Chuppster
Well-known member
Are you comfortable with half of your mounting bolts only being half-attached to your motor mount? I'm assuming you're going to direct mount the motor and not X-mount it correct?
Top Flite F8F Bearcat 0.60 size (Red Box Rescue)
- Thread starter willsonman
- Start date
Are you comfortable with half of your mounting bolts only being half-attached to your motor mount? I'm assuming you're going to direct mount the motor and not X-mount it correct?
Correct. Yes, I am comfortable... I'll be using washers on the back side to have a bit more even clamping pressure. While not entirely ideal, short of welding additional material on there, there is not much of an option. That and I've done this before. 
Correct. Yes, I am comfortable... I'll be using washers on the back side to have a bit more even clamping pressure. While not entirely ideal, short of welding additional material on there, there is not much of an option. That and I've done this before.
I agree that you should be fine. IF you were worried and wanted to go a touch overboard you could make a thin aluminum plate slightly oversized top and bottom, cut out the holes to match the recesses in the mount, and then place it behind the mount when you bolt everything up.
That being said, I think it will be just fine. Just give the motor/prop a wiggle after the maiden and again after the first few flights to make sure everything is still snug. Toss some threadlocker on there too.
So, let me go into some detail on this.
I started by drilling out the main holes and countersinking the holes for a tighter grip and increase usable thread count on the motor. I then used a dremel with a cutoff wheel to remove material and then a grinder to fully round things out. THe motor was mounted to the main holes with stock bolts that come with the motor. For the outer ones, I used bolts with the same thread but I use a lock washer and washer to keep things tight. I'm very confident that this will hold very well.
Moving on from there, I installed this part of the mount to the part on the firewall already. The bolts were only hand tight so that I could adjust the depth of the motor in the cowl. The cowl was installed and the prop installed and the depth was set. The prop and cowl were removed and the bolts were tightened.
It really looks the part with the prop and cowl on. I took my ESC and cut a couple holes in the firewall with a tapered drill bit. This allows some air to pass through the firewall to cool the battery area but also allow wires from the ESC to pass through. The ESC was mounted to the firewall with 3M automotive double-sided tape. This stuff is super strong and the location should provide ample cooling for the ESC.
So next up, I really need to fully commit to get the glass work done on the fuselage. It takes some time commitment so I need to just schedule it and get it done.
I started by drilling out the main holes and countersinking the holes for a tighter grip and increase usable thread count on the motor. I then used a dremel with a cutoff wheel to remove material and then a grinder to fully round things out. THe motor was mounted to the main holes with stock bolts that come with the motor. For the outer ones, I used bolts with the same thread but I use a lock washer and washer to keep things tight. I'm very confident that this will hold very well.
Moving on from there, I installed this part of the mount to the part on the firewall already. The bolts were only hand tight so that I could adjust the depth of the motor in the cowl. The cowl was installed and the prop installed and the depth was set. The prop and cowl were removed and the bolts were tightened.
It really looks the part with the prop and cowl on. I took my ESC and cut a couple holes in the firewall with a tapered drill bit. This allows some air to pass through the firewall to cool the battery area but also allow wires from the ESC to pass through. The ESC was mounted to the firewall with 3M automotive double-sided tape. This stuff is super strong and the location should provide ample cooling for the ESC.
So next up, I really need to fully commit to get the glass work done on the fuselage. It takes some time commitment so I need to just schedule it and get it done.
Unfortunately there has been zero progress as of late. I'm involved in a youth program through my church teaching boys 8-11 years old and I've been 3D printing a trebuchet and catapults for our time last night. Good fun and a good discussion of some basic laws of physics and how they relate to spiritual things.
Moving along, I STILL need to glass the dumb fuselage. I just need to hunker down and do it. Once it is on I can slather on a few coats of sanding sealer to build up the finish.
I've got a fresh set of retracts arriving today. I've mentioned in the past how dreadful my home field is and it REALLY takes a toll on landing gear, especially retracts. I ordered the beefiest and cheapest set I could find that could work with this model. Again, I'm not going full out scale here. Just something that will work. The sets I currently have would likely work but they are just too small and I want to do the retracts ONCE and once only. I'm going to rob the stock oleos from the Hangar 9 P-47. They are meant for a 14-pound airplane and I'm thinking this one will be 9 at worst. The retracts I've ordered state that they are good to over 20 pounds. Given that the case is not metal I highly doubt that but the metal trunion is the critical point. It should hold well. I'll drill out those puny grub screws for a much larger one. The small ones have a VERY bad tendency to strip out the moment you look at them. It is totally worth the modification to make sure the strut/oleo does not twist. There is also a lot of mounting area to help spread the load out so I can incorporate that into the wings. Can you tell I'm becoming weary of retracts?
Moving along, I STILL need to glass the dumb fuselage. I just need to hunker down and do it. Once it is on I can slather on a few coats of sanding sealer to build up the finish.
I've got a fresh set of retracts arriving today. I've mentioned in the past how dreadful my home field is and it REALLY takes a toll on landing gear, especially retracts. I ordered the beefiest and cheapest set I could find that could work with this model. Again, I'm not going full out scale here. Just something that will work. The sets I currently have would likely work but they are just too small and I want to do the retracts ONCE and once only. I'm going to rob the stock oleos from the Hangar 9 P-47. They are meant for a 14-pound airplane and I'm thinking this one will be 9 at worst. The retracts I've ordered state that they are good to over 20 pounds. Given that the case is not metal I highly doubt that but the metal trunion is the critical point. It should hold well. I'll drill out those puny grub screws for a much larger one. The small ones have a VERY bad tendency to strip out the moment you look at them. It is totally worth the modification to make sure the strut/oleo does not twist. There is also a lot of mounting area to help spread the load out so I can incorporate that into the wings. Can you tell I'm becoming weary of retracts?
I've made some progress. Actually great progress.
I received the retracts as previously mentioned and I took a look at them to check the fit to the oleos I had from the P-47. A dead perfect fit. My NiMh battery for my servo tester was a little saggy but the retracts still had plenty of torque to pull the gear up and down. Pretty happy with these other than the "aluminum" trunion looks like it was cast from cheap pot aluminum. You get what you pay for. We'll see how they hold up. The other nice thing is that there are not one but THREE grub screws to hold the oleo on. A bit overkill but at this point I'm looking for overkill in my life. They are also slightly larger than the usual grub screws on HK landing gear. I have to say, I think the placement in the wing is good and I think they may actually hold up.
Moving right along, I got the fuselage fully glassed out. Not only that, but I completed two additional coats of SS so it is ready to be sanded down. Per usual form, the empennage is a mess and needs some smoothing but everything else is looking pretty good. I'm not sure why I psyche myself out on this. It's stupid easy, not stinky or messy, and for some reason after I've not done it for a while I tend to procrastinate it. Builder's block?
Anyway, last picture, I swear. My wife walked down to the basement with a new shirt for me. I was totally shocked when it had my logo on it too! We think it's ok but it would be better if the logo were lower on the shirt, or just eliminate my name and make the graphic bigger. Several friends have expressed wanting one now that I've posted this picture to other social media platforms. At any rate, it was GREAT to get back into the shop and get some work done.
I received the retracts as previously mentioned and I took a look at them to check the fit to the oleos I had from the P-47. A dead perfect fit. My NiMh battery for my servo tester was a little saggy but the retracts still had plenty of torque to pull the gear up and down. Pretty happy with these other than the "aluminum" trunion looks like it was cast from cheap pot aluminum. You get what you pay for. We'll see how they hold up. The other nice thing is that there are not one but THREE grub screws to hold the oleo on. A bit overkill but at this point I'm looking for overkill in my life. They are also slightly larger than the usual grub screws on HK landing gear. I have to say, I think the placement in the wing is good and I think they may actually hold up.
Moving right along, I got the fuselage fully glassed out. Not only that, but I completed two additional coats of SS so it is ready to be sanded down. Per usual form, the empennage is a mess and needs some smoothing but everything else is looking pretty good. I'm not sure why I psyche myself out on this. It's stupid easy, not stinky or messy, and for some reason after I've not done it for a while I tend to procrastinate it. Builder's block?
Anyway, last picture, I swear. My wife walked down to the basement with a new shirt for me. I was totally shocked when it had my logo on it too! We think it's ok but it would be better if the logo were lower on the shirt, or just eliminate my name and make the graphic bigger. Several friends have expressed wanting one now that I've posted this picture to other social media platforms. At any rate, it was GREAT to get back into the shop and get some work done.
Chuppster
Well-known member
Assuming "SS" stands for Sanding Sealer, what's the difference between Sanding Sealer and Epoxy Resin?
You are correct. So, if you look up the MSDS for sanding sealer and water-based polyurethane (WBPU) they are essentially the same thing only WBPU is more dilute with water. The more concentrated formula of SS allows for a bit faster drying (less water to evaporate) and fills the weave of the cloth with fewer coats.
The main difference between epoxy and SS in this particular application is work. The epoxy is going to dry harder and that makes it a tad more dig resistant but not by much. Since its harder, it will take more effort to sand out imperfections. Then after sanding you have to do a final smoothing coat. All of this is true with SS but since it is softer, it's easier to sand. It also dries much faster on it's own and you can accelerate that with a hair dryer or heat gun. All we are trying to do with this is make a smooth base for final paint. No structure here as part of the glass work. The SS is a bit lighter too but since we are talking about such a thin layer, it does not amount to much. With SS, cleanup is easy and you can rinse and re-use your brush, and there are no really bad smells to speak of. I really do prefer it for these types of surface finishes.
On foam models you really want the epoxy finish as you really need the hardness and some added strength. The drawback is that when it sits in the sun, the foam will heat up and de-gas making bubbles under the fiberglass. To alleviate that you can skin the surface with balsa, but sort of defeats the purpose.
The main difference between epoxy and SS in this particular application is work. The epoxy is going to dry harder and that makes it a tad more dig resistant but not by much. Since its harder, it will take more effort to sand out imperfections. Then after sanding you have to do a final smoothing coat. All of this is true with SS but since it is softer, it's easier to sand. It also dries much faster on it's own and you can accelerate that with a hair dryer or heat gun. All we are trying to do with this is make a smooth base for final paint. No structure here as part of the glass work. The SS is a bit lighter too but since we are talking about such a thin layer, it does not amount to much. With SS, cleanup is easy and you can rinse and re-use your brush, and there are no really bad smells to speak of. I really do prefer it for these types of surface finishes.
On foam models you really want the epoxy finish as you really need the hardness and some added strength. The drawback is that when it sits in the sun, the foam will heat up and de-gas making bubbles under the fiberglass. To alleviate that you can skin the surface with balsa, but sort of defeats the purpose.
Chuppster
Well-known member
I'm assuming SS/WBPU over epoxied glass would be a recipe for a mess?
Not really. You'd for sure want to rough up the surface of the epoxy first. That will add surface area for better adhesion of the SS. A big fat forinstance in my current project... some of the glass around the firewall got adhered to the smooth epoxied finish on the front of the firewall. It took a bit of effort to remove it from the epoxy even though I was using 880-grit paper to trim the glass overage.
I guess I should have mentioned that for those who may not have followed my technique on this before. When I remove the cloth overage there is a bit of SS dried up over the edge of the surface. I run a low-grit sandpaper across the edge and it cuts right through the fabric. It's far easier of a method and safer too compared to using a razor blade. It also prevents you from cutting into the surface if the razor is at the wrong angle. YMMV but this is my approach and it works well. Any fuzzies from the edge of the cloth soak up more SS in subsequent layers of SS application.
I managed to sand down the fuselage yesterday. Took work but it wasn’t terrible. I grabbed the hatch as a test piece for some paint. I’m pretty happy with the finish but even happier with the color.
Chuppster
Well-known member
@willsonman please feel free to call me out if I'm inappropriately moving your build thread off topic, but I have semi-relevant question that I'd like to get your insight on. When doing an electric conversion, it seems to me like it's a challenge to get the weight far enough into the nose to be effective. Electric engines are much lighter than their similar-power glow/gas counterparts and batteries are a lot more dense than fuel. This can lead to a lot of weight (batteries) over the CG when you need it up by the motor (in front of the firewall on old designs). Most old designs leave plenty of room between the firewall and propeller for an IC engine, as can be clearly seen in your setup. Many modelers, myself included, very much do not like stacking lead on the firewall and would prefer to have the batteries further forward. How do you choose if a model is suitable for an electric conversion? Have you ever considered moving the firewall forward to accommodate batteries further forward of the CG?
Last edited:
Really an excellent question here. My approach has always been that ANY, and I mean ANY, model can be converted to electric. I've never made a selection of which one to do or not. I've just done it. I'm with you on not wanting to add lead in the nose if you don't have to. However, there are some constraints around those decisions that I've come to accept and somewhat ignore. The reality is that a CG is a CG. It does not care where the mass is, it just will not change. Any other decision then becomes peripheral. So, If you want your batteries as far forward as possible, you need to modify how your motor may mount or how much scale fidelity you may want to keep. I could have built up a proper motor box for the Bearcat and give myself those extra two inches to shift the mass forward. But that that takes a lot of work and adds more mass than the aluminum motor mount I put on there. On top of that, I have the cowl, which has two layers of glass on the inside and outside. It's heavy. Also, it's a radial engine model. If I end up needing additional mass in the nose, I can 3D print a nicely detailed radial to put up there. While it's not "mechanically functional" I see this as scale functional weight. It's fine if you disagree.
Years ago, I converted a Top Flite AT-6 Texan to electric and it needed 8oz of lead in the cowl to balance out. That is a LOT of lead on an electric airplane but later when I added a 3D printed radial, I was able to drop some of that weight and it looked MUCH better for it.
One final thought on this. Battery weight is still weight. If you add more battery you are still trying to fly more weight. Try to make that weight as efficient as possible. Sometimes it's better to keep your batteries exactly on the CG and add 4 oz. of lead in the tip of the nose. If you were to engineer a more open space to slide the betteries more forward to balance the airplane, you'd be adding at least that 4oz. in building material just to support the batteries in a new location. Give ant take. Balance it out. Keep it simple. And a math lesson: this will likely be a 9-pound airplane. If I end up adding a 1/4 pound to the nose, that means that 2.7% of the mass of the entire airplane will be dead weight. You will likely see at least a loss of 2.7% of performance from your motor by not using copper wires. Does that make you use ONLY copper wires for your electronics? Food for thought if you are pinching the efficiency numbers.
Summary video. I was having serious audio issues that I'm trying to get resolved so I've kept things short.
Chuppster
Well-known member
I appreciate you giving your thoughts on the subject. This has left me wondering if you have simply chosen airplanes that have a natural affinity to being converted to electric. I've made 2 attempts thus far, and I believe I've had a less successful experience than you. My first attempt was a .40 size Edge 540. I put a ".60 size" electric motor in the nose and placed a 2200 6s in the bay for the fuel tank. I then had to add around 10oz to motor mount in an attempt to balance it. The airplane still flew tail heavy. It was easy to hover and do various 3d maneuvers (because it had tons of power and it was tail heavy) but landing was stressful for both me and the aluminum landing gear. This winter I pulled the electric motor and put a Saito .62 in it, giving me a balanced airframe that weighs 10% - 15% less than before. A warbird with re-enforced landing gear might not mind that kind of weight gain, but I have a feeling this Edge will fly a lot better without having to tow those batteries around.
My other conversion has been of a 40" fokker D7. This model had required even more extreme nose weight and at this point I'm only continuing to fly/refine it because of curiosity. Right now I have 3 oz of lead in the nose and it's just starting to balance. I cut balsa out of the tail to try and compensate for the tail-heavy airframe. When I got it it had a .15 glow engine and it balanced but didn't have the power to take off. The last time I flew it I got in a snap spin unintentionally because of how tail heavy it was and ended up rebuilding the nose. This airplane was designed to have a low wing loading but I'd imagine it currently weighs about 20% more than it should.
The point I'm trying to make is that I while I believe any model can be converted to electric, I am inclined to think that some models are vastly more suited for the conversion than others. I hope that people reading your threads are inspired to do electric conversions themselves. However, I am weary that you are making it "look too easy*" because (I would argue) the models you have been adopting are more suited for conversion than, say, an WW1 biplane that had a 4lb Zenoah in it. I for one would be discouraged if I picked up a beautiful ol' glow model at a swap meet, bought all the electronics, installed them, then added 2lbs of lead in the nose only to find the model had such a high wing loading that it was stressful to fly.
*The conversion, not the detailing. While you make detailing look easy it still looks hard, but the final result is beautiful.
This is not meant as a criticism of anyone or anything like that! I'm just trying to share my experiences and open the conversation to help us educate one another and grow together in the hobby.
For sure, short nose-coupled airplanes like the DVII will be more challenging. I recall my O-1 Tummelisa needed a 4000mAh 3S pack along with 6-8oz. of lead to balance and this also is true of my SE5a. It needed a very good helping of lead shot in the nose to balance out. They flew great but like all WWI era models, take-off and landing are not quite as straightforward as we would like.
My experiences with these conversions has been good because generally the gas/glow models are overbuilt by a large margin. Your Edge though... In my experience as an observer of active IMAC pilots in my club has led me to believe that ANY aerobatic airplane has one major flaw... the landing gear. Even my MXS-R70 that is intended for electric has had over 6 landing gear failures and some were of the lightest landings possible. It's just a part of life with those airplanes.
I'm not trying to justify here but perhaps you are right in that I've just gotten "lucky" so far in my conversions.
My experiences with these conversions has been good because generally the gas/glow models are overbuilt by a large margin. Your Edge though... In my experience as an observer of active IMAC pilots in my club has led me to believe that ANY aerobatic airplane has one major flaw... the landing gear. Even my MXS-R70 that is intended for electric has had over 6 landing gear failures and some were of the lightest landings possible. It's just a part of life with those airplanes.
I'm not trying to justify here but perhaps you are right in that I've just gotten "lucky" so far in my conversions.
Chuppster
Well-known member
I had prepped the fuselage for primer on Sunday so with 70+ degree weather outside I took full advantage of it and shot primer while I worked on the wing.
Using CAD (Cardboard Aided Design) I made templates for the W6 and W5 ribs at the leading edge. These templates will key into the spar for the wing. This a bit crucial to ensure strength. I'll use hardwood as mounting beams for the retract units themselves. With the top and bottom of the airfoil profile matched, I cut in slots for the beams and then cut into the W5 template to make clearance for the retract unit. I traced the template onto W5 itself to use my dremel to remove material and check fitment.
With this planning out of the way, I'll cut the templates out of aircraft ply (not light ply). I'll epoxy these plates along with the beams. What I still need to resolve is whether or not I can make clearance inside the wing for the wheels to sit deeper. The issue is that the retracts operate at 90 degrees. There is obviously a few degrees of dihedral so I need to angle the retract a bit more so that when the gear is down, the struts will not be splayed outward. I've encountered this issue before but did not have room to properly set the angle due to the thickness of the wing being the same as the thickness of the wheel. What I'm thrilled about is that I was able to position the retract at the leading edge of the wing in such a way that the mounting point rakes the landing gear forward. Forward rake is always something I try to achieve if I can. It just makes landing so much easier on tail draggers.
Using CAD (Cardboard Aided Design) I made templates for the W6 and W5 ribs at the leading edge. These templates will key into the spar for the wing. This a bit crucial to ensure strength. I'll use hardwood as mounting beams for the retract units themselves. With the top and bottom of the airfoil profile matched, I cut in slots for the beams and then cut into the W5 template to make clearance for the retract unit. I traced the template onto W5 itself to use my dremel to remove material and check fitment.
With this planning out of the way, I'll cut the templates out of aircraft ply (not light ply). I'll epoxy these plates along with the beams. What I still need to resolve is whether or not I can make clearance inside the wing for the wheels to sit deeper. The issue is that the retracts operate at 90 degrees. There is obviously a few degrees of dihedral so I need to angle the retract a bit more so that when the gear is down, the struts will not be splayed outward. I've encountered this issue before but did not have room to properly set the angle due to the thickness of the wing being the same as the thickness of the wheel. What I'm thrilled about is that I was able to position the retract at the leading edge of the wing in such a way that the mounting point rakes the landing gear forward. Forward rake is always something I try to achieve if I can. It just makes landing so much easier on tail draggers.
Chuppster
Well-known member
Watching closely, I'll need to do this on my P40 if I ever get to it.
While no glue has been used, we have some major progress.
First up was to trace and cut out the ply plates and dry fit them.
With those dry fitted, I was able to put the retract into a vague position and take some measurements. I found that if I dropped the beam mount on the inboard plate by 3mm, I could get the struts to be more or less at the right angle at the extended position and also have the wheels properly tuck into and clear the top skin in the retracted position. I also verified the amount of forward rake in the extended position.
With wheels on I made an oversized circle for cutting out a hole for the wheels. The wheels are 3" in diameter and I went with 3.5" to make sure I've got good clearance. Learned that lesson on the Bugatti. 1/8" clearance is not enough so I went with 1/4".
Now more cutting. The above picture shows how I'm missing quite a bit of material at the trailing area of the landing gear so I just opted to remove the entire area and re-skin it.
Now, before I glue in anything, I need to prep the other side in the same way and make sure both sides are symmetrical. Therefore, more surgery is on the to-do list so we can properly prep for building out the retracts.
First up was to trace and cut out the ply plates and dry fit them.
With those dry fitted, I was able to put the retract into a vague position and take some measurements. I found that if I dropped the beam mount on the inboard plate by 3mm, I could get the struts to be more or less at the right angle at the extended position and also have the wheels properly tuck into and clear the top skin in the retracted position. I also verified the amount of forward rake in the extended position.
With wheels on I made an oversized circle for cutting out a hole for the wheels. The wheels are 3" in diameter and I went with 3.5" to make sure I've got good clearance. Learned that lesson on the Bugatti. 1/8" clearance is not enough so I went with 1/4".
Now more cutting. The above picture shows how I'm missing quite a bit of material at the trailing area of the landing gear so I just opted to remove the entire area and re-skin it.
Now, before I glue in anything, I need to prep the other side in the same way and make sure both sides are symmetrical. Therefore, more surgery is on the to-do list so we can properly prep for building out the retracts.
