew the snot out of her too, and was preparing to try a 3S 3300 mAh in it when I put her into a spin I could not get out of... and put her down hard into the tall grass. Minor damage to the fuse, cracked up the cowl again, and bent the gear. Already have it all repaired, except for the paint on the cowl! So I have a record of a crash for every day I have flown her... every frickin' time. I do push her way hardso its inevitable, but its getting old, especially after today when I finally had her flying perfect!
 

Today I CA'd the cracked through parts, then later epoxied them from the inside, sanded it down and did the Bondo work. Tomorrow sand the Bondo after letting it set all night, paint over the next three days (one for each color), and put her back to rights. Need to watch those spins. She does not like elevator in a spin, or hard elevator at all as it makes her roll... which is how I lost her. Now I know.
 

 

The Sbach today at the field, before the frickin' spin of death...

 

Hobby King Sbach 342 v2

A while back I saw my first Sbach 342, and I really liked its sleek lines and agressive tightly wound packaging. That was a foamy, from Parkzone or the like. I thought it would be really great if there was a small balsa version. I found a 1400mm one at Hobby King, but thought something smaller would be nice, around 1000mm, as space is getting to be a premium in my hangar, and the tails were snapping off the 1400mm Sbachs. Unfortunately no one had a single good thing to say about the 1000mm HK SBach as it was way tail heavy and had such high wing loading that you couldn't add any effective nose weight. Then v2 came out and addressed this problem, and more positive reviews are rolling out. Curiously the v1 is still on their website, so do be careful.

Today I decided to get the Hobby King Sbach 1000mm v2 with a Turnigy Park 480 850kv (275 watts), giving me a roughly 1.8:1 power to weight ratio. I have an Art Tech 40A ESC recovered from my ArtTech Diamond 2500 glider, and will swing a 10x7 APC prop to start with. I have some T-Pro MG90 metal gear analog servos and some Fusonic MG-D-9g digital metal gear servos coming... will need to decide which to use. I would like to use the 3S 2200mAh batteries, but not sure they may be too big. I'm pretty excited. She's a wicked nice plane, and I suspect there will be a few things to sort out, but hopefully she will prove a fun sport aerobat!

Crash-A-Day Program

It feels like that...
 
Took the PulseXT, Sbach, and Stearman out to BMF today. Perfect flying conditions. Kenny brought out his Stick, always fun to watch him whip that thing like a 3D machine (man can that boy fly...). Add that he's just plain good company.
 
The Hobby King Sbach 342 1000mm v2 flew wonderfully after her recent repairs. Had to shorten the canopy to get it to sit right; the firewall is pushed back about 2mm after that crash... hmmm. The cowl looks good too. I will need to get around to some cosmetic fuse work, but overall she looks good and flies sweet. She is a 3S machine. She flew well as a 4S, but heavy, slagging through turns, landing hard, and she tried to burn out her motor, curious since its rated for 4S. With a 3S 2200 - 2650 mAh she flies sweet. 3300 mAh bogs her down weight wise just a bit, but noticeably. With the 3S 2650 mAh she isn't super zippy but gets around well and has very good vertical. She snaps clean, accelerates well, and lands easily (though even with flaps she will stall a wing if one lands too slow). I did lose the tail wheel... tore right off in the hard scrabble grass. Fortunately had one I kept from the first Sbach. So, Power 15, 12x6 prop, 40A ESC, and 3S 2200 - 2650 mAh for a good 6 minutes of flight with 1.5 min bingo fuel. Rates are 30/30, 50/30 and 100/50. Flaps 20 and 40, though I may back the full flaps to 35 as she doesn't stall a wing at 35. I flew about a dozen packs with flawless performance, and I am starting to get used to her. Really love this plane and am already looking to get a 1500mm (55") version!
 
The Pulse, of course, flew flawlessly... practiced approaches and landings, long and short, with and without spoilers. Always predictable, stable and fun!
 

Then, there's the intrepid Eflite Stearman, pictured here just before she crashed. Last time I flew her I burned out the motor... or the ESC, not sure because they both work, but the motor fails at full throttle. Its also rated 4S, so I don't think its the motor, but that I am over peaking the amps on the ESC with the 12x6. I tried flying it 3S 3300 mAh today as its was designed for (so many repairs, I think its too heavy now, as evidenced by...) and she flew okay, a bit sluggish compared to 4S, working hard through loops and vertical. It was a fresh battery, 3 minutes into 8 planned climbing out of a low fly by the motor slowed then stopped and she dropped like a stone... managed to get the nose up at impact. Snapped a wing connection tab on the lower left wing, easily repaired. Snapped the landing gear clean off and chiseled off the bottom 2 cylinders of the mock motor, and broke the prop. No other damage. Spent the evening repairing the tab, building the landing gear block and recoting it, and cut two cylinders off an old Stearman cowl (I had just replaced this cowl the day before!) and grafted them onto the "new" cowl, with a near perfect repair. Needed to place a cowl tab, too. I also replaced the Hobby Wing 40A ESC with the Turnigy Trust 70A I had laying around. I haven't been using this ESC since programming it is a nightmare: the tones don't match the manual and the programming card is NIS at Hobby King. I mucked through the programming, and the only thing I need to test is the low voltage cut off... rather important, but otherwise the brake is now off and she runs sweet (In a curious set of design issues, Trust is the only Turnigy ESC I can't program with a Hobby Wing card, and the usual throttle range setting maneuver actually sets the brake as the throttle range is auto-detected). I believe I have auto-Lipo detect, brake off, auto timing and I have no idea what voltage cut off is... I ran the motor briefly at full throttle without load and it ran fine. I will power test it with a 12x6 prop and check the low voltage cut off. Need that damn programming card...
 
I was pretty pissed, mostly because this crash-a-day BS is annoying, and I am tired of repairing my planes... At least it wasn't the Sbach!

Sweet end of summer day!

A day off, the promise of possibly awesome weather, yeah, we are going flying!

Just took the Pulse XT60 with its RCG-USA 20cc, and the Sbach with its Evolution 10cc.

Jay and Louis were there flying their helis. When I first went up there were a few winds up high, and the rotor at the south end was active, but things calmed down amazingly, and it turned out beautiful just as I had to leave.

So the Sbach is tuned and running well. There was a curious period where in idle when I moved her from the start bench to the ground and held her nose up. The fuel pump failed to maintain flow and she quit. This repeated itself. I decided to just fly her anyway.  After a long flight I held her up again and she ran on fine. She flew well, ran perfectly. She needed some DR/Expo changes. I turned the ailerons down from 40% to 35%, and the elevators to 35%, and she tamed right down with a bit more authority. With the higher expo I was over driving the sticks, and my style is a bit more subtle on the controls. The Sbach is always a twitchy wench, one has to pay attention as she is very unforgiving. Remember, I had to put vortex generators on her wings.  She catches the thermals over the dump parking lot and rises rapidly, and is sensitive in the rotor between the south end Ents and the rise of the landfill we fly on the top of an after rising over the lot, drops like a stone in front of the trees, and then rises again as she approaches the runway on the top of the hill. She isn't unique in this habit, but does seem more affected. Combine that with a tail wind on the base in front of the trees and a 90 degree crosswind on final, and it can take 2-3 approaches before we get wheels down. And then we are hauling ass, so we run out of runway fast. FUN!

She doesn't have a lot of power, is fast, but runs out of vertical fast. That's with the 13x8 two blade. I decided to look at the 12x8 three again, so will fly her that way.

Incidentally, at the field her power switch failed. Noticed that the vibration when the engine was running was making the light blink.. I had my suspicions this past week and today she was twitching her surfaces like crazy and the engine was missing. We figured out it was the switch with that blinl, so I was flying her by connecting the battery directly to the reciever. This evening I replaced it with another one, exactly the same, and she is behaving.

I also flew the Pulse XT60. she flew without any drama. She still sputters in the midrange, but idles well and has plenty of power! She wasn't bothered too much by the winds, but that Hershey Bar wing liftes in the crosswinds. 

I now have them in the normal rotation!

Skyline/Goldwing Sbach 70 60" #2 Flight Ready

This morning I finished the setup on the second Skyline/Goldwing Sbach 70 60". You may recall the first one committed seppuku on only its 4th or 5th flight. I didn't blog this build as it went very much like the first one with a couple minor changes. One is that I made the rudder wires tighter.  I also used Du-Bro nylon hinge-and-pin hinges on the control surfaces with epoxy (the wide ones) instead of the flat fiber ones with CA.

She has the same power system and electronics. I have a 17x8 prop on her (turns out I had a 17x7 on before). I have ordered a 3 blade 16x8 EMP prop and a Du-Bro plastic 3 blade spinner. These don't come in 2-1/4', so had to get a 2". On a quick power test this morning I got a peak of around 1540 watts. Curious how the 3 blade will perform.

Common to both is that the wrong decals are included in the kit. Instead of the stickers for the red-white-black one, they come with the set common to the other colors. The white letters obviously don't show up on the white wings. General Hobby says they are sending the right ones, but last time even giving me a tracking number didn't get them in the mail so I am not holding my breath. The only one missing, really, is the large Sbach 342 that should be on the top left wing.

All in all, she setup. CG'd and looks identical to the first one. Looking forward to the maiden flight!

HK EPP Sbach Bebuild

Finally decided I was ready to rebuild the HK EPP Sbach I crashed back in April. She became uncontrollable and she crashed. I have to suspect that it was the HK Orange Reciever-3 axis Stablizer as there really was no other reason for it to fly the way that it did. A few weeks later the Edge 540, also equipped with that receiver-stabilizer combo was delayed responding to an up elevator command and came in a bit hard. I don't know that I will trust these reciever ones anymore, and threw out the one in the Sbach. I will fly it without stablilization for now. I just hate to throw them away, but its not worth the worry.

I collected all the pieces and disassembled the motor box. Looked over what I had and started putting things together. I missed a few pieces that I didnt recognize just where they went in the puzzle, which lead to some sequencing errors, but I was able to get a nice frame together.

The gear hard point after the major pieces were CA'd in place.

Front.

Back.

Epoxied wood into the front frame of the gear hardpoint to add strength.

The front fuse frame is also drying but thin CA. 

The epoxied wood supports. I laid up a lot of epoxy behind the wood to strengthen the puzzle pieces. There was a center piece I missed. I will look tomorrow at dropping a piece in from the top, but I think this is enough support.

Since the back of the hardpoint wasn't so broken up, I only added support to carry energy from the hardpoint into the fuse. If this comes out again the aircraft will not survive.

Tomorrow I will work on getting the motor box onto the fuse. I am gluing the EPP where its cracked and split, but its going to need some more support, and I am not sure how I am going to paint it. Not sure if EPP can take rattle can paint? I don't have air paint... some research to follow. I am sure I can find some brush paint.

The gear hardpoint went back together better than I expected. I am a little anxious about getting it to fit its tear away points, and know in the end this repair is adding some weight that will affect its CG and flight characteristics.

Either way, we are on our way.

Skyline/Goldwing Sbach 60" Build Day #3

Today I essentially completed the Sbach 60" (it's called a 70 for some reason, maybe the nitro engin size?). But like a building that's not done until the capstone is set in place, my Sbach isn't really done until the spinner is put on, and I still have some of the decals to put on.

 

First of all, today's minor annoyance. The wing securing screws are plastic, and the right wing one was stripped because the nut embedded in the wing was obstructed. When the packer put the screw in it stripped, so I had to replace it. It was M5, so I picked up a couple M5 cap screws at Home Depot. in the pic above, the left one is original, the middle the M5 cap screw, and the last the hybrid I made. I cut the plastic screw with a small tab left, which. I shaped it to fit in the hex top of the cap screw, applied some superglue and joined them. The cap screw top is a bit small to screw into the wing, so the thumb accessible top is nice. It's not supposed to be gorilla-tight, so doesn't need to tolerate a whole lot of torque. I was able to clear the obstruction with a cap screw. Works fine!

 

Major project for today is the cowl. I created a paper mock up and had marked the cowl bolt holes where I wanted them, midline and 10mm below the top and bottom edge. drilled the pilot holes.

 

The end of the fuse where the bolts will go before drilling.

 

Pilot holes drilled. Stepped up to 3 mm.

I used a trick I learned from building my Eflite Stearman (still have another one of those NIB) to transfer the holes in the fuse to the holes to the cowl. I tape a piece of paper or card to the side of the fuse and poke a hole through the paper into the drilled fuse hole. Place and center the cowl and drill a pilot hole into the cowl using the paper template.

 

I thought I had pics of how I set up the nuts inside the fuse. I didn't want to use servo wood screws which weaken over time, so I took M3 flat nuts and washers and fixed them into place. I inserted the M3 bolt just deep enough for the washer and nut to secure, with a small tip beyond. I used a small piece of hard wood to wedge between a flat spot on the nut and the firewall to hold it against torque and super glued it in place. I then set each one in epoxy. Once it dried I popped the bolt through the epoxy. I could of used those self wedging nuts with teeth, but I didn't have any and could find M3 sized ones at Home Depot. Once I had set the cowl in place, I used rubber grommets from my heli stock and used them to protect the fiberglass cowl. I had M3 fiber washers but I had changed my mind and used M4 bolts.

 

Cowl in place and all done. The prop plate is about 2mm forward of the front edge of the cowl. Perfect. Came out precisely centered (I set the motor without any offset)..

 

 

Put a couple of the stickers on, will finish those later. Once the spinner is on, I'll put the whole thing together and take some picks.

 

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