Keith Evans 3 Posted March 6, 2020 Share Posted March 6, 2020 I'm currently building an own design model and am looking to use spoilers for roll control as I want to use full span flaps . A few questions . I have followed A.G. Lennons advice regarding size and positioning of the spoilers , but I do not have any info re operating angles for speed of roll . Any suggestions ? Will the air flowing over the wing be sufficient to hold the spoiler in the fully down position or do I need to do this mechanically .? Thanks Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted March 6, 2020 Share Posted March 6, 2020 Mechanically every time As loose surfaces will resonate violently in relation to airspeed Quote Link to comment Share on other sites More sharing options...
Tim Cheal Posted March 6, 2020 Share Posted March 6, 2020 Keith, I am not so sure about models, but I assume the the same principle will apply. On full size aircraft if the spoilers become unpowered the low pressure above the wing (which is, arguably, what is keeping us flying) will cause the spoiler to partially deploy. Personally I think the affect will be less on a model, but it will depend on many factors (position, model weight, incidence etc....). Thus, I concur with Denis to hold them down. Tim Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted March 6, 2020 Share Posted March 6, 2020 Another option would be magnets, years ago I had a Chris Foss Hi-Phase Rudder/Elevator/Spoiler glider, spoilers being used for landing. These were on a simple pull cord which went to one servo in the fuselage to pull them open and had some fridge strip magnets to keep them shut. Quote Link to comment Share on other sites More sharing options...
John Minchell Posted March 10, 2020 Share Posted March 10, 2020 I have read a number of books on aerodynamics including Andy Lennon's. The consensus is that spoilers don't give as rapid a rate of bank as conventional ailerons would. With full span flaps you also create the wash in problem at the tips and alter the lift distribution, such that you are more prone to a tip stall. At least with flaps inboard and reflexed ailerons during crow braking, the wash out effectively prevents a wing dropping. Be interested to hear of your out come when flying the model. John M Quote Link to comment Share on other sites More sharing options...
eflightray Posted March 10, 2020 Share Posted March 10, 2020 Why not full span 'flaperons; ? . Quote Link to comment Share on other sites More sharing options...
eflightray Posted March 10, 2020 Share Posted March 10, 2020 Actually a better question would be, why do you want full span flaps ? . Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted March 10, 2020 Share Posted March 10, 2020 A club mate tried full span flaperons on an Acrowot it very nearly turned into disaster and he only managed to get it out the resulting tip-stall at the last second. He turned this "feature" off never to use it again. A. Quote Link to comment Share on other sites More sharing options...
Keith Evans 3 Posted March 11, 2020 Author Share Posted March 11, 2020 Hi all. Thanks for the input .I was inspired for my own design by Andy Lennon's STOL design "The Crane" as shown in his book " R/C Model Plane Design " and particularly the photographs of its very steep landing approach . If I could have got hold of the plans easily I would have built it .I've built his "Snowy Owl" a while back and enjoyed its construction and flying abilities . Not only has the "Crane " got spoilers for roll control but also ; full length wing flaps ; fixed L.E.slats ; Hoerner Vortex Retarder Wingtips ; a fully moving tailplane with an inverted airfoil and fixed leading edge slats fitted to a Tee Tail . Is that enough of a difference from a normal run of the mill trainer ? All the moving surfaces will be fully sealed . My own design is Called " Hi Tee " .It has a 60 inch wing span and will be powered by a 40 size engine. It is a low wing radially cowled tail dragger . This is quite a challenge for me but I needed something interesting to do over the winter period . Have I bitten off more than I can chew ? probably . I am not a wizz at flying , but for the last few years I have being playing about with what flaps can do for me in my current fleet . My limited aerobatics consists of rolls , loops ,stall turns and any combination of these . l like flying as slow as i can . Is this age related ? It will probably be ready for its maiden about May /June time . Will I be maidening it ? No way I'll be trusting that to John . Thanks for all your input . Quoting from Andy's book . "Spoilers offer the following advantages for roll control . There is no adverse yaw ,Yaw is in the direction of the turn . Do not need balancing . Work inverted . Simple installation .light . No lag response if located behind 70% of the wing chord ." Keith Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 11, 2020 Share Posted March 11, 2020 Keith If your control system allows it can be argued that 100% aileron differential (up only, no down) has the same effect as spoilers. Ailerons have the advantage of an instant response with the possibility of using aileron 'droop' in conjunction with flaps for STOL. Are you considering relying solely on spoilers? If so would they be used for roll trim? Just some thoughts. Quote Link to comment Share on other sites More sharing options...
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