The Other XB-70 Build | Valkyrie V2

[Pieliker96]

Main Gear
The main gear on version 1 worked well but was a bit tempermental - the solder joints in the main bogies cracked occasionally, which was a pain to repair. This time, I went with a simpler approach: brass rods through the side walls of a small aluminum u-channel section, with wheel collars holding everything together. It's more or less the same weight but quite a lot stronger. I also added some bits of wire to keep the bogies at the right angle instead of the previously used rubber bands.



Nose Gear
I've had the idea to make a braking system for a while now, it could have certainly been beneficial on the first flight of V1. The system I devised is constructed from control horns, brass tubing, and steel wire. The circular control horns have a radius filed into their splines that seats against the gear strut. When the horns are rotated, they cam outwards. They are synchronized by bits of steel wire sliding in the brass tube, free on one side and crimped on the other (the tubing is anchored in the holes of the control horn), which also butt up against the strut to provide a zero location . An appendage was anchored to the assembly to provide more leverage for the actuator servo. The outer face of the circular control horns and the inside of the wheels were coated with hot glue with a bias towards the outside to serve as a braking material. Springs were added between the horns and the wheels to keep the friction low when the brakes are not engaged; a free-running wheel could inadvertantly contact the braking face due to side loading of the gear.



Note that the brake is self-releasing: brake engagement tries to turn the control horns in a way that would disengage them. If the opposite were true, the mechanism could easily jam uncommanded. In addition, compressing the oleo strut decreases the braking action. Ideally, these serve as a sort of anti-skid and prevent the nose gear from being ripped out of the fuselage, depending on how effective the brakes turn out to be; the system is resistant to jamming and is positively actuated by the brake servo.

A bit of aluminum u-channel was crimped onto the upper part of the oleo. A flat was filed on the back of the channel to allow a seat and positive mount for the servo, after which it was glued and zip-tied into place. All of the hardware seems to clear the retracts. The servo is mechanically isolated from the steering system for simplicity.



Here's a gif of the brakes in action. If a picture is worth a thousand words, a video is worth a million.

The braking system is of minimal weight and adds a much-needed feature for such a large craft. Testing will tell how well it works.

Spars
Carbon fiber is awesome, super light and super strong. Version 1 used layered poplar square stock that was installed as an afterthought into the wings. The carbon fiber I'm using is a bit heavier but much, much stronger, and it gives me the peace of mind of not having to worry about the wings folding in flight. They'll also be used for removable vertical stabilizers, which had previously been bashed quite a lot during transport due to being in such an exposed position.



Servos
The main wing servos on the original craft were ES3054s, which were operating right around their specced torque figures. Combine that with the servos gradually working loose and having to be reglued, shoddy linkage geometry, and some sketchy wiring, and you've got a loss of primary flight controls waiting to happen. V2's wings will have much beefier servos with around three times the original torque, better anchoring within the wing, and more skookum control linkages. The remaining ES3054s will be used in their original positions at the vertical stabilizers and nose wheel steering as well as the brake servo and canard flap, which was previously a (rather inadequate) 9-gram.

ESCs
Heatshrink provides mechanical protection for the components on the PCB but also acts as a massive thermal insulator. The "heatsinks" on most ESCs are really just thermal masses, designed to soak up the energy and slowly radiate it away once the flight has ended. If you push the ESC too hard and overload that mass, you're in big trouble, because there's no good way to get rid of the heat - the only route is through the thermally restrictive heatshrink and into the air.

The thermal mass method works fine in most cases. If you do need more cooling performance, a simple mod is to cut off some of the heatshrink as seen below. This removes a good deal of that thermal resistance. If you'd like to go even further you can remove the heatsink and the thermal pad and just run the bare FETs (just make sure you've got a decent amount of airflow!) which can save a bit of weight and provide better cooling (provided the surface area reduction of "heatsink" to the FETs is more than offset by the decreased thermal resistance, although this may not be the case and therefore requires testing). Another mod is to add an actual real proper finned heatsink, which I have done in the past with great success. And of course, make sure there's a good deal of airflow, because it makes drawing away heat a whole heckuva lot easier than just using convection.



The ESCs on V1 were directly exposed to the airflow and stayed pretty cool (not "ouch" hot) over the short timeframe of the flight. In V2, they have been moved out of the intake duct airflow and will now source air from a yet undetermined source, most likely the nose gear hole or a NACA duct through the upper surface of the intake duct. The thermal mass alone is marginally enough to keep cool during a normal flight profile without airflow, as was determined through testing. A bit of extra airflow should remedy that.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[L Edge]

Like your work. Do a Google on "Brown University- New Bio-inspired Wing Design".
Nice way to lower the drag and increase flight time.
Thoughts on Horton H0 229?

 

[Pieliker96]

Like your work. Do a Google on "Brown University- New Bio-inspired Wing Design".
Nice way to lower the drag and increase flight time.
Thoughts on Horton H0 229?

Using turbulent flow as an advantage is certainly an interesting concept, as it is typically (at higher Reynolds numbers, at least) indicative of a stall, or a deficiency of aerodynamic performance. I think that paper is calling for a lot more research into these types of wings: how the effect scales to different Reynolds numbers, how to optimize the geometry, and how to efficiently simulate them.

The Ho 229 looks like it was pretty advanced, especially for the time. I wouldn't want to fly it though, early jet engines were quite unreliable and not having a vertical stabilizer is a bit scary.

 

[L Edge]

Using turbulent flow as an advantage is certainly an interesting concept, as it is typically (at higher Reynolds numbers, at least) indicative of a stall, or a deficiency of aerodynamic performance. I think that paper is calling for a lot more research into these types of wings: how the effect scales to different Reynolds numbers, how to optimize the geometry, and how to efficiently simulate them.

The Ho 229 looks like it was pretty advanced, especially for the time. I wouldn't want to fly it though, early jet engines were quite unreliable and not having a vertical stabilizer is a bit scary.

Have you thought about trying to duplicate ot design something without a vert stabilizer?

 

[Pieliker96]

Have you thought about trying to duplicate ot design something without a vert stabilizer?

I've got quite the backlog of designs I want to get done eventually, so far there aren't any without a Vstab. It would probably end up being an interesting engineering challenge if it turned out to be naturally unstable in yaw.

Vertical Stabilizers
Speaking of Vstabs, I made some today after finally getting a shipment of foamboard. The brick-and-mortar stores were sold out of the stuff with no ETA for restocking, but they were available online by the case. Some laser cutting and assembly and they're done.



Improvements made over V1:
-Removable for transport
-Will use double pull-pull linkage setup instead of a single push-pull linkage
-More accurate to full scale

A New-To-Me Building Method
I plan to build the wings and nacelle from DTFB, but the swan neck and front fuse will be done with pink insulation foam and hot-wire. I plan to use 3M Super 77 to laminate the sheets and cardstock / posterboard for the cutting templates, as they are easily laser-able. If anyone has prior experience with hot-wire and has any advice, put it down below.

Here's my rig. It's built from 1" ID PVC and has a 15" span of 30 guage nichrome, which is rather large for what I'll be using it for. Tensioning is provided by the natural springiness in the frame, which is preloaded when the wire is installed. It's powered by a cheapo 45A brushed ESC (rated for 2s, but seems to take 3s fine) and a servo tester, which are taped and zip-tied to the frame.



Parts will hopefully be arriving over the next week or so, progress updates will come as they do. Given how long the first one took me to build, I expected I wouldn't be able to finish this this summer. While that might be true, things seem to be moving along a bit faster this time, and will continue to do so if I stay motivated.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[L Edge]

It is possible without stabs. With some dumb luck, got it done. Worked with EDF 2D thrust vectoring gimbols and installed it wrong on one of my models. Got an ahaaa moment.
Result is I designed and built an X-47 B. No gyro, it is so simple with only 2 servos. Set up is elevons where extra sets of control wires going to the thrust vectoring nozzle. With the 2 axis off 45 degrees from horizontal, there is no action in the pitch axis when the elevator is moved, but when you apply aileron, the second axis moves not only the aileron, but now adds a vector in the yaw axis.

It took me some time to get the right amount of yaw thrust verses aileron deflection. (added two other aero principals for stability and voila!!!)
Floats like a butterfly on landing.

.

 

[Pieliker96]

Nacelle
I've more or less finished the nacelle at this point and am starting work on the mid-fuse/center wing. Here's some pictures of that in progress.


Outer shell completed. Instead of using an overlapping bit of paper on each joint, I opted to use scotch tape on the outside of a butt joint. It looks much cleaner from the outside, and there isn't any opportunity for glue to squeeze out and change the surface finish in any unwanted spots.


The nose gear attach point was a weak point in the last design (either that, or I abused it too much). This time around, I went for a box made of 1/8" plywood. With the internal webbing I'm carrying from the previous design, I'm hoping it'll hold up to the braking forces.


Ducting with EDFs installed & the EDFs themselves. Note the little tabs above the main gear holes that keep the mains from pivoting once retracted.


Vstab mounting points. There's a little clamping block at the bottom that can be accessed externally (although one of the screws has already stripped out - darn it, Murphy!). The fitment is fine-tuned to a nice friction fit with electrical tape, and should be able to keep the stabilizer in even without the clamp.


Temporary wiring and platform for taxi & thrust testing. I went with 95% FSA outlet ducts to give a bit more speed in the air, as they performed similarly to the 100% FSA ducts in static thrust. To save weight aft of the CG, they are made of standard printer paper instead of cardstock.


Previous vs. current ducting, inlet view (note: field of view is different due to using different cameras). Note the markings for mounting ESCs flush with the upper surface of the duct.


Previous vs. current ducting, CAD view. Seems a lot more spacious.

Control Scheme
I've had to do some creative consolidating of channels to fit in my 6-channel budget. The canard flap and brakes are on the same channel, as are the rudders and steering servo. The flap/brake is set such that the brakes are released when the canard is deflected fully trailing-edge down for takeoff. The brakes are at full when the canard flap is retracted. In an intermediate position, the dual rates for the vertical stabilizers / nose wheel are increased for taxiing (the brakes are mostly disengaged). I am also considering mixing some elevator into the canard, although I would have to give up the selectable steering authority capability to do so.

Taxi Test Results
All four EDFs were installed without bellmouths as the EDFs are too tighly spaced and I still have to figure out a good inlet ducting solution. as such, thrust was effectively reduced during the taxi test - although the weight on the nose gear was as well. The turning radius, especially with the increased authority setting, was considerably tighter than the first version. The brakes were able to hold the nacelle steady up to around 70% power, at which point the built-in anti-skid smoothly released them - this point depends on the coefficient of friction between the tire and the surface below as well as the weight on the tires and the force of thrust they are trying to hold back. A problem that needs to be addressed is that the mains retract pins are rotating in the trunnion block, meaning they can become misaligned. Footage of the taxi tests are coming soon in a build video log.

Nacelle improvements over V1:
-Supports removable Vstabs
-Reduced weight by removing non-cosmetic, non-structural foam
-ESC mounting is cleaner airflow-wise
-Better performing & lighter thrust tubes
-Stronger retract mounting points
-Cleaner and more open inlet ducts
-More scale accurate & More beautiful (see edge chamfers)
-Moved EDFs closer to CG

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[Rhaps]

Nacelle
I've more or less finished the nacelle at this point and am starting work on the mid-fuse/center wing. Here's some pictures of that in progress.

View attachment 173103
Outer shell completed. Instead of using an overlapping bit of paper on each joint, I opted to use scotch tape on the outside of a butt joint. It looks much cleaner from the outside, and there isn't any opportunity for glue to squeeze out and change the surface finish in any unwanted spots.

View attachment 173104
The nose gear attach point was a weak point in the last design (either that, or I abused it too much). This time around, I went for a box made of 1/8" plywood. With the internal webbing I'm carrying from the previous design, I'm hoping it'll hold up to the braking forces.

View attachment 173105 View attachment 173106
Ducting with EDFs installed & the EDFs themselves. Note the little tabs above the main gear holes that keep the mains from pivoting once retracted.

View attachment 173107
Vstab mounting points. There's a little clamping block at the bottom that can be accessed externally (although one of the screws has already stripped out - darn it, Murphy!). The fitment is fine-tuned to a nice friction fit with electrical tape, and should be able to keep the stabilizer in even without the clamp.

View attachment 173108
Temporary wiring and platform for taxi & thrust testing. I went with 95% FSA outlet ducts to give a bit more speed in the air, as they performed similarly to the 100% FSA ducts in static thrust. To save weight aft of the CG, they are made of standard printer paper instead of cardstock.

View attachment 173110 View attachment 173111
Previous vs. current ducting, inlet view (note: field of view is different due to using different cameras). Note the markings for mounting ESCs flush with the upper surface of the duct.

View attachment 173112
Previous vs. current ducting, CAD view. Seems a lot more spacious.

Control Scheme
I've had to do some creative consolidating of channels to fit in my 6-channel budget. The canard flap and brakes are on the same channel, as are the rudders and steering servo. The flap/brake is set such that the brakes are released when the canard is deflected fully trailing-edge down for takeoff. The brakes are at full when the canard flap is retracted. In an intermediate position, the dual rates for the vertical stabilizers / nose wheel are increased for taxiing (the brakes are mostly disengaged). I am also considering mixing some elevator into the canard, although I would have to give up the selectable steering authority capability to do so.

Taxi Test Results
All four EDFs were installed without bellmouths as the EDFs are too tighly spaced and I still have to figure out a good inlet ducting solution. as such, thrust was effectively reduced during the taxi test - although the weight on the nose gear was as well. The turning radius, especially with the increased authority setting, was considerably tighter than the first version. The brakes were able to hold the nacelle steady up to around 70% power, at which point the built-in anti-skid smoothly released them - this point depends on the coefficient of friction between the tire and the surface below as well as the weight on the tires and the force of thrust they are trying to hold back. A problem that needs to be addressed is that the mains retract pins are rotating in the trunnion block, meaning they can become misaligned. Footage of the taxi tests are coming soon in a build video log.

Nacelle improvements over V1:
-Supports removable Vstabs
-Reduced weight by removing non-cosmetic, non-structural foam
-ESC mounting is cleaner airflow-wise
-Better performing & lighter thrust tubes
-Stronger retract mounting points
-Cleaner and more open inlet ducts
-More scale accurate & More beautiful (see edge chamfers)
-Moved EDFs closer to CG

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

It looks so good!
But most of all I like how your post went into details. Keep the good tuff coming

 

[Pieliker96]

Taxi testing footage/brakes test, as promised (see 4:59)

 

[Crawford Bros. Aeroplanes]

Holy cow this is impressive! Love the molded fuse, it really helps get the scale look. Great job! Looking forward to V2.

Someday I'll probably get around to building something this size, most likely a YB-35 or a Boeing 2707. I'll probably be an O-2 and have an F-35 by then but it'll happen.

 

[Pieliker96]

Finishing the Nacelle
I've finally got around to sealing up the nacelle, which means I can get on with the wiring, ribs, and wings. This was after performing a series of thrust tests of the entire nacelle with different inlet ducting configurations. Here's the results of that:

The best result was with my custom intake. ("Top open" refers to the massive access door I was using to swap the intakes, this configuration is not suited for flight). It's six layers of DTFB with the paper removed and holes for the fans. The EDFs press fit into the back layer of foam, the other side has been hit with a 1/2" roundover bit.


Router bit profile vs. stock bellmouth.


IRL XB-70 rear inlet duct.


RC XB-70 rear inlet duct.


In-Progress pic.

In the end, I was able to match the static thrust performance of the original with more constricting thrust tubes and more reasonably-sized landing gear holes. I expect this to increase somewhat after finalizing wiring and using better batteries, although I don't expect I'll beat my target - I'll be happy if I get 4kg of static thrust out of this design. I do expect it to perform better in-flight due to the open ducting and constricted thrust tubes.

Canard
I forgot to put this in the post with the nacelle & vertical stabilizers, although it was included in the update video. It's twice as thick as before, has a stronger servo, and is much stronger mechanically.


Canard nearing full deflection.


Linkage setup and beefier servo.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[Pieliker96]

Here's some pictures of what I've been working on over the past couple weeks. There's a lot of photos, so buckle up! I'm planning on another build video log in the next couple of days as well.

Center Fuselage
I added ribs to and fixed up the wiring in the center fuse / wing box.


Installed the carry-through spar, starting to add the ribs. Note the bird's nest of wiring.


Every plane I build demands a sacrifice at some point. The parts in the background are reinforcements / rib doublers for surface attaching the carry-through spar.


Nose gear reinforcement webbing. This should hopefully help the nose gear structurally, which will (aside from the wing spar, firewall, and nose attachment) be one of the most structurally stressed bits of the airframe.


Cable management for the nose wiring. The ESC to motor wires are also braided to keep them together.


I added capacitors at the end of the internal leads for all primary flight control surfaces (rudders and elevons, will also be on the canard). The idea is to reduce noise to the servos and act as a little reservoir for occasional current spikes.

Wings
In an effort to make the joint between the wing and the fuselage less ugly, I built them directly on the mid fuselage.


Starting the wings. The excess was cut off to a planform of the wing, after which the ribs and secondary spar were installed.


The lower seam, much tighter than previous.


Both wings in progress - awaiting anti-rotation tabs, servos, and sheeting of the upper surface.


Anti-rotation tabs, made of 1/8" plywood. These were originally slated to be carbon fiber, but this provided a better way to secure the wings and allowed the carbon to be conserved for the join to the front fuselage. The screw retains the wing when it is screwed flush with the bottom wing surface.


Servo mounting (now much more proper and stronger), the rear anti-rotation tab, a small carbon fiber reinforcement to help with the aero loads of the control surfaces, a slot for the vertical stabilizer, and the elevon hinge inset.


Early stages of wing sheeting.


Bringing the trailing edge together. Halfway there!


Seperating the wing from the mid fuse to form a nice clean seam.


The elevon hinges were built into the foam, The elevons were later cut out, bevelled, and hot-glue reinforced externally.


Repeat everything and you've got some wings! Here's everything so far, minus the canard. It looks a bit weird without the glorious swan neck that so characterizes the B-70.

Improvements over V1:
-Uses thicker airfoil (better for low speeds)
-Uses actual airfoil (ag-11il, 80% thickness)
-Intentional washout
-Stronger spar
-Cleaner wing attachment & securing
-Stronger servo attachment
-Supports removable vertical stabilizers
-Better wiring and power delivery

Landing Gear
I never retracted the landing gear in-flight. (edit: this is incorrect, I briefly retracted them on the second flight before extending them again and crashing). On the maiden flight, as to not change the configuration of the vehicle, for the second flight, the same reason, and because they would no longer function reliably on the third flight. This makes sense considering I used the retracts oustide of their specced weight limits and abused them quite hard in two off-pavement crash-landings (with varying severity). I do intend to retract the gear on the maiden flight for the purposes of drag reduction.

Here's a gif of gear swing. It seems to be fairly reliable.

https://imgur.com/qkrzj7g

Next is learning hot-wire and figuring out how to attach the nose to the mid fuse.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[Pieliker96]

Second video log.

 

[Pieliker96]

We're nearing the finish line. This last bit is probably the most amount of effort I've put into something that is quite straightforwards to do.

Elevon Horns
These are pretty self-explanatory.


They're 1/8" plywood horns installed with pull-pull linkages and no linkage stoppers to reduce points of failure.

Hot-Wire
This was my first time ever doing hot-wire foam cutting - tips in how to improve my workflow and cut quality are welcome, as this took two days from making the stock to a glued up rough fuselage.


I laminated three bits of 2" pink insulation foam, planed it to height, and cut it into 3", 6", and 9" segments - this was the former spacing I used in the plans.


I then attached laser-cut paper templates to both sides of the slices and traced around them with the hot-wire. The surface finish could've been a lot better if I had used proper templates - paper templates had a tendency to crumple around the edges, causing the striations that can be seen. Wood templates would be nice, but I didn't have the required amount on hand and my laser is rather weak.


In addition to the carbon fiber spar, I also added two tabs (similar to those of the wings) to securely retain the nose. This is a massive improvement over the last-ditch effort of stabbing six skewers through the neck and spars on the day of the maiden flight.

Bodywork
Now I need to make it look somewhat presentable. This took a good five or so days of spackle, sand, paint, repeat.


First spackling, first coat of paint. I thought I would just add another coat of paint or two and call it done, but it was not to be.


The propellant from where the primer had been applied a bit too liberally ate away at the foam, leaving these pits that had to be filled with more spackle. After a number of cycles of painting and finding more pitting, the entire thing was pretty much coated with spackle.


At this point, it was rather hastily wet sanded with 400 grit and sprayed down with the last of the paint I had.


The result is something which looks good from afar but far from good, although it doesn't really pick up in the photos. The surface finish leaves a lot to be desired. In the future, I'll spend a lot more time on sanding and getting the hotwire finish tuned, but this'll certainly do for now.

Canard Installation
Next was getting the canard into the nose.


I cut slots on both sides and over the top to make a little hatch. After adding a little arc for the canard's trailing edge to deflect down into, I glued the canard in, glued the wiring into a convenient place, glued the hatch back on, and filled the gaps with more spackle.

Installing The Rear Fuselage
This was one of the things I had been stressing over. It turned out to be quite straightforwards.


I cut out the bits that were preventing the rear fuselage from seating properly until it seated properly. I also finished the sheeting near the wing's root chord leading edge and added a hole into the rear fuselage to pass the wires through.


And a little bit of spackle to smooth the seam between the two. An old ID card is ideal for applying and spreading it if you don't want to get your fingers covered in the stuff.


Test fit of the nose. I ended up adding some glue beads on one side and torquing the thing to get the canard more parallel to the wings, which was somewhat successful - it's still off by a few degrees.

Nearing Completion
It's nearly there, I can almost taste it.

These photos are full-sized because I think they deserve to take up your full screen.

Bananas for scale. I also added some windows made from vinyl (fancy word for "electrical") tape. Without them, it sorta gives off a "slenderman plane" vibe.

Conclusion
I'm nearing the point of making a maiden flight. The majority of the work has been completed. There are still some small things to get done - the battery tray and mounting mechanism, soldering the battery connectors, getting the batteries themselves, doing thrust and taxi and braking tests, and more. I'll be out of town for a couple of days for a family function, after which you should expect the final build log with all-up thrust tests, taxi tests, and brake tests. Assuming all of that goes well and I don't run out of time and have to go back to college, I'll take it down to a flying field and send it. "Whatever happens, happens", you'll know within two weeks.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

 

[OliverW]

We're nearing the finish line. This last bit is probably the most amount of effort I've put into something that is quite straightforwards to do.

Elevon Horns
These are pretty self-explanatory.

View attachment 176035 View attachment 176036
They're 1/8" plywood horns installed with pull-pull linkages and no linkage stoppers to reduce points of failure.

Hot-Wire
This was my first time ever doing hot-wire foam cutting - tips in how to improve my workflow and cut quality are welcome, as this took two days from making the stock to a glued up rough fuselage.

View attachment 176037 View attachment 176038 View attachment 176039
I laminated three bits of 2" pink insulation foam, planed it to height, and cut it into 3", 6", and 9" segments - this was the former spacing I used in the plans.

View attachment 176040 View attachment 176041 View attachment 176042
I then attached laser-cut paper templates to both sides of the slices and traced around them with the hot-wire. The surface finish could've been a lot better if I had used proper templates - paper templates had a tendency to crumple around the edges, causing the striations that can be seen. Wood templates would be nice, but I didn't have the required amount on hand and my laser is rather weak.

View attachment 176043
In addition to the carbon fiber spar, I also added two tabs (similar to those of the wings) to securely retain the nose. This is a massive improvement over the last-ditch effort of stabbing six skewers through the neck and spars on the day of the maiden flight.

Bodywork
Now I need to make it look somewhat presentable. This took a good five or so days of spackle, sand, paint, repeat.

View attachment 176044 View attachment 176045
First spackling, first coat of paint. I thought I would just add another coat of paint or two and call it done, but it was not to be.

View attachment 176046
The propellant from where the primer had been applied a bit too liberally ate away at the foam, leaving these pits that had to be filled with more spackle. After a number of cycles of painting and finding more pitting, the entire thing was pretty much coated with spackle.

View attachment 176047
At this point, it was rather hastily wet sanded with 400 grit and sprayed down with the last of the paint I had.

View attachment 176048 View attachment 176049
The result is something which looks good from afar but far from good, although it doesn't really pick up in the photos. The surface finish leaves a lot to be desired. In the future, I'll spend a lot more time on sanding and getting the hotwire finish tuned, but this'll certainly do for now.

Canard Installation
Next was getting the canard into the nose.

View attachment 176050 View attachment 176051 View attachment 176052 View attachment 176053
I cut slots on both sides and over the top to make a little hatch. After adding a little arc for the canard's trailing edge to deflect down into, I glued the canard in, glued the wiring into a convenient place, glued the hatch back on, and filled the gaps with more spackle.

Installing The Rear Fuselage
This was one of the things I had been stressing over. It turned out to be quite straightforwards.

View attachment 176054 View attachment 176055 View attachment 176056
I cut out the bits that were preventing the rear fuselage from seating properly until it seated properly. I also finished the sheeting near the wing's root chord leading edge and added a hole into the rear fuselage to pass the wires through.

View attachment 176057
And a little bit of spackle to smooth the seam between the two. An old ID card is ideal for applying and spreading it if you don't want to get your fingers covered in the stuff.

View attachment 176058
Test fit of the nose. I ended up adding some glue beads on one side and torquing the thing to get the canard more parallel to the wings, which was somewhat successful - it's still off by a few degrees.

Nearing Completion
It's nearly there, I can almost taste it.

View attachment 176060
These photos are full-sized because I think they deserve to take up your full screen.

View attachment 176061
Bananas for scale. I also added some windows made from vinyl (fancy word for "electrical") tape. Without them, it sorta gives off a "slenderman plane" vibe.

Conclusion
I'm nearing the point of making a maiden flight. The majority of the work has been completed. There are still some small things to get done - the battery tray and mounting mechanism, soldering the battery connectors, getting the batteries themselves, doing thrust and taxi and braking tests, and more. I'll be out of town for a couple of days for a family function, after which you should expect the final build log with all-up thrust tests, taxi tests, and brake tests. Assuming all of that goes well and I don't run out of time and have to go back to college, I'll take it down to a flying field and send it. "Whatever happens, happens", you'll know within two weeks.

-------------------- XB-70 V2: More Power, More Lift, More Engineering. --------------------​

She's a beauty!!! You've out done yourself! And I thought the previous one looked good... this one knocks it out of the water

 

[Pieliker96]

She's a beauty!!! You've out done yourself! And I thought the previous one looked good... this one knocks it out of the water

Thank you! I just have to ask... do you sleep?
It seems like you're always the first one anywhere on this forum

 

[OliverW]

Thank you! I just have to ask... do you sleep?
It seems like you're always the first one anywhere on this forum

Sleeping is for wusses! 🤣😂

 

[Michael9865]

Looks fantastic. Here’s to no wind blue skies and happy landings.

 

[Mid7night]

That's looking amazing dude! Well done, and well documented too. Great job on the log.

As I was scrolling along, catching up, I saw your initial pictures of the EDFs without any kind of inlet lip or intake and was about to comment. Then I kept scrolling and was relieved to see your detailed analysis and testing of different inlet configurations, and was pleased to see your final configuration. I haven't done multi-engine testing, but I have tested a single EDF on a thrust-stand, with and without the stock inlet lip: Removing the stock inlet lip results in roughly a 40% loss in static thrust! I knew it would make a difference, but I didn't think it would be THAT dramatic. So I'm very glad to see your final installation. Well done.

One concern: Brakes on the nose wheel. There is no aircraft that I know of, ever, that has brakes on the nose wheel. I don't bring this up for "not scale" reasons, but for safety. Braking with the forward wheel will tend to make ground handling unstable when slowing from high speeds. The nose wheel is in front of the CG - where the vehicle momentum acts from - so applying brakes on the nose will tend to make the tail want to push its way around front, as opposed to brakes on the rear wheels which are behind the CG which act as a natural 'drag' vector. Also nose gear structure tends to be less robust than main gear, so the stopping force of the entire vehicle may be too much for it. Again, this is all in reference to braking on landing or on a rejected takeoff. Low-speed braking won't show this problem, but I don't want you to be out on maiden and have the airplane ground-loop because the nose and tail want to switch places.

 

[Pieliker96]

That's looking amazing dude! Well done, and well documented too. Great job on the log.

As I was scrolling along, catching up, I saw your initial pictures of the EDFs without any kind of inlet lip or intake and was about to comment. Then I kept scrolling and was relieved to see your detailed analysis and testing of different inlet configurations, and was pleased to see your final configuration. I haven't done multi-engine testing, but I have tested a single EDF on a thrust-stand, with and without the stock inlet lip: Removing the stock inlet lip results in roughly a 40% loss in static thrust! I knew it would make a difference, but I didn't think it would be THAT dramatic. So I'm very glad to see your final installation. Well done.

One concern: Brakes on the nose wheel. There is no aircraft that I know of, ever, that has brakes on the nose wheel. I don't bring this up for "not scale" reasons, but for safety. Braking with the forward wheel will tend to make ground handling unstable when slowing from high speeds. The nose wheel is in front of the CG - where the vehicle momentum acts from - so applying brakes on the nose will tend to make the tail want to push its way around front, as opposed to brakes on the rear wheels which are behind the CG which act as a natural 'drag' vector. Also nose gear structure tends to be less robust than main gear, so the stopping force of the entire vehicle may be too much for it. Again, this is all in reference to braking on landing or on a rejected takeoff. Low-speed braking won't show this problem, but I don't want you to be out on maiden and have the airplane ground-loop because the nose and tail want to switch places.

Thank you! Fantastic point about the nose brake, I hadn't considered that.

If I remember correctly, some early 727s had nose gear brakes in supplement with the mains, they proved to be more hassle than they were worth and subsequently removed. I'm hoping my system doesn't encounter the same fate.

In the case that any odd tendencies crop up in testing, I can dial back the braking action or remove the system entirely.

I've designed the nose gear mount as stronger than the mains - it has to be, as nearly half of the weight is on the nose gear - the two mains take around quarter of the weight each. I think a plywood box with a good bit of glued contact area and some foam webbing on top should be enough, but testing is the only way to find out.