ELECTRIC FLIGHT U.K. - British Electric Flight Association

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even a bent nosewheel leg, but I took the hint and called the day's flying to an end even though I had more batteries ready to go. A couple of days later, I made 3 more flights, extending the model's repertoire as far as a rolling circle, but leaving the Lomcevak and Avalanche for another day! Debrief To summarise, I am delighted with the model's looks and flying characteristics. I found it exceptionally easy to land in breezy conditions, although it might come in a bit fast in a flat calm - I will have to wait and see! A few "tidying-up" tasks remain, including fitting a more scale-like 3-bladed propeller and spinner, and the plastic "oleo legs" need de-greasing and painting silver. It will then be ready for the new rally season, so if you want to see it fly, come along to one of the BEFA fly-ins during the summer. Meantime, for specifications and availablility of this model, or any of the others in the V-Mar range, contact MacGregor Industries on 01753 549 111 or at www.macgregor.co.uk A very happy Dave after the successful completion of the first flight 36 E.F.-U.K.
Variable Pitch Propellers by Don Stanley Whist browsing through my Internet files, I came across a file called “varioPROP” which I downloaded in 2002. This is a variable pitch propeller that has 2, 3 or 4 blades and is marketed by Ramoser Technik+Design. They claim that with the turn of a screw the propeller can be set to “exactly the desired pitch” and from the photograph it is of the type that rotates the blades to change the pitch. From my experience of designing and making and measuring propellers, I believe this to be a rash statement and I will explain why this is so. The pitch of a propeller is determined by the angle of the blade to the airstream, and the radius at the point on the blade that we are considering. It is defined as the forward motion made by the propeller as it “screws” its way through the air in one revolution of the blades assuming no slip between the air and the blade. This is generally called the “Geometric Pitch” which is dependent on the angle between the back of the blade and the plane of rotation. Most model propellers are of the constant pitch variety, which means that the pitch is the same along the blade and this gives the propeller its familiar twist. However, most commercial propeller makers usually incorporate a little wash out towards the blade tip. If we call the geometric pitch of a propeller P, the blade angle α, and r the radius of any point along the blade. Then P = 2.ð .r.tan α or α = tan-¹ (P/(2.ð .r)) A small error occurs here as the angle of the back of the blade is assumed to be the true aerodynamic angle of attack which is not quite the same thing. This is affected by the camber of the blades aerofoil section. The error is small and does not change the argument presented. So for a propeller of say 250 mm diameter and of 150 mm pitch (approx. 10” x 6”) we can calculate the angle α at various points along the blade (see table 1). Now we will increase the pitch by rotating the blade in the hub so as to increase the blade angle by 5°. We simply add 5° to each angle and recalculate the pitch r α p r new α new p 25 43.7 150 25 48.7 179 50 25.5 150 50 30.5 185 75 17.7 150 75 22.7 197 100 13.4 150 100 18.4 209 tip 125 10.8 150 tip 125 15.8 222 Table 1 Table 2 We can see immediately that the pitch has increased but is now no longer constant, and has in fact acquired quite a lot of “wash in” The reverse happens if the blade E.F.-U.K. 37
Page 1 and 2: ELECTRIC FLIGHT U.K. ISSUE No. 81 S
Page 3 and 4: Electric Flight - U.K. Issue 81 - S
Page 5 and 6: Chairman’s Chatter Dear members,
Page 7 and 8: You probably heard through the grap
Page 9 and 10: Right is shown the Reichard Sprinte
Page 11 and 12: Left: are the latest enhancement to
Page 13 and 14: Readers’ Models Your chance to sh
Page 15 and 16: The Hornisse away! Chris with his M
Page 17 and 18: A gentle flare, note the Fowler fla
Page 19 and 20: E.F.-U.K. 19
Page 21 and 22: 1) The battery pack of 9 Sanyo 800A
Page 23 and 24: the model was coming towards me. I
Page 25 and 26: Blackpool & Fylde Electric Day by J
Page 27 and 28: E.F.-U.K. 27
Page 29 and 30: E.F.-U.K. 29
Page 31 and 32: Oil get it done quickly! The origin
Page 33 and 34: higher than I could have achieved i
Page 35: touched down "on the numbers" and r
Page 39 and 40: The collected results are shown plo
Page 41 and 42: A year of Flying with LiPo By Malco
Page 43 and 44: safely accept 1.6A putting several
Page 45 and 46: Inside the hall E.F.-U.K. 45
Page 47 and 48: A Protech Ultimate hovering in fron
Page 49 and 50: The motor used is a double ended Tw
Page 51 and 52: John flying the completed CH-47 The
Page 53 and 54: The Lama uses contra-rotating rotor
Page 55 and 56: The 51st Toledo RC Exposition by Ra
Page 57 and 58: The LCD readout is mounted on your
Page 59 and 60: esults to your printer for hard cop
Page 61 and 62: Even using the ply, we can shave so
Page 63 and 64: Move servos, battery, and even the
Page 65 and 66: July 2005 (continued) 10th You are
Page 67 and 68: October 2005 2nd Unlimited Scale Co
Page 69 and 70: New to ELECTRIC FLIGHT? START HERE
Page 71: FANS Morley ‘Jet Elec’ Fan ....

ELECTRIC FLIGHT U.K. - British Electric Flight Association

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