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Building the Top Flite Giant Scale P-40 – P5 Wiring

I’ve finally gotten back to some work on my friend Kelly’s P-40.  Lately I’ve gotten the plumbing done on the fuel tank and sorted out the electronic kill switch, battery and switch wiring.  Here’s a shot before I buttoned up the throttle servo tray. 2014-06-01 10.51.59

The A123 2300mah battery is bundled up in the blue foam and tucked up against the bulkhead just above the back of the tank.  With a couple of custom fit foam spacers to hold it in place it has no where to go.  The circuit board for the ignition kill is also sandwiched in between the battery foam and the spacers.  The ignition kill indicator light projects up through the fuselage just forward of the instrument panel but is protected inside the canopy.

Here’s another with things a bit more “buttoned up”.

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Not quite finished up… throttle linkage is hiding in the sidewall, one of the remote receivers is not plugged in yet but most of the wires are wrapped up and the radio/servo tray is in place and hopefully will not need to be removed again before the end of this build.  One more short session buttoning up the wiring, fuel tank and ignition and I should be able to finish up the fuselage and move on to the final steps to complete the wing.  From there we will be nearing flight ready!

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Building the Top Flite Giant Scale P-40 – P4 Cowl Mounting

After we built the first P-40 (this one being round two) and got a few flights on it we began to immediately see problems with the cowl mountings.  It seemed impossible to keep the screws from backing out and even around the ones that didn’t the vibration immediately started chewing up the mounting holes.  No amount of reinforcing of the fiberglass helped and while bonded washers have proven to be effective in this role they would have completely trashed the scale lines of this bird.  So when cowl number two arrived I got creative and decided we needed a better mounting system that didn’t result in having to put a bunch of (I don’t remember the exact number  but it seems like 20) holes in the cowl.  I came up with a system of mounting using blocks epoxied inside the cowl with 2 guide pins and two bolts.  It seemed to be working quite well… right up until an unfortunate lack of airspeed, altitude and ideas destroyed more than just the cowl.  So fast forward to today and I had to recreate the mounting method.

This time I thought I’d document a bit in case someone else wants to try it.  It worked well but it’s a bit devilish to get the alignment right.  It’s amazing how tightly it holds though with only two pins and two bolts holding it and zero holes in the cowl to mar the great looks.  The basic idea is to use the two bottom mounting blocks on the firewall for alignment pins, then using the the blocks on the bottom front of the motor box to accept bolts that are reachable via the (already needed) exhaust cutout.

Here is one of the firewall mounting blocks after drilling and the addition of an “alignment pin”.

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Then I marked and drilled a block with a matching hole.  Where I was careful not to drill all the way through the firewall, this block can be drilled all the way through.  I matched it up to be flush with the outside edge of the block attached to the firewall and also beveled the hole so that the locator pin could be inserted easier.  Here it is after the initial fit.

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The tricky part is to then put the cowl on and get it aligned as perfectly as possible.  Using the spinner back plate helps.  Once it’s right, mark the inside of the cowl and get prepared to apply some epoxy.

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Importantly at this point, where the block is going to be glued to the inside of the cowl, you need to clean the cowl inside surface with something that will cut through the mold release agent (think wax) that was applied when the cowl was made.  You can use some acetone (caustic stuff so be careful and make sure you have good ventilation) and/or sand the surface before applying epoxy.  Standard clamps can hold these blocks in place until they are set.  If you do this in the general area before you mark the block locations it will make you life easier in the long run.  Ask me how I figured that one out!

Similarly, the forward mounting blocks must be carefully aligned, marked and glued in place.  These I pre-drilled to snugly pass an 8-32 bolt and drilled and tapped the existing bottom motor box blocks to match.  Thin CA (very thin preferably) will harden those threads nicely, though you may have to re-run the tap 15 minutes later to make sure the CA didn’t block the threads.  Here is one method of holding the forward blocks in place while the glue dries… This method used masking tape and a “cut to length” dowel.  If you look closely you can see the holes to pass the bolts through have already been pre-drilled.

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In order to be reachable from outside the cowl the bolts are inserted from the bottom.  Happily this results in a very firm mount.  I used allen bolts which require a fairly long ball driver to access in this position.  Once you have these all in place you may (if your like me) find the blocks don’t perfectly match the surfaces to which they are attaching and one or more may need to be redone.  Sometimes a little sawing or sanding to make the surfaces match will suffice.  Otherwise a hammer will remove the block and a layer of the fiberglass with it (if you epoxied it well).

I’ll edit this post in the next few days to add a picture showing the mounting bolts in place.  I’ve done this twice now and it probably took me 3-4 hours to get it right, even the second time.  It’s time consuming and painstaking work but it leaves no marks and the cowl seems rock solid when it’s done.

 

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Xion Wing Lock – Pt. 2

Last weekend at the field during the IMAC contest I lost one of the cams and the washer on the port wing of my Slick.  No big deal really… I have clips on my anti rotation pins on each wing so I needed a click of aileron trim and all was fine.  After the flight when I went looking for the reason I spotted the wing gap and on investigation found that the cam and washer were gone and the stud had rotated out a bit.  I didn’t have my spare so that wing went back to the nylon bolt for the rest of the day.

So what happened?  While it is impossible to tell for sure, I believe the problem was rooted in not seating the wing down snug against the body.  So when I locked the cam down it pulled the wing in a bit but not enough to put pressure against the cam and therefore with some vibration the cam escaped.  Maybe the stud rotated enough to further loosen as well.  Possibly contributing to this is that I have not glued the washers down inside the body either… perhaps if I had the slack in the system would not have been enough to allow the cam to escape??

The only other issue I can see is that perhaps the stud managed to pull out of the blind nut embedded in the wing root.  I am really not fond of blind nuts in any case.  I find most of them to be ill fitting/loose.  When used in conjunction with a standard bolt there just seems to be a lot of play and I have seen a bolt manage to walk itself out a thread or two before without rotating at all because of vibration and slop.

I have continued to use the system through another 6 flights or so and so far have not had a sign of any movement.  I may add some plumbers tape to the studs to cut down on “rattle” between the studs and the blind nuts before my next trip to the field.  Otherwise I will keep with it and see how it goes.

(Don’t recommend these anymore… see part 3)

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New Gadget – Xion Wing Lock System

While walking the aisles at the Weak Signals show in Toledo I ran across the Xion Wing Lock System.  These little gadgets are an interesting alternative to 1/4-20 or 6mm wing bolts that screw into the wing root to hold the wings in place on your favorite aerobatic aircraft.  After watching the demo a couple times and recalling the times I’ve found a wing bolt rolling around in the bottom of the plane or struggled to get a socket wrench or screwdriver onto the wing bolts… I thought these might be an interesting alternative.  So wallet a bit lighter, I pocketed two sets of these and moved on with high hopes.  Here’s a stock image of the Wing Lock system from the Redwing RC website.

http://www.redwingrc.com/images/xion_wing_lock_wing_bolt.jpg

As you can see, the wing lock system consists of a stud that threads into the wing root, a rubber washer that installs onto the stud inside your aircraft body and the lever/cam lock that slots into the stud and, when rotated 90 degrees to flat against the body of the aircraft, tightens the connection.  Here is an example installed in my aircraft.

 

photo 2

To get to this point you have to drill out the wing bolt holes a bit and screw the studs into the wings.  (The enlarged hole is only 1/8″ or less larger so going back to 1/4″ bolts is not a problem if you later decide these are not for you.)

Now I will be the first to admit that I’m a bit of a gadget fan when it comes to RC.  I like trying out the new doodads and these are no exception.  I must also say that my current system of nylon bolts backed up by clips in the anti-rotation pins works excellently… So why the new system?

In addition to the allure of getting to play with a new gadget, I have always had trouble reaching the wing bolts inside my airframe.  The bolts are close up behind the main wing tube and with my large hands it requires a screwdriver to get the bolts inserted and tightened.  I was hoping that these wing locks would resolve that issue.  They looked very easy to connect at the show…

So are these the ultimate RC gadget?  Will they keep your wings firmly in place? Are they the solution to my wing bolt woes?  Here’s my experience so far.

I flew 3 times today after installing the Wing Lock system.  The wings stayed firmly in place and the wing locks didn’t seem to have budged… Not the slightest movement or loosening was apparent.  There’s seems to be a lot of questions out there on the web about whether these things will hold.  I’d have to say I’m no longer concerned about that.  Based on my experience, I’d have to say that they do work as advertised in this regard.  In addition the craftsmanship seems to be excellent and they are very light, which is always a plus.

The major selling point on these seems to be that they make wing assembly quicker and easier.  In my particular application it’s a bit difficult to reach the assembly point inside the aircraft body and at first blush this system didn’t make that any easier.  My fingers still don’t reach there easily and I can drop these into the bowels of the airframe just as I did the wing bolts!  I must say they are significantly faster (no 15 turns of a screwdriver in a tight area) so in that regard the system works as claimed.  I do appreciate this because it can be a back breaker at times to reach the wing bolts.  Using the wing locks doesn’t change how hard it is to reach this part of the airplane but I can’t blame the Xion folks for how my airframe is laid out and they do go together faster than my old wing bolts so less time spent hunched over is an improvement.

Not much can be done about where I have to reach to attach my wings and where things land when you drop them inside this airframe…. so I’m going to try tethering the cam locks to help limit the number of times I have to fish out the parts!  Maybe by doing that and with a bit more practice installing the cam levers I can maximize the benefit of the system.

Overall I like the Xion system and they certainly make assembly of my aircraft a bit quicker.  It’s always difficult to justify spending $15-20 when you have something that works already in place but I don’t regret spending the money for the Wing Locks.  I think I’ll keep using them and will update with any new revelations or changes I make.  So far I’m still thinking these are pretty cool.

(Don’t recommend these anymore… see Part 3)

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