Harrier

[Andy]

As my Harrier has now made its first appearance, I thought I’d write a blurb on what I’ve been up to. It started life as a Guanli Sea Harrier ducted fan kit from Hobbyking but after seeing the later ‘big wing’ Harrier mods on RC Groups by Davylah and Scunna, I decided that was what I wanted, especially as mine would have the extra weight of a sound system. So the wing and lower fin were extended, wing root leading edge extensions, flaps and rudder added, plus various bits of reinforcing. It’s my first venture into the world of depron and I’ve made some mistakes, but I’m grateful to Ian for showing how it can be done. I decided not to do any paint finishing and leave off the canopy and nose cone until after (and if) it flies successfully.

My ten blade 70mm fan sounds a bit ‘Dysonish’ to so I decided it was going to start off as a prop jet which means less weight, more thrust and less noise to drown out the sound system. However the ducting and fan mount is still there if needed.

I want it to take off without the weight of retracts so the first runs were to see if it would track straight on its belly and maybe add a glider wheel later if needed. It’s got almost a 1:1 power to weight ratio so with a small amount of flap applied, I was half expecting it to leap into the air but it didn’t, although it did track straight. I managed to drag it into the air on one of the runs using full up elevator but it immediately rolled right, which I over corrected and it dropped into the long grass, but luckily no damage done.
Coincidentally in the May edition of RCM&E, Tony Nijhuis has a similar experience when trying a conventional (not vertical) dolly take-off with his very impressive VTOL Harrier.

The main problem seems to be that with the tail permanently on the ground, it can’t be rotated for take-off so I’m going to try the glider wheel which will give more speed and more importantly, raise the nose a bit. I measured the pull required on the ground to get it moving and it’s 2lb 8oz. Adding a wheel reduces this to 12 oz!
I’ve also read that although small angles of flap will increase lift, with some configurations it can result in a nose down pitching movement and obviously I can’t overcome that by forcing the tail down on take-off. So there may be some scope for tinkering with the flaps or not using them at all on take-off.

For anyone interested in sound systems, the one fitted in the Zero at the moment is a MR RC Sound module with one transducer and the Harrier is going to have a Model Sounds Inc. module with two transducers. MSI have a good selection of jet sounds.

Best of luck to Ian with his ‘swinger’.

Andy

[Mike P]

Nice write up Andy
Your right what you need to get a plane of the ground is speed and elevation and by adding flaps you will cause the plane to pitch nose down and with not enough speed for the elevator to work to lift the nose it's going to stay on the ground.
It would probably be a good idea to get a good hand launch from a club mate to prove and trim the flight carritistics so you have one less thing to overcome when it does leave the ground.
Cheers
Mike

[Mike P]

Should have read characteristic

[Andy]

Thanks Mike
I’ve been reluctant to attempt a hand launch, or even ask anyone else as the fuselage is very wide and difficult to grab hold of, but the video below shows it being done by grabbing hold of the fuselage strakes.
So maybe I’ll add those, which would make it easier to hand launch and also partially conceal the wheel.

And I’m afraid you might have just volunteered your throwing arm, so don’t wear it out on Ian’s Tornado!

https://www.youtube.com/watch?v=1S1zg-slvfA

Andy

[jason]

Andy, can't wait to see it, if it's anything like the video you posted, very nice!