Dukester

My Feedback: (31)

Been working on this off and on for a bit and finally got the baby lamyak 90% stuffed. All servos in, linkages done, engine mounted, throttle servo in. Just need to add tank, RX and battery (350 mah 2s lipo with regulator). Current weight is right at 15 1/2 ounces, and I figure I'll be right at 18 1/2 ounces dry. Still look to be under 12 ounces per square and even at 18 1/2 to 19 ounces total the .074 should pull it around fine. Won't be a rocket pull out but should do ok.

I'm looking to finish it up for a school yard maiden on Sunday.

Plane is a Yak design with laminar wing done by a guy on the ProBro site which I sized down for the .074.

Duke

AndyW

My Feedback: (1)

Looks good, Duke,

Can you give us some more specs. Engine RPM on what prop on what fuel?

You're using a LiPo 2S with a regulator. I have a regulator for the same purpose but I had intended to use ONE LiPo and up regulate to 5 volts.

What might the difference be between my way compared to your way?

Dukester

My Feedback: (31)

Andy,

The reg I'm using is actually set up for 6V for max performance from the HS-65s. The voltage is less important than the method. What you're doing effectively is using a transformer to step up the voltage and I'm using a switching reg to drop the voltage down.

In my setup, the reg sees 7.4V most of the time and basically switches the battery in and out of a capacitance circuit to maintain 6V. In power terms if I draw say 2.0 amps average working my servos hard (which is possible with the 3D manuevering in portions, maybe even up to 3 to 4 amps in very short bits with hard control inputs), then I'll be drawing an effective 12 watts (6Vx2A) for that time, which will still be 12 Watts seen at the battery side.

To step up the voltage you're effectively using a transformer type setup to raise the voltage. If I was using that setup, then my reg would see 3.7V most of the time and would output 5V, so if I was drawing 2A, that would be 10 watts out. The 10 watts has to come out a single cell this time which is only supplying 3.7V, so the effective amp draw is 10/3.7=2.7A (approx).

So there's probably no practical difference between stepping up to 5V from 3.7V and switching down to 6V from 7.4V in terms of flight performance, you can run a bigger cell so the extra amp draw probably won't hurt and your setup will probably be lighter over all. The only question would be ability to handle surge loads from both the battery and the reg side.

In effect, my setup weighs exactly the same as using a 4C 350mah nimh pack w/switch (about 44 grams) and is more robust in terms of surge loads than the nimh. You should be able to get in the 24 gram range on the same size lipo with the smaller DC-DC converters, but I would check the output power of the converter and make sure it's apropriate for what you need.

On the .074, I'll be running a block stock APC 7x3 initially on 20% fuel (synth/castor blend). I just swapped to a new cylinder/piston set so I need to do some break in before I tach it for performance, but I expect the numbers to be reasonable.

Kiteflyer

My Feedback: (17)

Dukester,

Any idea on how much fuel had you put through the original piston/cylinder set before it wore out? Also, did the engine experience any wear in other parts?

combatpigg

My Feedback: (3)

Duke, looks good. Are you a pretty good 3D flyer?

flyinrog

My Feedback: (1)

Thats pretty cool Duke,,it looks alot like the "Half-wit" from Jerimy Chin, I built the kit, but never covered it...it was also for the .061 and supposed to come in at 13oz,,then it got wished into the cornfield and lost in the mess, had an arrow shaft as part of the frame, but I used it for something else....but it didnt work there either....Rog

AndyW

My Feedback: (1)

Thanks Duke,

If you can find one, I'd suggest you try a Cox 7 x 3.5 or an MA, 8 x 3 combat prop.

Dukester

My Feedback: (31)

I'm only a fair 3D flyer, I do fly a lot of larger profile 3D, but the 1/2a bug is never too far away.

The original .074 piston/liner was the victim of a mistake by myself, I was messing with the throttle linkage and took the needle out one night. Then when I put it back in, I meant to run it the next day to reset it. But forgot and put the plane in the air without messing with the needle. So ended up with a one really lean run. The other piston and liner weren't really shot, but there was noticeable loss of compression. Since I figured this plane definitely needs as much oomph as I can get, I swapped out to the new P/L set.

I've built a couple of halfwits and they were real fun.

combatpigg

My Feedback: (3)

Duke, do you remember that .074 powered 3D video a guy brought here some time ago? He put that plane through a pretty awesome routine then landed it in his pick up truck. IIRC he said it was designed by Billy H for electric. I tried to duplicate it, but I think a lack of skill at setting the plane up and flying it skillfully keep me from posting a video.
I've always wished a specialized prop would come out, like a 8x2..maybe there is something in electric prop land that works better than the 7x3? In the hands of a real master, details like this don't matter so much I guess. A 8x3 gives sluggish throttle response in a hover and makes the engine hot...I've tried it. What would help there is to spend an hour whittling on a 8x3 to thin the blades, but at the rate props get broken, not realistic.
Your plane should make a nice compliment to flying the larger sizes. I like switching back and forth, it's kind of a relief to fly a larger profile after a session with a 1/2Aer.

Dukester

My Feedback: (31)

What is really noticeable for me is just how much more stable things are for 3D the bigger you get. I fly 1/2a and I'm on the sticks like crazy 100% of the time, my Mojo 25 is less, Mojo 60 even better, and the big 50cc Edge more stable. What goes up for me in the pucker factor and I still have to overcome that.

Pics below are of my Mojo 60 w/Saito 100. A long way from 1/2a but a super stable platform for 3D.

combatpigg

My Feedback: (3)

Gasoline scale sure is cool, but I don't know if I could ever get comfortable flying a couple of house payments around...[]

eroc144

My Feedback: (1)

Amen to that. A guy at our field lost one of those "couple of house payments" planes 2 weeks ago - it was brutal. One of his digital rudder servos locked up during flight, started to draw full power, and eventually ate through both the main and backup batteries. All of a sudden you've got a 10' wingspan, DA twin cylinder engine plane flying around on its own. "Luckily" it hit in the middle of an empty field, but it could have been worse. Net loss was in the multiple thousands. The rudder servo was a melted pile of plastic and metal gears.

And I feel bad when I lose one of my $39 scratch builds.

EG

flyinrog

My Feedback: (1)

I have a "one house payment" stick with a saito .65 on it,,BanjoAirplane used to 3D it,,I have flown it a few times, but dont 3D,,also have a Taco with a .25FX on it, BSarge made it for me, havent flown it yet, in fact I have hardly flown this year at all,,we are still sorting through my fathers belongings , it takes a lot of time and I am the only one of us that lives in town...Rog

Dukester

My Feedback: (31)

I had a Taco too. I've never run a 25FX, but if you ever run across a GMS 32 you might give it a try. Same weight as most 25s and is really a nice running engine. Good power and the one I have has good throttle response as well.

I understand you guys on the 'house payment' planes. I love the big stuff, but don't get low and slow without getting nervous. 50cc is the biggest I've gone and even then my enjoyment is limited by the constant awareness of exactly how much $$ is going around up there.