Hawker Sea Fury Build

[SDF]

This may take some time - my builds usually do - but I'm going to build a Hawker Sea Fury from the Pete Nicholson plan. I want to fit retracts and flaps so some mods will be required.

First problem is retracts:

I plan to use the E-Flite electric ones. The wing as drawn has a 9.5% thick flat bottomed section which was probably ideal on the Speed 600 powered original but is too thin to fit the retracts. The full size has a Hawker high-speed aerofoil 14% thick in the centre section but I’ve chosen to go with a Selig S8036 designed for the Top Flite P47 thinned from 16% to 14%.

Now we come to the angle of the dangle - The retracts on the full size rake forwards at an angle of approximately 16 degrees when extended and rake back at an angle of 20 degrees when retracted. How do you achieve that? Help was found here but not wanting to bend the legs I have chosen to use 18 degrees for both.

Being a sceptical so and so I wanted to convince myself that this would give the right angles with the leg close to vertical extended with a couple of degrees of tow out and lying flat in the wing when retracted. The pictures were generated using POV-Ray to model the retract in the S8036 wing to ensure everything was pointing in the right direction.

The video shows the retraction animated.

Electric Retract Model from SDF on Vimeo.

[Bob Cotsford]

are you sure you want toe-out? I thought you wanted toe-in to help the model steer in a straight line?

[Matt Jones]

Indeed, you want toe-in for improved ground handling

[SDF]

I thought I wanted toe-out but now you have me wondering. There seem to be conflicting views on this, both with full-size and models, with about a 50-50 split toe-in vs toe-out.

The toe-out camp argue that a turn on take-off / landing transfers load from the inner to outer wheel and the toe-out tends to self-correct the turn making ground loops less likely.

The toe-in camp's argument is if the aircraft is yawed with respect to the direction of travel the leading wheel is at a greater angle than the trailing wheel so producing more drag which tends to reduce the yaw.

I think the toe-in argument may be flawed as it seems to assume there is no turn associated with the yaw.

[Bob Cotsford]

Looking at the theoretical pictures, they don't appear to take into account inertia and Newton trying to make the vehicle carry on in a straight line. I say vehicle because it's the same for anything travelling on wheels. It wants to go straight on once it's built up some momentum (unless it's a tethered car). When I've accidentaly had toe-out it makes steering vague. With toe-in it's easier to get a straight take-off. I'll stick with toe-in because it works in practise.

[SDF]

Inertia is really what the bottom two pictures were getting at. The centre of mass tends to continue in a straight line as you say but it is someway above the wheels so the outer wheel in the turn gets loaded more and "steers" either into or away from the turn.

Our strip is sufficiently bumpy that I probably wont be able to tell the difference between toe-in and toe-out anyway but perhaps I should leave it adjustable to begin with.

The next problem is how to make the wing centre section structure strong enough to mount the retracts without adding too much weight.

[Bob Cotsford]

The TF kit uses ply doublers on the ribs extending from front to rear spars and recommends applying glass cloth and resin to the inside of the top skin to brace the wheel bay.

[SDF]

The original design only has the one spar so it sounds like I will need to add a second but I think only as far as the dihedral break. I was planning to cover the wings with lightweight glass cloth on the outside but I could do the inside of the wheel bays too. Does the TF kit use a ply plate or hardwood bearers to mount the retracts?

[Bob Cotsford]

Hardwood bearers, with options in the instructions for fitting Century Jet or Robarts kits. When I do start the build I'll be looking at fitting electric retracts to make things simpler. I've ordered some from HK which are supposed to be good for up to 4.7kg, if they don't look up to the job I've got some heavy duty all metal mechanicals as back-up.