MkI in PRU colours

The sole MkII 2-seater.  Grey upper surfaces, yellow under.

I have wanted to build a Welkin for ages (I wrote in 2005), and drew up plans for a 60” span model powered by 2 x OS 10 2 strokes about 20 years ago, with a late sketch of 2 SP600s as an alternative.  Electric power seemed the way to go, but at the time I was put off by the weight of the motors and the battery power needed for flight.  Now that I have experience of geared SP400 performance on lighter batteries, this seemed like a much better bet.  But why did I like the Welkin?

“Conceived as a result of the 1940 threat of high flying German aircraft, the Westland Welkin had a 70 ft wing span and high altitude Merlin engines.  Ten of the type flew at Boscombe; five crashed - four beyond repair.  Handling was poor...in all three axes; ineffective ailerons and elevators, rudder tramp at high speeds...” (taken from The Secret Years, flight testing at Boscombe Down 1939-45, by Tim Mason).  Worse still: “the whole saga of the Welkin’s procurement can only be seen as an ill-managed and fruitless adventure which amounted to a complete waste of money and effort”  (Dereck Collier writing in Aeroplane Monthly, February 1996)

Oh well, the full size obviously had severe problems caused partly by Westland’s terrible luck but mostly by the designer, Teddy Petter, not appreciating the effects of compressibility at relatively low Mach numbers at the heights he expected the Welkin to fly.  The engines were no help (poor old Westland - never seemed to get a good deal from Rolls Royce, look at the Peregrines on the Whirlwind) and their unreliability was compounded by non-feathering propellers, which in the event of engine failure immediately made a drama out of a crisis.  Although Westland were initially given a large order for the Welkin, it never progressed beyond its troubled early life and the contract was cancelled and the trials aircraft were scrapped - the sole Mk II, a twin-seat radar test-bed - was ignominiously nicked by scrap metal dealers and sold off in bits.  (Something like the Longmoor Military Railway, which was cut up and sold for scrap before the contract had been signed - another story!)  Shortly after the war, Petter felt too constrained by Westland’s move to American helicopter assembly and left for English Electric, taking with him the design of a twin-jet bomber.  No need for me to tell you what that was, but he obviously learned the lessons that the Welkin handed down in such a brutal fashion.

But...that lovely long wing, the closely cowled Merlins, and aircraft poised on the brink of being a classic, what the French call jolie ladie (ugly/pretty - or pretty ugly in plain English).

There were some design problems - how do you get the C of G far enough forward with that short nose?  How can the nacelles take the shock of landing without too much heavy reinforcement?  How do you make both halves of the rudder work as well as the mid-set tailplane?  Would it be better to make a 72” version for speed 600s and have power to spare for a retracting UC and flaps?  A chat with my fellow Christchurch modellers at a Club meeting sorted out the first problem (2 batteries in series, one in each nacelle), servos in the fin and tail solved the third and I can’t afford to make the big one this year.  So strength is the only problem, and I expect that some 1/4” sheet, fibreglass cloth and epoxy will take care of that.  What my Dad called “BFI” - brute force and ignorance!

Well, I wrote that a few years ago, but Trevor Hewson’s search for a twin-engined fighter to model ended in his clutching my plan and searching for a retract system (more on his website).  So here is the state of play with my MkI Welkin, resurrected after 7 or 8 years gathering dust on a shelf and loosely assembled on the kitchen floor. The wing is brand new, with a one-piece spar, replacing the fragile affair that last saw daylight at a Club evening in the Stanpit Village Hall. The motors are genuine Antiques Roadshow geared speed 400s and because of their weight, I don't need to make the MkII with the long nose. It does not have retracts and was designed at about 60" span.

I thought I would try acrylic varnish as a substitute for non-shrinking dope, and tissue cover the wings when they are fully sheeted. The paint job is going to be fairly easy: grey on top and PRU blue underneath - as you can see I had started it. The tailplane is on upside down, btw.

The wing sheeted and epoxied to the nacelles, with the aileron servos and power wiring in place, but still missing the wingtips. The ailerons are complete: the tricky bit will be sheeting the upper sections of the nacelles.

The tailplane slots onto the fin post seen in the earlier photos and the fixed rudder is glued directly to the rear of the post.  The elevators are pre-joined and hinged and are driven by a sub-micro servo buried in the lower fin.  It would be possible to have a working rudder, but somewhat complex and heavy.

The upper fin will be built “in the hand” and tissue covered.

Looking a bit more “of a piece” with a pink foam nose and a banded-on wing.  At this stage, with a 3-cell 3700 mAh LiPo fitted, she balances at the main spar and weighs an ounce under 2 lbs (and a potential wing loading of around 13 oz/sq ft)

I’ve ordered a canopy from Vortex Vacforms. 

2 Oct.  Spent and afternoon with Trevor recording rpm and current from various props on this Welkin, and the same on the motors he had bought for his.  The best props for the geared SP400 were a pair of Master Airscrew 8x6, recording 7200 rpm and 20 amps at full throttle.  The nosecone was made from pink foam on a balsa frame, covered with one piece of 0.4oz/sq ft glasscloth in front of a Club audience, just to prove that it could easily conform to a complex shape.  I got bored with even thinking about planking the nacelles and went straight for carved foam.  They are not quite right in this shot but 30 minutes should see them finished for covering, then out with the Rustin’s acrylic varnish and the tissue paper.  The outlines were cut with a bandsaw rather than HWC - much faster and lots more dust...

The only bad news is that the extention lead from the elevator servo, mounted in the fin, was pulled out the other day, so some keyhole surgery will be needed!

16 Oct 08.  Ready to fly, albeit without paint, markings, spinners or cowl fronts, but there is a fine tradition of test-flying electric aircraft in an unfinished state.  If it doesn’t fly, think of the saving in time!  Weight 2lbs 3oz, span 59”.

Unfortuately this was as far as it got.  The first flight was its last, and should have had a bit of nose-weight, as it never really recovered from a stall at 50 ft, impacted the ground slightly too hard in a landing attitude, and both motors snapped off their mounts, causing a lot of damage to the nacelles.

This project has taken up far too much time and is hereby closed!

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