Esher & District Model Flying Club

President: D.A.E. Smith B.Sc. (Eng.), C Eng., F.I. MECH. E.
Vice Presidents: M. Charles Esq. J.S. Barker Esq.

COMMITTEE

May 2003

From the Chair

Club Evenings - We all enjoyed the captivating talk by Jeff Barkway on his personal experience of the taking of Pegasus Bridge in WW2 as a Glider Pilot which got many of us thinking how brave he was and what a traumatic experience it must have been.
In April, Keith gave us a very interesting and informative talk on the 'practical use of computer radios', and I believe that we all learnt something from it. Many thanks Keith.
Flying Fields - Winter Farm. Much good flying has taken place and the last session will be 17th May but Take Note there have been several days of strong westerly winds and a complaint was received from the Quad bikers that a plane or planes flew over their area on landing approach. This must not happen, and if you are incapable of landing cross wind you should not fly - remember 'Safety is Paramount'.
Summer Field - Roger (the farmer) has rolled the area several times, all we have to do is cut the grass, so we will return there on Saturday 24th May. See Keith's map on how to get there.
B.M.F.A. Achievement Scheme - Congratulations to Paul Privett and Jamie Privett in passing their 'A' Certificate in March at their first attempt. Come on chaps, why not have a go; I know that there are more of you who, with a little effort, can do the same!! Don't be shy!!!

Keep 'em flying and happy landings     Tony Major

Diary

Wednesday meetings are now only once a month on the 2nd Wednesday in the month

Editor’s Notes

I have continued the 'theme' from the last newsletter of taking a look at the various less common model aircraft types. However, the 2nd club competition was spins and I was amazed how many people in the club didn't know how to spin an aircraft. Next issue, therefore, I think I might take a look at basic aerobatics from a beginner's viewpoint i.e. what you are trying to achieve and, where possible, how you can cheat a bit to make it easier.   Keith

Deltas

This being the 100th year of flight what better way to start than with a quick history lesson!

In 1901 Langley, head of the Smithsonian Institute in America, spent $100,000 of Government money designing and building a flying machine called the "Aerodrome" (By the time that the Wright Brothers "Flyer" had flown in 1903, they had spent a total of $1,000 of their own money!).
One of the many reasons that the Wright Brothers were successful was the fact that they made their own test equipment - including a wind tunnel - and proved that much (nearly all) of the available data was wrong. Unfortunately this did not stop the Smithsonian, in 1914, with the help of Wright's arch rival Glen Curtis, rebuilding and flying Langley's Aerodrome with stronger wings, a reshaped aerofoil and an 80-horsepower motor. This 'proved' that the Aerodrome was the first heavier than air man carrying aeroplane (Well how could a couple of country bicycle shop owners be better than the top government scientists!). This directly resulted in the original 1903 Flyer being loaned to the British Science Museum until 1948 when, after the Smithsonian had deleted all claims that the Aerodrome could have flown, Orville Wright had a change of heart and requested that it be given to the Smithsonian.

Langley produced copious data from his expensive test equipment. One set of results became a "Holy Grail" of aviation for years afterwards, this was the 'proof' that the faster a plane surface moved through the air the less energy was required to propel it. Extrapolating those results to Concorde's cruise speed would suggest that it ought to be able to reach New York on a couple of gallons of fuel!
What Langley had found was not that drag reduced as a plane moved faster, but as an aircraft in level flight slows down:
below a certain speed (or more correctly - above a certain angle of attack) the drag rapidly increases. This is known as being "on the back of the drag curve" and can be highly dangerous. The aircraft will sink rapidly and, unless you have copious excess power available, the only way out of it is to push the nose down - the last thing a pilot will want to do if the ground is already rushing towards him!
Langley had discovered what is known as 'vortex' or 'induced' drag - which can be defined as the drag due to lift. This is the major source of drag at low speed. 'Parasitic drag' - which can be thought of as the sort of drag that streamlining, nicely rounded corners and fillets reduces - is much more important at higher speeds.

Fortunately, for most modern aircraft, induced drag is kept as low as possible. Many aircraft are likely to run out of up elevator or stall before they get into trouble. Models such as fun flyers stall at such a low speed that they live most of their lives in this high drag region but, of course, they do have copious excess power!

Two things are guaranteed to increase induced drag dramatically: Low aspect ratio wings (short wingspan/wide chord) Sweepback Guess which form of aircraft has exactly that configuration? More than one full size aircraft - and plenty of models of this type have crashed because of getting on the wrong side of the drag curve. This form is the Delta. A typical model delta drag curve is shown right. Airspeed is shown against the percentage of engine power absorbed by drag at that speed. For this {fictitious} example, by 72MPH, parasitic drag consumes 100% of the engine power - the aircraft will not fly any faster without losing height. Typical Drag Curve for a Delta The total drag is lowest at about 27MPH this will be the aircraft's best climbing speed as more than 70% of power is available to climb. It will also be the minimum descent speed if the engine fails.

Slowing down further than this the drag quickly rises. By 12MPH,Induced drag is absorbing 100% of engine power. It will not be possible to climb at all unless the nose is pushed down to increase speed. Slow down any further and descent is the only option.

This graph assumes that the wing does not stall, which brings me to my second point about deltas - they usually don't stall. The airflow over a conventional wing will become turbulent and break away from the airfoil at some angle of attack. The wing will quickly lose most of its lift - i.e. "stall". As a delta wing's angle of attack increases, the tip vortices increase in size until they eventually cover the whole wing. The fast flowing vortices maintain low pressure (and therefore lift) over the top of the wing although at a cost of very high drag.

So what are the good and bad points of delta assuming that they are properly set up and have a good engine?

Because deltas go where you point them and don't stall they are usually quite easy to fly as long as the pilot is experienced enough to be able to keep up with the speed that they are moving (or the set up and design will allow it to be flown slowly when required). Generally, the 'back of the drag curve' and orientation are the only problems.
It seems a shame that many deltas have rear engines and their C of G too far forward as, to me, the ability to fly them very slowly is as much fun as flying them very fast.
The secret to flying a delta slowly is first to remember that the elevator controls speed and engine controls height (which is true for all aircraft types). Set up the approach speed you want with elevator and then control the approach height with power. If you get close to needing full power then ease the elevator forward to increase the speed. If you cannot get the 'plane to slow down, the trick is to slowly move the C of G back until the plane is just starting to get twitchy to fly. You should then have a 'plane that will fly fast and also do slow Concorde style nose high landings (propeller allowing!) which can be great fun!
Deltas should not be capable of spinning. To spin an aircraft requires that one wing is stalled and deltas don't stall. I did manage (at a good height) to get a Delta 362 to spin once and it looked very impressive as it came down. How do you get a delta out of a spin? Nope, I didn't find the answer to that one! Keith

The New Field

I really do not consider it safe to publish details of the field on the Internet - The farmer would not thank us if people turned up and tried to use it. The paper or email version or of the newsletter will be with you by 20th of May - contact me if you have not received a copy for any reason.

To wet your appetite I have included a couple of photos of the field.

The Gate to the field (Left of the Car)

View into the field from near the gate.

Parking is to the right of the right hand track. Walk down the left hand track staying close to the trees to the pits. The runway will be more or less dead centre of this picture. There is one house, shown magnified above, which is probably the best part of a mile away however, common sense dictates not flying anything noisy in its direction as much as possible.

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