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Old 12-11-2011, 10:25 PM   #1
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T/T Rare Bear Build Log

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As with last winters Harvard, I thought I would document the process with this one.

As this has been on my "Lust List" for a long time I grabbed at the opportunity late summer to acquire this project. Too bad it is now out of production as hopefully it will fly as nice as it looks.

It was NIB and well packaged, but there was evidence of water damage to the tail feathers. Otherwise the only things missing were the retracts. As it ended up that was not as big a problem as I thought.

For anyone thinking this is an ARF, even though the major bits are assembled there is still considerable work to do putting it all together correctly. And that is without my inevitable tendency to "Improve" on what I see.

After inventory and planning the steps I started getting the bits collected, such as engine and servos. Another great advantage was finding a couple of assembly threads. There is one converted to electric and it had a wealth of hints and tips. One regarded the fact the C/F rods for the tail were too long and forcing things could damage the internal structure. I also found reports of tail failures. The general consensus was flutter. Considering the soft balsa and flimsy metal rods used for the stock elevator linkage I tend to agree. Due to this the first mod was moving the elevator servo to a custom tray in the tail and fabrication of two 4/40 link systems. At this point I avoided the bother of a retractable tailwheel, but that is one option for the future.

One other weakness that showed up immediately were the aileron servo trays. Just a slight amount of pressure had them fall apart and I am wondering about the other structures hidden within the wings. The assembly seems to use a contact style adhesive that does not penetrate the wood very well. I tried to get some CA into the bond areas, but without a total teardown will just have to cross my fingers.

Later in the game I worked on the tail area. I replaced the brass load bushing on the bottom of the rudder with one of teflon as I hate any metal/metal contact points where vibrations can create an RF source. Anyone experiencing what happens with a loose muffler will know what that means. RCJETMAN was generous enough to give me one of his Pull/Pull servo wheels and I modified both the cables and servo mount to allow for adjustment at the servo and, using a 4/40 ball link, load compensation on the servo output shaft. The tailwheel had the steering arm attached directly to the wheel fork, which would have had it very close to the fuse cover opening. I cut that off and mounted a separate arm at the top of the shaft where the retaining collar was originally. It removed the risk of the rudder linkage binding and also provided a much more direct path for the springs.

Due to the previously mentioned water damage and instances of tail failure I pulled the skin from one horizontal stab and replaced the wood. I also covered the stabs and elevators with a layer of 3/4 oz cloth and finally got to use the Ontario Adhesives EZCote. It has the consistency of slightly thinned Elmers wood glue. The difference occurs after application, where all but the last few percent evaporates and provides a hard surface. It just took quite a few applications and sanding to fully fill the weave. Again, one solution created another as I went with Ultracote and it did not like the impervious surface. I had to rip off the first effort and speckle the nice smooth surface with a poker wheel to provide an exit path for adhesive outgassing. As it was it still required careful heat application and following along with a wet rag to get a result I wanted.

In regards to durability I threw out the stock CA hinges and used larger size pin hinges. I replaced the standard brass coloured cotter pins with my own bent and cut from music wire. The key here is to ensure absolute alignment on installation to end with a smooth and stress free hinge line. What helps there is using a remaining length of music wire fit through all the hinges till the epoxy, or in this case, Gorilla Glue, fully cures. I used the GG here as the hinge slots. especially in the vertical stab, were huge and ugly right from the factory. A blind man with a saw could have done a better job.

Even a heavy mix with FLOX would have had a hard time filling those gaps, (and staying there) until cured. As with the Harvard, every hinge was taken apart and lithium grease applied to the hinge area and pin and the bond area cleaned with alcohol before going at them with the GG. The expansion on this stuff is incredible. If you are careful it can cure a multitude of sins.

The second mod and one that proved time consuming was an idea gleaned from the aforementioned electric conversion thread. What really made it stick is this is used with my friend's turbine machines where quick access is required. Since they can experience extreme speeds and g-forces I imagine they will tolerate the more modest stresses here. Rather than fasten the canopy down to the fuse with a multitude of small screws I carefully built and bonded an internal structure to the canopy to give it rigidity and a method to attach it to the fuse. Although difficult working through the rather small cockpit opening it proved to be a lot stiffer than expected. Using a pair of small springs, wheel collars and the butchered ends of a couple of PC 9-pin plug thumbscrews I fabricated a pair of quick release springs. The forward part fits into the fuselage frame with a trio of small diameter C/F rods. Drilling those was accomplished through the firewall opening before that part was installed.

This idea proved so good I will likely try it on the Seawind.

One thing to note was I moved the aft main bulkhead forward to directly behind the cockpit opening. This strengthened the fuse where it was required the most and also provided an anchor point for the quick release pins. Drilling for those was also accomplished through the small cockpit opening.

One advantage of this method is all the controls and switches can be mounted internally, keeping anything ugly such as power ports or remote glow fittings from marring the nice exterior. I fabbed an isolation mount for the receiver and power distribution center and then a panel mount to the front of the cockpit area. This houses the two switches for RX and servo power and I also butchered a remote glow adapter and fit it to the center point in the panel. Due to the rather unique power profile of the main A123 pack I only have a battery status indicator for the much smaller 4 cell Rx pack. The charge ports on the panel are active and the one for the SERVO supply is tied to the 2S A123 pack balance lead for charging and so I can plug in the appropriate loaded tester. I will keep my initial flights short and monitor the status as I gather some history of pack useage and charge state.

Another mod and one posted on RCC a while ago regarded the motor mount system. The stock gear includes a pair of isolation beams, but although designed for a 2-stroke, the Saito 125a simply would not fit without some creative hogging that I thought proved too much for whatever gain they could provide. I replaced them with some fiber beams that hopefully will provide enough damping.

I used the same method for the cowl as the Harvard, consisting of the fake radial cut and fit with an air duct system to ensure flow only around the engine. It took a bit of effort to create the underlying structure and aligning it all to the inside of the cowl. The cam covers were just large enough to get in the way. Instead of my previous method of thin cardboard as a template I used a heavy plastic sheet to mark the cowl cutouts. This proved a much better practice as I can see more of what I'm doing early in the game and the plastic provides a rigid pattern once the cowl is reinstalled. As you can see in the last pic I decided to fab up some fake exhaust outlets for each cutout. Simply a set of alloy tubes fit to a wood bulkhead. They are open at each end and the bulkhead protrusion has been cut to a minimum to prevent any restrictions.

Other than the rebuild of the servo trays the only mods to the wings were the installation of what remains of my coffee maker filter to the back of the air inlets, (for a bit of scale detail) and the replacement of the stock retract system with a pair of RCLANDER servoless retracts. The stock system has a single servo mounted to a tray in the fuse that also serves to hold down the fuel tank and I had already tried that system with a pair of Robart mechanicals. This would necessitate connecting and disconnecting the mechanical linkage with the wings, a rather inelegant solution and one that would be impossible with my internal switch/glow panel in the way. The standard linkage paths are now accomodating the servo leads into the fuse.

The removal of the retract servo in the fuse provided a free area close to the firewall for the LiFE pack, (too large to fit the stock tray above the motor) and the larger retaining plate in its place gave a nice mounting point for the CC BEC PRO used to regulate it to 6V. Later there is the possibility that area can fit a smoke tank and pump if that is in the cards.

As of today the plane is finally sitting on her own two feet. I replaced the stock 3" main wheels with 3.25" as we fly from grass and there is more than enough room in the wells. The difference does not alter the stance away from stock to any appreciable degree and it still looks aggressive.

At this point the only remaining items on the list are to complete the gear, (basically taking everything apart to file flats on the shafts and Loctite everything upon reassembly) and try to figure out some simple way to retain the wings. The stock system has a screw inserted through the wing into the C/F tube. Don't like that idea. I want something more guaranteed holding them on and am looking into thumbscrews from inside the fuse. Access is a bit tight for these old fingers so the solution will take some thought and searching through the bins for anything useful.

The clear canopy was like all the rest of the plastic bits in that cutting and sanding are required to clean up the edges. Only much more so there due to the fact the canopy has to fit the frame cutout tightly. There are decals to cover the bond area and simulate the painted frame and these would show any inconsistency around the bond line. As with the Harvard I used the wallpaper glue from Home Depot and it took over 2 weeks to fully cure due to the close fit and the fact the plastic does not allow for air contact like a wood underlayer. In this case I had to cut out a bit of the seat behind the pilot and blow a fan into the opening to start the curing process. Now that is complete I am deciding to reseal the canopy as I am worried a day in the hot sun could blow the bond layer loose. May end up just providing a tiny bleed hole.

Hopefully soon I will upload some pics of the wing attach and gear installation. On that note I will likely have to fab up my own gear doors. The stock are thin plastic and will not fit the larger diameter leggings.

I will also go into more detail regarding difficulties with stuff I did not modify. One of those has to do with the spinner, but all that can wait. Enough blathering, here are some pics.:
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Last edited by Cougar429; 12-12-2011 at 08:46 AM.
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Old 12-12-2011, 02:37 AM   #2
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Re: T/T Rare Bear Build Log

Nice work!
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Old 12-12-2011, 10:46 PM   #3
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Re: T/T Rare Bear Build Log

I like it.
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Old 12-13-2011, 05:48 AM   #4
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Re: T/T Rare Bear Build Log

Looks great....any time set for the maiden???

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Old 12-13-2011, 09:00 AM   #5
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Re: T/T Rare Bear Build Log

I wish I could forecast a date, but with the abysmal weather we had this year and field allowed a half dozen or so flying sessions, (AGGGGH!).

The plane will likely be set aside till the spring. There are several other winter build projects planned, the F-15 and F-20 I grabbed from other RCC members earlier are next in queue. There is also the ever present N/P Seawind project lurking in the background. Talk about a plane requiring gads of improvements to reach some level of confidence! Just realized I seem to collect orphaned, out-of-production machines.

From the look of things I will have several maiden flights to make when things open up again. Over the winter we fly at a soccer field that is not the best for test flying a new machine.

As promised I will cover a few difficulties encountered during the build.

The first was listed earlier and that was the requirement to trim a slight amount from the two C/F rods for the tail feathers. Not much, but forcing them together would have caused damage internally.

Next was a bit more prevalent and one that still can be a problem. The fuse is VERY thin and picking it up incorrectly can cause deformations and possible damage to the skin and paint. I shudder to think what could happen if I have to put this in on her belly. In the pics of the rudder servo you can make out a repair to the skin. Unless some structure was added this may be an ongoing concern.

I have no problem adding longerons, especially tying the main and tail sub structures together. However, I am reluctant to add any more weight aft of the CofG till I check the balance with the rest of the systems installed. Waiting for another adapter for the Slimline Pitts as the first seems to have been lost in shipment. The order was placed mid October.............

The reason I have the Harvard spinner installed now is the gobbing huge stock unit has cutouts that don't conform to the Garupner 3-blade I picked up at the London Swap Meet. Unfortunately their own manual is pretty limp when it comes to letting you know what it fits. Here is a direct quote from their instructions:

Appropriate for engine type and preferred performance
You can see paint missing from the cowl in several of the pics. The bond to the fuse seems much better, but even removal of the low-tack painters masking tape has the gold come off with it.

When the cowl comes off again for the muffler installation I will take pics of the fuel system. For all that room I had some fun figuring where and how to mount the filter.

For now things are going to be mostly placed on hold. Along with helping the wife decorate and clean, have to concentrate on grandson proofing the build room for the Holidays.
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Old 01-28-2012, 05:47 PM   #6
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Re: T/T Rare Bear Build Log

Time for the latest update. With the Holidays and other commitments I put aside this one till the muffler adapter arrived. That has been an ongoing problem since October and I finally decided to have another go.

I set aside the F-15 and went after the retracts legs first. I acquired the Robart units earlier and they had some problems, first being the nylon jammed into the top end. I had to drill and tap to remove it and once some dimensions were recorded had brass bushings turned that included a shoulder to extend the upper tube and give more meat for the 5mm rod to seat in. End result was pretty good, with drilling and tapping for the set screws a minor affair. Pulled it all apart again for painting and then fit them to the retracts.

In all this was not that bad. Had to do some hogging on the well to accommodate the scissors and will eventually fab up some glass doors once it has some time under the wings. If I have any complaint it is that the RCLander retracts show slop when extended. I really don't want to pull them again, but that may be required if don't want it to ground handle like it had too many.

I have been thinking of the wing attach for a while and had to come up with something more elegant than the screw from the bottom of the wing into the C/F tube. I relocated the aileron servo entry in the wing root and beefed up the original area to fit an internal retention setup. The longest process was waiting for the epoxy/FLOX on the internal doublers to set. The wings turned out easy with doublers added to the open area behind the tube slide. I modded some old fan adjusters with 10/24 threaded nuts and sharpened the end of one stud to create a pointer on where to drill the fuse. . That was threaded into the blind nut, then slid onto the tube. A bit of a wiggle against the fuse side and a mark was left to set the drill. The final result has the studs from the wings enter the fuse and then be held on with the threaded thumb rigs. I can just fit my fingers in there and may fab up some more thumbscrews just in case one is lost.

The last effort so far was the addition of reflective duct tape to the exhaust outlet areas, identical to the real plane. I must say that although this stuff has an aggressive adhesive, the windex must be ABSOLUTELY dry before it sticks down for good.

Hopefully the muffler adapter(s) will finally arrive this week and I can get it ready for its maiden in the spring.
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Old 01-31-2012, 12:46 PM   #7
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Ontario Re: T/T Rare Bear Build Log

Hi Cougar: Nice work, a lot of it, your efforts will make this beast a "rare" flyer and a joy in the air.
I read previous posts of ther building this plane and the problems they've encountered. it appears you have all the bases covered. Well done!! flytwice
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Old 02-01-2012, 12:02 AM   #8
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Thumbs up Re: T/T Rare Bear Build Log

I have used one of those servo Isilators before. They work good I think.
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Old 02-01-2012, 05:20 PM   #9
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Re: T/T Rare Bear Build Log

Thanks. I picked that up at the Kitchener Swap Meet last year and this is the first opportunity to permanently install the unit. I also have one of the earlier versions that will wait till it finds a home.

One of the best features is the ability to separate the receiver and servo power sources. The receiver battery is 5V and only about 500MAh while the servos are fed by a Thunderbolt 2S LiFE pack stuffed over the fuel tank. I run the entire Harvard system from one of these and except for the fact it is difficult to determine pack capacity when you first start to deal with them in a new plane, I can see more of these in my future.

You can also double up the servo power sources, but since the Castle BEC Pro has two outputs I opted to simply plug both in.

On that note I have been a bit concerned about the tank location so low in the fuse and may wait to try the motor out or elect to proactively work on a solution. I can either add a Perry VP-20 or reverse the battery and tank location to have it more central to the carb height. It always surprises me since initial views on a new craft always make me think there is lots of room, but even with the larger machines, once the systems start to be installed things get tight in a hurry.
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Old 02-01-2012, 06:29 PM   #10
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Re: T/T Rare Bear Build Log

Nice work!
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