RE: First Scratch-Built. Does it look like it could fly someday?
The wing section could be a little thicker. Also you are not allowing much thickness at the trailing edge for mounting the ailerons. Typically there's a solid strip that acts as a foundation for attaching the hinges. The other implication is that you'll be using fairly narrow strip ailerons again since the trailing edge is so thin where the sheeting joins together. Thin airfoils are actually quite "in" these days for the sake of doing the more aggresive 3D maneuvers. So on that count you're quite in style. But if you want to have the wide ailerons needed for that style then you're going to have to add in sub spars at the hinge line which is typically something like 25% ahead of the trailing edge to allow forming the structure needed for the hinging systems and to close off the gaps to lock the structure. Your wing is also tapered more than I'd suggest. Especially given the thin airfoil you are using. Highly tapered wings on models tend to get quite viscious at tip stalling when you slow down for landings. Light weight goes a long way to countering this issue but there's nothing wrong with going with a lower taper ratio either. It also appears to be a relatively high aspect ratio for an aerobatic model. Not by much but somewhat. Of course you're not showing the ailerons on there so that may change the final aspect ratio depending on how wide you planned on making them.
Posted on: 11/19/2009 2:35 AM by Author "BMatthews" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=9264508

Play nice while I'm away, m'kay?
I'll be away from my moderator duties for the next two weeks while I fight off the onset of SADS by spending two weeks on the sunny island of Kauai. Since I'm the only moderator assigned to this forum there's not going to be anyone riding herd on you lot so please play nice. If something comes up that needs attention just use the report-A-post feature and one of the higher ups will drop in to make things right. And I do NOT expect to see a smoking crater in the ground and party stuff all around when I return, GOT IT! ? ! ? If you're all nice I'll give each of you one of those little umbrellas from the pineapple drinks I'm going to be existing on while away. It's a tough job but I've trained long and hard and I'm up to the task... BOOYAH! See ya'll in a couple!
Posted on: 11/19/2009 2:12 AM by Author "BMatthews" in the forum ""1/2 A" & "1/8 A" airplanes"
http://www.rcuniverse.com/forum/fb.asp?m=9264488

RE: Polyspan with Japanese Tissue trim
Yep, that pretty much covers it. The only other hint I'll offer to add is that I found the tissue lays down easier and seals more firmly if you place it and then mist it very lightly with just enough to make it go limp. Don't worry about the moisture. Even if it does cause some blushing that'll go away with the next coat of thin clear. You want the dope to be dry but I found it works best if it's newly dried. So plan on the last coat going on an hour or so before you apply the tissue. The thinner has an easier time activating it that way. There's a catch to doing something like scallops on the wing though. If you want them to line up with the ribs you'll need to space the points a couple of % tight so that when you mist the tissue and it slackens and goes limp the stretch that occurs will then line up the points with the ribs. To see how much to fudge this put a scrap stripe of tissue on the wing and mark the location of the inner scallop point or the wing's center line on one end and the last rib on the other. Now holding the strip in the air mist it with some water from a plant mister to dampen it. No need to be soaking wet, just damp is enough. While it's damp measure the distance between the two marks. Compare that to the same distance on the wing. There's going to be roughly 3/16 to 1/4 inch difference for a wing panel on a typical 1/2A model. Based on this you will want to squeeze the points in by the difference divided by the number of points to set the spacing. Then when you mist the tissue the scallop points will line up with the ribs. The first time I used scallops it caught me off guard this way. The second time I fudged the spacing a little like this and they came out really close over the span.
Posted on: 11/18/2009 8:37 PM by Author "BMatthews" in the forum ""1/2 A" & "1/8 A" airplanes"
http://www.rcuniverse.com/forum/fb.asp?m=9264044

RE: Penetration
Well, it's hardly fair to compare golf and cotton balls to this issue. I'd suggest go back and read the parts about how light models can penetrate just fine if they are engine powered. The only time your analogy sort of applies is in the case of lighter and slower gliders with higher than normal amounts of drag. Like the Goldberg Gentle Lady. The design is such that they do not like to fly fast without generating a lot of drag even when ballasted. Anyhow, there's more to it than just pure weight and momentum such as with the ball throwing analogy. It's about model design, pitch stability trim and maximum flying speed. A slow model can be clean and light so at first it seems like it would not penetrate well. But if it's clean and has extra power that power can go into producing a higher flying speed. So when you look past the golf/cotton analogy a bit further the cotton ball equivalent can do just fine or do even better than the golf ball provided the other features are there to carry the day.
Posted on: 11/18/2009 8:26 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9264011

RE: Spoilerons or Flaperons?
Yep, not a good idea to split strip ailerons that are that narrow. It's far too narrow to get a really significant flap effect from the inboard portions and it'll slightly reduce the aileron response. The best way around this would be to cut away and install new control surfaces so the new ailerons and flaps could be more along the line of 1.5 inches wide. Then you'll get enough effect to make the work worthwhile. At that point split the flap and aileron spans so they are equal on each side. For just adding some lift for takeoffs and drag for landings you can drive both flaps with one servo. However if you want to play with coupling the flaps and elevator or play with crow and other options then a full 4 servo wing with all the mixing bells and whistles will be needed.
Posted on: 11/17/2009 5:57 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9259662

RE: How important is dihedral for a Low Wing?
But hugger, you're Something Extra and Balsa Nova are both mid wing models. Aspect ratio or not we've already determined some time back that they'll fly nicely without dihedral because of this wing location. Getting back to the flipped fuselage Stik that he wants to build I'd say that it'll work fine if done as mentioned but it won't be perfect. Remember the old Top Flite Contender? That one had a rep for doing all the bad things mentioned in terms of adverse roll from rudder application. But it only bothered a few folks. Those that it did bother either added a pinch of dihedral or, as I recall, modified the wing tips to give them some upward angle so the wing acted like it had some tip dihedral. That would be a definite option for this case. It would maintain the simplicity of building a one panel "slab" wing yet provide the hint of dihedral like roll coupling. I'm thinking that if the tips were angled down it would have the same anhedral effect for the shoulder wing version. I'd just go with the stock wing and try it as the low wing conversion. If it turns out that the model displays some issues with rudder induced roll coupling to the point that it is annoying then hacking off the tips and angling them up would be far less trouble than cutting into the wing's center section and attemping to arrange for some dihedral. I'm assuming here that it comes with a one piece wing in the box. If it's a two piece setup that you join then adding a touch of dihedral would be quite simple. Just a new joiner with a "kink" in the middle and an angled wedge of sheet balsa as a gap filler. Also daRock mentioned above about how just flipping the fuselage would raise the fin and rudder area and how this would increase the rolling side effect. That's an excellent point and suggests that the fuselage should stay in the original configuration. To convert to a low wing configuration just make a new cutout in the sides and bottom which would then be glued onto the upper wing mount area. That would maintain the fin and rudder area being low and fairly centered around the thrust line and go a long way to reducing the adverse rolling effect you'd get when flying knife edge.
Posted on: 11/17/2009 5:44 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9259656

RE: BAE HAWK FLAPS
You're my hero of the week for doing this! :D Some seriously nice results you've got there so far. I was a bit dubious that slotted flaps would work at all for our model size. But from the sounds of it you're clearly seeing it work with great success. A flap that redirects the air such as this will greatly increase the achievable lift coefficient for a given size wing and be a big advantage in models where we want to achieve a very wide speed range to allow blistering fast speeds but still slow down to acceptable landing and takeoff speeds. And since size counts when it comes to high speed drag being able to make a smaller model with the same size jet turbine or EDF means the high speed can be higher. Yet with the lift you'd get from flaps that can maintain directed flow you can safely go smaller and still get the lift at regular landing speeds to allow the use of a smaller wing and model.
Posted on: 11/3/2009 5:10 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9225777

RE: Penetration
[quote]ORIGINAL: Bozarth But let's not attribute this ability to some magical aerodynamic feature called wind penetration. Increased mass flying at a higher speed has higher inertia and momentum, which will reduce the effects of gusts.......[/quote] Quite right, quite right. There's nothing magical about it. Mind you to SOME extent model trim comes into play. For examble a trainer that is set up for a higher degree of pitch stability may tend to balloon when it runs into a localized gust that momentarily raises the flying speed until the model is slowed enough to restore the original trimmed airspeed. Fighting this along with the tendency to drop the nose when encountering a sudden lull or back wind due to strong turbulence would make such a model more demanding to fly well in turbulent conditions compared to a model that is much more pitch neutral to changes in airspeed. Examples of such would be racers, pattern or 3D models and serious speed gliders that are set up for only a small or even no pitch stability margin. I wonder if such things are part of what the penetration myth is all about? As you say though, all this can be fully explained in regular terms once we know what version of "penetration" the person subscribes to.
Posted on: 11/3/2009 4:56 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9225757

RE: Penetration
Kurt, at the basis of it you're entirely right. And in the world of the sailplane or slope flyer penetration is merely the ability to make ground in a headwind which translates entirely to flying faster at an acceptable L/D. But in the powered model world it has taken on a slightly different meaning. Good ol' sematics and misunderstanding that becomes generally accepted. For power models it's just a case of advancing the throttle to make ground as long as the model isn't trying to fly in a wind that is faster than it's top forward speed. But the only time I can see that being an issue would be scale biplanes or slow parkflyers that do not have a high top speed. Instead the accepted meaning of penetration for sport power flyers seems to be one that indicates a model that rides through turbulent air in a stable manner. If all of you stop and think about how folks have used the term penetration and read into their statements what they are implying at the time I think you'll find that this is most often the case. I think it was "stolen" from the glider guiders and twisted to mean "stable in wind" instead of able to cover ground. It's a misinterpretation that's not hard to see. A fast glider coming back upwind will often look like it's on rails as it punches through any and everything turbulent in it's path. Only when it slows down again will it seem to bobble about in any turbulence. A power flyer seeing that and hearing folks say "WOW! LOOK AT THAT BABY PENETRATE!" could easily take away the wrong meaning. This thread has pretty much covered all the meanings but some of you seem to think that it should only have ONE meaning. But it just ain't the case. Rightly or wrongly it's been transffered and made to mean different things to different groups within the modeling community.
Posted on: 11/3/2009 12:35 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9225167

RE: What airfoil to use?
Here's some choices for you. A few of them are intended for fast slope planks. http://www.aerodesign.de/english/profile/profile_s.htm A symetrical airfoil will work but it'll still require just a hair of reflex so in the end it would still act like you're flying a cambered section upside down even though it's a very slight camber. But if the model will spend as much time upside down as right side up then it would be the airfoil of choice. But if you're after a model that can fly in lighter to moderately heavy winds on the slope and hold its own at thermalling then one of the airfoils shown in the link would be better.
Posted on: 11/2/2009 9:33 PM by Author "BMatthews" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=9223846

RE: Golf ball dimples
Exactly as banktoturn says. There's nothing at all magical about dimples. They are just ONE form of turbulator that happesn to work on golf balls. Raised pimples would work just as well but the clubs would beat them inward so dimples are used to avoid being damaged by the impact with the clubs. In airplanes a wide number of variations on turbulators or invigorators are used. They all work just fine. Topspeed, instead of the shape you show what you should be doing is running the upper surface shape through something like Xfoil and design it to avoid any sudden pressure transitions that would lead to the need for turbulators. Some fudging on the car would be needed due to the extremely small aspect ratio. Also it's been shown in a number of other efficiency cars that cowling in the wheel wells is highly benificial to better mileage. Or if that isn't practical as on the front then smooth wheel hubs and a curled in rear edge to the wheel well to aid the trapped air to get back out onto the outer side skin could be benificial. Also by far the more aerodynamic design is the long tail that extends well back and tapers off to nothing. This was proven very ably by the old Porsche long tail LeMans racers. They swept the field and within a year or two an overall length or maximum overhang length rule was introduced. But since those sort of tails are not practical the Kamm cut off tail is the best compromise. And best of all it helps pull up air from below the car and thus aids traction at higher speeds. Your wheel wells will also need blisters above them. As shown you do not have a realistic clearance for suspension travel. Otherwise it's a highly interesting doodle though. Nicely done.
Posted on: 11/2/2009 9:19 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9223817

RE: BAE HAWK FLAPS
Report back with the results. This is the sort of thing that not many ever bother to play with. It would be interesting if you were to tape on some 2 inch long length's of kitting wool on the flaps outside of the prop blast and have someone view them through binos while it's doing slow flybys. If the slot is helping you should see the upper surface tufts pointing down to the trailing edge to a marked degree. If the slot isn't able to fill in the stagnation bubble on the upper side of the flap then the tuft will be fluttering strongly in the vortex flow. Try different angles to see how well it works out. At some point it WILL stagnate and produce more drag but up to that time it should be a slower flying speed with little power. Once you drop the angle a bit more and it stalls the flap despite the slot you may find that it requires a nudge more power to maintain height and/or flying speed.
Posted on: 11/2/2009 9:05 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9223784

RE: Golf ball dimples
I'd be afraid that it wouldn't go fast enough to outrun the guy chasing me with a pitching wedge.... :D
Posted on: 11/2/2009 4:15 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9221868

RE: Thinking outside the box.
For a 1/2 size equivalent a sheet of Depron would be my material of choice. A lot less work than using sticks and if you round the two front corners it should reduce some of the inevitable deformations. In fact there's a number of depron PBF like electric models that are basically square for span and chord and sport a fuselage shape along with the fin to provide side area for doing knife edge stuff. Now adding side area may take away some of the PBF antics that require an easy yaw to give a skid to the side but the point is that it's an option. In fact I noticed that the LHS has Depron sheets that I could likely build two models from.....
Posted on: 11/1/2009 12:10 PM by Author "BMatthews" in the forum ""1/2 A" & "1/8 A" airplanes"
http://www.rcuniverse.com/forum/fb.asp?m=9220064

RE: whats your thoughts on this
I like it as is other than I really think it needs a nose cowl to help the jet illusion. You are showing a tail cone to aid the cause but no nose cowl? SHAME :D A plug made from some lumberyard house wood and then do the pop bottle molding trick would turn out a cowl in pretty short order. Also a couple of thoughts- - removing the taper off the rear bottom and making the top in a slight arc would more closely resemble todays fighter jets. It would not greatly increase the building time or complexity. In fact the flat bottom on the fuselate might make it easier to do the box on the building board. The part where the fins mount would still be kept as a straight line to make mounting the fins easier - While it'll fly just fine as is and act like a more or less regular short coupled model a part of me would like to see it stretched in length and chord and shortened a little in span to more closely resemble the long and lean jet fighters. Pitching manuevers would suffer a little due to the inertia moments but the roll response would be amazing. It would become a totally different airplane in flight manners even though it would obviously be from the same family design wise. Perhaps a T2 version? Also you're showing the 1/16 wing skins as optional? I'd suggest that they are mandatory. If you just covered those sticks with material it would fold up pronto either from flutter or during the first G event.
Posted on: 11/1/2009 12:01 PM by Author "BMatthews" in the forum ""1/2 A" & "1/8 A" airplanes"
http://www.rcuniverse.com/forum/fb.asp?m=9220043

RE: What to do with a crashed electric heli.....
It's a small and lightly loaded model. What feels flimsy to you with your big model familiarity would feel like it's made of steel girders to a free flight modeler that's used to using about 1/4 the amount of wood you did and then covering it with tissue and dope. For the size and for what it is the wing looks fine to me. What film did you use to cover it? I know that there's a couple out there that provide all the stress skin strength of a soap bubble... :D
Posted on: 11/1/2009 3:00 AM by Author "BMatthews" in the forum "RC Gliders, Sailplanes and Slope Soaring"
http://www.rcuniverse.com/forum/fb.asp?m=9219360

RE: Stab twist: one side. Effect?
Nice discovery on that as a technique! We'll keep the virtual internet fingers crossed for you.
Posted on: 11/1/2009 2:43 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9219349

RE: Stab twist: one side. Effect?
[quote]ORIGINAL: dick Hanson Here is another trim which is fun to play with IF on puts a small plate at the top TE of the rudder What is the effect on pitch? [/quote] You mean sort of like a Gurney flap but on both sides? So it's flat to the airflow? If it's at the top of the rudder's trailing edge it's going to act like up trim and lift the nose..... unless the trailing edge is strongly swept back or forward in which case it'll cause some up trim for a swept back TE and a down trim for a swept forward TE. But that'll fight the drag induced up trim so it would take a really strongly swept forward TE to see any nose down tendency from the plate. So... what do I win? :D
Posted on: 11/1/2009 1:54 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9219235

RE: Stab twist: one side. Effect?
[quote]ORIGINAL: frets24 ...compound issues are; 3)stab is acting as a stabilator with a negative ang of atk causing tail down/nose up=climb tendency [fig 3 & 4] requiring up elevator trim,(more drag on left, more rudder?) while at the same time... 4)the greatest twist is at the left tip again creating a moment offset by an arm causing left roll tendency [fig 5] requiring aileron trim none of this looks good for an air frame that has a bad rep for left snaps on take-off [/quote] Close. In point 3) it's DOWN trim you'd need to balance the stabilizer's twisted in negative declage in order to cancel out the climb that the twist would try to induce. Moving the elevator does two things. It alters the usually symetrical stabilizer airfoil into a cambered airfoil and it alters the center line of the overall stabilizer airfoil. The center line being from the leading edge to the trailing edge. So moving the elevator does these two things all at the same time. On the side with the twist it would be passing through the air in such a way that it would appear to be a cambered airfoil that is "flying" inverted. And that isn't going to do any wonders for the drag it's generating either. And as Dick says this higher trim drag will try to push the tail to the right/nose to the left and require some right rudder to counter it. But again, given the amount you're showing in that first picture the effect would be quite minimal. By all means fix it but if you run into any major stumbling blocks in doing so and can only remove some of the twist then I wouldn't lose any sleep over it. Other factors play bigger parts in the requirement for trimming. For example if an aileron wasn't aligned well with the wing on one side so that there was a step in the airfoil shape it would likely have more effect than the stabilizer twist you have shown here.
Posted on: 11/1/2009 1:47 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9219221

RE: Golf ball dimples
My bad on calling the lift from the spin being due to the Coanda effect. It is the Magnus effect. I'm getting my effects all mixed up.... :D
Posted on: 11/1/2009 12:53 AM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9219137

RE: What to do with a crashed electric heli.....
You're too modest. It has captured the spirit of the 1-26 in FINE style even with the slightly out of scale turtledeck area. And I hope it's the camera wide lens perspective effect but the wing tip angles in the picture make it look like the wing is twisted like a prop... :D One is pointed strongly to the floor and the other to the ceiling light! Looking forward to reading about the flying sucess.
Posted on: 10/31/2009 6:00 PM by Author "BMatthews" in the forum "RC Gliders, Sailplanes and Slope Soaring"
http://www.rcuniverse.com/forum/fb.asp?m=9218246

RE: BAE HAWK FLAPS
At our size and reynolds numbers I'd suspect not a lot. The function of the slot is to direct high speed air over the leading edge of the flap surface and in effect produce a "blown" surface that is resistant to stall so it can more ably direct the upper surface air downwards. But at our sizes the air does not flow the same way through a scale gap as it does through the full sized versions. And most of us lack the wind tunnel needed to develop a working slotted flap that will be effective in our sizes. But all is not lost. If you just copy to scale the original system the gap may or may not help but it most likely won't hurt. If it doesn't work as intended then your flap will act like a plain flap and that's not so bad either. As for hinge design and any associated tracks or other hardware you'll need to ask about options in another forum that's related to such things.
Posted on: 10/31/2009 5:51 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9218226

RE: Stab twist: one side. Effect?
The amount of roll induced by the stab twist will be very, very minimal. It's the sort of thing that a pattern flyer would notice but most others would not ever be able to detect with any degree of certainty. However what you ARE going to find with that twist is a strong tendency to climb that will require a pretty good amount of down trim to equalize. Go easy on the heat if you try that option. I strongly suspect that by the time you get it hot enough to let the wood and resin ease up to twist it back that the paint will be bubbling and peeling off. You may be "stuck" with Dick's option along with a bit of paint touch up.
Posted on: 10/31/2009 5:45 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9218208

RE: Golf ball dimples
It's hard to go back and say what the original reason for dimples on golf balls was. But there's no doubt that they have a number of effects. One, as Sport Pilot said, is to aid in the generation of lift up or to the side through aiding the Coanda effect when a spin is imparted on the ball. However other factors weigh in as well such as the delay in airfow separation which is the real topic of this thread.
Posted on: 10/31/2009 5:37 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9218191

RE: can you compensate for weight?
It's not a question of power to weight. At some point when the wing loading goes up the handling goes from pleasent to cut throat. That's why the Spitfire pilots hated the later higher powered planes more and why nice models become not so nice when overweight regardless of fiting a bigger engine to them in an attempt to compensate.
Posted on: 10/31/2009 5:27 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9218177

RE: Elevator SNAPROLL
An idea occured to me while replying to another thread. It could be worth a try and might produce a simple fix to this issue. I've guoted my thought from the other thread below. [quote]Actually there MAY be something you can do to help this. On some of my gliders I've had good luck with adding turbulators to slightly delay the high drag mush that comes near the stall. They are also supposed to slightly increase the angle where the stall occurs. You MAY find you have some luck with adding turbulator strips on the outer third of the wing on the side that drops away consistently. On the other hand if it drops off either way about equally then try adding turbulators to both sides. Locating them to do the most good is a guessing game but I'd suggest a double thickness of 1/8 automotive trim striping tape at about the 8 to 10% chord point. If it doesn't help move this strip forward a little towards the 5% point. Just be aware that a key element of this type of model is the ability to stall and snap violently on demand. To avoid it when NOT wanted it's up to the pilot to adjust to the model's needs. The pilots of the full sized airplanes have to do the same thing. Anyhow the big outcome of this is that the model may not snap the same upright as inverted or the same from one side to the other if you end up with the tubulator on the one side only. Adding more strips of different lengths may or may not fine tune the stalling charactarisitics but I just don't really know. At least it's something that's easy to play with and try different things.[/quote]
Posted on: 10/29/2009 3:53 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9212760

RE: can you compensate for weight?
Ah, the famous tip weight for takeoff. That's been discussed as well and it would not have a place in this model unless it turns out that it's out of balance laterally and you're just trying to correct it to put the lateral balance back onto the centerline. There's a thread about this article that came out in MA recently as well. It MAY, and I doubt even that, have a place in some trainers or scale models but it sure doesn't belong on any sort of aerobatic model. I'd start by using something like the Robart incidence gauges to check for warps down to a high degree of accuracy and from there ensure that both ailerons are faired into the airfoil shape and not sticking up or down even slightly. Also check overall rigging of the wing to the fuselage and to the fin for even a hint of misalignment. Diagonal measurements from equal points out on the wing to the fuselage centerline back by the tail should be accurate to within 1/16 to 3/32 inch. And you can't trust the fuselage either. Set up some sort of rig to test the fuselage for straightness and that the fin is accurately mounted with a 1/2 degree of this tested and known good line. If you read that other thread you'll find that there's a general consensus that radically tapered wings on our models are rather critical to a number of factors. Even small airfoil differences can cause what you're getting. But by far the worst thing is a heavy model and a strong taper ratio. It's just a bad combination that makes the model hyper sensitive to tip stalling. And if there's any sort of misalignment or side to side differences in the wing it'll encourage a stall and snap to one side or the other pretty consistently. About all you can do is try to find any minor differences, especially in the outer 1/2 of the wings, and "fix" them so both wings are identical. Actually there MAY be something you can do to help this. On some of my gliders I've had good luck with adding turbulators to slightly delay the high drag mush that comes near the stall. They are also supposed to slightly increase the angle where the stall occurs. You MAY find you have some luck with adding turbulator strips on the outer third of the wing on the side that drops away consistently. On the other hand if it drops off either way about equally then try adding turbulators to both sides. Locating them to do the most good is a guessing game but I'd suggest a double thickness of 1/8 automotive trim striping tape at about the 8 to 10% chord point. If it doesn't help move this strip forward a little towards the 5% point. Just be aware that a key element of this type of model is the ability to stall and snap violently on demand. To avoid it when NOT wanted it's up to the pilot to adjust to the model's needs. The pilots of the full sized airplanes have to do the same thing. Anyhow the big outcome of this is that the model may not snap the same upright as inverted or the same from one side to the other if you end up with the tubulator on the one side only. Adding more strips of different lengths may or may not fine tune the stalling charactarisitics but I just don't really know. At least it's something that's easy to play with and try different things.
Posted on: 10/29/2009 3:50 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9212754

RE: Aileron
[quote]ORIGINAL: Campgems .....  I'm rebuilding a 1/3 scale Laser 2000 and I was wondering how they would work on it. .......[/quote] I had totally missed that part or read it and it didn't register. There's no way I'd use either the angled wire in a box system or the Durant system in your case. The biggest reason is the issues of installing either one in a rebuilding situation. Either systems would require major work and demolition to incorporate into an existing plane and for no actual flight benifit. Add to this the need for a very high degree of accuracy with either system to ensure that the servo axis lines up spot on with the hinge line or that the bend on the torque activator lines up dead on the hinge line axis. You just do not need that sort of extra concern in a rebuild. During new construction it wouldn't be so bad since it would be easier to arrange assembly jigs and measure alignment more easily. But on a rebuild you're not going to have a good way to ensure that amount of accuracy in the placement of these systems. And frankly it's just more work to cut into an existing model for this than it's worth. Neither of the systems give you any advantage other than a visual one for neatness. And both bury the servos in a way that makes adjusting or replacement a total PITA. On a model of this size external horns on the underside of the model are all but invisible anyway. If the model uses surface mounted servos and you're just looking to tidy up the installations just lower the servos deeper under the surface so just the output arms are exposed. Just putting the bodys of the servos under a hatch or patch of covering material will make things look a LOT cleaner but still allow ready access to them for servicing. A far more sensible compromise all around in my opinion. Especially given the opportunities for damage to the servos from pushing around such large surfaces or if those surfaces should suddenly be leaned on by an external force. I don't fly the big stuff like these but it seems to me that burned out servos and stripped gear trains would not be all that uncommon on these models.
Posted on: 10/29/2009 3:27 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9212708

RE: question about airfoil
Yep, the only place where it would be worth using a semi symetrical airfoil is during slow speed. The rest of the time the stock airfoil would be just fine. And instead of building new wings adding flaps to alter the camber for the slower speed would be a lot less trouble and more flexible in use. 10 to 15 degrees for takoff will provide the extra camber to be able to lift off at a lower airspeed. Then using 60 to 80 degrees will provide lift AND drag for landing. As a side benifit using flaps also induces a strong washout effect in the wing so you don't need to worry about tip stalling during landing or takeoff unless you get really greedy in trying to climb too fast or stretch the approach in a dangerous manner. Even better would be to add both flaps and a drooping leading edge. But that may be too much work.
Posted on: 10/29/2009 3:06 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9212652

RE: can you compensate for weight?
There's nothing you can do for an overweight design. And what you're seeing isn't unusual. Check out the ELEVATOR SNAPROLL thread that is currently running for a case of the same problem and comments on things to look for. But in the end if it's overweight there's nothing to be done for it other than learn to fly it in a way that avoids the bad things and promotes the good things. Getting the CG in the right place would be a good first step if it's not there already.
Posted on: 10/29/2009 2:52 PM by Author "BMatthews" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9212617