Horseman3381
Well-known member
Ever since I first learned of the B-36 I have been enamored with the shear concept of it. So naturally, when I got into building and flying RC airplanes it was at the top of my list of planes to design and build.
For those not familiar with the B-36 "Peacemaker”, it was a strategic bomber built by Convair and operated by the USAF from 1949 to 1959. The B-36 is the largest mass-produced piston-engine aircraft ever built and has the longest wingspan of any combat aircraft ever built at 230 ft. It was powered by 6 Radial engines & 4 turbojet engines. The B-36 was the first bomber capable of delivering any nuclear weapons in the U.S. arsenal without aircraft modifications. With a range of 10,000 mi and a maximum payload of 87,200 lb, the B-36 was capable of intercontinental flight without refueling.
Entering service in 1948, the B-36 was the primary nuclear weapons delivery vehicle of the Strategic Air Command (SAC) until it was replaced by the jet-powered Boeing B-52 Stratofortress beginning in 1955.
My current B-36 is version #3 in my line of scratch built B-36’s since I got into the hobby in 2016. The first plane was a 5’-9” wingspan profile version using 6 quad motors. I was able to get 40 or so flights out of this version in the fall of 2016. However, when I built the plane it only had a singe 1/8” dia. Carbon fiber rod in the wings that ended just before the ailerons. This meant that when the plane flew the wind tips bowed up several inches making the ailerons ineffective and the plane flew with using mostly rudder. Eventually late in the fall during a flight the left wing finally had enough and the tip broke off midflight at the end of the carbon fiber spar.
That Winter I built version #2 which was almost identical to version #1 except this version had 24’ of 5mmx1mm carbon fiber strips in the wings and fuselage (I may have over done it a bit). This version flew much better as the ailerons actually worked. However, when I brought it to Flite Fest 2017 on the first flight there a Mini Mustang mistook me as an enemy bomber and kamikaze style took the front of the plane off.
After version #2 went down I decided to update the design to address the two questions I got every time I flew the profile versions. “Where are the Jets?” and “Where are the Bombs?”.
Specifications:
When I designed this version of the plane it needed to:
With the criteria set for version #3 I started the design using the partial plans below as a template. I brought them into AutoCAD 2017 and scaled them to the biggest wingspan/fuselage length that would fit in my car.
After setting what the size of the plane would be I determined that it would accommodate 5” or 6” props and if I were going to do things perfectly to scale, 16mm EDFs. I decided to use Flite Test A pack motors with 5x3 3-blade props to match the 3 bladed prop the real plane used. When looking for EDF’s the smallest I could find were 28mm. I decided having non scale EDF’s was more important than not having them at all and moved forward with the 28mm units. With the number of servos in the plane I needed to use a BEC to power them. I discovered while testing the plane a single 6V BEC does not have the capacity to power all 15 servos and added a second BEC to power the bomb bay servos independent of the control surfaces. Now with the overall scale of the plane and power plants selected I could push through with the design.
Before you ask; unfortunately I do not have any build photos. When I was building this I had no intention of doing any sort of build log so did not think to take any.
Also, to save time and multiple confusing paragraphs on how the plane is wired see the wiring diagram below:
The fuselage of the plane is designed around a box spar that tapers towards the tail and is fitted with formers for the skin. I knew the batteries would have to be pretty far forward so I made provisions for a forward battery hatch. However, to make wiring easier I added a second hatch just behind the wings to house the receiver and elevator servo.
The fuselage spar is sized so that the bomb bay door hinge is where the lower face of the spar meets the sheeting. There are triple foam formers at the end of each bay to add rigidity as the bottom of the spar is removed in this region.
I wanted the bomb bay doors to be bi-fold like on the actual bomber. Figuring out the geometry and how to make it happen wasn’t too hard, it just took a few hours of playing around in CAD. However, installing them and getting what I had laid out on paper to work ended up taking over half the time spent building the plane. The doors are operated using a guide wire that connects to the end of the doors and keeps them from swinging out, instead allowing them to “slide open”. I had initially thought I could build the doors out of foam using small formers to keep their shape, however this proved futile and I ended up 3D printing them. The 3D printed doors had issues and I had to print 4 versions of the doors before they printed cleanly and fit close enough for me to be happy with them.
To power the doors there are 2 servos per door one at each end. To open the doors I used a control horn at the hinge point (In retrospect, I wish I had used a single servo per door as the I was not able to get all the servos to align perfectly causing the servos to hum constantly). The doors are all wired to the same channel. Initially I did this by y-harnessing them all together. The problem with this is that when it was done the bomb bays were filled with wires. Fortunately, when I went to hobby king to order more y-harnesses and I found servo splitters that I could use instead. This made the wiring a lot simpler. The bomb bay doors are programmed to take 2 seconds to open not only for scale appearance, but also to decrease the strain on them when opening and closing.
The nose landing gear is not retractable and steerable using a 9g servo. It was constructed as shown in the diagram below.
The horizontal stabilizers are built using a double layer of foamboard with 1 BBQ skewer for reinforcement. The elevators are not connected from one side to the other. To control them there is a single servo offset from the center of the fuselage so that the hole on the servo horn is in the center of the fuselage. Because of the distance between the elevators and the elevator servo the wires run through brass tube inside the fuselage to keep them from flexing.
The vertical stabilizer is also a double piece of foam reinforced with reinforced with BBQ Skewers. For the rudder servo, I cut a hole large enough for a 9g servo in the forward part of the stabilizer.
The rear access hatch for the receiver and elevator servo is simply done by cutting 3 sides after the skin was applied, and cutting through the foam but not the paper backer on the 4th side to make a hinge. There are backers on the front and back of the opening and a backer on the side of the hatch so it will stay closed during flight. Inside the hatch I added a barrier piece of foam so the wires going to the received wouldn’t get tangled in the elevator servo. When making the front access hatch I did the same as the rear hatch except I made the part that holds the hatch closed more complicated than it needed to be. I also found that when the plane was completed it was too tail heavy. To balance the plane I ended up having to modify the front compartment to hold two 3s 2200 batteries in lieu of the originally planned single 3S battery. I also had to slide them further forward than originally planned.
For the wings, I used the “FT Kraken” plans as a template and adjusted them to match the size & shape of the B36. I used FT mini motor mounts as firewalls. I thought about using mini power pods in the design, however that would have caused the nacelles to be much larger, and like the cowling of the “FT Mini Corsair”, the nacelle covers would have prevented them from being removable. The ESC’s for the motors are located on the bottom of the wing inside the lower nacelle cover to allow airflow over them.
The EDF’s are 28mm units from the UMX A-10. I used servo plugs to wire the motor to the 6A esc’s. The pods for the EDF units are a single layer foamboard cylinder that tapers in on the back. The pods are glued to a double layer foam board strut reinforced with BBQ skewers that run into the wing. The ESC’s for the EDF’s are located under the wing in the outer most nacelle. Wiring the wing was the second most complicated part of the build as there are a lot of wires to run in a small space, and all the wiring and test running of the motors had to be done prior to gluing the top-back portion of the wing down.
Due to the 6 channel limit I had imposed on the build I was unable to include flaps (not that there was room for the servos and wires in the wings anyway). This also meant that the plane would have fixed landing gear. To anchor the gear into the wing I bent a C shape into the wire to fit inside the wing. I then cut out a matching pattern into a rectangular piece of foam, and put one more piece on top of that to hold it into place. This is glued this down behind the spar with the gear wire exiting the wing just inside of the inner most nacelles.
The first two profile planes I called B36-A’s because like the real plane they did not have jet engines and had single wheel rear landing gear. As I was adding jets to this version I decided I needed to upgrade the landing gear to a 4-wheel bogie style as well. Each bogie consists of four 1 ½” wheels. The wheels are attached to each end of a short section of aluminum C-channel. The channel has a hole drilled slightly off center towards the front to attach it to the gear strut wire. By adding a rubber band to the front of the gear this allowed the gear to rotate, but keeps the front wheels up in flight to allow for smoother landings.
As the B-36 was designed strictly as a nuclear bomber and never carried standard ordnance, I decided it would carry 2 large droppable bombs. For the bombs I found some small “Nerf Vortex” balls with the whistles in them. I glued FT servo horns on them to attach them to the bomb drop mechanism, then painted them green with yellow accents.
The bomb releases use 9g servos. I attached wires to each servo horn and ran a wire through a guide (brass tube for rear, piece of servo horn for front). The wires then spanned a gap where they would pass through the servo horn on the bombs before embedding into a piece of foam to keep the bomb in place prior to being dropped. The servos are set up so that the wires are different lengths and assigned to a 3-position switch so that I can drop them one at a time. (See the photos above)
I added the Cockpit Canopy and Radar Dome which are built out of foam board. The 4 observation domes are half’s of ¾” diameter foam balls. I gave the balls a coating of hot glue before attaching them to the fuselage.
When the plane was substantially complete I covered the edges and seams with paper surgical tape, then the only thing left was to add was paint. I decided to paint the plane in the livery of "The City of Fort Worth" which was the final B-36J built and is located at the Pima Air & Space Museum in Tucson, AZ. I started with a coating of Rust-Oleum white primer. After taping off the areas that were to be white I applied the aluminum paint. The black, red and blue paint are Testors. I used thin painters tape to mask off and applied these with a brush.
The plane, like the real B-36, takes a little while to get off the ground. But once it is in the air handles well. It fly’s best at 3/4 to full throttle and will get 6 min flight time with 40% battery left on the 3S and 60% on the 2S. With the 6 props tuning and 4 EDF’s burning (figuratively) this sounds amazing in the air. It has a relatively high stall speed which makes landing under power necessary, and makes me wish I had figured out a way to install flaps (or at least thicker landing gear wire). The best part about version #3 of this plane is that when I am asked where the Jets and Bombs are, now I can answer.
The plans are attached. They are laid out on 22"x34" paper with the components in a 20"x30" area. Plans do not include a few of the accessories like the cockpit and radar dome as I winged these. I tried to adjust the plans for build modifications I made, but I'm sure I forgot at least one of them. I also uploaded the .stl files for the doors. The file is for one set of doors and will need to be printed twice.
For those not familiar with the B-36 "Peacemaker”, it was a strategic bomber built by Convair and operated by the USAF from 1949 to 1959. The B-36 is the largest mass-produced piston-engine aircraft ever built and has the longest wingspan of any combat aircraft ever built at 230 ft. It was powered by 6 Radial engines & 4 turbojet engines. The B-36 was the first bomber capable of delivering any nuclear weapons in the U.S. arsenal without aircraft modifications. With a range of 10,000 mi and a maximum payload of 87,200 lb, the B-36 was capable of intercontinental flight without refueling.
Entering service in 1948, the B-36 was the primary nuclear weapons delivery vehicle of the Strategic Air Command (SAC) until it was replaced by the jet-powered Boeing B-52 Stratofortress beginning in 1955.
My current B-36 is version #3 in my line of scratch built B-36’s since I got into the hobby in 2016. The first plane was a 5’-9” wingspan profile version using 6 quad motors. I was able to get 40 or so flights out of this version in the fall of 2016. However, when I built the plane it only had a singe 1/8” dia. Carbon fiber rod in the wings that ended just before the ailerons. This meant that when the plane flew the wind tips bowed up several inches making the ailerons ineffective and the plane flew with using mostly rudder. Eventually late in the fall during a flight the left wing finally had enough and the tip broke off midflight at the end of the carbon fiber spar.
That Winter I built version #2 which was almost identical to version #1 except this version had 24’ of 5mmx1mm carbon fiber strips in the wings and fuselage (I may have over done it a bit). This version flew much better as the ailerons actually worked. However, when I brought it to Flite Fest 2017 on the first flight there a Mini Mustang mistook me as an enemy bomber and kamikaze style took the front of the plane off.
After version #2 went down I decided to update the design to address the two questions I got every time I flew the profile versions. “Where are the Jets?” and “Where are the Bombs?”.
Specifications:
- Wingspan – 6’-4”
- Motor – (6) Emaxx MT1806 (A pack motor) & (4) E-flite 28mm EDF’s
- Prop – 5x3 3-blade
- Battery – (2) 3s, 2200mah & (1) 2s 2200mah
- Servos – (15) 9g servos – (2) Aleron, (1) Elevator, (1) Rudder, (1) Front Gear, (2) Bomb Drop and (8) bomb bay door
- 11 sheets of foam board
When I designed this version of the plane it needed to:
- Fit in the back of my car without being disassembled.
- Operate off a 6-channel radio (I only had a DX6 at the time)
- Have functional Bomb Bays and functional EDF Jets.
With the criteria set for version #3 I started the design using the partial plans below as a template. I brought them into AutoCAD 2017 and scaled them to the biggest wingspan/fuselage length that would fit in my car.
After setting what the size of the plane would be I determined that it would accommodate 5” or 6” props and if I were going to do things perfectly to scale, 16mm EDFs. I decided to use Flite Test A pack motors with 5x3 3-blade props to match the 3 bladed prop the real plane used. When looking for EDF’s the smallest I could find were 28mm. I decided having non scale EDF’s was more important than not having them at all and moved forward with the 28mm units. With the number of servos in the plane I needed to use a BEC to power them. I discovered while testing the plane a single 6V BEC does not have the capacity to power all 15 servos and added a second BEC to power the bomb bay servos independent of the control surfaces. Now with the overall scale of the plane and power plants selected I could push through with the design.
Before you ask; unfortunately I do not have any build photos. When I was building this I had no intention of doing any sort of build log so did not think to take any.
Also, to save time and multiple confusing paragraphs on how the plane is wired see the wiring diagram below:
The fuselage of the plane is designed around a box spar that tapers towards the tail and is fitted with formers for the skin. I knew the batteries would have to be pretty far forward so I made provisions for a forward battery hatch. However, to make wiring easier I added a second hatch just behind the wings to house the receiver and elevator servo.
The fuselage spar is sized so that the bomb bay door hinge is where the lower face of the spar meets the sheeting. There are triple foam formers at the end of each bay to add rigidity as the bottom of the spar is removed in this region.
I wanted the bomb bay doors to be bi-fold like on the actual bomber. Figuring out the geometry and how to make it happen wasn’t too hard, it just took a few hours of playing around in CAD. However, installing them and getting what I had laid out on paper to work ended up taking over half the time spent building the plane. The doors are operated using a guide wire that connects to the end of the doors and keeps them from swinging out, instead allowing them to “slide open”. I had initially thought I could build the doors out of foam using small formers to keep their shape, however this proved futile and I ended up 3D printing them. The 3D printed doors had issues and I had to print 4 versions of the doors before they printed cleanly and fit close enough for me to be happy with them.
To power the doors there are 2 servos per door one at each end. To open the doors I used a control horn at the hinge point (In retrospect, I wish I had used a single servo per door as the I was not able to get all the servos to align perfectly causing the servos to hum constantly). The doors are all wired to the same channel. Initially I did this by y-harnessing them all together. The problem with this is that when it was done the bomb bays were filled with wires. Fortunately, when I went to hobby king to order more y-harnesses and I found servo splitters that I could use instead. This made the wiring a lot simpler. The bomb bay doors are programmed to take 2 seconds to open not only for scale appearance, but also to decrease the strain on them when opening and closing.
The nose landing gear is not retractable and steerable using a 9g servo. It was constructed as shown in the diagram below.
The horizontal stabilizers are built using a double layer of foamboard with 1 BBQ skewer for reinforcement. The elevators are not connected from one side to the other. To control them there is a single servo offset from the center of the fuselage so that the hole on the servo horn is in the center of the fuselage. Because of the distance between the elevators and the elevator servo the wires run through brass tube inside the fuselage to keep them from flexing.
The vertical stabilizer is also a double piece of foam reinforced with reinforced with BBQ Skewers. For the rudder servo, I cut a hole large enough for a 9g servo in the forward part of the stabilizer.
The rear access hatch for the receiver and elevator servo is simply done by cutting 3 sides after the skin was applied, and cutting through the foam but not the paper backer on the 4th side to make a hinge. There are backers on the front and back of the opening and a backer on the side of the hatch so it will stay closed during flight. Inside the hatch I added a barrier piece of foam so the wires going to the received wouldn’t get tangled in the elevator servo. When making the front access hatch I did the same as the rear hatch except I made the part that holds the hatch closed more complicated than it needed to be. I also found that when the plane was completed it was too tail heavy. To balance the plane I ended up having to modify the front compartment to hold two 3s 2200 batteries in lieu of the originally planned single 3S battery. I also had to slide them further forward than originally planned.
For the wings, I used the “FT Kraken” plans as a template and adjusted them to match the size & shape of the B36. I used FT mini motor mounts as firewalls. I thought about using mini power pods in the design, however that would have caused the nacelles to be much larger, and like the cowling of the “FT Mini Corsair”, the nacelle covers would have prevented them from being removable. The ESC’s for the motors are located on the bottom of the wing inside the lower nacelle cover to allow airflow over them.
The EDF’s are 28mm units from the UMX A-10. I used servo plugs to wire the motor to the 6A esc’s. The pods for the EDF units are a single layer foamboard cylinder that tapers in on the back. The pods are glued to a double layer foam board strut reinforced with BBQ skewers that run into the wing. The ESC’s for the EDF’s are located under the wing in the outer most nacelle. Wiring the wing was the second most complicated part of the build as there are a lot of wires to run in a small space, and all the wiring and test running of the motors had to be done prior to gluing the top-back portion of the wing down.
Due to the 6 channel limit I had imposed on the build I was unable to include flaps (not that there was room for the servos and wires in the wings anyway). This also meant that the plane would have fixed landing gear. To anchor the gear into the wing I bent a C shape into the wire to fit inside the wing. I then cut out a matching pattern into a rectangular piece of foam, and put one more piece on top of that to hold it into place. This is glued this down behind the spar with the gear wire exiting the wing just inside of the inner most nacelles.
The first two profile planes I called B36-A’s because like the real plane they did not have jet engines and had single wheel rear landing gear. As I was adding jets to this version I decided I needed to upgrade the landing gear to a 4-wheel bogie style as well. Each bogie consists of four 1 ½” wheels. The wheels are attached to each end of a short section of aluminum C-channel. The channel has a hole drilled slightly off center towards the front to attach it to the gear strut wire. By adding a rubber band to the front of the gear this allowed the gear to rotate, but keeps the front wheels up in flight to allow for smoother landings.
As the B-36 was designed strictly as a nuclear bomber and never carried standard ordnance, I decided it would carry 2 large droppable bombs. For the bombs I found some small “Nerf Vortex” balls with the whistles in them. I glued FT servo horns on them to attach them to the bomb drop mechanism, then painted them green with yellow accents.
The bomb releases use 9g servos. I attached wires to each servo horn and ran a wire through a guide (brass tube for rear, piece of servo horn for front). The wires then spanned a gap where they would pass through the servo horn on the bombs before embedding into a piece of foam to keep the bomb in place prior to being dropped. The servos are set up so that the wires are different lengths and assigned to a 3-position switch so that I can drop them one at a time. (See the photos above)
I added the Cockpit Canopy and Radar Dome which are built out of foam board. The 4 observation domes are half’s of ¾” diameter foam balls. I gave the balls a coating of hot glue before attaching them to the fuselage.
When the plane was substantially complete I covered the edges and seams with paper surgical tape, then the only thing left was to add was paint. I decided to paint the plane in the livery of "The City of Fort Worth" which was the final B-36J built and is located at the Pima Air & Space Museum in Tucson, AZ. I started with a coating of Rust-Oleum white primer. After taping off the areas that were to be white I applied the aluminum paint. The black, red and blue paint are Testors. I used thin painters tape to mask off and applied these with a brush.
The plane, like the real B-36, takes a little while to get off the ground. But once it is in the air handles well. It fly’s best at 3/4 to full throttle and will get 6 min flight time with 40% battery left on the 3S and 60% on the 2S. With the 6 props tuning and 4 EDF’s burning (figuratively) this sounds amazing in the air. It has a relatively high stall speed which makes landing under power necessary, and makes me wish I had figured out a way to install flaps (or at least thicker landing gear wire). The best part about version #3 of this plane is that when I am asked where the Jets and Bombs are, now I can answer.
The plans are attached. They are laid out on 22"x34" paper with the components in a 20"x30" area. Plans do not include a few of the accessories like the cockpit and radar dome as I winged these. I tried to adjust the plans for build modifications I made, but I'm sure I forgot at least one of them. I also uploaded the .stl files for the doors. The file is for one set of doors and will need to be printed twice.
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