Tim Costello

I am designing a big flying wing with sweepback and need some info on varying the wing-section from root to tip please. I have discovered that one should incorporate what is generally called 'gradual wing twist', or washout to be more exact, from root to tip. This should be about 2 or 3 degrees for the popular sweptback wing model, using a constant reflex type wing-section and 30 degrees of  sweepback on the tapered wing.  There is a second approach. Again, the usual 'reflex' wing section is used at the root, with its rear part gently curled upwards. This section would gradually change to a different one at the tip. Perhaps a semi-symmetrical one?  I need advice here please about what section to use at the tip and what amount of gradual washout to use.  However there has been an interesting development in recent times as a result of new wind tunnel work and computer modeling. It transpires that there is no need for a reflex wing section for about the first 25% of the wing from the root outwards. However, the wing out near the tip does need a reflex wing section or profile. The reasoning is that the centre of the wing has not got enough moment-arm from the centre of gravity to the centre of lift for the wing section shape to matter very much. Using a reflex section here is  unnecessary and will just cause some drag.  However, remember that the wing, out near the swept-back tip, is actually acting as a tailplane for the model. This part of the wing, just like a tailplane on a fuselaged model, needs to provide a ‘nose-up’ force to counter the natural ‘nose-down’ tendency of a wing. Thus the need for the ‘up-elevator’ effect provided by the curled-up rear part of a reflex wing section. That discovery makes perfect sense to me. In a follow-up Eureka Moment I thought of a new method of elevon control to fit in with the above findings.  I could use thin, soft, springy balsa laminated to paper-thin plywood for the elevons, the whole length of the trailing edge, but firmly glued to it, un-hinged. So my proposal is this:  The flexible elevons would not be hinged as usual but would be glued completely to the wing trailing edge along its whole length. The servo, push-rod and horn would be out near the wingtip so that when, say, 'up elevon' is applied, the whole elevon is torsionally twisted along its length as only the outer part gets the benefit of the horn action. So the elevon would be twisted up fully at the tip, less so at the half-span point and none at the root where it would hardly move at all and indeed is not needed to do so aerodynamically. Isn’t this worth trying?  Comments welcome please, in the spirit of experimentation!   Also this is where I need some advice - about what tip section to use and why. I feel that a semi-Symmetrical would be just right  but with how much washout?  I feel that a reflex section at the tip is a bad idea, especially when down elevon is used.  There are just too many changes of airflow direction where least needed with a high possibility of tip-stalling. A semi-symmetrical section makes a lot of sense allied to a few degrees of 'up-elevon' to act as reflex. None of this interferes with the aileron function of the elevon. Flying Wings are a greatly under-used type of model, especially in competition, as they have many advantages over fuselaged models. On a human level they should have the outer 10% of the port wing painted a bright fluorescent Humbrol 209 Orange so you will never lose the model to frequent orientation problems.  Remember Jack Northrop and his successful range of flying wing bombers? The only reason they were not commissioned into the US Airforce was because the Senators who controlled the finances at the time thought they were too futuristic!

I am trying to buy a Flying Wing glider of traditional balsa/ply construction and so far have not found a single supplier!  I don't want a foam/EPP type on this occasion but an ARF swept wing model, pure glider or electric, about 4 feet to 8 feet span and I am amazed they are not listed anywhere in Europe.   Thunder Tiger did produce two wonderful models, the "V-Bat" and the "Velocity 2". While both models are listed by Google they are not actually in the shops anymore. So if anyone knows where I can buy one please e-mail me or reply [email protected].    It was always a most magestic if not mystical sight, to see a couple of flying wings aloft against a blue sky with the sun shining through the wing structure. Various countries on the European mainland held 'tailless gliders only' competitions with mass launches. Now that was really a sight to behold!   I look forward to any replies.   Tim Costello.

Thank you for taking the trouble to reply to this weird problem so here is the story: The ESC has gone back to the shop for exchange. My pal and I think the model shop just 'unloaded' the nearest ESC to hand onto us with no thought as to suitability. We can't remember the make or model but it was a physically big size for a small model and definitely read '7 - 16S Lipo'.    Unfortunately the instructions for programming are gone back too but I have since then gleaned a possible cause of the low revs. Have you heard of 'Voltage Depression'? We electric flyers are becoming like doctors now!  Anyway, when you switch-on and the ESC sees a lower voltage than it is made to handle (as in our case) or if it sees a low voltage caused by a worn out on partly discharged battery, it simply switches the motor to low revs to allow it to draw more amps. This is presumably to ensure the vital formula Volts x Amps = Watts still applies. I found this on the wattflyer.com forum about the 'Super Simple' low-cost ESCs.   Another (trusted) model shop pal said that if the ESC is too big, in voltage and amperage terms, for the motor/battery combo, it will only act like a switch producing just two outcomes: off and full revs and the full revs will probably be low.   Our shop has shamefacedly  agreed to order the correct size ESC as recommended by Multiplex for the Twister. They obviously didn't have it in stock so palmed off the big one on us. I think that says it all......   Tim.        

I have a Multiplex Twister with the supplied motor. I use a good quality 3S Lipo and the model shop sold me a speed controller marked: '7 - 16S Lipo'.    The problem is that the motor doesn't give enough revs to power the model into the air. It just flies about 10 feet mushing onto the grass even with a good hand-launch. The motor doesn't sound being at full revs, no 'scream' and very little wind coming out the back and no 'pull' while in my hand.   So is the ESC just too big for my 3S cells (marked 7 - 16S remember) and somehow soaking up the volts?   Any help will be appreciated as I think I have been sold a pup in the ESC.   Tim in Dublin.    

I know I'm only a year or so late but now SLEC have brought out the Fun Fly with laser cut formers, fuz sides and other parts, die-cut balsa parts and laser-cut wing ribs hollowed out!  I bought the kit on the strength of these alone and am building a modified version using all the parts.  Looking a bit like the USA 'Gee String' model mixed with a Spitfire.  I have added rounded wing-tips, curved elliptical trailing edge/ailerons, also the tailplane and fin.  I have abandoned that upright squared-off fuz rear top and added a nicely rounded top to it and the front tank cover and engine cowling. A bubble cockpit on top of the wing and the tailplane on the rear fuz underside keep the thrustline forces correct. It looks great so far and will fly with my Saito 40. On a visit to my local artists supply shop I found them selling lovely coloured self-adhesive plastic off the roll. There is a heavy backing paper but the plastic sheeting is light and very sticky. I'll probably use Balsaloc to help it stick. If anyone is interested in this I will post details and my progress.                                                  Tim in Dublin.