In a flap!

by Ian Nelson

Back in editions 131 and 132, I wrote about my building and flying of the Hangar 9 P40 Warhawk; that was in April and May 2007. Since then this aircraft has flown many hours and won a couple of Scale (flying only) contests. It has been flown at Old Warden on a couple of occasions. There was a lot of talk about the 'wobbly' twist-tract undercarriage and how it would easily fail on any other ground other than concrete. That has been totally unfounded in the hundreds of landings this aircraft has done, not one undercarriage failure. I digress! What I had found is that on the landing approach the aircraft was very 'slippery' with a high landing speed. I tried everything to slow the aircraft down but still it would float on.

This year I decided to refurbish the aircraft, for two reasons. One, to replace the tatty looking covering and two, to fit split flaps to try and reduce the approach speed. The refurbish would also give me a chance to make the aircraft unique and not the usual ARTF clone with many relatives! So a trawl of the internet found the P40 Warhawk site with lots of examples. A simple scheme was chosen, Olive Drab top surfaces and Light Grey (gray) undersides a US Army scheme with the impressive cowling shark's teeth design. So, the whole airframe was stripped and I found it was in excellent condition considering the amount of 'sorties' it had had. A credit to Hangar 9 was the excellent build quality throughout the airframe; including the substantial main undercarriage mounts. There were a couple of cracks in the wing leading edge sheeting, attributable to grabbing the wing with excessive grip, these were soon repaired and strengthened with thin cyano.

The engine cowling was giving me some concern as it is only a thin epoxy glass item and had suffered a number of stress cracks and pieces missing around the cowl mounting holes. I reinforced the inside with epoxy and wing joining tape, reinforcing the cowl screw holes with steel washers. The most difficult part was removing the epoxy paint on the external surfaces of the cowl, it took lots of 'elbow-grease' but eventually it was back to its substrate ready for the new paint scheme.

So to the main modification of split flaps on the wing trailing edge (right). First I removed the trailing edge sheeting from the root to the ailerons up to the scale line on a set of drawings I had, I then cut the exposed ribs in half lengthwise and inserted balsa spars between them to provide a strong structure for which to mount the flap hinges. As you can see in the photo, just outboard of the wheel well are the bearers for the flap servo box. In the photo you can see that I have drilled the flap spar for pin hinges, I found that the geometry of these did not work so I changed them for standard flat hinges with metal pivot pins.

The flaps are just 1/8 th (3mm) liteply with a balsa leading edge (below). I have not detailed with rib structure as the full-size but, it would not be difficult to do them retro.

The installation of the extra servos was simple, just as you would do with aileron servos. The flap inner surface and inner shrouds were treated with sanding sealer and painted primer green. The area was re-sheeted and the whole airframe covered in Oracover obtained from Horizon Hobby. The cowling was primed and sprayed with Spectra enamel and then fuel-proofed; I have yet to paint on the shark's teeth, that will be done over winter in the warmth of the dining room (I haven't told the wife yet)!

So it was now just a matter of installing the engine and radio and get to the flying field. The Warhawk is powered by an ASP 91 4-stroke so I was not worried about the extra weight as it always had lots of power before the modifications. I set the flap ranges at 10 deg (take off) and 45 deg for landing. There is no need to use flaps on take off as the take off roll is short; although they can be used for scale effect if wished. I familiarised myself with the aircraft again, gained height to 3 mistakes high, reduced speed and lowered the flaps to 10 degs, there was no change in attitude so I put down full flap, again no change in attitude and I was able to bring the speed right back and it performed a very mushy stall with no problems. Throttled up, flaps retracted and continued my flight. On the downwind leg I lowered the flaps to mid and lowered the undercarriage, there was a noticeable drop in speed so I nudged the power up a little, the Warhawk responded well. Onto base leg there was no problem in the turn and levelled up onto finals, about 100 yds from touchdown I lowered full flap, the aircraft almost came to a standstill, so I nudged up the power. The speed was very low with a good attitude, the aircraft landed gently on its mains and then lowered onto the tailwheel; it looked good and landed in half the length than before. A successful modification. It has flown many times since and is absolutely viceless. As you can see from the picture to the left she looks good on approach with her flaps deployed.

Happy (flapped) Landings!

modelflight 1 on the building board!

Using the identical power train based on which John Wheater wrote his Volts & Amps for Dummies modelflight freebie to help me get to grips with elecric flight, John is building a model which he tells me will be named modelflight 1.

He has been teasing me a bit, just giving a glimpse of the construction as he progresses, and here is what he initially revealed!

But now, with addition of that wing mount, the model style is revealed ...

...and we see the recognisable shape of the most elegant of all the old timers, Joe Elgin's 1938 Playboy. 'Modelflight 1' is the senior version at eighty inch span. The original was sixty. John says he built one donkey's years ago and flew it successfully in Vintage Texaco competitions, around 1980.

here's the wing.

And finished - thank you, John!

Try this link to miew John's in-flight video

http://www.youtube.com/watch?v=ap35bRxh9Ao