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1/4 Scale Bud Nosen Designed Citabria

PsyBorg

Wake up! Time to fly!
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#21
Does that carb have two or three needle adjustments? One will be idle, one will be mixture and sometimes there is a third one for mid range mix. Usually the one for main mix is at the inlet where the fuel line goes into the carb. If there is a mid range screw it will be in the valve that opens and closes to allow more air. Those are hard to get right since there are so many factors to tuning a nitro motor. Air temp, and humidity are two huge factors which is why these motors have to be tweaked every time you start them. Once you learn how to adjust for higher or lower weather factors its easy and quick to do each run.

If it only has two screws you may have to change out the venturi to better match your altitude and such to get that final good tune.
 

Joker 53150

Mmmmmmm, balsa.
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#22
This one only has the high and low adjustments. All I have done so far is make it actually run, and done very minor preliminary work on the high needle. I've read a couple tuning guides and it looks straight forward, it'll just be another learning experience.
 
#23
Some of it is expensive-ish, but believe me that there are incredible deals out there. Swap meets are the best example. That 1/4 scale Cub I pictured was $100 at a swap meet, including servos and 23cc gas Zenoah engine installed. I spent a couple bucks re-building the carb, the landing gear wires and fuel line, but I think that was about it. Total investment was well under $200 which includes gas to drive 4 hours round-trip to the event. This Citabria wasn't nearly as great a deal as the Cub, but it was still cheap enough for me to jump on it.
Holy crap! you wanna sell me that for 200$? :black_eyed: The problem is that I dont have drivers license and the closest clubs are about an hour away, and i kinda dont wanna ask my mom to regularly drive me. But maybe I can convince her to drive me once... If any of you guys have a suggestion for a club in San Diego I really want to find one. From what I can tell none of them have great websites and almost all of them have a pretty big membership fee:( I would rather spend my money on planes then a club, oh well *sigh* But I will look for a swap meet. Thanks for the suggestion!
 
#24
A very nice little group of flyers. They all look real nice and I am sure they fly well also. This is a very interesting post. Keep whacking away at that Citabria.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#25
Weather has been absolutely horrible for flying, so I used the time to get some work done on the electronics on a couple planes. The Citabria needed a battery pack, as I was taking the LiFe pack from my 1/4 scale Cub to power it and that wasn't going to work when I wanted to take both to the field again.

The original plan was to use a LiFe pack, but I went with a 2S LiPo and 6 volt regulator instead. While many swear by the LiFe packs, their discharge curve scares me a bit. They slowly drop in voltage for quite a while, before suddenly dropping fast, and I'd hate for that fast drop to happen while I'm flying! The 2S LiPo will work well and the actual charge on the pack will be easier for me to monitor.

I also applied the first coat of paint to the cowl, followed by a light sanding. It's currently waiting for calm winds so I can give it another coat or two. Other than the cowl, the only thing it needs before flight is for the engine tuning to happen. Can't wait!
 

agentkbl

Illegal Squid Fighting?
#26
lipos have a similar curve to LiFe batteries... I think that the LiFe is actually better. if you wanna be really safe though, you can't beat lead acid! but for real, a nihm wouldn't be a bad alternative.
 

Joker 53150

Mmmmmmm, balsa.
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#27
The big concern with LiFe (in my opinion) is the fast drop-off once it is getting ready to die. Normally I won't be out flying so much that I'd discharge a pack, but I'm more comfortable with the discharge curve on a LiPo. Plus, my Taranis will let me hook up a battery monitor to it so I can get real-time info on the charge left. It's just peace of mind for me!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#28
I finally got a chance to take the Citabria out to the field to have the nitro-heads take a crack at tuning the Evo 100 engine for me. I was able to get it running, but couldn't get it to transition from idle to full-throttle without dying. Not too surprising, since this is my first nitro engine and I've never had anybody show me how to tune them before.

After tinkering around with it for a while the main guy I was working with was stumped. We simply couldn't get it running right, so our assumption is that there is either a clog or air-leak somewhere that is keeping it from running right. This engine sat for a decade or so, and you never know...

So no maiden, yet. However, I decided to give up on nitro and convert it to gas. I've been on the fence regarding nitro anyway, and figure I'll stick with gassers and electric birds. That'll give me less stuff to haul to the field, which will be nice. Another club member has three 26cc gas engines that he's been planning to sell, so I'm going to check out two of them to see which one might be the right fit for the Citabria. First is an Evolution 26cc with a Pitts style exhaust, followed by an RCGF 26cc, also with a Pitts style exhaust. I'm leaning towards the RCGF based on parts availability and better placement of the carb, but will decide after I have both in-hand to check.

It's really bugging me not having flown this plane yet! :(
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#29
Looks like I'm moving forward with swapping the nitro engine for a gasser! One of the guys at the club I fly at said he has a couple 26cc gassers that he wanted to sell, so I checked on what he's got and settled on this RCGF gasser with a Pitts style muffler. It has an electronic ignition and rear-mounted carb. Just eye-balling it, I think I'm going to need to do some surgery on the firewall to get the prop at the right location, but that shouldn't be too hard.

Hopefully the outlets for the exhaust are close to where they were on the nitro engine, but it does look they may exit further forward. Fingers are crossed I can get them to exit in the same location to avoid surgery to the cowl!

So once it's removed, the nitro engine and fuel I got for it will be sold off, which should cover my cost for the gasser.

IMG_5283.JPG

IMG_5284.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#30
I finally got a chance to measure for new standoffs for the gasser. It'll require between 2-1/4" and 2-1/2" for the standoffs, and I found a set that comes with additional spacers that should work perfectly.

However...

The original nitro engine was mounted on a 1/2" thick base that was epoxied to the firewall, and I'll need to remove it to set the engine back far enough so the prop isn't too far out of the cowl. I could probably just cut a hole in the firewall for the carb to stick into, but the base isn't big enough for the new engine. It won't be easy, of course. Oh well, I'll make it work.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#31
Flite Fest is over, <sob>, time to get back to work! The gas engine I'm installing is slightly longer than the nitro that was installed. About 1/2" longer, which is the same thickness as the mounting plate that was glued to the firewall. So my job for the evening was to pick up mounting hardware and remove the plywood plate!

It came off much easier than expected, as it was only really glued around the edges. Otherwise, the bolts going through it kept it from moving around. Not the most secure, but it worked. It took only about 15 minutes of drilling holes and prying at it, which is far better than the sanding and cutting job I was prepared for!

IMG_5458.JPG


Mounting posts arrived a few days ago. I figured 2-1/2" was long enough, but I was wrong. :( Oh well, I can half-ass it with some spacers while I order the next longer length. Mounting hardware is 1/4" x 4 bolts.

IMG_5459.JPG


When I got it, the seller told me the plane hasn't been flown, although the "firewall archaeology" is telling me at least two different engines were mounted to the firewall, as there are different hole patterns. It's possible that it never did fly, who knows... Not a big deal. I knocked out the old captured nuts and will plug the holes before re-sealing the firewall with epoxy. Since this isn't a super thick firewall I'll reinforce it with another layer of ply on the inside, along with some epoxy to secure it.

IMG_5460.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#32
Mounting the engine, MOMENT OF TRUTH, will it be lined up properly? I was really hoping that the cross-hairs the plane's builder made on the firewall corresponded properly with the prop shaft hole at the front of the firewall, and from what I could see it appeared to be for that purpose. So I grabbed some 1/4" ply and laid out the bolt-hole pattern for the engine, and then transferred them to the firewall. The 1/4" ply will be glued to the inside of the original firewall which will substantially strengthen it for the new gasser. Once the ply with the captured nuts was in place I bolted the engine in place for the first time, and it was darn-near perfect! I like the spacing between the prop and cowl and the prop is centered nicely in the original hole. I've got a couple props that will work once it's ready to start, but the 18" just looks too big and the 16" looks a bit small, so I'll order a 17" eventually for it.

Next up is getting the wiring and gas tank sorted out.

IMG_5464.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#33
With the firewall reinforced heavily from behind it was time to clean up the front a bit. I took a 1/4" hardwood dowel and cut a bunch of plugs. There were 15 old holes in the firewall that needed to be plugged, so I drilled them all out slightly bigger to allow for a good fit, squirted a little TiteBond II in the hole, and tapped them into place. Once dried, the entire firewall was given a light coat of epoxy to fuelproof it.

Three new holes were added to account for the throttle pushrod, sparkplug wire, and the pickup wire to the electronic ignition box. A fourth may be drilled to control the choke lever, unless I can run a manual line through the cowl somehow.

After a little more test-fitting with the engine it looks like I'll need to cut a hole in the cowl to make room for the spark plug boot. The exhaust outlets may also need to be clearanced a bit, but it won't be too bad. The cowl will also then need the old holes from the nitro engine filled. It may also need some extra work to allow for better airflow, but for the first flights it'll go without the cowl.

IMG_5465.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#34
The easy-ish part of installing a gasser is outside of the fuselage, mainly because there is plenty of room to work and move things around. Once you get to the inside of a finished fuselage you're trying to stuff 20 pounds of stuff in a 10 pound bag!

So the engine is done (other than just plugging in a fuel line) on the outside. The plug wire is in place and the pickup wires are routed inside as well. But that's the easy-ish stuff.

IMG_5466.JPG


Inside I need to install a gas tank and do a little wiring before I can test-fire the engine for the first time. It's used, but from a reputable source, so I'm not too worried about it, but I still want to make sure it runs properly before finalizing all the inside stuff.

This engine uses an electronic ignition instead of the old-school magneto. It's supposedly more reliable, efficient, whatever, but it also comes with more required hardware and more headaches. Personally, I like the old magneto engines for the simplicity. With any gas engine, a real concern is the ability to kill the engine from the transmitter or with signal loss. Programming a failsafe or a switch to either close the throttle completely or to choke the engine (or both) can accomplish this task, but if your receiver dies and the electronic ignition box still has power the engine will keep on running, which makes a bad situation much worse. Especially on larger planes! When it comes to electronic ignitions, an optical kill switch is the answer.

The optical switch is a pretty cool piece of technology. It is connected to an auxiliary channel on the receiver and simply looks for a signal to be on or off. If it's getting the signal from the receiver it assumes everything is good and allows the engine to keep running. If the receiver dies, loses power, or if you flip the "kill" switch on the transmitter the signal goes "off" and the optical switch then kills all power to the electronic ignition. So if you fly out of range and lose signal, turn off the transmitter, have a receiver battery die, or simply turn off the battery for the receiver the engine dies. Some fields require this for all gas engines. To help determine if power is on for the ignition the optical switch has an LED which you mount somewhere it can be seen. When the LED is on, there is power going to the electronic ignition. With the LED off the ignition is dead. Here's the basic optical switch:

opt 1.jpg


This is a basic diagram showing how the optical switch is used, and how it'll be installed in the Citabria. All of the excess wiring, servos, etc is removed for clarity. My setup will use a 6 volt battery for the electronic ignition and the 5 volt for the receiver and servos. I'll also have separate physical switches on the side of the plane to kill power to the ignition and/or the receiver. That will let me test servos or check programming without sending power to the ignition, another level of safety.

opt 2.jpg


As mentioned, I'm adding switches to the fuselage side to kill power to the individual batteries. There are various styles and sizes available, but I've used this type before and really like it. It's a bit bigger and more obvious than others, but I can live with that. This isn't a highly detailed and scale plane to begin with...! The switch assembly also has charge ports built in so the batteries can be charged easily without running extra cables into the fuselage or removing the wing.

opt 3.jpg


Right now it looks like I'll be on track to at least fire the engine tomorrow, although I had to order a couple pieces that are needed before I can officially say it's ready for flight. Oh well, no rush! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#35
It lives!



So the engine is mounted well, but the gas tank, batteries, switches, and electronic ignition are all still unfunished and admittedly a bit half-ass for now. The only goal was to see if the engine ran well enough to proceed with final installation or if I needed to do some more work.

Even without the parts installed fully it ran much better and stronger than the previous nitro engine. About 5 ounces of gas was put in the tank and I was happy to see that the engine pulled gas fairly quickly. I was spinning it with a cordless drill until I get a better setup for this prop adapter. With the choke full on I heard it pop, so I moved the choke to half and started it by hand. It took a dozen flips, but it finally jumped to life and was running. That's when I took the video, with the choke partially on, so it wasn't responding well to the throttle. :eek: When I realized the choke was still on I turned it off and it really smoothed out. I don't think there is any need to touch the high or low needles at this time, which is a big relief.

While playing around a bit with the throttle the engine suddenly died, which was a bit of a concern, as it had plenty of gas left and the batteries were charged. Then I noticed the clevis on the throttle had lost it's pin and the throttle closed completely which killed the engine. I put a wire in there temporarily, drained the gas from the tank, and fired it up to remove the gas from the lines and carb. The clevis will be replaced when I start doing the final mounting of components, which will happen once a few items arrive in the mail. Can't wait to see it finally fly! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#36
One thing I'm not super thrilled about is the need to drill extra holes in the prop. It's fairly common on bigger engines and is easy enough to do with a drill press. This makes using a standard electric starter more difficult. Since it's the first time I've run across it I'll need to see what the best route is to get a nosecone/spinner on this bird.

IMG_5468.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#37
It's not related to this build, but I like going off on tangents so I'll put it here anyway. Listening to the Angle of Attack Podcast this morning, they had Crash on to talk about his first time going to FTFF. Sounds like he had a fantastic time, and I'm glad to have gotten to "press the flesh" with him in person at the event. The best part (for me, at least) was that I got mentioned a few times in the podcast. That gave me a smile, and thumbs up for Crash getting reasonably close to pronouncing my last name correctly. :)
 
#38
One thing I'm not super thrilled about is the need to drill extra holes in the prop. It's fairly common on bigger engines and is easy enough to do with a drill press. This makes using a standard electric starter more difficult. Since it's the first time I've run across it I'll need to see what the best route is to get a nosecone/spinner on this bird.

Do you think you could get away with putting a few shorter bolts in the backplate on the engine side only with the bolt heads being the only thing going in to the back side of the prop? Since the bolts are only there to keep the prop from spinning on the hub I think that would be more than enough to serve the purpose.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#40
Do you think you could get away with putting a few shorter bolts in the backplate on the engine side only with the bolt heads being the only thing going in to the back side of the prop? Since the bolts are only there to keep the prop from spinning on the hub I think that would be more than enough to serve the purpose.
After doing some research most people are telling me that I don't really need to drill the extra holes in the prop, and that for a 26cc gasser the center bolt is sufficient. Oh well, this prop is already done. :) I'm trading e-mails with the folks at Tru-Turn about their spinners to make sure I've got the right size. I've got a couple plastic ones collected over the years and need to verify what size will be best first.