CMAD Miss Foxy Lady build thread

[KRProton]

Okay, now we're really going to glue on the engine mount. Most pylon racing builders are familiar with the procedure of "potting" the engine mount permanently to the firewall. A film of epoxy (usually epoxy mixed with filler to prevent it from flowing) is added to the back of the firewall to securely bond the mount to the firewall. The theory is that a secure joint between the two provides for the most solid system for the best engine performance. I don't know of anybody who doesn't do this, but again I haven't seen the inside of everybody's airplanes. For all intents and purposes, the bond is permanent, but if the model e is ever destroyed in a crash, the mount can usually be separated from the firewall if it is in a condition that it can be used again. Ask me how I know. Some modelers would never recycle parts that have been involved in a crash. Some do.

Roughen the back of the engine mount and the front of the reinforcing ring so glue will adhere.

Now is a good time to be sure the needle valve and fuel passages are thoroughly cleaned out. Here, I'm spraying carburetor cleaner through all the openings.

Some modelers allow the bolts to become permanently glued into place. But I like it so the bolts can be tightened more later, after the epoxy has hardened. Sometimes, you don't want to tighten all the bolts evenly so the mount can be biased to one side or the other for perfect engine alignment with the front of the fuselage. Also, even if you tighten all the bolts the same, I like to leave them ever-so-slightly lose so I don't squeeze out all the epoxy. Therefore, I apply light dabs of petroleum jelly to the threads of the bolts and the holes in the ring so I'll be able to fully tighten the bolts later.

Gather some paper towel squares, some Q-tips and denatured alcohol for cleanup as you go. I also have some home-made tools for distributing the epoxy around the back of the firewall later.

[KRProton]

I don't want to spend too much time on what kind of epoxy I use, but I use MGS 335 laminating epoxy with a mixture of slow and fast hardener to provide a working time of over an hour. Typically, for gluing in firewalls, I'll also mix it with structural fillers such as milled fiberglass and flocked cotton to thicken it up, but here I'll be using the MGS just for fuelproofing and some jell epoxy with milled fiberglass for a fillet around the front and back and for gluing on the engine mount...

I like to make sure the firewall is absolutely, positively fuelproofed, so I brush on a coat of MGS epoxy.

Also coat the entire inside of the engine compartment (previously scuffed and smoothed with sandpaper). I like to smooth it out with my finger.

I'll use a paper towel square to absorb any excess epoxy. This just adds an additional layer of fuelproofing which probably isn't really needed.

[KRProton]

This is the epoxy I use with milled fiberglass. It's a jell epoxy. I did a write-up of this stuff that will appear in the May RC Pylon Racing column in Model Aviation.

There is already somewhat of a fillet around the front of the firewall, but while I have everything going, may as well build up a bit more of a fillet. Apply the epoxy around the firewall.

I dab my finger in denatured alcohol to distrubute and smooth the epoxy for an even fillet.

Apply a film of epoxy to the back of the engine mount. Use care not to get any epoxy on the fuel fittings. In the case of this particular airplane, the firewall was aligned perfectly with the front of the fuselage, so the engine mount may rest flat against the firewall not neediing additional epoxy to support it at an angle. Therefore I added a relatively thin film of epoxy.

[KRProton]

The same as was done before, place the engine mount on the firewall, and then use the two 4-40 rods and one of the engine mounting bolts to align the engine mount with the mounting holes in the firewall.

Apply a film of epoxy/milled fiberglass t the front of the engine mounting ring -- this time a thicker film.

Also same as before, slide the engine mounting ring onto the two rods coming out the back of the firewall all the way up. Thread the first engine mounting bolt to the ring.

Install the other bolts, only gently snugging them up.

Tentatively mount the engine and take a look at the spinner alignment. Make any adjustments necessary.

[KRProton]

Once you have the engine mount where you want it to perfectly align the spinner with the front of the fuselage, tight the engine mount bolts about 80% of what you would consider tight. We don't want to squeeze out all the epoxy.

See the fillet of epoxy that has squeezed out the middle of the engine mount? This must be completely removed, or else you will not be able to get the fuel fitting on the end of the needle valve mound down and into the hole if the assembly ever needs to be removed for maintenance sometime in the future. Use a Q-Tip with denatured alcohol or whatever else to wipe away that epoxy.

Make sure you have cleaned up any epoxy from wherever else it may not be wanted - especially the fuel fittings and the fuel cut cup. I also built up a small fillet of epoxy around the fuel cut cup.

[KRProton]

You may have noticed in a previous image, or looking down inside at the back of the firewall of your own MFL, that there is no glue around the back of the firewall. Most modelers will absolutely insist that, as well as the front of the firewall, that the back of the firewall must also have a fillet of glue. A secure firewall and engine mount system are key to good engine runs. Make a fillet around the back of the firwall as best as you can. This may be done now, while you have your epoxy going, or later, after the epoxy on the engine mount has hardened.

As best as you can, use a wire or something similar to dab epoxy all the way around the firewall. This is also why I have added the fuel cut system now.

I use a rounded dowel and another dowel with a "football-shaped" piece of wood on the end to pack and distrubute the epoxy all the way around the firewall as best as I can. I dip in denatured alcohol frequently so the epoxy in the fuselage doesn't stick to the tools. It can get rather messy, but do your best for a good fillet that will absolutely, securely lock the firewall down.

[KRProton]

Okay, we're pretty much done with this sometimes messy prodecure...

Double, triple and quadruple check that you have the spinner alignment to the front of the fuselage that you like. On mine, I had to remove the engine a couple more times to minutely shift the mount and tighten the bolts for perfect alignment. But now it's perfect.

When everything is done, you may want to give the fuselage a wipe-down with a larger paper towel square wetted with denatured alcohol to be sure all the finger prints and epoxy smudges are gone. Let the model sit overnight for all the epoxy to fully harden.

[KRProton]

Been out of the work shop the last few days, but today I caught the 2nd of two MFLs I'm building up to the first, so I just got the engine mount epoxied in. This time, I did it slightly differently for the fuel cut cup. Rather than drilling the hole in the firewall first, and then grinding the notch in the engine mount to match, I did it backwards from that and ground the notch in the engine mount first, and then drilled the hole through the firewall for the fuel cut cup to match. The location of the circular notch in the engine mount is defined by the small space between the bottom engine mount mounting bolt and the fuel fitting in the mount. Knowing that, I figured it would be easier and more accurate to match the hole in the firewall to the notch in the engine mount, rather than the other way around. So I ground (grinded?) the notch - actually biased slightly toward the bolt hole. I then fastened the mount to the firewall using the engine and the spinner to position the mount exactly where necessary, and then temporarily tightening mount. I placed the fuel cup into place, upside-down, using it as a guide to mark the center of the hole. I used a long 1/16" drill but to mark the center of the hole, then same as before, I drilled a 1/8" hole to prevent the screw on the end of the 3/8" auger bit from pulling through too quickly.

Here, the engine mount has been securely, but temporarily tightened to the firewall with the ring on the back of the firewall.

I placed the fuel cut cup into place, upside-down, and used an extended 1/16" drill bit to mark the center of the hole.

Without the fuel cut cup in place, I drilled the rest of the way through the firewall. Next, I enlarged the hole with a 1/8" drill bit and carried on the same as the first model.

[KRProton]

Nothing new here. I already showed this on the first installation, but just a couple more pics for interest...

This is the fillet of epoxy reinforced with chopped fiberglass before adding the engine mount.

All done, a perfectly aligned engine and ready to proceed to the next step after the epoxy hardens overnight.

[KRProton]

What do do next? How about mount the horizontal stabilizer (stab):

Clean up and chamfer the ends of the carbon fiber stab tubes with some sandpaper. Here, a Before and After picture, the Before on the top.

I use a #11 blade to debur the aluminum receptacles in both stab halves.

Usually, it seems the stab tubes are provided a smidge too long. Test-fit the stabs together with the tubes. If necessary, trim the tubes so the gap at the rear tube will be 1" or a bit less and the gap at the front tube will be 1-5/16" or a bit less. Re chamfer the ends you may have trimmed.

[KRProton]

There is usually a little "web" in the middle of the holes in the fuselage for the stab tubes. This is just leftover from the molding process. I use a 3/16" drill inserted and twisted by hand to cut away that thin web -- no need to chuck in a drill.

Insert the stab tubes into the fuselage. Mine fit "perfectly tight," but if you feel the tubes are too tight, or take too much force to insert, you can open up the hole lightly with some rolled up sandpaper.


On all the MFLs I've done, the stabs always fit pretty well to the fuselage with a minimal, even gap, but I take a few minutes to make the gap a little better, but not necessarily to perfection -- just a small improvement keeps me happy. NOTE: IF you sand the ends of the stabs too much chasing a perfect fit, you may end up removing too much material and the halves may become too close together not allowing the aluminum elevator joiner to fit properly.

Slide the stabs to the fuselage. First, make sure that, when the stabs are tight to the fuselage, the elevators are not contacting the fuselage causing them to possibly hang up. In this pic, the left elevator is contacting the fuselage.

If necessary, sand the ends of the elevators to create a small gap. The way I do it is to stick a full sheet of 120-grit sandpaper to my workbench and hold the stab at the elevator while I drag it back and forth. This helps keep the end of the elevator square and true.

Replace the stabs to the fusealage and look at the gap. Here, there is a sufficient gap between the elevator and the fuselage, but the front end of the stab is contacting the fuselage creating a gap at the back of the stab. If I sand the stab just a bit -- at the front, this will shrink and even the gap. Don't forget to look at how the stabs fit the top of the fuselage. Afterall, this will be the side we can all see.

[KRProton]

Make sure to take a look at the fit between the stab halves and the fuselage on the top. Continue to make any minute adjustments so the stab halves fit the fuselage nicely. Be sure not to remove too much material.

Once satisfied with the fit of the elevators and the stab halves to the fuselage, lightly sand the edges to remove any paint or fiberglass "fur" on the corners.

Lightly sand both sides of the fuselage where the elevator joiner will pass through. This is so you can mark with a pencil. With the stab halves in place, mark the sides of the fuse where to cut the slots for the aluminum elevator joiner.

[KRProton]

Next, the holes will be cut in the fuselage sides for the elevator joiner. A note here; use care not to cut into the top sufrace of the stab fillets on the fuselage. This won't cause any problems, but cutting into the upward surfaces of the fillets just defeats the neatness of the job and the appearnce of the plane.

I use a 1/16" grout cutter bit at full speed to start the first cut. Initially, it will be a pretty uneven hole, but it can be cleaned up as you go.

Using care not to cut into the top sufrace of the stab fillets, continue to trim the hole until you can get the joiner to pass through both sides.

[KRProton]

Let me pause to describe how I install and connect the elevator pushrod which will come later on. As you can see, there is an indentation molded into the left side of the fuselage where a passage is to be cut to accommodate installation of the elevator joiner with the torque rod bolt and thread-on horn from the side. For a couple reasons, it is my personal preference not to cut this passage. Without the hatch required to conceal the hole, there is a little less work and cutting to do and one less thing to tape on (though, once taped in place, the hatch stays put with the exception of refreshing the tape every now-and-then). Mainly though, I just object to cutting a hole in the fuselage back there for fear of weakening the area. However, probably 99% of the builders out there cut the slot to facilite installation with no problems at all. I just like to keep it cleaner. The down side is that it can be slightly more tedious to connect the torque rod into the joiner when the joiner is already installed in the fuselage, but I feel it is still easier my way (or rather, Craig Korsen's way - apparently, Craig is the oone who came with this idea) than to fit the joiner assembly from the side and then close the clevis. This is just a head's up for the way I will illustrate installation in this buid thread.

Determine which is the front and back of the aluminum elevator joiner. With the screws partially installed, fit the joiner up to the slot in one of the stab halves. In the top photo, you can see that the head of the screw is not parallel with the top of the elevator. This is the wrong way and not how the joiner fits into the elevaotor. As you can see in the bottom photo, the head of the screw is parallel with the top of the elevator and is oriented correctly.

Use a fin-point felt-tip pen to mark an arrow on the top of the joner noting which way is forward.

Flip the joiner over and use a nail or piece of sharpened wire to scratch arrows pointing toward the front of the joiner. Unlike the ink arrow on the top, these arrows will not rub off and will come in handy as you progress through the build.

[KRProton]

Now it's time to perfect the passages you've cut into the sides of the fuselage for the elevator joiner. We need to make sure there will be enough elevator deflection without the joiner interfering with the fuselage...

I have a couple sanding tools including strips of plywood with sandpaper glued to them and a small, square needle file.

Install one of the elevators and tightly hold the joiner in the slot while deflecting the elevator up and down to make sure the elevator has enough deflection. About 1/4" of up elevator and 1/8" down elevator should be more than adequate to be sure the joiner will never interfere with the fuselage and bind the elevator servo.

Use your sanding tools to open up and true the edges of the hole for the elevator joiner as needed. Here, the back of the joiner is contacting the back of the opening, so a little more sanding/filing fixes this intereference.

Perform the same procedure for the other elevator.