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Hammerhead

May 02, 2015



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Hammerhead

Hammerhead

Built 1985 (destroyed prior to completion)

 
 

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

Wing Span: 72-1/2"
Avg. Chord: 11-3/8"
Wing Area: 825 square inches
Aspect Ratio: 6.4:1 (5:1)
Length: 48-1/4" from back of propeller to elevator hinge line
Engine: O.S. 1.08
Servos (5): Aileron (2), Elevator, Throttle and Rudder
 
 

Plans

I have received numerous requests for Hammerhead plans.  This model is high on the list of things to do, but I have several other projects ahead of it.  I am hoping to get a new prototype built by the end of next year.

The plans will need to be revised and lettered, so please be patient.  It will be a while before they are ready.  When the plans are ready to be released, I will post information here about how to obtain a set.

Thanks to everyone for their interest.

 
 

Current Update

I was just reading this article again because I am considering building another Hammerhead as my next project.  I decided to build from the original plan before deciding what revisions may be necessary.  My guess is that it will fly like a balloon with all that side area and sheer volume to weight.

 
 

About Hammerhead

Hammerhead is the third in a series of designs intended to be scale-like sport aircraft.  My intent was to capture the flavor of a scale aircraft in a sport design.  Unfortunately, Hammerhead never flew.  The completed airframe was tragically destroyed prior to covering.

The first in the series was based upon well-established Ugly Stik type parameters.  The aircraft had it is outlines enhanced and more "body" added to the fuselage.  Although it flew well, but it wasn't the model that I really wanted.  I wanted something that looked "real."

The second model was closer to what I wanted and flew better than the previous model.  This one had flaps that allowed the airplane to land at what seemed like a walking pace.  I flew this model for a few months and even built a set of floats for it.  It never made it to the water, but I still have the floats.

The model is long gone though.  One day I got out of bed and said to myself, "I haven't done anything incredibly stupid lately and today I am going to do something about it."  With that thought in mind, I set off to the flying field.

A little while into the second or third flight of the day, I deliberately put the model in a straight-down, full-power dive to see what would happen.  A few seconds later I found out.  The elevator began fluttering and a half-second after that the stabilizer cracked and jammed the elevator into a slightly down position.

Because the model had flaps which when lowered caused a the nose to pitch up, I probably could have returned the model to almost level flight.  The model was far enough away that it never could have made it back to where the pilots were.

Unfortunately, lowering the flaps never entered my mind.  I killed the engine, but at the speed it was going (terminal velocity), the impending crash turned the model into splinters - the combination of any five of which could not have made a single toothpick.

That model had a Fox Eagle III .61 engine which was way more than it needed.  A good .45 would have been plenty.  I fully expected the head to be ripped from the crankcase or at the least, the crankshaft to be bent.  In fact, the only damage to the engine was a broken needle valve.  That still impresses me to this day.

HammerheadOn the positive side of things, I had enough flight hours with that model to get some useful information in designing the next model.  The flying qualities of this model were fine, but it still did not look "real" enough for me.  I also felt it was too light.

I wanted something a little more solid in the air - substantial enough that she wouldn't be a floater and have a solid feel when coming in for landing.  After a few more months of sketching, drafting and erasing, I finally had a design that embodied the aircraft I wanted to build.

I wasn't trying to engineer a precision aerobatic aircraft with this design.  However, I did want her to be able to perform any standard maneuver gracefully.  At the same time I was also trying to create an airframe that had a lot of drag so it would fly at a more constant speed without gaining a lot of airspeed in a dive.

What was clear to me from the beginning was it should look like it came straight out of the Golden Era of aviation, but more toward the end of that time period - the last of the fabric-covered aircraft.  The thought I kept in my mind was 'What would Bücker have built as a monoplane in the Jungmann series?'

 
 

Construction

The fuselage design is essentially a box with formers around it to give it shape. I roughly duplicated the outline of the Jungmeister for the aft end of the fuselage and added plenty of stringers.  I used a little artistic license when designing the forward sheeting by adding a few curves - the most prominent of which is behind the cockpit.  It is probably not realistic, but I liked it.

To make the wing resemble a scale, fabric covered wing, I spaced the ribs more closely than the usual sport model.  They should probably be even closer together.  The ailerons are traditional barn door style, albeit they are large barn doors.

Most sport designs have the forward sheeting wrapped back to the main spar.  I have can not think of a single full scale airplane that is sheeted this far back.  I narrowed the sheeting quite a bit compared to the average sport model.  For added strength, there are four full-span spruce spars.  Both the front and rear spar pairs have shear Webbing.  The rear webbing had not been completed when these photos were taken.

I would have liked to build a larger aircraft, but I have always been cursed with mid-sized cars.  This restriction limited the wingspan to about six feet.  I also wanted this aircraft to be durable.  Building it would take about four times as long as a Stik model so I wanted it to last.  I have had my share of airplanes that slowly decompose and look very tired after only a few flying seasons.

hammerhead03.jpg (26274 bytes)

My original inked drawings.  Holes were added to formers and flying surfaces after the prototype was built.  Hammerhead will fly one day.

My intention was to use a painted fabric finish rather than plastic covering so the finish would last longer.  My experience is that the covering is what actually loses its appearance even when the structure is sound.

Plastic coverings allow fuel to seep into the wood through the seams. They also wrinkle horribly after a while and the wrinkles become more difficult to remove after the covering has been heat shrunk several times.

In retrospect, the tail surfaces on this model are overbuilt.  I am sure it was over-compensation due to what happened to the previous model.  I used 1/8" balsa as a core for the tail surfaces and then used 1/8" ribs to give them a scale look.

The nose turned out to be a little on the short side making her tail-heavy.  When I build the next version I will strive to make the tail lighter by cutting holes where I can and selecting lighter woods.

I am also considering using a built-up core instead of sheet while retaining the ribs to give it an airfoil shape.  I am really looking forward to building Hammerhead again.

 
   
 

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