Proof Testing an aluminum fuselage

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This is my third post today!  I've already posted on CG calculations in a tricycle gear ultralight aircraft (such as our Belite), also on a Chinese ultralight aircraft which was built for less than $400.  Please rummage around my block and look at all the posts.

I made some changes to the aluminum fuselage tricycle gear design, then immediately proof tested them.  I think the results are very impressive.  You can see for yourself in the pictures.  I always enjoy seeing pictures of lightweight structures which hold many times their own weight.

Here are the three tests I made:

1.  Elevator @ 62 mph @ maximum deflection @ 150% of load calculation.  Calculation was made with flat plate area of elevator at coefficient of lift of 1 of the elevator.  According to airfoil theory, this represents maximum force when a flat plate is used as lifting surface.  (This includes many aircraft of many designs, including our 'prewelded steel elevator' option on our Belite ultralight aircraft.)

2.  Rudder @ 62 mph @ maximum deflection @ 150% of load calculation.

3.  Twisting effect of rudder on fuselage, @ 62 mph @ maximum deflection @ 150% of load calculation.

Let's look at the pictures.  First of all, the elevator deflection test:

Elevator force proof test in ultralight aircraft from Belite

The force shown here is in the weaker direction of the fuselage (down, not up.)  What you see here is 110 pounds on the end of the fuselage.  The fuselage is clamped down the bench.  My calculations showed a maximum force of 73 pounds, and so I proof tested at 110 pounds.  There was no permanent deformation of the structure.  The only part of the structure really showing the strain was the diagonal elements immediately below the weights.

Then we tested the rudder force.  This was done by placing the fuselage on the side, and adding weight.  Since the rudder is much smaller than the horizontal stabilizer, the weight is lower.  I calcuated a max force of 48 pounds, so I tested at 75 pounds.  Basically the same setup as the prior test, except the fuselage is on the side.  Here's the proof test:

Proof test of total rudder force on a Belite ultralight aircraft fuselage

And the third test was the most fun:  adding a steel rod to the rudder to demonstrate strength in rudder twisting torque.  My calculation on this showed a max force of less than 25 pounds, at a distance of 16 inches from the fuselage.  So I proof tested at 150%+, 37.5 pounds hung at at the appropriate ARM.

Proof test of rudder twisting on Belite ultralight aircraft with aluminum fuselage

You can see the actual fuselage twisting just slightly.  This wasn't a permanent deformation, just a slight accommodation which disappeared after the force was removed.

The steel bar is bending a lot.  In the actual aircraft, the rudder force is supported by the flying wires which connect the rudder to the elevator (and also the fuselage, of course...)

The purpose of all of this was to show that the strength of the fuselage is adequate, even without fabric covering.  Also, to show an alternate way to create the fuselage out of aluminum for a tricycle gear configuration.

My comments:

1.  The structure clearly had a lot of reserve.  If I wanted to increase strength, it was obvious where to add a couple of aluminum members to avoid Euler's buckling.  (Need to know more?  Go Google Euler, pronounced 'Oiler'.)

2.  I encourage customers and ultralight enthusiasts to understand these kinds of tests.  Maybe even do them on their own airplanes.

3.  The calculations were for flat plate areas of the elevator / rudder, not  the horizontal stabilizer / vertical stabilizer.

4.  Any control surface movements which the pilot initiates from the top of the green airspeed (in the yellow to the red, Vne, from 63MPH to 80MPH) must be proportionally limited by the pilot.  In other words, make slight and smooth control surface movements when you are operating in the yellow arc, just like a real airplane.  Because a Belite ultralight aircraft is a real airplane....

Here's some bonus pictures of the tests:

Looking down the fuselage of an ultralight airplane, with load applied.  There appears to be a huge reserve in the fuselage strength.

That's me!  :-)  I am also building a flaperon at the same time.  And looking distracted.

The joy of torque.

The joy of strength in a structure.

 The entire weight of the aluminum fuselage (including the cabin) in this Belite weighs about 40 pounds.

Chinese Ultralight Aircraft for $395???

Please note: James' blog has moved to a Wordpress site. To access it, please visit http://jameswiebe.wordpress.com/. All posts have been transferred to the new site, and all new posts will only be accessible via Wordpress. Thank you for your interest!


Unbelievable post I found, but itseems to be real.  A mechanic in China built his own ultralight aircraft, with 3 (three!!!) engines, for $395.

Let's keep hope alive in ultralight aircraft!

Here's a pic:

And here's the original post.

You've got to see all the pictures.

Calculating Center of Gravity in a Tricycle Gear Ultralight Aircraft

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A few days ago, I posted information on how to calculate the Center of Gravity in a Belite taildragger ultralight airplane.  Today, I provide an update for tricycle gear aircraft.

You should review my original post, here.  After you review it, consider the following example for a tricycle gear plane.

Note that the nose wheel has a NEGATIVE arm, as it's distance is negative from the firewall.  All other arms are positive.  Remember to weigh the aircraft with an empty fuel tank; add the fuel and the pilot weight as shown in the equations as below.

Center of Gravity, Tricycle gear ultralight aircraft calculations:

DESCRIPTION, WEIGHT (in lbs.), ARM (in inches), MOMENT (lbs x inches)
Front nose wheel, 70, -5, -350.
Main wheels, 180, 49, 8820.
Pilot, 200, 39, 7800.
Fuel, 30, 56.6, 1695.

Total weight is 480.
Total moment is 17965 (-350+8820+7800+1695)

ARM of the aircraft is 17965 / 480 = 37.42"

This aircraft is in the CG range. 

REMEMBER, you must measure the actual ARMs of your ultralight airplane using a plumb bob from the firewall, and the aircraft must be level.  (This may be a little easier to do in a tricycle gear plane, as the plane is mostly level to begin with.)

I hope you find this useful, no matter what kind of aircraft you fly.

What is the world's lightest aircraft?

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I'm asking:  what is the world's lightest airplane?

I'm not asking what is the world's smallest:  that honor may be held by this airplane, the Bumble Bee II.  Read about it on Wikipedia.

The Bumble Bee II is definitely not light, weighing in at 396 pounds.  Any Belite is lighter than that.

But Guinness points to an aircraft called the Wee Bee as the world's lightest.  (I find the name Wee Bee very interesting!)

You can read about it here, and they claim it had an empty weight of 210 pounds.   It looks fairly fatal, because the pilot rides on top, face first.  Any accident is going to be a killer:

The 1949 Popular Science article this photo is taken from is a must read.

And it's a Wee Bee.  Just can't get over that.

A Belite can be built with a weight of 210 pounds.  But Belites are definitely not the lightest planes in the world:  what about the Easy Riser, of John K Moody fame?  It weighed a little more than half what our planes weigh.

And also, what about various Human Powered Aircraft?  These have been around quite awhile. Here's a pic of one, in flight:

Human Powered Gossamer Condor, in flight

So I'm really asking:  what is the world's lightest, gasoline or electric, human carrying airplane with an enclosed cockpit?

Here are the rules:

1)  Must be gasoline or electric.  (Disqualified Human Powered, which weigh less than 100 pounds...)

2)  Must have an enclosed cockpit.  (Disqualifies the WeeBee)

3)  Must be fairly conventional:  wings, engine, tail, or canard.  (Disqualifieds weird stuff, like balloons.)