COMBAT BUILD - HEFA Ground School 2013

[retiredVTT]

I made some revisions with my motor installation. I found the shaft to be too long and rather than cut it off, I elected to loosen the rear grub screw and tap the shaft back 3/8". That will move the "flat" part of the shaft to the outside of the motor so I installed a 3mm wheel collar on the rear shaft and it's grub screw will tighten onto the flat of the shaft.

Then I opened the center hole of the firewall motor mount so I could use a "collet" style prop adapter and slide it into the mount. Because my collet adapter has a wide hub, I now can use only the two widest holes to secure the motor. However by using Loctite on the threads of the mounting bolts I should have a secure motor. There are collet adapters with smaller hubs that would allow using all four motor mount bolts.

I found that I still had a gap of 3/16" at the rear of the spinner, so my last step was to cut out a 1/8" ply ring and epoxy it to the front of the original mount. This reduced the spinner gap to a decent 1/16".

Bill

[CF Av8or]

P-40 Landing Gear Tubs

This is for the consideration of the P-40 builders only.

Okay, so you might call it going a little beyond the simple combat model requirements, but I’ve decided to incorporate another scale detail into my P-40. This is such a unique visual feature of the P-40 that I felt it was worth the trouble of reproducing. If you feel the same way, or are just really bored, feel free to give this a go.

The P-40 has landing gear (lg) that retract rearward with the wheels rotating 90 degrees and tucking up into the wing and the struts retracting into these protruding tubs. They give the wings a very distinctive look from the front and from above and below, as well.

I decided to reproduce these using pop bottle plastic, as this is both lightweight and incredibly strong. Of course they could also be shaped from blocks of balsa wood, but balsa is expensive and empty pop bottles are free (okay, they’re actually worth 10 cents).

I’ve used pop bottles to produce all kinds of plane parts, including canopies and cowlings. It also turns out that the average wooden broom stick makes a perfect form for these lg tubs which are about 1” in diameter. The idea is to shrink the pop bottle around the broom stick, using heat from a heat-gun, to form perfect half-tubes with a spherical end.

I used a 2 ltr President's Choice ginger ale bottle (as it has straight sides, unlike a Coke bottle) with the label peeled off. The top third of the bottle is cut off to allow access to the bottom of the bottle. To take up the excess space in the huge bottle, I inserted a 1X6” pine board along with the broom stick. The end of the broom stick is held firmly in place inside one of the knobs at the base of the bottle and heat is applied strategically to the plastic to cause it to shrink around the broom stick. There’s a bit of a science to this in order to get the bottle to shrink tight properly around the broom stick and it may take several bottles and trial attempts before you get it right. Hey, it’s only 10 cents a shot…

Once shrunk to your satisfaction, the excess bottle is cut away to release the sticks and the plastic is trimmed to lines I drew on the surface with a Sharpie. The more the plastic is shrunk, the thicker it gets, so at the rounded end it is very thick and will likely require cutting with a band saw. The rest can be more easily cut with scissors or a knife. Once cut away, it needs to be trimmed to the lines and a power sander is helpful here.

Each tub is then glued to the wing, centered 3-1/4” from the aircraft center-line. Note that the rounded end protrudes from the front of the wing. The tubs were glued in place on the underside of the wing with thick CA and kicker. I then applied a bead of hot glue to the joints and smoothed out a nice looking fillet with a large (tongue depressor type) popsicle stick. I was not able to get the plastic to shrink enough to form a complete rounded sphere at the front of the tub, so I went back after the tub was installed and filled the top, at the wing leading edge, with epoxy and micro-balloons to form the remainder of the sphere. This was sanded to a nice smooth, faired-in shape after it cured.

Taa-daa! P-40 landing gear tubs! Give it a try, if you feel ambitious.

[CF Av8or]

[rhyneheimer]

sorry to miss this thur, but you're all better off in vic's hands when it comes to painting anyways... see you next week, good luk, have fun

here's 2 pics of my P-51 after installing a sub-firewall. i decided to move the motor back 3/4" so as to flush mount the spinner and not have to add a filler plate on the face of the firewall to fill the gap, plus to move the CG back with the new heavier motor. importantly, the down and side thrust angles are maintained. spinner shown is not the one i'm going to use, but will be similar - this one has too thick of a back plate and won't accept the nut on the collar unfortunately (applies only to the P-51 spinners, we'll be getting new ones). the collar passes through the front firewall, and grub screws are now accessed from the side between the firewalls. motor mount bolts are accessed through the front firewall. the rear firewall is glued in place, but for now, that 2nd rear plywood piece (touching the motor) is just a spacer ie not glued. just in case. in case of what? i do not know.

this is what i did, but vic will fill you in further re any mods to your build beyond those he already explained