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This issue was so lethargic in its emergence that we have entered into another year since the last issue. So, this issue now becomes volume two. I will try to preserve some order to the upcoming information as it was presented since there is so much information to get out during the next few issues

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We were very fortunate to have Donald R. Crawford giving us another informative presentation.

Mr. Crawford spoke about his wind tunnel design. He original built this 22 years ago and wrote an article for Homebuilt Magazine. He kindly gave use a copy of the article which appears in this newsletter.

The table top wind tunnel was a very nice presentation of what is going on with air movement. We observed flow over an airfoil and objects. This was happening with absolutely no formulas - an excellent easy setup to visualize what is occurring. Dons’ friend made a very nice small airfoil for the wind tunnel with a flap and forward slot which were moveable.

This simple and economical wind tunnel was amazing. Up on the projection screen was smoke trails contouring over a four foot airfoil from an actual 4 inch airfoil. The big secret to this wind tunnel is the use of carbon dioxide smoke made from dry ice.

A pan of water heated by a Fondue heater keeping the dry ice melting and from cooling down the water. Don used real aviation grade dry ice bought at RALPHS for $1.10 a pound. There projected on the screen was the large 4 foot airfoil. Don was carefully changing the angle of attack as we witness laminar flow to full stall with

A pan of water heated by a Fondue heater keeping the dry ice melting and from cooling down the water. You can see that Don only used the best bottle water for the Design Group PHOTO BY Jim Christy

We observed flow over an airfoil and objects. The round object is a cap from the bottle of water. You could see the vortices on the large screen produced behind the round object. PHOTO BY Jim Christy

Looking behind the small prop and motor, pulling the carbon dioxide smoke over the projection screen and objects. PHOTO BY Jim Christy

the flap up and down and the forward slot opened and closed on the airfoil.

This $16 dollar wind tunnel was able to show us air currents over tubes, balls and airfoils. This was an outstanding use of simple material to bring real visualization to aerodynamics. This complex subject was done with a simple and safe visual presentation.

Don stated that the machine is some what limited due to its speed and small airfoil which are working in the 2000 Reynolds number range. There is also the small problem with condensation and need for new fuel (dry ice). Bottom line it does what it was design to do very effectively. As Don Crawford stated “Lippisch Doesn’t Have Any Thing on me”.

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ISBN 0-9603-9340-4 ISBN 0-9603934-1-2

DD--GGuullll Attached to this newsletter are photos and specification for a project started by the original Design Group. Robert Jordan gave us a presentation on the design and aircraft. As designed it was to use a Volkswagen engine, state of the art for auto conversions at that time. The D-Gull was constructed mostly of aluminum. With a fiberglass nose and fuel tanks. The two large looking mushrooms on the lawn are the fuel tanks (see photos). It is now going to a new home in Tucson Arizona. The design work was done by Ray Melberg (EAA 2484) who started homebuilding aircraft in the 1930s. About 9 years ago Sport Aviation did a write up on Rays MG-2 aircraft. If you have not read it before take a glance you will discover a lot about Ray Melberg.

Me ting Schedule:MMeeeeettiinng Sg Scchheedduullee::

2007 Meeting Schedule 10:00 am

FlaBob Airport Chapter One Hanger

MMaayy 2266 NNoo DDGG22 MMeeeettiinngg

But we will have a Roadable Aircraft Vehicle Meeting At the Old Chapter One Club

House on May 26 June 23 July NNoo MMeeeettiinngg August 25 September 22 October 27 November 24 December 15

Check this site for any schedule updates and changes.

http://www.eaach1.org/calen.htmlCheck this site for newsletters

http://www.eaach1.org/design.html

Design Group Meeting got a lesson on Propeller problems from Bob Chase. Bob has given us many informative talks on his ultra light endeavor. John was holding the prop for all to see. He kind of looks like the Sergeant of Arms for the group standing there holding the prop.

A little thought on the importance A little thought on the importanceof the Reynolds numberof the Reynolds number

When designing and testing large-scale aircraft and airfoils it becomes especially practical to work with scaled-down versions. To get accurate data from tests the scale models must have dynamic similarity between scale model and the full scale version. One of the most important factors in aircraft design is known as the Reynolds Number. It is a unit-less number that represents the behavior of the airflow including the boundary layer. WHERE: ρ= is the density of the fluid

(for air at sea level, ρ=.002377 slug/ft^3 V= is the velocity of the airflow, in ft/s D= is the chord of the wing μ = is the coefficient of viscosity, (for air at sea level, μ=3.737*10^-7 (lb*sec/ft^3) Please note the need for consistent units. The Reynolds number equation is very powerful and can give a multitude of initial design information. The Reynolds number (Re) is the ratio of inertial resistance to viscous resistance for a flowing fluid. The Reynolds number is a non-dimensional (unit less) factor governing resistance due to viscosity (among other things). When a solid object and a fluid are in relative motion like an aircraft flying through the air it is usually the fluid that yields to the solid. Solids are held together by intermolecular forces and atomic bonds. If the cohesive forces between the particles in a solid are considered significant and long lasting, then the cohesive forces in a liquid are weak and short lived. In a gas they are virtually nonexistent. You might think that fluids are a pushover for a moving solid, but this is not always the case. As an object moves through the atmosphere, the gas molecules of the atmosphere near the object are disturbed and move around the object. Aerodynamic forces are generated between the gas and the object. The magnitude of these forces depend on the shape of the object, the speed of the object, the mass of the gas going by the object and on two other important properties of the gas; the viscosity, or stickiness, of the gas and the compressibility, or springiness, of the gas. To properly model these effects, aerodynamicists use similarity parameters, which are ratios of these effects to other forces present in the problem. If two experiments have the same values for the similarity parameters, then the relative importance of the forces are being correctly modeled. “By 1921 more than a score of wind tunnels had been constructed the world over. But all those of

substantial size were operating at normal atmospheric pressures. This meant that the experimental results obtained using scale models in the tunnels were open to question because a special parameter called the Reynolds number did not match those encountered in the actual flights of full-scale aircraft. In other words, the Reynolds number of 1/20-scale models being tested at operational flight velocities would be too low by a factor of 20. Reynolds' classic experiments had shown that airflow conditions could be radically different for model and full-scale aircraft. Since the Reynolds number is also proportional to air density, an obvious solution to the problem of scale effects would be to test 1/20-scale models at a pressure of 20 atmospheres. The Reynolds number would then be the same in the wind tunnel tests and actual full-scale flights." If the same atmospheric pressure were used for experiments with wind tunnel models as a full-size aircraft would encounter under actual conditions, the experimental results would be invalid. In order for results obtained with a scale model in wind tunnel experiments to be valid, the Reynolds number needs to be the same under wind tunnel conditions and in regular atmospheric conditions. The way to ensure this is to increase the air density inside the tunnel by the same proportion as the model is smaller than the full-size aircraft. When an airplane wing needs testing, one can make a scaled down model of the wing and test it in a wind tunnel using the same Reynolds number that the actual airplane is subjected to. If for example the scale model has linear dimensions one quarter of full size, the flow velocity would have to be increased four times to obtain similar flow behavior.

Alternatively, tests could be conducted in a water tank instead of in air. As the kinematics’ viscosity of water is around 13 times less than that of air at 15°C, in this case the scale model would need to be about 13 times smaller in all dimensions to maintain the same Reynolds number, assuming the full-scale flow velocity was used.

The results of the laboratory model will be similar to those of the actual plane wing results. Thus there is no need to bring a full scale plane into the lab and actually test it. This is an example of "dynamic similarity".

The factor that is called the Reynolds number was discovered by Osborne Reynolds of the University of Manchester in 1883. Reynolds discovered the ratio that has since been called the Reynolds number when examining fluid flow characteristics-how a liquid flows in a pipe. (His theory also helps to outline how air flows across an aircraft wing.) He demonstrated that the motion of a fluid may be either laminar (in smooth layers) or turbulent, and that the change from a laminar flow to a turbulent flow can happen suddenly. The transition from a smooth laminar flow to a turbulent flow always occurred when the ratio PVD/µ was the same, where P = density of the fluid, V = velocity, D = pipe diameter, and µ = fluid viscosity. This ratio is now known as the Reynolds number.

The full implications of the Reynolds number were never realized by Reynolds who considered the ratio merely as a criterion for the critical velocity in pipe flow. Lord Rayleigh has shown that it is a non-dimensional factor which governs all problems on fluid flow frictional resistance, and that similar non-dimensional constants exist for many other natural phenomena. Lord Rayleigh showed that the scale model tests gave comparable results only when the non-dimensional factor of the model is equal to that of the large object when working under its design conditions. By equating the non-dimensional factor of the large object to that of the model, the test speed of the model is obtained. This is known as the corresponding speed and the comparison of the two conditions between the large object and the test results of a scale model at its corresponding speed is known as the principle of dynamic similarity. In actual subsonic flight, airfoils with low Reynolds number flows are laminar and those with high Reynolds number flows are mostly turbulent, keeping in mind that the Reynolds number is the ratio between density, velocity, diameter, and viscosity (For an airfoil in flight rather than in a wind tunnel, D would be the distance between the leading and trailing edge called the chord length along a flow.) Low Reynolds numbers make the problem of airfoil design difficult because the boundary layer is much less capable of handling an adverse pressure gradient without separation. Thus, very low Reynolds number designs do not have severe pressure gradients and the maximum lift capability is restricted. Low Reynolds number airfoil designs are cursed with the problem of too much laminar flow. It is sometimes difficult to assure that the boundary layer is turbulent over the steepest pressure recovery regions. Laminar separation bubbles are common and unless properly stabilized can lead to excessive drag and low maximum lift. At very low Reynolds numbers, most or all of the boundary layer is laminar. Under such conditions the boundary layer can handle only gradual pressure recovery. Based on the expressions for laminar separation, one finds that an all-laminar section can generate a CL of about 0.4 or achieve a thickness of about 7.5%. Thus the Reynolds number is a measure of the viscous and convective time scales. A large Reynolds number means that viscous effects propagate slowly into the fluid. This is the reason why boundary layers are thin in high Reynolds number flows because the fluid is being convected along the flow direction at a much faster rate than the spreading of the boundary layer, which is normal to the flow direction. Airfoils behave differently at different Reynolds numbers; in general you get a higher stall angle and correspondingly higher lift from an airfoil at higher Reynolds numbers. You can see this from most airfoil performance charts, like those in Theory of Wing Sections. Airfoils operating at

low Reynolds numbers generally experience laminar separation bubble formation which degrades overall airfoil performance through loss of lift and increased drag. Aerodynamic forces depend in a complex way on the viscosity of the gas. As an object moves through a gas, the gas molecules stick to the surface. This creates a layer of air near the surface, called a boundary layer, which, in effect, changes the shape of the object. The flow of gas reacts to the edge of the boundary layer as if it was the physical surface of the object. To make things more confusing, the boundary layer may separate from the body and create an effective shape much different from the physical shape. And to make it even more confusing, the flow conditions in and near the boundary layer are often unsteady (changing in time). The boundary layer is very important in determining the drag of an object. To determine and predict these conditions, aerodynamicists rely on wind tunnel testing and very sophisticated computer analysis. The important similarity parameter for viscosity is the Reynolds number. The Reynolds number expresses the ratio of inertial (resistant to change or motion) forces to viscous (heavy and gluey) forces. From a detailed analysis of the momentum conservation equation, the inertial forces are characterized by the product of the density r times the velocity V times the gradient of the velocity dV/dx. The viscous forces are characterized by the viscosity coefficient mu times the second gradient of the velocity d^2V/dx^2. The Reynolds number Re then becomes: Re = (r * V * dV/dx) / (mu * d^2V/dx^2)

Re = (r * V * L) / mu

where L is some characteristic length of the problem. If the Reynolds number of the experiment and flight are close, then we properly model the effects of the viscous forces relative to the inertial forces. If they are very different, we do not correctly model the physics of the real problem and predict incorrect levels of the aerodynamic forces. What does all this mean? Basically comes down to the reality that you can make a wing section smaller in scale, but, you can not scale down a molecule of air. Due to that modest notion an air molecule reacts differently to different size objects. So, you need “dynamic similarity” or a ratio which can transfer data between dimensions precisely. That’s the way I got it figured!

Osborne ReynoldsOsborne Reynolds August 23 1842–21 February 1912August 23 1842–21 February 1912

Osborne Reynolds (23 August 1842–21 February 1912) was a British fluid dynamics engineer. He was born in Belfast, Ireland and died in Watchet in Somerset, England. He graduated from Cambridge University in 1867 after studying mathematics. In 1868 he became a

professor of engineering at Owens College in Manchester (a predecessor of the Victoria University of Manchester, merged with the UMIST in 2004 to become the University of Manchester), and was only the second to hold this role in England. He retired in 1905. Reynolds famously studied the conditions in which the flow of fluid in pipes transitioned from laminar to turbulent. From these experiments came the dimensionless Reynolds number for dynamic similarity—the ratio of inertial forces to viscous forces. In 1877 he was elected a fellow of the Royal Society, and in 1888 he won the Royal Medal. Reynolds also proposed what is now known as Reynolds-averaging of turbulent flows, where quantities such as velocity are expressed as the sum of mean and fluctuating components. Such averaging allows for 'bulk' description of turbulent flow, for example using the Reynolds-averaged Navier-Stokes equations. Reynolds' contributions to fluid mechanics were not lost on ship designers ("naval architects"). The ability to make a small scale model of a ship, and extract useful predictive data with respect to a full size ship, depends directly on the experimentalist applying Reynolds' turbulence principles to friction drag computations, along with a proper application of William Froude's theories of gravity wave energy and propagation. A crater on Mars is named in his honor and the Reynolds Building at the University of Manchester is named after him.

NOTICE OF PROPOSED RULEMAKING NOTICE OF PROPOSED RULEMAKING(NPRM)(NPRM)

PPaarrtt 00,, SSeeccttiioonn 000000 ((aa)) 11((cc))

SSeeccttiioonn II - No pilot or pilots, or person or persons acting on the direction or suggestion or supervision of a pilot or pilots may try, or attempt to try or make, or make attempt to try to comprehend or understand any or all, in whole or in part of the herein mentioned Aviation Regulations, except as authorized by the Administrator or an agent appointed by, or inspected by, the Administrator. SSeeccttiioonn IIII - If a pilot, or group of associate pilots becomes aware of, or realizes, or detects, or discovers, or finds that he or she, or they, are or have been beginning to understand the Aviation

Regulations, they must immediately, within three (3) days notify, in writing, the Administrator. SSeeccttiioonn IIIIII - Upon receipt of the above-mentioned notice of impending comprehension, the Administrator shall immediately rewrite the Aviation Regulations in such a manner as to eliminate any further comprehension hazards. SSeeccttiioonn IIVV - The Administrator may, at his or her discretion, require the offending pilot or pilots to attend remedial instruction in Aviation Regulations until such time that the pilot is too confused to be capable of understanding anything.

What this is and what it is not!

It is important to remember that this newsletter is merely a conduit for information passed among members sharing their experiences. Its established purpose is fellowship and encouragement. It is NOT the intent to give authoritative advice on aircraft construction or design. All contributing writers disclaim any liability for accuracy or suitability of information that is shared. You can assume that all or some of the information in each issue is not correct for aircraft design. This is simply a collection of notes which where taken at the Design Group meeting and placed with other items into a newsletter format. Lots of items will come from the meeting as best as one can interpret what is stated. Many items will come from other sources such as books and internet files (Grabbing from any source to make it useful) and a lot will come from the internet to expand what was talked about at the meeting, like the Reynolds number material in this issue. (I will take it where I can get it.) Speak out if you were wrongly quoted or something misinterpreted, no harm was implied, only lack of knowledge in understanding and interpreting what was said. So with that said. Welcome to the second year of the newsletter. If others would like to contribute articles, stories and materials in the future feel free. (Everyone thank Donald R. Crawford for his article and Jim Christy for his photos which were used in this issue.) The newsletter should provide a way for us to communicate with each other. It is a place for those of us who want to network, connect and share information to do so. Anyone can write anything to whomever about any aircraft or aviation design ideas. With any luck we will learn something from everyone and hopefully someone can learn one thing from us.

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DDDeeesssiiigggnnn GGGrrrooouuuppp 222 2nd Roadable Aerial Vehicle

Work Group Meeting

MAY 26, 2007

10:00 am At FlaBob Airport

At The Old Chapter1

Clubhouse at Flabob

Me ting Schedule:MMeeeeettiinngg SScchheedduullee::

2007 Meeting Schedule 10:00 am

FlaBob Airport Chapter One Hanger

May 26 NNOO DDGG MMeeeettiinngg

BBUUTT RRooaaddaabbllee AAiirrccrraafftt MMeeeettiinngg MMAAYY--2266--22000077

June 23 July NNoo MMeeeettiinngg August 25 September 22 October 27 November 24 December 15

Check this site for any schedule updates and changes.

http://www.eaach1.org/calen.htmlCheck this site for newsletters

http://www.eaach1.org/design.html