Top Flite F8F Bearcat 0.60 size (Red Box Rescue)

[willsonman]

So, to start modifying the cowl, I'm using a piece of cardboard as a guide. I traced the perimiter of the cowl onto the the surface. I used my compass to draw a couple of arcs... basic geometry here. Draw an arc that crosses over the center of the circle. Keeping the compass at the same setting. relocate it to any other place on the circle and draw another arc. The two points that intersect will create a mid line that perfectly intersects the center of the circle.


This creates a reference for me to mark the cowl for lines exactly in the middle on each side.


Using a square, place the edge along the base of the cowl and draw a perpendicular line to create a center line for our wedge that we will cut out.


Measuring the height of the cowl we then draw out a piece of cardboard to reference/ trace the wedge to be cut out.


Then this is transferred to the cowl and we verify that 1/2 inch at the front lip is the maximum amount to be removed.


Next is that somewhat sketchy part. The razor saw is our tool of choice here. As gentle as I tried, there was still cracking of the plastic due to how old and brittle it was. Still, It's a fairly clean cut and can easily be cleaned up with bondo. After the cut is made, I tacked the two halves back together using medium CA. Due to the curvature of the cowl, the halves do not exactly match up but this was known to happen. I could have made the cuts with more meat left on to sand it flat but with how brittle the part is, I did not want to chance more cracking.


The side profile is perfect and we still have good clearance for the mounting ring. From the top view you can see where we need to add a bit of bondo to round out the opening more. Again, this was known. Also note that because of the modification, the trailing edge is no longer flat to seat onto the mounting ring.

One seam was not tacked so that I have room to flatten the trailing edge, set the gap to maintain a good fit to the mounting ring, and allow for any adjustments prior to final glass work.


All that being said, the process was easy but moving forward, after I glass the seams on the inside and work the bondo magic to clean it up, I will likely glass the outside of the entire cowl with epoxy to give it strength. I'm considering using heavy glass with a finish layer on top. A simple finish layer will not provide much strength. This means more weight, which may not be a bad thing but I do not want to have a situation in the future where chips and dings require me to sand off paint to do this process at a later time. Any kind of damaging nose-over at a field means possible loss of pieces or the cowl becoming a crazy jigsaw puzzle to piece back together.

 

[willsonman]

Been a busy week but I managed to take some time last night to mix up some epoxy and lay up the seams of the cowl. Two layers of cloth here.

 

[willsonman]

Glass still felt a bit soft last night. Probably due to the cooler temperatures in the basement. Going to leave it another day to harden up more but it was hard enough to trip excess glass and preliminary sanding. I measured the offset of the angle and I need to trim off 1/8" on both sides to make it flush and even. Given how brittle this thing is, I'll likely mark a line and then use my dremel drum sander to take the bulk off and finish with a sanding block. Cutting with the razor saw seems a bit risky. Then I'll slather on more bondo for final shaping/filling.

 

[willsonman]

I was able to make some messy progress over the weekend. I got some bondo on the cowl and I think it turned out pretty great.

The sides were covered but I also wanted to make sure that the sides were rounded and not pointy. The dark blue that is going to go on this is going to be revealing. I sanded round-wise to make sure this transitions was fairly smooth.


I also added some to the inner lip of the cowl to round it out. I've gotten pretty good at sculpting these airplanes by eye over the years, so I went with my gut. I think it paid off here. Nicely rounded and the opening looks even.


Just to check how well-calibrated my eye is, I put it on my cutting mat to see how off I was... really not bad at all.


So from here you can see in the first picture I still need to grind down the trailing edge. At least the mark was made. That took some time as I wanted to get it right... measure three times and cut once. I also have thought about a plan to get this cowl strong without going bonkers with multiple glass layers. Any way I do it is going to be work and messy work at that. There will be copious sanding and a final top coat... with more sanding. So, doing it the lightest way possible seems to be the order since the bondo had made this cowl quite heavy now. I've got a plan that I think will work. We'll see how well it comes out.

I hope to be able to grind down the trailing edge and do a glass layup to cure out tonight. Stay tuned.

 

[The Hangar]

I was able to make some messy progress over the weekend. I got some bondo on the cowl and I think it turned out pretty great.

The sides were covered but I also wanted to make sure that the sides were rounded and not pointy. The dark blue that is going to go on this is going to be revealing. I sanded round-wise to make sure this transitions was fairly smooth.
View attachment 156662

I also added some to the inner lip of the cowl to round it out. I've gotten pretty good at sculpting these airplanes by eye over the years, so I went with my gut. I think it paid off here. Nicely rounded and the opening looks even.
View attachment 156663

Just to check how well-calibrated my eye is, I put it on my cutting mat to see how off I was... really not bad at all.
View attachment 156664

So from here you can see in the first picture I still need to grind down the trailing edge. At least the mark was made. That took some time as I wanted to get it right... measure three times and cut once. I also have thought about a plan to get this cowl strong without going bonkers with multiple glass layers. Any way I do it is going to be work and messy work at that. There will be copious sanding and a final top coat... with more sanding. So, doing it the lightest way possible seems to be the order since the bondo had made this cowl quite heavy now. I've got a plan that I think will work. We'll see how well it comes out.

I hope to be able to grind down the trailing edge and do a glass layup to cure out tonight. Stay tuned.

Looking good!

 

[willsonman]

Thanks!

While life rolls on, my hobby time gets a bit in flux. As a result, I did not have time to glass the cowl but I did take time to use the sanding drum on my dremel to flatten the trailing edge of the cowl. It's perfect and no further damage incurred. I previously noted, though briefly, that the angle from the modification would require a bit of fit and finish for the mounting ring. In addition to the angle change, there is also the layup of glass on the inside of the cowl that makes things a tight fit. So, I used my dremel to create a slight bevel to the mounting ring and it did help but I think I'll be better off smoothing out the glass layup on the inside. To do this, I really need to have the outside glassed for strength. so that is the next order of business on the cowl.

I took a few minutes to perform some minor surgery to the wing. The fixed landing gear and its mount need to be removed in order to fit retracts and such. I used a razor to cut away pieces of the balsa skin to reveal the entire mount. What I found was a slathering of epoxy that was not cured prior to the balsa sheeting. It was a mess but also of note were metal plates that were supposed to retain the metal into the wood... they were simply epoxied in place with no screws into the wood. Hard to describe as I did not snap a picture but it surely would have resulted in eventual failure. I used my razor saw to cut the sides of the mount where they met the ribs and a few taps of a hammer on the metal gear rod knocked the epoxy free, cracking it, to remove the entire mounting block with the metal rod. Just one side done but I'm confident that I'll be able to be more invasive to make a proper gear mount for the retracts.

 

[Chuppster]

Thanks!

While life rolls on, my hobby time gets a bit in flux. As a result, I did not have time to glass the cowl but I did take time to use the sanding drum on my dremel to flatten the trailing edge of the cowl. It's perfect and no further damage incurred. I previously noted, though briefly, that the angle from the modification would require a bit of fit and finish for the mounting ring. In addition to the angle change, there is also the layup of glass on the inside of the cowl that makes things a tight fit. So, I used my dremel to create a slight bevel to the mounting ring and it did help but I think I'll be better off smoothing out the glass layup on the inside. To do this, I really need to have the outside glassed for strength. so that is the next order of business on the cowl.

I took a few minutes to perform some minor surgery to the wing. The fixed landing gear and its mount need to be removed in order to fit retracts and such. I used a razor to cut away pieces of the balsa skin to reveal the entire mount. What I found was a slathering of epoxy that was not cured prior to the balsa sheeting. It was a mess but also of note were metal plates that were supposed to retain the metal into the wood... they were simply epoxied in place with no screws into the wood. Hard to describe as I did not snap a picture but it surely would have resulted in eventual failure. I used my razor saw to cut the sides of the mount where they met the ribs and a few taps of a hammer on the metal gear rod knocked the epoxy free, cracking it, to remove the entire mounting block with the metal rod. Just one side done but I'm confident that I'll be able to be more invasive to make a proper gear mount for the retracts.

I've found myself doing a lot of cowl work this building season. It feels so strange to spend so much time working on such a small part of the airplane, but the payoff is that it is a very visible and important part of the build process. Your dedication is impressive and I thank you for sharing your techniques with us.

 

[willsonman]

This is true! The front end is really what is key to getting the right look and working with out of production parts is a pain but a necessary evil. Glad you are getting something from all this.

 

[Chuppster]

This is true! The front end is really what is key to getting the right look and working with out of production parts is a pain but a necessary evil. Glad you are getting something from all this.

Fortunately most of my work is closing needle/muffler holes. I do not envy your efforts to reshape the cowl, but I am impressed by your methods.

 

[willsonman]

Yeah, smaller holes are much easier and a simple coat of high fill primer would suffice to completely blend any seams there.

 

[willsonman]

It has been far too long since I've updated this thread. Work and life have been busy so I've had limited time. I've also been doing a few repairs that were needed on other aircraft.

I did manage to glass the outside of the cowl. Heavy 6oz cloth with a .75oz cloth over top.


With the glass cured over a few days I trimmed up the overage and did a bit of light sanding just to get a sense of things. I sanded out the inner lip of the cowl to mate with the mounting ring and the fit is snug but good.


The finish is bumpy and will require some sanding work. I'll likely use a power sander to make quick work of it. There are a few spots that will need some spot putty, which is expected. Overall, I'm happy with the outcome. It is much heavier but I'm more confident that the cowl will not disintegrate just by looking at it.

I need to get more momentum on this project so rather than working out the complicated challenge of the landing gear geometry, I'm going to move onto the Fuselage. The battery hatch needs to be cut and trimmed out so I can make recess cuts for the exhaust. A battery tray needs to be built and some overall shaping needs taken care of. Once I get back into a groove I can move back to the wings and get the gear sorted.

 

[willsonman]

I should also note that I did order and receive the motor for this project. I'm loving the FT monster radials and the shaft is a perfect fit for the 4-blade prop... not to mention the power should be right for this model. It arrived this past weekend so I can really move forward with the fuselage without any excuses.

 

[willsonman]

I've covered how I make my hatches on these type of conversions in the past so I'll not include every detail. In short, I use pins from the inside of the fuselage to mark where the formers are and draw reference lines. I did not want the hatch to interfere with the cowl so the leading edge was moved back from the firewall by 1.5 inches. I noted where the front of the canopy would go and made a reference mark there as well. Using my razor saw, I cut the cross-grain of the fuselage first. This keeps the part I'm cutting away more stable as cutting the lines with the grain first makes the part wobble more as I cut the cross-grain. Some cutting on the inside was also necessary to fully remove the hatch but it was pretty minimal.


Form there, I used a piece of cardboard to trace the outline of the front lip and made two identical formers from light ply that would fit the hatch and the fuselage and butt up against each other. As they were Identical, I clamped them together and drilled two holes for locator dowels (bamboo skewers) so I knew they would line up. I'm using the top balsa stringer as a reference for location so I knew things would line up easily. I put some hardwood behind the former in the hatch and drilled out the holes for the skewers. What I'm left with is two mating surfaces that key into each other.


Since the fuselage is already got the stringers there was just the matter of the aft plate. This will eventually get a magnet to hold the hatch on along with the plate for the hatch. Using the same tracing method, the plate was installed.


The hatch needed the sides reinforced with some scrap balsa sticks. Measure and cut to length with the razor saw. If you look closely at this picture, you can see some of the issues I've been discovering with the original build. Lots of gaps between the skin and the formers. Wood glue was used so the joints are solid but there are clearly areas where an ace bandage would have been beneficial when sheeting. The hatch still needs an aft plate and a magnet. The diagonal cut should allow me to move the hatch sideways to free the magnet closure but I may install a 1/64" ply reinforcement to the top of the hatch to allow me to get my fingernail under to pop off the hatch if needed.


I should note that I used medium and thin CA glues for these parts. I was able to knock all of this out in about an hour. I get that sometimes it makes folks nervous when you are cutting a big gaping hole in a wood fuselage but the key for hatches is to make sure the main structure stays intact for strength, like not cutting through those side stringers.

 

[willsonman]

Former made for the hatch and installed. I also cut away some excess wood that would possibly protrude into the battery area. Magnets installed. Removal is easy with simple side force.


Elevator and rudder servos needed to be installed. I used simple hardwood beams at the aft end of the underside of the wing opening. This would free up the front for other things like the receiver and battery tray. Essentially right under the cockpit area. Using Futaba S3102 servos. digital and metal geared so they have the same approximate torque and speed as full-size S3004 equivalents that the kit would call for. Smaller package and they were on-hand. Ball links make a nice connection with no slop.


The battery tray was made using a plank of light ply. Used a dremel wheel to cut slots for a velcro strap. Some additional beams were needed to screw the tray into. I took my largest battery, a 6S 7000mAh pack, and it easily fits in this area and it is as far forward as possible.


Next up is to cut out recesses for the exhaust vents. This is a nice scale feature that also serves to have moving air in the cowl to cool the motor and ESC. I'll review the plans again to approximate the location. I've also not decided whether I'll draw up a print to do this or just put in some scrap balsa and sand to shape.

 

[willsonman]

Looked at the plans... looked at reference pictures... sighed a little... died a little inside. So the main side stringer would have to be cut for an EXACT location of the exhaust. I was not about to do that. I settled on raising it a little and not sweating that detail too much. I used the TLAR method to figure out how wide to make it as well as how long down the side of the fuselage to make it. Drew on some reference marks and back to the tried and true razor saw. Seriously... if you do not have a razor saw... spend $12 and make your life easy. I cut the front corner at the firewall first and then gently down the sides. I did not remove the entire piece here. I then used a dremel cutoff wheel to mainly cut the firewall. Finished it off with a plain old blade from my hacksaw. With the front part cut loose, I then carefully cut away the balsa at the front lip of the fuselage to retain the balsa sheeting.

With the cuts out of the way, I installed a balsa block to the back of the firewall for the sheeting to glue to. I used warm water to soak the balsa sheeting at the bend. One side did crack a bit but I kind of expected some. Not big deal to sand that out. I added triangle stock on the inside to give added grip to the sheeting and some triangle pieces to fill the voids on the top and bottom of the recess. I then added some small triangle stock, cut from square stock, to the corners. Sanding these down a bit revealed a shape I'm very happy with and only a total time investment of 45 minutes or so, with some CA added to the tips of my fingers.


I had to dry fit the cowl and check the look. It's plenty close enough but my eye still wants it lower. Oh well. Hyper-detail is not the objective here. Getting some lines to complete the look as well as adding some functionality was the driver. I did add some spackle to fill some deeper voids.


With all of the fuselage modifications now completed, I am moving on to shaping. Next up is to shape the tail a bit better and do a minor sand-down to get an overall feel of the finish. I'll put on a coat of sanding sealer. John Morgan dropped me a line suggesting it. His rationale was that in his experience with old balsa, it is so dry that when you hit it with anything wet, the balsa can go wonky and you need to sand and correct that. So, hitting it with an initial coat of sealer will reveal any of those and harden things up a bit. I'll then go over the entire fuselage with spackle and sand it all back. There are gaps where the skin meets the structure and the thin glass finish will reveal those. It's all surface prep now.

 

[wilmracer]

Looking great! Interesting point about the old balsa responding to moisture and pre-sealing to expose issues. I wouldn't have thought about that but honestly it makes sense.

 

[TooJung2Die]

What is a "Top Flite Red Box"? Is there something unique about it other than the box color? I searched.

 

[willsonman]

What is a "Top Flite Red Box"? Is there something unique about it other than the box color? I searched.

It's a fair question. Top Flite would release kits in their standard form in one way or another. The majority of their kits were of a scale subject of some kind. The "Red Box" moniker was indicative of additional scale features or ability to build with additional details. It later evolved to the "Gold Edition" series where higher quality of wood and pre-made detail parts were also provided. Parts like intake vents and such were vacuum formed plastics that previously needed to be made from sculpting balsa. By today's standards, these are expected parts in kits so it makes sense that newer folks in the hobby may scratch their heads on this. The essential take-away is that kits used to be just a box of balsa. The quality of the balsa and die cuts were what differentiated one kit from another and evolved to providing "extras" and provisions for modifications.

I sanded down the fuselage as well as used my 3D printed razor planer to carve down the tail balsa piece. It's a subtle difference but makes the read end look more curved and less like a bulbous poo is coming out the back of the airplane. I used a foam brush to apply a heavy coat of sanding sealer to the entire fuselage and cockpit areas as well as the tail planes. I decided to try letting it cure out without accelerate the drying process with a hairdryer. I was curious about how hard it would dry but I was also not wanting to force the wood to warp over it's natural tendency. I checked on it a few hours later and there seems to be little warping and a light sanding will be all that's needed. Some spackle is still needed but nothing more than what would be normal. The leading edge of the H-stab is pretty banged up so I need to be careful there and make sure it is a clean edge when finished.

 

[willsonman]

Not much done over the weekend but I did get spackle applied in two layers to build up low spots. I also sanded it all back and it's ready for glass.

 

[willsonman]

Work has been kicking.my.butt.

Moving along. I managed to get the V-stab and the hatch glassed using my normal method of .75oz. cloth and Sanding sealer/WBPU. They really are the same thing. I used 100-grit sandpaper to sand the edges of the glass overage on the hatch and the glass just trims right off.


I got my motor mount in the mail so I went ahead and checked the plans for thrust angle. No right thrust as far as I can tell from the plans or instructions. There is some down thrust that required me to raise the mounting point of the motor at the firewall by 4mm. I drew a reference line above the center line on the firewall and marked the vertical center. The Great Planes medium brushless motor mount comes with a template for drilling. The top holes were fine but the bottom ones were going to interfere with the stock mounting beams. Thankfully there are additional holes on the mount further down so those holes were utilized. I used blind nuts (also called t-nuts) behind the firewall with 3 washers between the firewall and the mount, only at the top. These washers create the down thrust angle that is called for. I also mounted the cowl ring with a corresponding spacer I had on-hand.
View attachment

And then I put on the cowl just to check the look.


The head-on shot above you can see marks made on the mount for the motor. These are for the bolts on the back of the motor to bolt on the motor. They will be drilled and cleaned to make sure there are no metal shavings to get into the motor. Once the motor is on I can then adjust the mount to get the proper distance from the firewall to the prop mount.