Newsletter Issue 24 – April 2016

Blackburn Flyers Newsletter

Issue 24 –  April 2016

Model Build

This is issue 24 of our monthly newsletters, so it has been two years since the start of the project, it is amazing how fast the time flies.

This month we had the first formal inspection by two of the Large Model Association inspectors on 14th April 2016.  Everything went well and we discussed the following topics.

General construction: The inspectors were pleased with the general construction of the seaplane and the progress since the beginning of this year.

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Torsional Rigidity : Robert Blackburn had problems with the long thin fuselage design as it is not possible to stop the tail section’s twisting easily. This issue was considered as a part of the design and some sections were oversized to reduce the impact and was discussed in great depth with the inspectors.

It was concluded that the covering would have a significant improvement on this twisting.

It was also suggested to carry out the flight trials at one of the flying clubs in Nottingham area as the weather is generally calmer and stable there.

Aerodynamic and response characteristics were assessed using a freeware program Xflr5. This program is widely used to assess initial model design characteristics and is widely used by students for the BMFA Heavy lift design challenge.

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The longitudinal axis looks to have a reasonable tail volume and good stability, the forward Centre of Gravity (C of G) is recommended for the first flight, the full Computational Fluid Dynamics (CFD) model indicates ~15% static stability.

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Land flying: To ensure that the structure is stable, the first couple of flight trials would be from land. This means that we need to make provisions for wheels on the floats or attach temporary trolleys to the plane. The discussions lead to the position of C of G and how the plane sits on water as the floats are in front and it is not possible for the plane to sit upright with the current geometry.

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Follow on from these discussions, the small model was used to illustrate how the seaplane floats on water.  A G-Clamp was used as ballast to bring the C of G to the required position and was floated on the Mat’s fish pond.

The seaplane appears to sit in a 4 degree angle from its horizontal position resting on all three floats.

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Float Construction: Inspectors wanted evidence to ensure that adequate float provisions were made with the finished anticipated weight of the seaplane. The float construction method of using Polystyrene sheets with foam filler as adhesive was also discussed. The inspectors advised on using Pro-skin to cover the bottom of the floats to make them more resistance to impact during landings.

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Propeller: One of the propellers were damaged during the initial engine runs and we are unable to purchase a matching propeller. We had a spare one on order since October 2015 and the supplier is telling us that there is no forecast as when they could supply one to us. One of the inspectors suggested that to purchase a pair of replacement ‘Menz’ propellers which could be purchased in UK.  We are currently looking at the suitability of the available sizes and pitch to match the engine.

Wing joints: The inspectors were impressed with the machining of the wing joints that were carried out by RexRob engineering at Brough. They advised that covering the wing section would be a problem with the single end-ribs and suggested to use doublers, which has since been implemented.

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Weight of cables: Gareth drafted the specification for cabling and it was built to the print by Cablescan. The seaplane is tail heavy and the inspectors suggested to use the standard heavy duty servo cables which is 22 awg – 0.64mm in diameter for the tail section which is significantly lighter than the 16awg – 1.3mm diameter cables currently used.

Position of the Fuel tank in the Nacelle: The Nacelles were completed and assembled by Supercraft.  During the inspection it was noted that there is no need to pressurise the fuel tank using the exhaust feedback as proposed and the fuel tank could sit at the carburettor level behind the bulkhead.

 

Build Next steps:

The next major milestone is to cover the Seaplane with the ceconite covering fabric and make it ready for its first flight trial late next month.