RE: How to cure stall snap to the right
[quote]ORIGINAL: scrambow I've started flying a new 27% Hangar Nine CAP 232G. All is well except for a nasty snap to the right when it stalls; high-speed and low speed both. I have checked the incidence on both wings at the fuselage and the tips and they are the same on both wings. The horizontal and elevators are equal as well. The CG is right in the middle of the range recommended by the manufacture. Any cures for this? [/quote] Thank you hdsoar and Darryl. There's likely nothing seriously wrong with the airplane. It's doing what it's designed to do, and Caps do it very well, if you learn to control it. There are several possibilities as to why it always snaps to the right however: If the CG is centered laterally on the airplane, the aileron gaps are sealed airtight, and the ailerons are trimmed correctly and free of warps, equally torsionally stiff, etc., then, at the moment of stall, the rudder is not in the right place (ball is not centered) to properly counteract the sum of the yaw moments produced by the spinning propeller. Try adding a bit of left rudder trim and/or commanding a TINY bit of left rudder while practicing low speed, wings level stalls and see if you can't get it to stall more or less wings level initially. That will give you a better feel for it. If you need to add left rudder to keep it from rolling right while practicing partial power wings-level stalls, then you need to trim the rudder left. The rudder may even need to be left of center at neutral and this is OK; it may be needed to correct for spiral slipstream, excessive right thrust, insufficient vertical stabilizer offset, etc. This may not give you perfectly straight flight at high speed however, so you will have to decide whether you want to try to use mixing (I don't), or trim for high, medium or low speed stall. There's lots more to it but you get the idea. You get to decide how you want to set it up based on your skill, preference and flying style.
Posted on: 9/29/2007 11:15 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=6430233

RE: Suhkoi rudder coupling
The model you have selected has a nearly scale outline. It will have to be completely re-designed to become a decent so-called 3D plane. Not that it wouldn't be a thoroughly enjoyable plane to fly; you just will not have something equivalent to a QQ Yak or the likes. You'll have a (nearly) scale model. If you want something really neutral, pick a different plan to build.
Posted on: 9/29/2007 10:54 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=6430142

RE: How do I flat spin
[quote]ORIGINAL: hydro-don Hey guys I have a stick like model that will only spin about 45 degrees nose up. It balances about 35% and snaps out of a loop at 1/2 elevator. It will do a flat turn, rudder, opposite aileron effortlessly, so my question is can this plane be made to flat spin? How much rearward CG can one safely fly with? Is short coupling more desireable or does it not matter? [/quote] Length of tail alone cannot tell. Size of rudder and elevators is more important. You, as the pilot, are in the best position to tell us whether your plane will flat spin or not. Try some of the techniques listed. A common full-scale way to enter a flat spin (because it produces consistent results), is to enter a normal, power-at-idle, upright spin to the left, with ailerons neutral (or negative spin with right rudder), then, after a turn or two, smoothly increase power and apply right aileron simultaneously until the nose comes up and the rotation rate decreases. If this technique doesn't do it, try some others. Factors affecting spins are many and complex, and nobody fully understands them all (otherwise flight testing would not be necessary), so it can seem like an art at times. Sometimes a seemingly very small change can have a dramatic effect on spin characteristics. There are some generalizations that can be made: Side area ahead of the CG is "pro-spin" (aids spin entry/hinders recovery), or destablizing. Area aft of the CG is anti-spin (hinders spin entry/aids recovery), or stabilizing. Fin/strake/dorsal area below the horizontal stabilizer when upright, or "above" the horizontal stab when inverted, is anti-spin. If a plane has sufficient rudder and elevator authority, and a sufficiently rearward CG, then aileron application is not necessary for spin entry, but it affects spin characteristics, sometimes dramatically. Planes tend to flat spin better to the left, because of gyroscopic precession. Planes with low thrust lines tend to flat spin better upright, and the opposite is true for high thrust lines. All these effects are interdependent and one or more can override others. A few airplanes that can be made to spin, cannot be made to recover from the spin. And some airplanes that cannot recover from upright flat spins, or can recover with difficulty, can recover easily from inverted spins, like the F-4U. An examination of the empennage in the context of airflow from "below" compared with "above" will reveal the primary reason.
Posted on: 7/3/2007 11:22 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=6065777

RE: Can you believe this flies?
[quote]ORIGINAL: psk560 The wind was straight down the runway today light and variable. I'm sure it would do great upwind but the downwind side could be interesting with the much smaller airspeed. LOL. Craig [/quote] The wind by itself doesn't affect the airspeed. The groundspeed, yes, but not the airspeed.
Posted on: 7/3/2007 10:53 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=6065668

RE: elevator induced snap.
[quote]ORIGINAL: da Rock <snip> ABSOLUTELY !!! Exactly the truth about this topic. Aerobatic airplanes REQUIRE elevator deflection that can and will stall the wing. And that means you have to fly loops and such with less than that deflection. That's one of the primary reasons Dual Rates were invented. It's not an error in design or a failure of the airplane that some of them tend to stall out of loops or stall off on one wing when landed too slowly as many inexperienced flyers instantly assume. It's the pilot using too much elevator and/or trying to steer with ailerons when the steering should be accomplished with the rudder. Tune your elevator throws. Tune your dual rates. Tune the CG location. Then tune all three again. Then tune your flying skills. [/quote] Ditto. da Rock speaks da Truth!! Know thy airplane!
Posted on: 6/21/2007 10:22 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=6015718

RE: wing rock?
reflex didn't help my giles. lightening it and moving the cg aft did. doesn't mean it would't help anyone.
Posted on: 5/4/2007 3:05 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5811131

RE: wing rock?
[quote]ORIGINAL: rzarikian so... how can it be eliminated or reduced?? [/quote] The best way is to start with an airplane known to have the features I have already alluded to. You might be able to improve an existing plane by making sure there is enough elevator throw and that the CG is far enough aft. Wing tip plates might help by improving yaw stability and reducing span-wise flow. A ventral fin and/or rudder extension is almost certain to help. And, practice, practice, practice.
Posted on: 5/2/2007 4:54 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5802280

RE: How do I flat spin
Positive flat spins to the right don't usually work as well, or at all, because gyroscopic precession raises the nose when yawing left, and lowers the nose when yawing right. This is the flight condition where gyroscopic precession is most noticeable. My personal preference is to start the spin without aileron, then feed it in as I increase power.
Posted on: 5/2/2007 11:07 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5801050

RE: wing rock?
Anything that reduces pitch authority can be a contributing factor for wing rock, but this is not the most important factor for wing rock alone. Even so, a well-aft CG is desirable for "3D", so a pitch-neutral CG is generally best. i.e. as far back as you can get it without having it climb on it's own when you roll it inverted, or becoming unstable.
Posted on: 5/2/2007 6:13 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5800312

RE: wing rock?
Small yaw oscillations at and beyond stalling AOA can set up resonant rocking. The more stable your airplane is in yaw [i]at high AOA[/i], the less it will rock in harriers. Ever notice most planes harrier better (rock less) when harriering inverted? That's because the stab and rudder is in relatively clean air beneath the stab. Upright, much of the stabilizing fin area is blocked by the stab/elevator. Airfoil and wing planform have an effect too, but somwhat less predictably. Generally the sharp LE, thin airfoils are favored because they stall very easily at low AOA. They don't try to unstall as much as the thicker airfoils and therefore tend to rock less.
Posted on: 5/1/2007 3:02 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5797250

RE: Aileron Differential question
[quote]ORIGINAL: Flyboy1958 Now from what I have read, you should pull up to a 45* line and roll right. If the plane walks to the right, I have too much down aileron? Just sounds backwards to me, because if I roll to the right, with the left aileron going down, wouldn't that make the plane walk to the left with too much down aileron, more drag and so forth? What am I not understanding? [/quote] Even on a positive 45d up-line, the wing is positively loaded, though not as heavily as in level flight, and adverse yaw works in the conventional way, i.e. too much down aileron causes yaw in that direction. But here's a twist: In a 90d up-line, the nose will yaw slightly toward the aileron with the greatest deflection, or presented area. So if both ailerons move up more than down, in this case the nose will yaw right when applying right aileron, and left when applying left aileron, [i]ceteris paribus[/i]. The above method uses a 45d line as a compromise between level flight and a 90d upline. I think a 60d upline might also be a good compromise, since it will result in even less differential, which suits me. But if you have an airplane that is symmetrical with neutral incidences, and symmetrical surface hinging, just set the aileron throws as equal as possible, then fly the thing. These effects cannot be eliminated for all airplanes and flight conditions; they can only be made small enough that they are not noticeable to the judges under most conditions. Incidentally, I don't use the above method because of the relatively strong P-Factor effect that exists in a 45d upline. You end up ignoring P-Factor, while deciding how much differential to program. What about the 45d inverted uplines? Now you've fouled things up, though maybe not to a large degree. Full-scale acro pilots (I'm one of them) don't spend time trying to optimize aileron differential and rudder mixing. They spend time practicing using the rudder to correct for these effects. That way, with practice, they can use the right amount of rudder for any flight condition, instead of trying to find an automatic compromise that only works perfectly in one flight condition. I know this flies in the face of the conventional wisdom that you have to set up and trim your airplane the way the big dogs do to hope to compete in pattern/IMAC. To each his or her own!
Posted on: 4/20/2007 10:47 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5744263

RE: Aileron Differential question
[quote]ORIGINAL: alan0899 ...G'day Mate, Differential actually reduces the amount of down aileron, & leaves the up aileron as is. The method described in the trim chart is easier to understand. You fly the plane towards yourself, pull up until vertical, release sticks, then half roll, then you are looking at the top of the plane. That way, Left is left & right is right. [/quote] The above method is specialized for pure aerobatic planes, and can be used to find the right amount of differential to use for Comp-Arfs and such that use top-hinged ailerons. The aerodynamic differential that exists as a result of the non-symmetrical hinge location (or wing incidence, etc) will cause heading deviations that can most easily be seen and corrected using the above test. It is NOT a suitable test for the amount of differential to use for a Cub or a PT-19. For the latter airplane types I fly straight away from me in level flight at a moderate cruise speed, and use rudder at lower speeds to make up the difference. Differential is any case with different amounts of up and down. It doesn't have to only refer to reducing the down. What if I wasn't using all the throw and I chose to increase the up? The effect would be the same, and it would still be differential aileron throw.
Posted on: 4/20/2007 9:57 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5744064

RE: What's the different between a pusher and puller props?
[quote]ORIGINAL: dick Hanson ...see picture of EDGE... [/quote] Off topic: How do you like those tip plates? Cooling drag can be HUGE. Racers know that too.
Posted on: 4/12/2007 10:33 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5704126

RE: What's the different between a pusher and puller props?
[quote]ORIGINAL: vmsguy ...That being said, I'm thinking more from a pure aerodynamic standpoint. Say you have a 10-6 prop on both of the above setups. Would the shape of the prop bladed differ? Like the rate of twist, thickness of prop blades, etc. I hope that makes more sense this way... [/quote] The shapes of the blades would not differ. The same propeller theory applies to both tractor and pusher props. There are aerodynamic results on the aircraft however, like no slipstream effect, if there is no tail in the slipstream, etc..
Posted on: 4/12/2007 7:10 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5703567

RE: airfoil choice for heavy lift ducted fan
Are you asking about the airfoil for the fan itself?
Posted on: 4/11/2007 11:32 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5699044

RE: What's the different between a pusher and puller props?
You can't just mount a tractor prop on an engine that is facing backwards because the engine needs to rotate the wrong direction for the prop. So you either need a pusher prop, which is different only in it's direction of rotation, or an engine that rotates the wrong way, and use a tractor prop.
Posted on: 4/11/2007 11:28 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5699026

RE: Lowering of engine on thrust line
Chris, what is the specified CG for this model in %MAC?
Posted on: 4/10/2007 12:37 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5693943

RE: Lowering of engine on thrust line
[quote]ORIGINAL: Tall Paul With a "lifting tail", the plane becomes a one-speed airplane. It will be trimmed at one speed. To get that trim.. very little elevator deflection, the c.g. will need to go aft. It's basically a low wing Telemaster. [/quote] Or would be a low wing Telemaster if the main wing's airfoil wasn't symmetrical. That throws off the relationship between the wing and tail as compared to the Telemaster. With the Telemaster, as speed increases and the tail rises, so does the wing, since it's also strongly cambered. No so with chris's model, because as speed increases with it, the main wing doesn't experience as much of a lift increase in proportion to the tail, hence the 15-18 clicks of up-trim needed. Also, raising the thrust angle effectively moved the CG aft under power and that made the problem worse. I would want to know the tail volume, etc, before I moved the CG back much on this particular model, knowing only that the tail has positive camber. It might work fine, but it would be a lucky guess at this point.
Posted on: 4/10/2007 12:29 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5693909

RE: Lowering of engine on thrust line
[quote]ORIGINAL: RCPAUL What in the original post makes one think the tail is undercambered? He said flying tail. Paul [/quote] For simplicity, I take the geometric convention, rather than an aerodynamic one, and every time I use the term "positively cambered", I mean greater camber on the top surface of the airfoil than on the bottom. I never stated the tail was undercambered, nor that I got the idea that the tail was positively cambered from the "original post". The Original Poster, chris de jon's reference to a "flying tail plane" a few posts ago, caused me to correctly assume he meant one with more curvature on top than on bottom. This agrees with his description of the airplane's flying characteristics. Positively cambered airfoils are not necessarily undercambered. A NACA 24012 has a positive camber, but is not undercambered. I realize that a positively lifting tail does not have to be cambered at all (but might be much more efficient with positive camber), but as I mentioned earlier, a tail with positive camber may lead one to assume that the tail always lifts positively (which I believe many equate with the term, "flying tail" ) , but this isn't necessarily true, since CG and NP must be considered as well. My real point here is that we really don't know for certain whether the tail of chris's airplane lifts positively or negatively in any flight condition. We only know that the airplane needs a lot of up-trim, and needed still more when the thrust angle was increased. We can say that the tail lifts positively at all times, but more so at high speed, or we can say that the tail lifts negatively at all speeds, but less at high speeds, or some combination. Still, we have a clue toward a hypothesis: If the tail was lifting positively, then raising the thrust angle would increase the nose-up moment, forcing the tail down, requiring down-trim. But if the tail was lifting negatively, and we raised the thrust angle of THIS airplane, it might free up the positively cambered tail to to produce a nose-down moment, which would require up-trim. Therefore, my hypothesis, subject to refinement, correction or abandonment, is that even though this tail has a positive camber, it is possibly lifting negatively at the speeds chris has flown it. This might indicate that the designer did not have a good grip on stability theory, though that is not meant as a criticism. Chris, If it was my airplane I would at least try going to down-thrust instead of up and see if that helps. I know it seems counter-intuitive but taken with your earlier observation, it makes sense to at least try it. Just be ready to re-trim again.
Posted on: 4/10/2007 11:37 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5693546

RE: Lowering of engine on thrust line
"O"riginal "P"oster. Your airplane has a very unusual configuration with it's symmetrical main wing and cambered tail. As configured your plane is not meant to be seriously aerobatic, but gentle and slow. Unless you change the tail to one with a symmetrical airfoil, you will not be able to rid it of it's current tendencies, though you might be able to reduce them in accordance with pimmnzs' suggestion. Airplanes with tails like your airplane's sometimes have the characteristic of nosing down at higher speeds, which I would expect your airplane to do, since the camber alone will cause the tail to rise with higher speed and the symmetrical main wing's lift increase depends only on it's incidence, not it's camber. It's even possible, again depending on configuration, that if flown at a sufficiently high speed, the nose would "tuck" and not recover no matter how much up elevator was applied. The term [i]elliptical[/i] is usually applied to the wing planform (shape as seen from the top or bottom) or it's lift distribution, not the airfoil.
Posted on: 4/10/2007 11:12 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5692777

RE: Lowering of engine on thrust line
[quote]The model is an 84" low wing, with a flying tail plane.[/quote] Admittedly this was an assumption on my part but I thought the OP meant positive camber (curved on top) by the above remark. I await correction by the OP. If my assumption was wrong, then my suggestion may also be wrong since it was based on the above assumption. I was trying to come up with a plausible reason why angling the engine further upward would result in an increase in up-trim required. I think I have one.
Posted on: 4/9/2007 2:09 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5688727

RE: Lowering of engine on thrust line
I agree that the characteristics you observe are caused by the positive cambered tail. It is lifting too much (or not providing enough down-force). That's why so much up-trim. Raising the thrust angle has the effect of moving the CG backward under power. This frees the tail up to lift even more. Sounds like you need down-thrust, not up, but you need a better tail airfoil even more if you want to do aerobatics. Incidentally, just because the tail has a positive camber, does not guarantee that the tail lifts. If your CG is at 25-30% MAC, it almost certainly is not lifting, but rather pushing down as is conventional, but with the disadvantage of having a positive camber.
Posted on: 4/9/2007 8:44 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5687832

RE: Wing-Lift Increasing Idea (Tested by me)!!!!
Even Beech didn't consider all the factors from the beginning. Composite structures tend to be locally severely damaged by lightning strikes so for certification they had to add a metal mesh within the skin to conduct electricity through the airframe and minimize damage. This was not a trivial bit of re-engineering. This added weight and expense and may have been what ultimately killed the Starship. So the purpose of the composite structure was totally defeated, at a much greater cost than a metal structure would have been. At least that's the way I remember it. I welcome any corrections. Look also at the Porshe PFM Mooney. Great idea but they couldn't or didn't want to use a vacuum system so the FAA required two completely independent electrical systems to ensure sufficient redundancy for IFR operations. With only one electrical system and no backup battery, an electrical system failure in instrument conditions would have resulted in a fatal crash every time. The airplane was simple to operate but who cares? It had a crummy useful load and it wasn't as fast as other Mooneys. But it was innovative. It's great to innovate but somtimes the cost can be very high when all factors are considered for the intended function. Still, the industry learned a lot from Beech's mistake and maybe on the whole, a little Preparation H does feel good. Oops, I digress. I mean there has probably been a net benefit to the industry from Beech's expensive experience with the Starship. Thanks, Beech/Raytheon! This isn't to say that just because an idea doesn't catch on, that it wasn't a good one. Maybe sometimes the airplane mafia conspires to keep good ideas down to avoid competition. Nawww, that never happens.
Posted on: 4/4/2007 10:55 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5663806

RE: Why does it fly?
[quote]ORIGINAL: Bax I did read of an incident where an F-15 2-seater had a collision and lost a significant amount of one wing panel. The airplane was controllable enough to be able to safely land. Wonder if that was an "urban legend" type of story, though. [/quote] I heard or read something similar while I was in the USAF.
Posted on: 4/2/2007 12:48 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5653718

RE: Control surface placement
[quote]ORIGINAL: spinn Any thoughts on coupling rudder and ailerons through my transmitter? [/quote] Many people like to do this but for properly coordinated turns, the correct amount of rudder for a given amount of aileron varies with the AOA and speed. So mixing it in will only be correct for one flight condition and you will be applying too much rudder or not enough for every other condition. It takes practice and really paying attention to the airplane but you can get better rusults and more satisfaction from doing it yourself, IMNSHO.
Posted on: 4/2/2007 12:33 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5653662

RE: fUNTANA fRANKENSTEIN BUILD
At worst you might experience slightly worse directional stability at high AOA than with rounded fuselage corners. Or there may be no noticeable difference.
Posted on: 4/2/2007 12:18 PM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5653608

RE: Wing-Lift Increasing Idea (Tested by me)!!!!
:)
Posted on: 4/2/2007 11:49 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5653503

RE: Why does it fly?
[quote]ORIGINAL: nexstar22 actually with planes such as f-16's, there lift is created by the wings, untill the angle of attack becomes so great that the lift is no longer generated by the air moving over the wings, but is actually created by the thrust of the engine alone...as for most rc planes the power to weight ratio is so great that the lift generated by the wings is really only needed for straight and level flight. thats why we can acheive crazy manuvers that cant be done in a real plane. [/quote] So are you saying that if the wings broke off an F-16 during a tight turn, or they broke off a 40% Edge during a harrier or a wall, nothing would happen? It would just keep flying at high alpha until the pilot tried to level it out, then it would fall from the sky? Remember, even a stalled wing produces some lift.
Posted on: 4/2/2007 10:06 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5653126

RE: Why does it fly?
I'm with you on those Yaks and such. All those swiss cheese laser cut plywood slab sided clones get a little monotonous. Still, they fly well. I miss building in earnest but with three kids and my full-scale flying pastime in addition to my real job, I get precious little time for it.
Posted on: 3/27/2007 10:18 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5623983

RE: Why does it fly?
It's a "stand way off and squint" scale Phantom!
Posted on: 3/27/2007 9:15 AM by Author "mesae" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=5623734