Thursday, July 20, 2017

Mitchell U-2 R/C Plane Project Pt. 4

I wanted to get this out today as the R/C plane project has started to really take shape.  So with that in mind I am still hopeful that this project will literally get off the ground someday soon.  Here is where I am at with it as of this morning.

After my recent motorcycle trip to Colorado I was overjoyed to receive more filament for my 3D printer so that I could complete the construction of the fuselage for the plane.  Pictured above is the front and back halves of the fuselage.  The rear section with the blue tape on it had been curing over night so now I was ready to join the two parts.

These two photos of the final assembly of the fuselage worked out rather nicely as the 3D printed parts only need to be held together with a couple of small clamps while the last joint of the fuselage was epoxied and again cured over night.  The fuselage shown above is 16.5 inches long 4.5 inches tall and 4 inches wide where the wing meets the fuselage.  Lots of room inside for extra weight to be added so that I can get it balanced for it for glider test flights.

I then only had to put the canopy on the fuselage and insert the pins installed in the wings into the mounting holes on the fuselage.  It looks pretty impressive already.  With a wingspan of 68 inches and total weight at this point at 2 pounds I am more than happy with the end result even if it is just a static model so far.  The 3D printed parts (fuselage, canopy, wing root edges and the wing tip vertical stabilizers) took 40 hours to make with my 3D printer.

I blocked up the plane on both side to get this shot and looking at it I think that would be exactly where the main landing gear would be mounted.  

I have the fuselage and the canopy pretty well smoothed out at this point. The wings and the fuselage I will not paint until I am sure it actually flies.  No point in going crazy over making it look pretty at this stage of the project.  That can wait till later if all goes as planned.

Inside of the fuselage the wings are held on with some odd shaped washers that I found at my local builders store a couple of weeks ago.  I think they will work out pretty well to hold the wings on when I do the test flights. They are a nice snug fit so I would be really surprised if the wings moved much at all when mounted this way.

I still will have to work out the details of mounting the canopy to the fuselage.  I plan on using magnetic mounts for this part of the construction.  I ordered the neodymium magnets I need a couple of days ago and I suspect it will be next week before I have them in my hands. In the meantime I will work out the 3D printed mounts for the magnets so I can install have them ready when the magnets do arrive. 

Once I get everything assembled I plan on shooting video of the first test flights.  I say flights in the hope that the plane will actually fly.  It could be test crashes for all I know.  Actually I think I have a pretty good shot at getting the project off the ground. I will have to balance the plane so the center of gravity is correct then I will have much better odds of actually getting the plane to fly. 

I flew  large R/C gliders years ago so I have a pretty good idea of how the plane should be set up to fly.  The gliders I flew had wingspans of over 7 feet.  I loved flying them so now to have a model of the actually plane that I built will be even better yet.  Hopefully it will all work out in the end.  Again as before I am still keeping my fingers crossed on the this project just to be on the safe side. 

Saturday, July 15, 2017

Mitchell U-2 R/C Project Update Once Again!

Sorry for not posting anything over the past couple of weeks. I have been on a major road trip this past week doing research on parts for another project that will be happening very soon.  I don't want to get into it at this point but I am sure a lot of you who read my blog regularly will be excited by the project when I do post it in the coming weeks.  So let me get you caught up at least on the Mitchell U-2 Project.

As most of you have already read in the past couple of posts I have been working on a R/C model of the airplane that I built years ago called the Mitchel U-2.  A 34 foot wingspan flying wing.  I have not found any models of my plane so I decided to try and make a radio controlled model of it myself.  I was finally able to get back to work on the project today.

Here once again is an image of what the R/C plane will look like once it is completed.  It will have a 68" wingspan. 1/6th scale of the full sized plane.  If all the test models work out ok this will be the end result of my efforts.

Here is the canopy that I have pretty well smoothed out.  I will have to do some wet sanding yet on this part and figure out the magnetic mounts that I will need to hold it in place for the plane but so far I am very happy with the shape and smoothness of the part.

Here the first two sections of the fuselage have been joined together.  I used epoxy/micro-balloon mixture at the joint along with several layers of fiber-glass on the inside to hold the nose section securely in place.  I will use the same process on the remaining two sections of the fuselage to put it all together. It should do the trick nicely.

This is one of the inner wing sections being assembled with the mid-wing section.  Again I used the epoxy/micro-balloon mixture to join these parts together.  The sanding block was laid on top of the inner wing section just to hold it flat against the table while the putty mixture dried.  You can see a small piece of wood on the outer edge of the of this assembly.  This will keep this wing section tipped up at the right angle while the resin mixture cures.

Here is a view of the opposite wing with the outer wing section and wing tip being attached to the inner and mid sections of the wing.  Again pieces of wood were used to hold the outer wing tip at the correct angle so the dihedral on the wing could be created and matched on both sides of the plane.

Once the wings assemblies had cured properly I was able to take these four shots of the wing to show you what dihedral is. With the wing tips tipped upward as you can see in the photos the wing becomes more stable and the plane will want to fly level.  I had to place a small 2 X 4 piece of wood where the fuselage would be to keep the inner wing section flat against the work table.  Then the wing tips would be in the right orientation as shown in the photos.

In order to hold the wings on to the fuselage I needed to mark and drill two holes in each wing to hold dowel pins for this task.  I used my drill press and managed to get the 1/2" holes drilled accurately as I could. Surprisingly drilling Styrofoam worked.

I drilled the holes four inches deep and then secured the pins in place using the epoxy/micro-balloon mixture once again.  I poured enough of this mixture into the holes and then slid the pins into place so they could cure overnight.

To make sure the pins would match up exactly with the mounting holes that will be in the sides of the fuselage I 3D printed an exact template of the fuselage side where the airfoil shape meets the wing.  The holes are exactly the same in the template and the fuselage.  Should work perfectly.

After the mounting pins had been installed and cured I mounted an additional 3D printed plate that will match up with an identical surface on each side of the fuselage.  This will help make the end of the inner wing safer from accidental damage due to either flying or even assembling the wings to the plane.   

Lastly I decided to add a 3 ounce layer of fiberglass over the joints where the wing sections meet.  It will add very little weight and give the wing much more strength when flying the model.  

I just received an order for more 3D printer plastic today so I will be able to continue my work on the fuselage.  Hopefully I can get this completed in the coming week and get the glider test model ready for it's first flight.  I also have figured out the center of gravity (CG) for the plane so this will help a lot in making sure that the plane is neither nose or tail heavy. 

I don't plan on covering the wing at this point.  Hopefully I will have some successful test flights for the glider version.  Once this works out then I will figure out battery, radio, and servo locations and get that all working properly.  So one step at a time.  Once I am certain that all will work out as planned then I will think about possibly covering the wing to make it even stronger and give it a nice finished look.  Again just will have to see how testing goes on the glider version first.  Keep your fingers crossed.