BBA/Winter Build 2017/18 - Top Flite Corsair

PsyBorg

Wake up! Time to fly!
I wonder.... for the gear doors.. if a single shaft could be used thru the wing and worm gears used to open and close them. The doors would use the 45 degree gears sorta like used in heli tail rotor drives. Then the whole thing could be operated in sync from a single servo set to run 360 degrees like a motor. But on a wing like the corsairs that single shaft might be an issue. Maybe a thicker steel wire could be used out to the doors where the worm drives would be solid mounted.

Would something like that work for straight wing planes and possibly convert over to operate flaps of a single servo too?
 

willsonman

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I think that would work but may be overly complex. The angles at which the gears would seat would require some rigid reinforcement to ensure the teeth engage properly. RC car or truck u-joints could be used to overcome the bent wing but again, you would need a support with a bearing to make sure the joint did not slip.

Moving along, I stopped at the LHS to see if they had some Sullivan Gold-n-rod. No luck so I went on the prowl for some ideas in my various parts. I found some long thin steel wire that was quite flexible but rigid enough for what was needed. I then looked over the wing to see how much I would need to tear into the wing...

Remember way back when I removed the original aileron linkages? As a refresher, there was a single servo in the center of the wing with a single push rod out to both elevators with a bell crank system. I removed all that for a dual aileron servo setup so that I could program a bit of aileron differential for more scale maneuvering.

So, I cut out a small portion of the wing center section top sheeting. I noticed the holes from the push rod sleeve and instantly remembered all of this. I removed some additional sheeting and had to do a little bit of drilling to re-install some sections of the sleeves.
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I had to drill out this hole a bit on both sides as it was blocked a little by the supports for the flap servo mount rails. The small section of balsa removed allowed me to get the drill angle right.
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At the bottom here you can see the grey sleeve protruding through just in front of the flap servo.
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Inside the wheel well, I drilled a new hole for the sleeve so that the proper clearance for the push rods can get good leverage on the hinges.
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Since the push rod has to cross the span of the wheel well I wanted to be sure that the oleo cleared the push rod at it's height. All cleared fine but I feared a bit of flex in the push rod across this span.
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Using a dremel cutoff wheel, I carved in small recesses for some nylon push rod to act as a smaller sleeve to prevent flexing of this push rod. Some CA to secure it and I'm in business.
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So here is the final look. Both push rods go through the inner sleeve to the center of the wing. I manually tested this out and there is some friction from the bend in the sleeve but it is fairly minimal.
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I'll pause here to get the other side done and mount the servo. It is a bit hard to explain in words how this will work. Pictures of the finished product will explain things far better.

I'll try to explain how each side will work by describing one side. The idea is that the push rods for each door will be linked to the servo arms on opposite sides of the servo. As one rod pushes, the other will pull causing both doors to operate in the open or close position. Referring to the last picture above, the doors are open. To close them, the push rod on the left needs to be pushed and the one on the right needs to be pulled.

Clear as mud?
 

PsyBorg

Wake up! Time to fly!
OHH I just worked it out in my head how them door hinges work. Is it possible to get a close up of those so I can see the pivot and how the lever works? I have been struggling trying to figure how to get bomb bay doors to work properly but always end up with the mechanisms not working in snyc or when the do work in sync they dont line up properly when open or closed.
 

willsonman

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Sure, What you really are looking for is offset door hinges. The hinge point is just under and inside of the edge of the seam where the doors meet the wing. When swung open, the offset hinge allows the door to lift up and away from the wing surface. The different holes on the hinge allow you to use push rods from different angles to accommodate how the offset nature of the hinge works.

Hope that helps.
 

willsonman

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I thought about it as there is one on Thingiverse but it required hardware so it was just easier to order some already made.
 

willsonman

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With the first set of doors done it was a pretty easy job to get the other set on. Some measuring here and cutting there.
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Kind of a bit of a rat's nest in there but I'll be tidying things up with the servo wires. The next step was to make a servo tray and get the push rods connected correctly.
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Here is the money shot. On the top and bottom portions of the arm, push rods are connected to one side's inner and the other side's outer doors. Linkage stoppers allow be to adjust full closure evenness on both sides.
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I posted a short video to FB last night that I'll include in my next video update. Up next is to draw up a sliding mount for the oleo. This will slide along the oleo and keep the front door aligned. The front doors will have a pin hinge to pivot on but the mount will go around the oleo and be glued to the door. Once I have this all set, I can connect everything to the Rx and do a bit of programming. I'll pressurize the air tank and do some fine adjustments on the main gear retraction and time the cycle. From there I'll set a delay in my Tx for the gear door closure so that the doors do not bind or interfere with the main gear retraction sequence.
 

Ray K

Ray K
Looking at the pictures in post #230, I'm reminded of the wheel wells of full-scale planes. A controlled rat's nest of wires, pipes, conduits and switches. By the time you get all that dressed up, it really will look a lot like the real thing.
 

willsonman

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LOL, it may look like some resemblance but I have no plans to go to that level of detail on this build.
 

willsonman

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I'll be relieved when I get the shot with the gear extended and the front door on as well.

I uploaded a few more items to Thingiverse. If you like dropping things from R/C aircraft I highly suggest you check them out.
 

willsonman

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So I had limited time last night for building but I did get to a great milestone. The unfortunate part is that in my haste, I neglected my documentation so pictures are sparse today.

I had a dental appointment and before that I took 5 minutes to draw up the sliding mount in Fusion360 and popped it onto the printer. I had a first run when I got home but the opening was too large. two adjustments and 30 minutes later I had another that fit perfectly.

For the front doors I installed flat pin hinges into the LE of the opening and removed a bit of material from the door for the hinge to be recessed into. I glued the door to the hinge and checked for fitting. All was great. I then glued the rear of the door to the sliding mount that was printed and it works flawlessly.

I installed small segments of tubing in the wing to connect the retracts and installed the wing with the air lines connected and cycled the gear for the first time since the wing was framed up and in skeleton form. All was fine... and then I put her down on her legs.

The immediate thing here is that the wheels do look a bit small but most of that is the camera angle and a bit of parallax. The other part is that while the look is good... it's not perfect. Let me go on to explain this below.
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In this close up shot you can immediately see the issue where the wheel touches the front door. There is some heft to her at this point and the oleo is compressed slightly compared to not having any weight on her mains.
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Discussion:
Seeing this issue I've reflected back to try and figure out where I'm going wrong on this. I've determined a number of factors so I'll go through them one at a time.

1: The front gear door shape was determined by they shape of the die-cut part supplied in the kit. I did not think about this when I cut the doors as these are intended for fixed gear that would have no compression. The kit instructions do not have any gear doors when using retracts as this is intended to be more of a sport scale model with no front door and just a round opening in the wing for the wheels.

2: Referencing full-scale pictures, the door shape is wrong. the lower portion is narrower and the right side (reference picture above) does taper slightly to the left, not straight down.

3: The wheels also are positioned a bit more outward away from the struts on the full-scale to accommodate brakes. Something I did not do due to the shallow recess of the wheel bay in the wing.

The Fix:
Looking back at previous pictures of the wheels in the bay with one door down, I think I can add one more nylon washer to push the wheel outward. I also will remove 1-2mm of material on each side of the lower part of the door and taper it properly as the full scale did. I'll add back that thickness to the wing sheeting so that a clean look is maintained when the gear is retracted.

I'm getting into full disclosure of a mistake but, frankly, these things happen when you try to make a sport-scale model into a scale one. All this in mind, it really is fairly minimal work to fix and After that I need to work on plugging everything in and have a looooong conversation with my Taranis. On that note I want to point out that I use a digital servo tester that tells me what the wavelength of the PWM frequency. This in mind, I can set exactly what I need for the throws on the fiddly bits like the bomb drop, door retraction, tail gear retraction, canopy slide, and of course the air valve movement. While it's nice to have the mechanics worked out perfectly, it rarely happens that way. I'll write down some of these numbers before I go into my programming. It MAY be possible to tie in the tail gear retraction and the gear door retraction into one channel... but it depends on the mechanics. I never thought I would have to think about conserving channels on my Taranis... EVER.
 

willsonman

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It's entirely possible. I'm trying to keep things fairly simple for such a complex model setup. I do have a DSM2 module that I could use for the cockpit animations, should I chose to go there.
 

Joker 53150

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Dual receivers via module bay link if necessary?

You don't need to use the module bay with the Taranis to run two receivers, you can do it using the XR8 (or similar) receivers. One is bound to the TX for channels 1-8 and the second is bound for channels 9-16. There may be better/easier ways to do it, but this is still an option. You could run both off the same battery or run separate batteries for each for redundancy in case one fails.
 

willsonman

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No no, I'm using an X6R receiver with a s.bus to pwm converter and have access to all 16 channels without an additional Rx. The DSM2 bay would give me ANOTHER 9 channels on DSM2. I also have a DJT module that I could put on there to stack on an additional 8 channels on the FrSky protocol. So I have options.