Pilot RC Sbach 25% 30cc

[peason]

I told Paul K. that I'd take a stab at a build thread, so here goes.  Back in January, I decided that rather than build a number of smaller planes this year I'd focus on one build and go for quality over quantity.  I decided to jump into my first gas build.  After a lot of research, the Pilot-RC (PRC) Sbach seemed to meet my needs: a good sport flyer, some 3D capability to grow with, a wide flight envelope, and a reasonable price.  Chief Aircraft distributes PRC in the US and had some good deals in early January for motor-plane combos.  I had read a lot of good things about Chief so I opted for the 25% version in Thrush Blue with a 30cc DLE. 

Like all of us, I have to watch my pennies (in the case of this project tens or hundreds of dollars), so I made some compromises and carefully researched my options.  In particular, I decided on PowerHD servos (gasp), instead of the tried, true, and uber expensive HiTec, Futaba, etc servos.  I'll delve into the details and the research that I did, and why I chose them over others.  I also decided to use LiFe batteries and explore the basics of redundant power systems even though this level of power isn't needed for a 30cc. 

The build plans include the following:

30cc DLE gas engine with a generic canister from Chief
Xoar 18x8 prop for break-in
PowerHD 8309TG Servos
Dual LiFe batteries
Wike Power Distribution System (and smart switch)
Tech Arrow Ultra IBEC and switch for ignition
Spectrum AR8000 with Satellite

I'll go through some of these items and why I chose them in subsequent posts, but here's a few pics of the unpacking.

[McDRacing]

Nice!!

[Red]

That's great looking Paul. I have flown the 100cc one and if this smaller one is anything like it, you will love it! It's a fantastic flyer. Looking forward to the build.

[gheumann]

If this thing flies anything like the model in RealFlight, it ought to be a great plane. Looking forward to seeing it!

[adam_clement]

Paul,

  Can't wait to get some more gassers at the field. Plane looks great. I will try to get some pictures of the way Bobby mounted his canister for you. His install was very clean. By the time you lay everything out there is not a lot of room left inside. Good luck.

Adam

[peason]

I'd love some pictures of Bobby's setup - the canister fits OK but there's little room for a vibration isolation mount for it.  I've got a few more pics and a status update for you guys.  I haven't been able to get a lot done but I'm making slow but steady progress.

[peason]

I've been working on the electrical system, mocking it up on the bench.  I'm pretty happy with the Wilke power distribution setup.  It routes battery power from two batteries via a smart switch directly to the servos.  It also has a 5V regulator for the RX power (3A) allowing you to run 5V servos off of the receiver's ports directly.  The battery switch is set up for LiFe batteries, and performs a fail-safe: if one battery fails, it's isolated and power is drawn from the other battery. 

Using 20C 1400mAhr LiFe batteries (2x = 2800mAhr).  This should be plenty for the type of flying I do for 3 or 4 flights.  It's important to cycle LiFe's before you use them, so I set my iCharger up for LiFe and cycled the batteries on in in regenerative mode (fast discharge) about 5 times. 

For the ignition setup, I wanted to do something a bit different so I went for a Tech Arrow ultra BEC / switch.  This unit has a BEC that is massively filtered from the LiFe's to keep ignition noise out of the receiver.  It then has an opto-isolated interface that allows you to turn the ignition on or off.  It also has a nice blue LED that indicates the motor on/off state.

The following pictures show the schematic of the setup, and my benchtop layout of the parts (minus the ignition and one servo).  More in a bit on servos...

[tall n skinny]

It's going to be great. Can't want to see it fly.
John

[peason]

Finally well enough to go work on the Sbach for a few hours this afternoon, nasty bug... been with me for 4 weeks now.  Anyway, got the servos installed, decided to change the rudder servo to an XQ-S4016 for a bit more umph, 200oz-in at 6V should be plenty for this plane. 

Got the motor mounting set up, it's kind of weird that you have to trim the fill stock on the motor box to mount the standard motor that the plane was designed for...  It fits great and the cowl and spinner fit perfect.

I'm now deciding if I want to mess with putting the canister in this plane.  Looks like I'll have to tear up quite a bit of the bottom of the plane to get it in there.  I'm considering a baffled pitts muffler as a compromise.  Might be a bit loud, but certainly not as loud as stock.  I'll take this week and chew on the idea - Adam, do you have pictures of Bobby's setup?

[peason]

Decided to purchase a Pitts muffler for the Sbach.  Will keep the canister and possibly do the upgrade in the future, but I'd like to get this thing air worthy sooner rather than later.  Working on hooking up the throttle and fuel system.  No pics for a while but will post when I get a chance.

[peason]

Brought the Sbach to Oroville for the long weekend to try and finish it up.  I've got the final balance and motor run up/tune to do tomorrow (Monday) and I should be wrapped up.  Hope to fly it next weekend at the club (weather and travel permitting). 

[adam_clement]

Plane looks great Paul.  With you, Gabe and Wylie getting gassers maybe we can get something with bigger planes going. It's nice to hear some noise out of planes once in a while. What day R U flying? Sat or Sun?

Atom

[peason]

Unfortunately unable to fly Sunday, but after messing with it, I still didn't get the Sbach to balance.  Ended up removing most of gear in the nose and building a small tray over the fuel tank to mount the electronics.  I've got battery hold-downs that will fit in pockets next to the firewall step, and will try again to balance this next weekend.  Will post pics of what I finally come up with.  Prior to doing this work, the CG point was about 1" behind the rear of the spar.  I'm shooting for the center or the leading edge of the spar.  I'd have to say that 3 big servos in the tail aren't helping things...

May try some heavier A123 batteries or some NMH batteries that I can perm. attach to the motor box under the cowl.  There's always lead... a quick test indicated that I needed 7 oz of lead to get in balance.  That's a lot, even for a 12-13lb plane.  Maybe I'm just over-thinking the problem.

Paul

[gheumann]

CG too far aft?

TWO WORDS: Bigger Motor!




/Greg

[peason]

You're right Greg, had I known that the CG was going to be this tough I would have shopped for the largest motor I could fit.  The cowl is tight with the 30, and the 35 DLE is about the same weight.  I built an electronics tray above the gas tank that helped a bit, and made some foam covers for my dual LiFe batteries that allowed me to push the batteries to the step in the firewall.  Going to add weight to balance.

Ready to run the motor a bit this week, will follow up with pics.  Plan to maiden it next weekend.  Adam - will you be around Saturday AM?