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Dart Number One

May 02, 2015



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Dart Number One

Dart Number One

Completed March 2006

 
 

Airfield Models (http://www.airfieldmodels.com/)Prototype Specifications and Equipment

Wing Span: 16"
Length (overall): 28"
Avg. Chord: 13-3/16"
Wing Area: 211 square inches
Aspect Ratio: 1.2 / 1
Weight: 4.8 ounces
Wing Loading: 3.3 oz./sq. ft.
Servos (2): Graupner C141
 
 

About what little I know about Darts

I really like darts.  They just look wickedly fast.  That's about the only thing going for them as far as I can tell.  I doubt they turn real well and the elevator won't be nearly as effective as the sport models we're used to.

Disorientation is probably a serious problem with darts.  When I get to the point of building a powered model you can bet that it will have a highly visible color scheme such as the top being white with large, Day-Glo orange circles on the wings.

 
 

Prototyping

The models discussed in this article are meant to be prototypes for R & D purposes.

First Sketch of Dart Number OneI haven't taken a photo of this yet, but the thing that turned on the light bulb for this model is a DoodleBug I built.  The fins are triangles.  I put them on my building board and noticed they created a dart shape when the roots were placed together.  I obsessed on this idea to the point that I knew I had to try it.

 Over the course of the week I worked out the design shown to the left and determined the location of the Mean Aerodynamic Chord (MAC) and the theoretical location of the Center of Gravity (CG).  All the models on this page are scaled from this drawing.

Using CorelDraw I scaled the model to the largest printable size I could fit on a standard sheet of paper by rotating a single panel of the wing.  The model came to be about 12" long with a 7-1/4" wing span.

As soon as I mounted the servos I realized this version wasn't going to work as an R/C glider.  It would have been too heavy and required me to buy some type of micro onboard equipment.

Small Dart PrototypeI put the model aside and began working on a larger version that could use R/C equipment that I have on hand.  It would roll into the ground immediately upon launch which will be discussed later in this article.

Because of the problems with the larger model I went ahead and completed this model as a free-flight glider.  It had the same problem so I asked about it at RC Universe and the general concensus is that the model needed a fin.  I added one and it was more stable but not stable enough.  It did a Dutch roll kind of thing for the entire flight.

A second fin having more area was cut out and that resolved the problem.  The second fin was increased in area by taking the initial shape and making it taller.  The model flies rock-steady now.  Both fins are shown in this image.

 
 

Dart Number One

For the first R/C glider version I decided to increase the size to use radio equipment I already have so that if the model is a resounding failure I won't have invested much in it.

I designed the fuselage to provide as much leeway as possible to locate the radio for balance.  As it turned out the model balanced where I think it's supposed to by mounting a 110 mAh battery just behind the cockpit and the receiver directly behind the battery.  Unfortunately, the servo extensions I had on hand were either too long or too short and added about the same weight as using a larger battery and moving the receiver to the rear of the model.  (This was supposed to be a simple project... do they ever turn out that way?)

Dart Number One - Silicone HingesI made hinges using silicone adhesive.  I wish I could remember where I read about this type of hinge so I could credit the source, but I can't.  As I recall the builder used the hinges for a sailplane.  The hinge is light weight and seals the hinge line.  In any case, it's something I wanted to try and they're the only thing that hasn't been a problem.

I am very impressed with this hinge and plan to use them on progressively larger models to study them further.

The finished prototype was built in about two days.  When the model was completed a good toss would result in the model spinning nose first into the ground about 20 feet away.  There was never any damage other than a scuffed nose.  The model had no fin at this point.

For whatever reason, I didn't think a flying wing absolutely needed to have a fin, but I guess I was wrong about that.  At this point I went back to work on the smaller prototype as already discussed.

When I made the first fin for the small prototype I made a fin to scale for Dart Number One.  As I previously mentioned, the small prototype had the Dutch roll with that fin so I assumed that Dart Number One would exhibit the same behavior.

On April 1, 2006 our club had an airshow.  I took the model to show my friend Mike.  He kept bugging me about flying it so when the show was over and the audience was gone, I handed Mike the transmitter and gave the model a toss.  He said the control was sluggish, but manageable.  The important thing was that the model flew straight with a good glide path - it didn't roll over as it had when it didn't have a fin.

The next flight I took a short run and gave the model my best javelin toss at about 30 nose up.  The model flew very straight for nearly 300 feet.  Mike flaired it nicely for landing.

I can't throw any harder than I did and the model was only in the air less than 10 seconds.  All indications are that this model can advance to the next step now.  The Center of Gravity is close to correct and won't cause any serious problems.  Hand launching doesn't give us enough flight time to determine how well the model will turn, but the ailerons did work.

What I should do at this point is bungee launch the model.  I don't have one and don't know if it's worth the investment.  We may just link a bunch of rubber bands together and see what we get.  Unless that reveals a problem with the model then I'll probably move to building a new model identical to this one except to mount a Cox Black Widow .049 on it.

 
 

Looking to the Future

Ultimately my goal is to build a powered model with a high RPM electric motor or glow engine.  I don't have much interest in a dart glider but I have thought about dropping a glider or e-power version from my Senior Telemaster.  Steelie211 posted about dropping it from a Gonzo.

The "real" version will have a built up sheeted wing that should fly better and won't warp.  The sketch at the top of the page  is more or less how I'm thinking about building the wing.  It's kind of like Thwing! in that it has a series of spars that will have a skin laid over them to create the airfoil.  The spars are drawn on both right and left wing panels in the sketch.

Shown only on the right wing panel are lines from the root rib to the leading edge that cross the spars.  These are caps I'm considering adding between the spars and the wing skin.  What I'm thinking is that the caps will curve across the spars and translate that curve to the skin.  If the skin is laid directly over the spars it will probably create ridges.

In any case, my vision for this model is to have an airfoiled wing, a real fuselage and lots of power.

 
 

Small Dart Prototype

Dart Number One

Dart Number One Dart Number One Dart Number One Dart Number One
       
       
       
Dart Number One Plan    
 
 

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Gallery of Radio Control and Display Models Built by Paul K. Johnson
Gonzo - A 3-Channel Radio Control Model Aircraft

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Copyright 2006 Paul K. Johnson