Switchblade XP from Arkansas [J&H Aerospace]

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Time to rob an old model for radio gear...

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So far, I has pretty much followed the J&H Aerospace instructions. But I am about to make a hard turn. :y:

The instructions call for an ultra micro receiver board, such as those for Spektrum radios. But I use Futaba and Tactic radios, and I haven't found a micro receiver board for them.

So, what is a "ultra micro receiver board"? A roughly 1 inch square circuit board, that has a receiver and servos (and sometimes an ESC) built into it. I will be using micro components, but not quite as small.

And I have to order another micro servo. :fly:
 
SPECIAL NOTE: The instructions advise that you do NOT paint your model.

I felt it was more important, for me, to add a light coat of paint to be able to see the model.

I may regret this. We shall see.
 
Over the years, I have learned that a single color model is difficult to see in the sky. So, I painted the bottom orange.
And the top is white.

May I ask what paint you used? And did you determine how much weight was added? I have one of these kits in the queue to start after LDRS.
Thanks for your build thread.
 
Over the years, I have learned that a single color model is difficult to see in the sky. So, I painted the bottom orange.
And the top is white.

May I ask what paint you used? And did you determine how much weight was added? I have one of these kits in the queue to start after LDRS.
Thanks for your build thread.

PAINTS: Used Rust-o-leum "Safety Orange" and Testors "Flat White". I used light coats; just enough to see.

Edit - I used these paints simply because I already had them.

WEIGHT: I did not do a 'before & after' weight measure on the painted parts/body. I cannot find an "Overall Weight" of the model listed in the instructions.

CENTER OF GRAVITY [CG]: I also cannot find where the CG is listed. Although there is a detailed section on testing the model for glide performance.

I broke my scale a couple of months ago; guess I need to get a new one. In this thread, I will supply my findings on Overall Weight and CG location. :pc:
 
I am using a Tactic radio system, which I do not recommend. It is a good radio system, but Tactic is part of Hobbico, which was recently purchased by Horizon Hobby. Horizon Hobby is the main dealer for Spektrum radio systems, and will likely discontinue Tactic radios. Such is life.

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Note that the servo is a "micro" TSX1.9; it weighs 1.9 grams. By the way, these are now on backorder.
 
Let's work on the mount for the servos. Lightly sand the surface.

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And glued in place with medium CA.

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Starting on the control rods, that connect the servos to the rudder and elevator. Man, they are little! Graphite rod with wire z-bends. J&H gives detailed instructions on installing them.

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Clothes pin with a balsa strip to help hold the rudder in position while I install the pushrods.

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Welp, time for the designer to chime in...

First off, nice job on your build. It looks great!

Switchblade XP was my first commercial R/C design and at the time I put it into production, I was quite pleased with it since it was pretty much the only R/C rocket glider kit available that could fly on 13mm engines.

Unfortunately the XP is really, really marginal on takeoff weight. I can get 40-45 seconds off a piston on an A10-3T, and 30-35 seconds without a piston, but only in calm weather (these do weathercock badly if you don't use a piston). This is the reason I elected to discontinue the kit. Never got any complaints...perhaps my customers were just understanding of how extreme of a design it is, but I just wasn't satisfied with it after two years of flying the design on a regular basis.

Anyway, I said all that to say this: anything that adds weight over the design specs makes this airplane very difficult to launch successfully. I'm concerned that with your electronics package weighing at least double what mine does (~3g for the pkz brick vs 5.5-6 for multiple rotary servos+external rx) plus the accompanying drag of the additional parts (not trivial at all, much to my chagrin on several occasions). That said, there is a possible solution to all this. Since you need nose weight anyway, contact me through the J&H website and I'll send you an 18mm pod and nosecone that will fit (you said you needed noseweight anyway ;) ).

Anyone else who runs into weight issues with our kits is also encouraged to do same.

To those still mourning the fact that we won't restock the XP, we're about to release a replacement that's bigger, better, and actually does launch reliably on 18mm A engines, even without a piston. You're still stuck with Spektrum. :facepalm:
 
Thanks for looking in, Maxout.

Did you have to add noseweight to your Switchblade-XP? What was the CG location?
 
OK, ever forward........ POWER. :caffeine:

Here is my 3.7 volt 70 mAh battery (right) and charger (left). Charger uses a USB port.

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Sorting out the receiver, servo extensions, and servo wires. Using a little tape to help hold the wires. Trying to put stuff where it WON'T get crispy.

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And the battery goes on the other side of the boom/fuselage. Using Velcro to hold stuff.

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And with the battery in place. I still have to sort out excess wire.

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Did some glide tests, and I was quite surprised by the results. The Center of Gravity [CG] was much further back (from the leading edge of the wing) than I expected.

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The CG was roughly 1-3/4 inches from the leading edge of the wing, measured at roughly the hinge point on the inner part of the wings. (See the second picture, with the ruler.)

The bad news is that I am nose heavy. Time to do some component rearranging.
 
At this point, the overall weight of my Switchblade-XP is 31 grams.

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Adding my "simulated motor weight", the gliding weight of the model is 35 grams.

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Next step is to get some motors.
 
Gary,

I got your email with contact info this weekend and will get an 18mm pod shipped to you in a couple days.

You mentioned some things about CG and noseheaviness. As a free flight guy, I tend to design my models with very large tail volume coefficients which allow me to put the CG pretty far aft as you have observed. The numbers you indicate look good and I wouldn't move the CG further back from there. Try adding some up elevator trim and see if that sorts the glide out somewhat. You should be able to get a pretty nice flat glide from your Switchblade after a little bit of trimming work. Please bear in mind that I do not ascribe to the 0-0 wing/stab incidence convention that pervades the rocket gliding community. I prefer setting the CG in a known good location and leaving it there, adjusting glide trim using stab incidence changes. This has worked will for over 80 years in hand launched gliders and even with fixed incidence power free flight models which reach almost 100 mph on the way up (think the Sylph rocket glider, except 70-80" span, just as fast, and powered by a screaming gas engine instead of a rocket). I think the 0-0 myth has done more to damage participation in boost gliders and rocket gliders than any other issue.

Bottom line, CG looks good, just add up elevator until happy with the glide.

I wrapped up the testing for a new swing wing R/C model this weekend. 18mm A-C power, considerably larger than the Switchblade. It will eliminate the performance issues I ran into with the Switchblade XP.
 
Sometimes I'd misplace tiny components or it would pop out of my tweezers when grabbed, so I ended up assembling everything inside a largish plastic storage bin.

This is a very important point and we're trying to get away from teenie tiny parts on the newer designs. The smallest components on the Fliplock and Swingshot are the plastic wing bearings. Less stuff to install too!
 
Ever forward! (and quickly, when you use CA glue)

Got the engine pod on:

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And here is the nose cone. That piece of wire is very special, and is secured with kevlar string.

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I fly for sport and have the free flight (non-RC) version--I'm really happy with the glide performance. It hung up there for several minutes on only a 1/2A3-2T.

Wanted to pass along a tip: the kevlar line that keeps the wings securely folded in launch position may loosen a bit over time. The solution is simply to (gently) bend the nose hook forward to tighten things up.
 
No pics, but I had a successful first flight!

I paid the price for the heavier equipment: I think I had a about a 15 second flight. About halfway down, a couple of swifts decided to fly in formation with my Switchblade-XP.
 
Here is a more detailed description of my flight. :fly:

LAUNCH

I was using a 1/8" launch rod, but I was using an E-pad. So, I did not use a guide rod like J&H Aerospace recommends.
[Edit: The E-pad has a 10 inch diameter blast plate, so you cannot set the guide rod next to the model.]

There was practically no wind, and it was late evening. Since I was at my RC field [Kennett, MO], I set the launch rod at a 5 degree angle, away from me. I set the Switchblade-XP on the launch rod with the rocket glider body on the same side as the 'lean' of the launch rod.

My thinking was that, when launched, the Switchblade-XL would arc over on the fuselage-side of the model. THIS DID NOT HAPPEN.

On launch, the Switchblade-XP went fairly straight up, with a slight arc away from me in coast phase.

APOGEE/COAST

This was truly the "heart in my mouth" moment. Because the model arcs over, and..........the pod hasn't popped............the pod hasn't popped..........POP!!!!

GLIDE

When the wings swung into position, the model responded quickly. I did not trim the model, just flew as is. It glided ok, and responded well to the controls. But I didn't search for thermals, since I was concentrating on a successful flight.

By the way, about half way down, I noticed a Swift about 1 foot above my Switchblade-XP, and 5 feet back. Then I noticed a second Swift, about 1 foot above and 3 feet behind the first Swift. They matched my glide path, and flew off when my Switchblade-XP landed. Pretty cool. :cool: :cool: :cool:
 
A shame no one makes a 13mm with just a tad more thrust duration and a shorter delay. A 3-sec delay feels like forever when you're watching your glider plummet down picking up speed while you wait for the engine pod to pop free.
 
A shame no one makes a 13mm with just a tad more thrust duration and a shorter delay. A 3-sec delay feels like forever when you're watching your glider plummet down picking up speed while you wait for the engine pod to pop free.

I think J&H Aerospace is headed the right direction, by moving these models up to the A/B/C motor sizes.

I intend to "use up" my three remaining A10-3T motors, then do another thread to convert this model to the 18mm motors.
 
Gary,

I'm really happy to hear that your XP flew successfully. I was really concerned about the takeoff weight, but you pulled it off excellently.

The original reason for using 13mm motors was to be the only one on the market. In time I concluded that was just a bit ridiculous of a goal and that having something with good performance is more important. Hence the SwingShot which has power to spare and then some.

If you don't have the 18mm pod yet, you should have it soon. If it was flying well on the 13mm setup, expect to need a little tail weight to get the CG back where it's happy.

As you've seen now, swing wing gliders launch super straight. That's what I love about them--launch like a laser beam. I'm really hoping to build a big swing wing someday. Probably about 60" span and power by F and G motors for the NAR records.
 
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