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1/4 Scale Bud Nosen Designed Citabria

Joker 53150

Mmmmmmm, balsa.
Mentor
#41
Joker that is one seriously nice plane!
Thanks, it's been a fun (and aggravating at times) project so far!

Some parts arrived, so it's looking promising for a maiden flight this weekend if I can get all the work done. First up, the "before" picture showing the original power switch and fuel filler. The fuel port is nice, but I'm trying to standardize on two main types of filler, so this one is getting replaced. The power switch would be fine if I only had one battery, but I'm going to run two of 'em. I could either add a second switch or replace this one with a dual switch. The two visible covering patches are spots where I removed stickers the builder hand put on - both were to cover holes in the fuselage where he originally had switches (I think). The "slot" right above the landing gear is where the wing spars are inserted. A single bolt then holds each strut in place from the inside.

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The new dual switch assembly and fuel port are now installed and the old switch hole needs to be patched. Admittedly the dual switch assembly is kind of big and bulky, but it's machined aluminum and has decent quality switches and wires. It'll also allow me to charge each battery individually while the plane is fully assembled. I used the same switch assembly on my clipped wing 1/4 scale Cub as well as the full wing 1/4 scale Cub, and it's very handy. Having two switches allows me to kill power completely to the electronic ignition and/or the receiver & servos as needed. It does require cutting a fairly big hole in the side of the fuselage for it to fit, but it's worth it. In my opinion...

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The to-do list:
Mount the gas tank.
Mount the electronic ignition module.
Finalize gas line routing.
Mount both batteries.
Install new RX and route the servo plug wires.
Remove the wheel skirts, as my first flights will be on grass and they won't hold up.
Program dual rates.
Replace throttle clevis.
A few other things I'm probably forgetting... :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#42
Almost ready for a maiden...! :) The gas tank is installed, the vent line was added, both batteries secured as far forward as I could comfortably get them, the receiver was installed, failsafe programmed, kill-switch was setup/programmed, etc.

Regarding the kill switch, I'm referring to the optical kill switch which also works as a failsafe in case the receiver loses signal from the transmitter. It's the safest and most sure way I know of to kill an engine that uses an electronic ignition module. Part of the system is a red LED that tells you if the ignition is live or not. Red light = live, no light = dead. On other planes I've installed the LED up inside the front windshield, thinking it would be easiest to see there. However, I've since noticed that on bright sunny days the LED is actually hard to see due to reflection off the windscreen plus the sunlight shining down on everything. I'm trying something different with this plane, and I installed the LED near the switches and fuel-fill port. It's also under the wing so it will likely be in the shadow of the wing. Maybe it'll help, maybe it won't. Worst case is I move it and put a tiny patch over the hole I drilled.

In this pic you'll notice the LED is on, so the system is live. The rear receiver power switch is on (down position) and the forward ignition switch is also on (again in the down position). Since the LED is on, that also means the transmitter is on and the kill switch I assigned is in the "run" position. Kind of confusing, but after you work with it for a while it all starts to make sense and becomes second nature.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#43
Well, the Citabria is loaded in the truck for a trip to the field tomorrow. Weather looks promising, so fingers are crossed. It'll be the first time the plane is completely assembled (other than the cowl), so I need to verify the CoG. Extra weights are going along for the trip just in case. The 1/4 scale Cub is going along as well, although I'm not sure I'll fly it. The next three days all look very good for flight, so Monday will be a day off to head up by my dad's place to fly with him again. Should be fun!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#44
Maiden flight report!

The weather was decent today, although winds were marginal at times. I took the Citabria out to at least fire the engine and do some ground-testing. It's the first time it's been completely assembled (other than the cowl). It fires up and runs well, although the 16" prop is just a bit too small. I have an 18" prop, but that's too big. The 16 will have to do until a 17" arrives. All are in the recommended prop sizes listed by RCGF for this engine.

So a little tweaking was done to the programming, and it was run around the ground for a while as a shake-down. Nothing fell off and the engine was running well, so I decided to get it in the air after a few last minute checks.

The CoG was slightly nose-heavy from where the plans show. Batteries were charged, all bolts are tight, time to light this candle!

Well, that first flight turned my pants brown! It was VERY tail-heavy, and was hard to control. The rudder has a ton of authority and really helped me straighten it out to complete the lap around the field and line it up into the wind for a (hopefully) survivable landing. Surprisingly, when it was coming in and power was low it behaved a little better and I was able to land it without any damage. Another pilot at the field watched the flight and was impressed that it got back down in one piece. I'll chalk that up to a lot of luck and favorable winds.

I added 5 ounces of lead to the engine mounts and prepared to try again. This time the nose was certainly hanging lower than it previously was as the CoG was tested.

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The second flight was much better, although the rudder was way too sensitive. A couple laps around the field and it was flying nice and straight. It also needs a little tweaking to the programming for throttle control, but overall I'm happy.

Then it came time to land. One thing I've always had problems with on planes this size is determining exactly where they are in relation to the runway. The size makes them look closer than they really are so I have to be very careful to NOT land off the end of the runway by accident. As I was coming in I noticed the engine burbling a bit, which I thought might just be from idling too low. I gave it some throttle to go back around for another landing approach and suddenly the engine died. It was moving fairly quickly and about 40' in the air, but over the tall grass surrounding the field. I tried to aim it back and hopefully get back to the mowed surface, but no dice... :( THUMP! I did the walk of shame, expecting the worst, and here's what I saw.

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Luckily, it was just a broken prop and a slightly bent right landing gear. Oh, and the tail wheel was missing. :confused: That probably fell off after the first flight and I was wondering why it was needing so much runway to take off the second time around! :) I couldn't find any other damage, so after getting it home I spent an hour re-bending the gear, swapping the prop, putting a new tail wheel on, and also changing the muffler (the old one was a bit beat-up and didn't seal well). Tomorrow I'll do some more programming changes and give it another shot at the sky!

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So my big question was WHY did the engine die? Well, it may have been out of gas. I didn't fly very long, but I never filled the tank completely and there was a bunch of ground-testing with it that burned more than expected. At least I hope that's what caused it to quit.
 
#45
Dang, I am glad it was just a broken prop and some landing gear! It's a really nice looking bird, but they all have a self life right?

The whole story with being tail heavy and engine dying I am surprised it was not worst, thankfully it was not worse... I really like these big gassers. Being an motor electric fan myself, they are fun to see other people deal with all the issues in having one, and I just get all the fun seeing them fly at the field Hahaha... Really glad you didn't destroy it so we can see more pictures of it later on.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#46
Oh what a difference mowed grass makes! So yesterday I took two 1/4 scale planes out to play, the Citabria and one of my Cubs. The Cub did something it never does, nose-over on landing. It's normally well-behaved, but the grass was so long it just slowed the plane down much too quickly. The Citabria also nosed-over at landing, and ended up breaking off the top of the rudder. :(

After leaving much earlier than expected (no sense in flying if you can't land safely) I quickly patched up the Citabria rudder so it could be taken out again today. This time I flew at my dad's field, a 3 hour drive. While the drive is boring, it's a nicely maintained field with great guys.

Both planes again made the trip and I put 30 minutes on the Cub and about 40 on the Citabria. There is some tuning that still needs to be done on the Citabria, but overall it's a well-mannered plane. Originally I had a 16" prop on it, but after breaking it a few days ago I switched to an 18". Both are in the recommended range for the RCGF 26cc gasser. The 16 seemed to run better and had more throttle range, while the 18" sounds like it's bogging down slightly at anything over 1/2 throttle. I haven't done any tuning since switching to the bigger prop, mainly because I'm waiting for a 17" to arrive. 16" looks small on this plane and 18" looks too big, so I'll go for 17" and tune it from there.

Now that I'm satisfied it'll run properly and not die during flight, I'll start the process of fitting the cowl over the new engine and patching unnecessary holes from the old nitro engine. For sure it needs a cut-out for the spark plug boot, and it may need some clearance for the exhaust outlets.

She's a keeper! :)
 
#47
When I started reading your last post I was thinking that the Citabria was cursed, but it sounds like you're getting it worked out. Some planes are like that, they just take a while to get the bugs worked out. I'm sure you're up to the task!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#49
Looks like I'm also excising demons on the trim-job the builder did. After one flight yesterday I noticed one of the red stripes on a wing coming off, so I removed it to avoid losing it mid-flight. Then, when taking it apart at the end of the day I found a couple of his trim pieces on the bottom of the wing also coming off. I'll try and re-stick them, and if that doesn't work I'll simply cut and install new ones.

Thinking long-term, if this plane keeps making me smile I'll probably re-cover it in a more traditional Citabria scheme. The existing covering works for now, but is a bit aged. It also needs a new windscreen, and I'm thinking about adding a side-door for access.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#50
With the Citabria project approaching the finish line, there are a couple last details that need to be done. The cowl needs to be installed, some clean-up inside the fuselage is needed, prop selection and a little engine tuning, etc. So with one project winding down it's time to decide what will be next on the work bench.

Work on a couple very big projects is on the horizon (1/3 scale Sopwith Pup and a 27% scale L-19), but I'm holding off on those until weather gets too cold for me to fly regularly. There are also a couple other "smaller" projects to pick from, including the Sig Kadet Senior I've been re-building, an old-school Kadet Mk 1, a Bird of Time, an F-4 Phantom, a Sig Ryan STA, or a few other kits which haven't been started yet.

However, one plane is standing out and will probably be my next project, a 1/6 scale Stinson Reliant by Marutaka/Royal. It's got an 84" wingspan, and was purchased last winter at a swap meet. I wasn't sure what the seller meant when he told me it was probably built for display, as it had a nitro engine, pushrods, etc installed. Turns out, it was really just for display and not set up to actually fly. Strange, as the build and finish quality was pretty nice. But the hinges were glued solid, as were the pushrods and tail wheel. So I put it aside to wait for the right time to tackle it.

The Stinson Reliant has beautiful lines, and is truly a classic plane. This plane is also just the perfect size to use many components and parts I already have. It'll use the Zenoah 20cc gas engine from the 1/4 scale Cub lost to a crash earlier this year, and a quick test-fit shows me it should be a great fit. I've got various servos that'll work well from other salvaged kits, along with the gas tank, pushrods, and other pieces needed to complete the build. Even the covering is accounted for in my hoard. So this plane shouldn't cost much to get it up and running, which is nice. Over the next week or two I'll get the parts put together to make sure I've got everything. For now, here's the color scheme I'm liking for it:

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Joker 53150

Mmmmmmm, balsa.
Mentor
#51
Cowl work was easier than expected (so far). All I needed to do was cut a small hole to allow room for the spark plug boot, which only sticks out about 1/4". The two holes from the original nitro engine will be fairly easy to fiberglass shut. I'll need to look at some baffling inside the cowl to get airflow over the cylinder head, as the front vents on the cowl don't line up well with the head and I fear most of the cooling air will simply blow right past the head. After watching some videos on baffling it looks fairly straight forward, so I'll get started on it this weekend.

A pushrod for the choke on the carb was also required since the engine does need to be choked when starting for the first flight of the day. With another plane I simply used a servo and pushrod, but I'm running out of space for the needed parts in this fuselage, so I'm doing a temporary fix until I decide on a long-term solution. A guide was fabricated and bolted to one of the engine mounting bolts, which would allow me to simply run a heavy wire from the choke lever out the front of the cowl. This gives me easy access to choke the carb as needed, as long as the engine isn't running! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#52
Here's the simple cutout needed for the sparkplug boot.

IMG_5547.JPG


And if you look closely you can see the choke cable just to the left of the prop. Tomorrow I'll start on the ducting to force air down over the cylinder head.

IMG_5548.JPG
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#53
It's been 1.5 flying seasons since this Citabria first flew for me, and it lives up to the design by being very aerobatic. She does land fast, however, and would benefit from flaps to slow it down a bit. Since that would be major surgery on the wings it'll have to wait. Lucky for me the flying fields I use have plenty of room and few trees! :)

So the Citabria has flown 21 flights, for just over 3 hours of flight time (not a lot, I know, but the hangar is full of planes that all want to fly so no individual plane gets a ton of hours). The last flight was August 12, 2018, which ended poorly. I mis-judged where the plane was in relation to the mowed landing strip and ended up in some tall grass. The plane made a quick stop and at first the only visible damage was a broken prop. Upon further inspection I noticed the windscreen was cracked and that the right wing wasn't staying tight up against the fuselage. The wings are held on by 4 screws (2 per side) which go through a pair of metal tubes. One of the tubes for the wing had a wallowed out hole from the stress of the landing and needed some repair.

I didn't take a bunch of pictures as it was fairly easy work. The center section of the wing had the original covering stripped along with the top & bottom sheeting. All that remained were the 3 ribs and support structure for the tubes. The metal tube was repaired and the center section was re-sheeted with 3/32" balsa. It still needs a final sanding before covering, and you can also see some damage to the windscreen in the picture. A quick test with the wing tells me the damage is taken care of and solid. While I'd love to use a fabric-style covering like the full scale Citabria uses, I'll use simple white MonoKote here to match the rest of the plane. Eventually I'd love to strip the plane and re-do all of the covering, but that's not going to happen this year. :( Too many other projects! :)

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