|Aug 06, 2006, 03:46 AM|
DIY Jet 176% Build Thread
A few weeks ago, I came accross the thread for the DIY Jet, a neat little pusher jet design. Originally the plane was designed to be a match for the AC-DIYMOT-VL motor kit that is sold by Air Craft in Japan. A Do-It-Yourself plane for a Do-It-Yourself motor, a simple enough concept. Here are a couple shots of the original plane and the original motor kit.
For those that have not seen the original plane, here is a link to that thread: DIY Jet Build Thread
And just in case anyone is interested in the original motor kit, here is a link to that: Air Craft DIY Motor Kit
The plane looks to me like a semi-scale model of a BAE Hawk with a straightened wing. All in All, a pretty cool looking little plane. The original DIY Jet had a 50cm wingspan (19.7 inches) and a 65cm fuselage length (25.5 inches). To keep things simple, the plane had 3 channel control: Throttle and Tailerons. I saw a video of the plane, and it really scooted along!
I was in the mood to build a couple new planes to take to the Vegas get-together in November, so I thought I would give this one a try. As you all probably know by now, I like my foamie jets to be a little bit on the larger size, so I took the original DXF file, which was posted on the designers website, and started playing around with it in AutoCAD.
First I blew it up 142% to double the wing area. I ended up with a plane that was 32.5 inches long, with a 25.5 inch wingspan. This made it just about the same size as Steve Shumate's series of Park Jets. I wanted something a little bit larger, so I blew it up to 200% to see what that looked like. Now the fuselage length was 51 inches, and the wingspan was 39.4 inches (1 meter). I liked this size and started laying it out to plot.
The parts just would not lay out nice at that size without wasting a lot of plotter paper, so I started to re-think it a little. I checked the maximum print size for the 36" wide paper in the plotter, to stay within the margins, and re-scaled the parts based on that. I ended up with a 176% enlargement of the original plane, and that fit real nice on the paper.
The final size of the plane would be 44" long, with a 34.25" wingspan. This makes it just a little bit smaller that my 6mmFlyRC 133% F/A-18E SuperHornet. Here is a photo of the parts drawing plot. The sheet of paper is 3 x 5 feet, and that is a 48" metal ruler on the bottom edge as a size reference.
As I said earlier, the original version of the plane had tailerons and throttle control. No rudder and no ailerons. For a small plane, this works great, since there is almost no mass in the roll axis, but for a plane of this size, I wanted to have full 4-channel control. To do this, I need to make a few changes to the design. Adding ailerons is the easy part. The trailing edge of the wing sweeps forward slightly, with the tips about 3/4" ahead of the root. You can see this at the right edge of the above photo. To lay out the ailerons, I took my 48" metal ruler, which is 2" wide, and lined it up with the 2 rear tips of the wings, and drew a line down the other side of the ruler. This makes the ailerons 2" wide at the wingtips, and 2-3/4" wide at the root. Then I laid the fuselage top template on the wing template and traced the fuselage width onto ht ends of the ailerons. Finally I drew a line 1/4" outside of these lines to create the cut-off point for the end of the ailerons.
Next was the modifications to the tail. Since the original plane had tailerons, the movable control surfaces were rather large. Here is a photo of the original tail section templates.
Originally I thought about making 2 seperate elevators and running them on 2 seperate servos. However that would take 5 servos all together, and seemed like a little over-kil. In the end I decided to make a full flying Stabilator by cutting the stabs off even with the fuselage edges. Then I could use a carbon fiber tube to act as a spar and pivot, just like the method most of the Park Jets use. I drew a couple lines on the stab template to show where I needed to cut.
I will place the carbon fiber spar tube so the back edge is on the existing hinge line, so I have the proper amount of control surface behind the pivot point for good aerodynamic balance. Next, I cut the templates out from the sheet and pinned them to the foam. Then I traced around the edges with a red fine point Sharpie pen. Here is a shot of the first piece of foam with all the fuselage templates and the rudder pinned into place.
I debated back and forth whether to build this one out of BlueCor or White Foam. In the end, I decided to go with white foam. I am planning on covering this one with UltraCote when I am done, just like I did on my F/A-18E SuperHornet. The UltraCote makes a very nice finish on the plane, and it strengthens the foam a lot!
The foam I am using is very similar to Depron, but is a slightly different type of foam. It is 6mm thick, and has a very smooth surface like Depron, but it is a little more rigid, and it tends to snap easier than Depron. Since I will be covering the finished plane with UltraCote, this is of no concern, since the UltraCote covering makes the foam almost impervious to breaking. Another benefit of this foam is that it comes in 24" x 48" sheets, so none of the pieces of the kit need to be spliced together. All the parts can be made in one piece, as you can see in the above photo.
After I got done tracing the templates with the Sharpie pen, this is what the parts all looked like. You will notice that in addition to the fuselage parts, there are 2 wing panels, 2 rudders and 4 stab halves. I will be laminating these pieces together so all of the flying surfaces are 2 layers of foam thick. The fuselage will be built from 1 layer of foam, with doublers placed in the wing saddle area and the fuselage bottom to stiffen up the fuselage a bit.
I weighed a sheet of this foam, and each sheet weighed 6.1 ounces, just about the same as Depron. Even though I am using 3 sheets of foam to lay out all the parts, there is a lot of unused foam on each sheet, so I sort of guesstimated that I am using a little less than 2 sheets of foam in total, so all the foam pieces should weigh about 11-12 ounces when cut out.
Well, that is a far as I got tonight. I still need to cut all the pieces out, and then I can start building. The motor I intend to use in this plane is rated at 450 watts, and my goal is to keep the weight of the finished plane down to 3 pounds or less. That way I will have over 150 watts per pound, and with that much power, I should have unlimited vertical capability.
Since it is time to go to bed, I will sign off for now. Stay tuned for on-going updates as the build progresses.
Till next time...............
|Aug 07, 2006, 12:42 PM|
Haha some are already addicted !!
General question about motors. Shall their bearings be lubricated with any kind of thin oil ? How often ? I'm new to electrics and I regularly see that "bearings should be changed"... Any hint ?
|Aug 07, 2006, 12:43 PM|
Me and the Mrs. worked on house cleaning yesterday, plus I had to paint a room in the house, so not much got done on the build project. I did manage to squeeze in about an hour and cut out all the fuselage parts and a couple of the stabilators before I got "caught" and was reminded to get started painting the room.
I will get the rest of the parts cut out this afternoon, and post some progress photos later tonight.
See you later.
To answer your question, if you are running a brushed motor that has sleeve bearings, then you should oil the bearings with a drop of oil every 2-3 flights or so. If you are running a motor with sealed ball bearings, then no oiling is usually necessary. In fact, on some types of ball bearings, if you oil them with the wrong type of oil, it can be worse than not oiling them at all. Mixing different types of oils can cause the oils to react with one another and then cause the oils to congeal and mess up the bearings.
|Aug 08, 2006, 01:21 AM|
What size fan are you wanting to use? The plans are available for download in PDF format for the original sized plane in both full sheet and tiled format in the original thread, which is located here. Original sized DIY Jet thread
A DXF version of the plans is available at the designers website at this link. DIY Jet Home Page
If you want a larger version of the plans, I offer a plans service for enlargements of the plans for several foamie jets. The prices run from $10.00 to $25.00 for a set of plans, plus shipping, depending on the enlargement and sheet size. Send me a PM with the details, and I will see what I can do.
|Aug 08, 2006, 01:54 AM|
Part 2 of the Build Thread, Parts Cut-out
As promised, I am back with an update for today. since it is already 10:25pm Pacific time as I am writing this, most of you guys back East have already gone to bed, (at least those of you that have a life! ) but you can catch this tomorrow morning.
I finished cutting out all the parts today, and it went very well. I only went through 3 #11 X-acto blades on all the parts, and did not have to go to the Band-Aid box at all! (Don't you just hate it when you hang the tip of your finger just a little too far over the edge of your ruler! None of that today, thank you very much!
Here is a shot of the first piece as it was cut from the sheet. This is one of the rudders.
Even with doubling up the foam for the wing, rudder and stabilators, ther are only 12 pieces of foam for the entire plane. Since the fuselage is a basic box, and the wing goes through the middle of the fuselage, there are not any fuselage formers. When built, the plane has an air scoop in the nose to cool the battery, and one in the tail end to cool the motor. The firewall has holes in it to let the hot air out, so the entire fuselage has "flow-through" ventilation. Here are all the parts for the kit, neatly laid out on the floor.
A very simple design that should go together very quickly! I will be cutting some foam strips to put into the corners of the fuselage. These will reinforce the fuselage and provide a little more material to sand on to round off the corners. I will also cut a reinforcing strip to layer the bottom of the fuselage in order to help protect it from belly landings.
I did a test fit of all the alignment tabs, and trimmed a couple to fit that were a little too wide. Then I dry-fit everything together and held the parts in place with a few strips of blue painters tape. A few minutes later and Voila, we have an airplane!
Looks pretty cool doesn't it! I took a few more photos from some different angles to show off the lines of the plane. For a size reference, it is 44" long, and has a 34.25" wingspan.
The rear part of the fuselage looks taller than it really is in the back, because the fuselage sides drop down to form 2 sub-fins on the bottom of the plane. These extend about 2" below the bottom of the fuselage. If you look closely behind the stab in the last photo above, you can see where the sub-fins angle up to meet the bottom of the actual fuselage. These can be seen more clearly in the parts layout photo at the top of this post.
Well, now that the framework was there, I took the plane and set it up on my digital scale to see how much all of the bare foam pieces weighed. Here is the plane, carefully perched on the scale.
And the final weight is.........................
Drum roll please...................................
9.2 ounces! I had originally guessed 11-12 ounces, but it looks like I only used the equivilent of 1-1/2 sheets of 24" x 48" 6mm foam for the entire plane. All of the tape strips holding it together probably weigh about 0.2 ounces, so the bare airframe weight of the plane is 9 ounces! Looks like we are off to a good start. For the next installment, I will add up all the weight of the gear that will go into the plane, and make a guess-timate as to the amount of glue and covering material that will be used, and come up with a projected finished weight. Then at the end, I can see how close I came.
That wraps up tonight's report. More to come in the days to follow.
Till Then ...................
|Aug 08, 2006, 01:24 PM|
I will do a preliminary weight & balance on the airframe with the batteries and motor taped in place and see where the CG comes out. If it is too tail heavy, I may switch to a different motor.
|Jul 30, 2008, 03:07 AM|
Not Dead, Just in "Deep Hibernation"
Most of you probably already know, but since I started Innov8tive Designs to import and distribute the awesome line of Scorpion motors and speed controllers I have had ZERO time to build models for the past 18 months! I looked over the pieces stacked neatly in the closet the other day, and thought about the plane.
Fortunately, I was able to quit my day job back in September, so Ihave been able to go from a 130 hour work week to a more leisurely 80 hour work week, so I do have a bit more time now. Right now I am getting ready for the IRCHA show in Muncie, Indiana which will be held August 14-17.
You will probably find me more often these days using my other user account which is "Innov8tive". I do intend to get some time back at the workbench some time in the near future, and hopefully, I can get this project completed before the end of the decade!
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