The Squirrel came up in the “Cross Files” column by Don Ross.
Check out Flying Models at your nearest news stand. It’s a great magazine that I’ve been following since childhood.
I was pretty surprised to see Squirrel make it all the way there to the Don Ross column which I’ve been following since childhood!
Alp Tekin Ozan from Edirne City, at the most North-Eastern edge of Turkey has been involved with teaching free flight classes, namely P30, F1-H, F1-A and F1-B.
Here’s a quote from Hip Pocket Aeronautics.
I’d like to point out the inherent stability of Darcy Whyte’s (Canada) popular SQUIRREL design. It has NO DIHEDRAL, no pylon, but has vertical UPRIGHT wing tip plates. In analysis when the wing banks an impending lateral SIDESLIP is instantly countered by a roll moment from the UPRIGHT TIP PLATES. Therefore an impending spiral is halted and the wing is brought back to horizontal. This is STABILITY.
The proof might be to try a wing with an UPSIDE DOWN wing tip plates. I fear this will increase the spiral tendency and a CRASH. I’d rather not try it. –Ding
I did a lot of QA this summer. Many people made them that had no previous experience. They followed the printed instructions with no help. The idea was to see where people would consistently get stuck.
These two young ladies built a few of them in their store on Bank Street.
aileronA movable flap at the rear of a wing that is used to help control the airplane. There are often two that move in opposite directions. They help control the roll of the airplane. If the right aileron is deflected up, it will cause the right wing to drop (roll right). If the right aileron is deflected down, it will cause the right wing to raise (roll left). On an airplane that is controlled by a pilot the ailerons are often mechanically linked together so that they automatically move in opposite directions when deflected by the pilot. Some airplanes have ailerons that are controlled independently to permit differential reflection.
Ailerons that are controlled in a way that is not symmetrical. Often they are configured so that upward deflection is more than downward deflection. To roll the plane right, the left aileron is deflected down and the right is deflected up. With differential, the right aileron would be deflected up more than the left one would be deflected down. The reason is that upward deflection is more efficient and causes less drag.
This refers to the shape of a wing when viewed as a cross section showing the shape running front to back. Wings are often flat bottom or under cambered for slower aircraft and more symmetrical for faster airplanes. The thickest part of a wing is often towards the front about a third of the way from the front.
Something is flying when it is aloft.
This refers to the angle between the centre line of the fuselage from a side view and the direction it is travelling through the air . It can be thought of the extent to which a wing is deflected up as it moves through the air.
It is often used to describe the angle between the center-line of the wing and the center-line of the fuselage of the airplane from a side view.
The putting together of prefabricated parts to make an airplane.
Balsa (ochroma lagopus) is a light wood that is found mostly in South America. Harvestable trees are between 6 and 10 years old and exist only 2 or 3 per acre in the rainforest. Though the tree grows rapidly it is not suited for growth in groves due to the oversized leaves. It’s density is amongst the lightest of woods and it is the softest of all hardwoods. Pound for pound it is remarkably strong.
An airplane that has two sets of wings that are used to generate lift. Often one wing is mounted above the airplane body and the other is below the body of the airplane. On an airplane we often think of each pair of wings (left and right) as one wing. So in a sense a bi-plane has four wings.
The act of making parts and then putting them together to build an airplane.
This is the distance from the leading edge of the wing to the trailing edge. It’s the width of the wing.
A model airplane like the squirrel can climb if it’s well trimmed and is wound up properly. It will ascend, increasing in altitude above the tree tops or higher.
It is a common practice to have a timer on a rubber-power airplane that when triggered will cause the airplane to come down. The timer is mechanical or electric and is usually installed so that when activated it unhooks from the elevator and causes the airplane’s nose to drop. A Squirrel has a built in de-thermal system. When the elastic is fully unwound it drops off the rear hangar and weight from the elastic plus the propeller causes the center of gravity of the airplane to change and help the airplane descend.
This is like the angle of incidence except it is measured from the direction of actual air flow to the centreline of the wing rather than an arbitrary center line of the fuselage.
An airplane’s wings from the front view intersect at an angle that is referred to as a dihedral angle. If the wings are completely in line with one another the dihedral angle is zero. A positive dihedral, where the wings are angled upward, increases roll stability of the aircraft by increasing pitch roll coupling. The squirrel dihedral angle is zero.
An aircraft dives when it pitches it’s nose down and looses altitude. It can be caused by inadequate power or improper trim settings.
In a structure that uses sheeting, it refers to a second layer used to increase strength.
On a propeller driven airplane the thrust angle is often angled downward meaning it is pushing the air up a bit. This is so that it will not catch the wing and increase the lift as the propeller speed increases. It decouples the thrust and the airplane’s pitch.
In rubber-model airplanes this refers to the length of time that the airplane flies.
A contest where models are timed for how long they fly.
This is the capacity of a material to store potential energy and release it efficiently.
A movable part of the horizontal stabilizer (rear wing) of an airplane that is used to pitch the airplane.
F1b (ef one bee) is a class of model airplane that uses rubber-power, also called the Wakefield. The category has a maximum of of 30g of rubber motor and an airframe weighing no more than 200g. The wing area must be less than 19 square decimeters.
A fin is a term that refers to a small wing that is not involved in lifting the weight of the aircraft, but whose function is control and stability. An example would be the vertical stabilizer (winglets) at the wing tips of the squirrel.
A movable part of the wing that is used to change the shape of the airfoil. Flaps are generally kept in a neutral position and then lowered (both moved downward) in order to give the effect of an under camber in the wing. This lowers the stall speed and permits the airplane to fly slower. Flaps are lowered for landings and takeoff when the airplane is flying it’s slowest.
A type of wing that has a curved upper surface and is flat at the bottom. It is a common airfoil. The type of wing used in the squirrel has a flat bottom, but the upper shape of the wing is also flat with a turbulator at the leading edge of the wing.
A model airplane that does not have a remote control system or a pilot inside it. It must be inherently stable so that it can keep flying without needing any changing control input.
The “body” of an airplane. In a simple rubber-power model it is often just a stick.
In a gear driven system it refers to the ratio between the first and last gear in a drive train. For example, if you pedal your bicycle pedal once and the rear wheel turns three times, we would say that the gear ratio is 1:3 or 1/3. In this case the bicylcle does not use gears, it uses chain and sprocket so it’s also correct to say drive ratio rather than gear ratio.
Rubber powered models often use a mechanical winder to assist winding up the elastic motor. On these devices the gear ratio is often 1:5 or 1:15, meaning one crank on the winder translates to five or fifteen turns on the elastic. They may be referred to informally as “5 to 1” or “15 to 1”. This is backwards but is considered correct because they are talking about elastic turns to crank turns (the inverse).
This is a place where two pieces of material are held together by glue. In model planes it is often balsa to balsa. In larger airplanes other wood types are used such as basswood, spruce, oak, birch and so forth. Birch is often used as a plywood which is layers of wood with different grain patterns. The layers are held together by glue.
A gull wing is a wing which has more than one bend in it. The most common is a wing that is mostly flat but has a upward bend towards the wing tips.
When joining two pieces of material it is a filler that helps increase the surface area of the glue joint and adds more material around the glue joint for increased stiffness and strength.
See “propeller hub”
A structural beam that has the shape of the letter “I” when you look at the cross section. An i-beam is very stiff and is good for construction of buildings, aircraft and many other applications. In balsa model construction the wing spars and webbing act as an i-beam running inside the wing.
For springs and other elastic devices, it is the factor that relates to the desire of the material to return to it’s original form. It relates the force applied and the amount of deflection or distortion of the elastic material. The k-factor is useful along the linear part of the deflection where the amount of force and deflection are related in a linear fashion.
The act of releasing a model airplane. With smaller airplanes like the squirrel it is a very light toss. Other models may require higher speeds such as a catapult launch.
The front edge of a wing. That is the edge that is facing the oncoming wind as the airplane flies.
Leverage is a mechanical principal that allows motion to be amplified in terms of distance and force. For example, if you use a lever to lift a car, you are amplifying the force (in exchange for a much shorter distance). If the distance from the fulcrum of the lever to the load (the car) is 1 cm and the distance from the fulcrum to your hand which does the work is 100 cm, then the mechanical advantage of the leaver is 100:1. So the car weighs 500kg, then you would only need to apply enough force to lift 50kg. But to lift the car 1m you would need to move the lever over a distance of 100m (actually more because in the configuration of a jack you move the lever back and forth).
In an aircraft this is the force which overcomes gravity and allows the airplane to fly. It is created primarily by air flow over and under the wing but the whole airplane is involved in the dynamics of lift.
In elastic rubber motors application of lubrication is good for the longevity as well as the efficient use of the stored energy. AmourAll which is a product for cleaning dashboards of cars is a perfect product for this use. It preserves the rubber, protects it from sun and offers excellent lubrication. Also Johnson’s Baby Shampoo and Joy Concentrated Liquid Detergent work.
The skill of using ones hands to perform manual tasks. Model aviation is an excellent way of improving one’s manual dexterity.
A practice in rubber-power, free-flight airplane enthusiast groups of launching many airplanes at once. Mass launch can also refer to airplanes being launched from different places in the world but at the same time.
This refers to a person who creates models such as model airplanes.
An airplane that has one main wing that does most of the lift. Sometimes flying surfaces such as the horizontal stabilizer (rear wing) contributes to lift. In those cases the airplane may still be classified as a monoplane.
See “rear motor hanger”
The body or fuselage of a simple model airplane. Because it is often just a stick plus the elastic motor, it is called the motor stick.
Stiff and strong wire that is used for construction of model airplanes. It has an excellent elasticity as well as the ability to be bent into different shapes.
This refers to something that varies. For example a model airplane can oscillate between climbing and diving if the airplane is not trimmed properly for level flight.
A small airplane that can fly in a small area such as a living area or parlor.
A more specific case of orthogonal where two lines are perpendicular if they are at a right angle from each other.
When an airplane stalls then recovers then stalls then recovers etc. It is an occilation that can occur if there is no pilot or in a free flight airplane if it is not well trimmed.
It refers to rotation of an airplane about an axis parallel to the wing. If it pitches so that the nose of the airplane is higher than the tail, we say it is pitching up. When the nose is dropping we say pitching down. Pitch of an airplane is controlled by the elevator amongst other things.
Pitch is also used to describe propellers. The pitch of a propeller is how far it would travel in each revolution if there were not losses or friction. So a 5 inch pitch propeller would travel forward 5 inches for each revolution.
This is the tendency for an airplane to stay level with respect to pitch. If some force such as a wind sheer causes the nose of the airplane to drop, the airplane will self correct itself without any pilot to deflect a control surface.
This refers to a wing that has more than one joint that is bent. A conventional wing has one bend in the middle so that it’s shaped like a “v”. That is referred to as a dihedral joint and there is a dihedral angle. A polyhedral wing has more than one place with a bend it it.
A contest that is held by a director at one location and the participants from all over the world fly their airplanes and record their scores themselves. They then send their scores to the director who compiles the results to produce a leader-board.
Most postal contests use email instead of postal services now. Web pages are used to share the results.
This is energy which is stored. For example when you wind the propeller and elastic band in a model airplane, you are storing potential energy in the elastic band. When the airplane is released the potential energy is converted to kinetic energy as the propeller turns.
This is a general principal and applies to many other mechanisms. If you carry a pail of water to the top of a hill, the pail of water has potential energy that can be converted to kinetic energy when it flows down the hill.
A collection of wing like blades that when mounted to a hub can be rotated to produce thrust or air motion. They may have many blades. Two bladed propellers are most common. They are described by their diameter and their pitch. Pitch refers to the angle of the blades.
This is a system of attachment of a propeller to a rubber-powered airplane. Often referred to as a “hub” or “mounting hardware”.
A mounting system for a propeller on a rubber-powered model airplane.
Any mechanism for mounting a propeller on a rubber-powered model airplane.
A model airplane or other product that is made as an experiment. Often production models are based on a succession of prototypes.
Abbreviation of Remote Control or Radio Control.
This is a hook or attachment system to attach an elastic band to a model airplane. This refers to the point of attachment at the back and is often removable to permit the elastic band to be attached to a winder. It is often made from plastic or music wire. In the Squirrel it is a toothpick.
Abbreviation for Rise Off Ground. If a rubber-power airplane has wheels, it can be released onto the ground and take off by itself.
In an aircraft this is the movement of the airplane which is rotation about an axis that runs along the fuselage or the direction of travel.
A roll is also an aerobatic maneuver where the airplane performs a complete 360 degree rotation. So the airplane starts off level, flips upside down then continues rolling until it is upright again.
In a model airplane this is the tendency for the airplane to resist rolling. So if a wind sheer blows the model causing one wing tip to drop, the model will automatically put itself back level without a pilot correcting the situation.
This refers to the use of an elastic band as an energy storage system. It is done by attaching the elastic to a rotating hook at the propeller end and a stationary hook at the other end. The propeller is attached to a bearing so that when it’s hook is turned the propeller turns. The propeller is then wound causing the elastic band to become twisted. When released, the elastic spins the propeller as it unwinds.
How to calculate the number of turns for an elastic:
Length of motor divided by weight in ounces
square root
Multiply 6.35
Multiply by Length of motor in inches
Tan II 1.25 or 1.35
SuperSport multiply 1.14
A fin-like structure at the back of an airplane that is partly responsible for yaw stability.
In model airplanes, this revers to a genre of models that are a replica of a real airplane. For example if the model is one fiftieth of the size of the real airplane, then it would be a 50th scale or 1:50.
It’s a spacer. See “wing shim”
On a powered airplane, if the thrust angle is off to a side, it is called side thrust. This is common in propeller driven airplanes because the side thrust can compensate for the effect of torque and such.
This term refers to the situation where a model airplane gets so high that it becomes a speck in the sky and then disappears out of sight to the naked eye. If this occurs, you may want to bring a pair of binoculars next time.
A movable part of a wing that can be lifted up in order to create drag. On some gliders they are on the top surface of the wing and can be flipped up to act as brakes. On some airplanes they use the same movable surfaces that are also acting as ailerons. They are then called flapperons. If both are raised they’re called spoilers, if both are lowered they’re called flaps and if they are moved independently they’re acting as ailerons. This is accomplished with some computer controlled systems that permit electronic mixing of different inputs.
A fin like wing at the rear of an airplane that contributes to pitch and yaw stability. Most airplanes have a vertical stabilizer and a horizontal stabilizer.
When a horizontal stabilizer is tilted as compared to the wing. This can be used to turn an airplane.
The condition where a wing’s lift is reduced by turbulence. When the angle of incidence is increased and passes a threshold and then turbulence is created above the wing, the result is a stall.
The stall speed of a given wing is a function of the angle of incidence. So at one angle of incidence there is a certain stall speed, and at another angle of incidence there is another stall speed.
An airplane can stall at a high speed if the airplane is pitched up quickly. If the lift isn’t enough to cause the airplane to follow a curved path matching the increased pitch, then turbulence can form causing a stall. This is referred to as a high speed stall. A high speed stall is often accompanied by a rapid roll of the aircraft because the stall may not occur symmetrically across the front of the wing. This causes one wing to have more of a stall condition than the other and with a difference in the lift coming from each wing caused by rapid acceleration from pitching, the airplane may roll violently. In aerobatics this is done deliberately and is called a snap roll. (The airplane’s roll is caused by pulling up abruptly on the controls). Another version of this is the stall-spin. This is when the stall condition is induced long enough that the airplane will start spiralling downward due to a lack of symmetry of the drag and lift.
An enforcement of the dihedral wing joint on an airplane that runs from the bottom of the airplane to the wing. It increases the strength of the wings but adds little weight. It creates some drag and is good for slower flying airplanes.
The tail of an airplane includes the rear components. It could include the rudder, elevator, vertical and horizontal stabilizers.
When an airplane goes on a runway from stationary, to rolling, to flying.
In rubber-power airplanes, it is important to estimate the adjustments, then do some test flights with the elastic partially wound. This allows the operator to see the behaviour of the airplane, make the appropriate adjustments then re-test. As the airplane approaches optimal adjustments, more and more winding is put on the propeller/rubber band.
A thermal is a pocket of air that is rising. Birds and gliders can use this upward draft to generate lift. Birds, models and full size gliders can climb to thousands of feet using thermals.
One way a thermal forms is when a warmer area such as a parking lot is surrounded by a cooler area such as grassy fields. The temperature difference could be because of the colour differences, green grass colour vs. black asphalt.
The air over the parking lot is heated. Once warmed it is lighter. It clings to the parking lot until the size of the blob of lighter air is light enough to break the clingyness of the blob to the parking lot. (Much like a leaky faucet drips rather than sprays continuously because of the surface tension in the water). Once the air mass is big and light enough it will travel up. Air rushes in underneath it to take up the space. The pattern repeats as the new air eventually is heated enough to fly away.
So a particular parking lot may have a frequency of releasing thermals on a particular day. You can figure out the frequency by standing in the parking lot. When you feel the thermal leave you will feel gusts of wind for a short bit. You can time the distance between these gusts and come up with a frequency for that thermal source. It is often 5-7 minutes. Once you know it you can make use of it. For example with a hand launch remote control glider, you will wait for the thermal and make an attempt at launching into it. With a rubber-power airplane you may want to avoid it because it’s gusty and may speck out your airplane.
Thrust usually refers to the force generated by a propeller or other thrust system in aviation.
It is force but applied about a point. It is measured in distance times force. Example 20 foot pounds is a torque that would be equivalent to the turning power of a wrench that is one foot long and twenty pounds of force being applied. Or a 20 foot wrench with one pound of force.
This is an older term that is now mostly replaced by the term rubber-power.
The edge of a wing that is facing back or away from the direction of flight.
The act of making adjustments to an airplane so that if flies best. With free-flight aircraft this includes making test flights, observations and corrections to the airframe, center of gravity and any control surfaces. With an RC aircraft it includes flying the airplane “hands-off”, observing and making corrections to the neutral positions of the control surfaces until it can fly hands-off for a lengthy period of time. With aerobatic aircraft it includes other adjustments such as performing inside and outside loops and observing what corrections are needed to keep the airplane tracking. Making adjustments to the control system as well as moving and adding ballasts (weights) inside the aircraft.
A collection of triangles that can increase the stiffness of a long structure. It is often used in bridges but can be used in model airplane design.
This is a device that is attached to a wing that causes turbulence. It is often constructive turbulence that may increase efficiency or performance of the wing in some way. Some personal aircraft such as the Cessna 150 have a sandpaper like finish to the leading edge to cause a tiny layer of turbulence and soften the stall characteristics.
When a fluid such as air moving around a flying surface moves in a random chaotic way rather than a smooth and predictable way.
In a rubber-power airplane this the number of times the propeller or elastic has been wound.
This is a wing whose profile (airfoil) is concave on the bottom. Under cambered airfoils are known for performance at low speeds.
This is the act of flying model airplanes in public places instead of a designated area. People fly them in parks, malls, schools, dance halls and such. The term is more for when they are not officially organized to fly there.
A vertical stabilizer is a vertical flying surface or air foil that assists yaw stabiliy at the rear of the airplane. A squirrel’s winglet is an example of a vertical stabilizer that assists roll stability and increases the efficiency of the wing.
A mechanical device for winding the elastic rubber band on a rubber-powered airplane. They usually deploy a gear box and can greatly increase the convenience and speed of winding up an airplane. They also can result in longer flights because they permit the elastic to be prestretched and then wound very evenly.
A device used to generate lift for birds and airplanes.
The angle that a wing is positioned compared to the center-line of the fuselage of an airplane. It is often just a few degrees.
On an aircraft this refers to the ratio between the weight of the aircraft and the surface area of the wing.
A mechanism for attaching a removable wing to an aircraft. In many model airplanes the wing mount system involves a rubber band or nylon bolts.
In the construction of a wing, any beam running from the leading edge to the trailing edge may be referred to as a rib. They often have the shape of the airfoil of the wing and also act as a former.
The location of the fuselage of an airplane on which the wing is mounted. This is in the case of a removable wing.
In the case of the Squirrel this is a small spacer that is placed underneath the front of the wing. This gives the wing a positive angle of incidence that is required by it’s design.
This refers to the distance from one wing tip to another.
Wings are often swept back like a delta or a jet. This increases roll stability. Some flying wing type aircraft use sweep instead of dihedral.
Is a small fin like structure at the tip of a wing. They are used on the Squirrel model in order provide excellent roll stability. In commercial jets they are used to increase fuel efficiency.
This is the tendancy for an airplane to keep it’s heading. The rudder or vertical stabilizer plays a roll in this.
