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Blue on Top

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Blue on Top last won the day on April 3 2021

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  1. High wing versus low wing (another tradeoff of course) 1. High wing is less drag. Interference drag with the fuselage is less as the intersection angle is >90 degrees. Intersection angle on a low wing is 84-87 degrees (bad ... that's why there is typically a fairing). 2. Stability is better with a high wing (weight is below the wing). This is why dihedral on a low wing is much greater than on a high wing. 3. A strutted high wing is significantly lighter ... but draggier. BUT look at the advanced Boeing designs that have really high aspect ratio wings ... that are strutted. 4. Fuselage on a high wing can be shaped as needed because its effects are on the bottom of the wing. On a low wing, the fuselage should not be made narrower until after the trailing edge of the wing ... or a long, fillet fairing needs to be added. 5. No fuel selector is really required. Don't laugh. You'd be surprised how many people die every year from fuel starvation (fuel in the airplane but not getting to the engine ... wrong tank selected). 6. Hard to put wheels in the wings ... but good for getting in during bad weather or shading at Oshkosh from the sun. Again, tip of the iceberg.
  2. T-tails have pros and cons, too. 1. A T-tail is less likely to spin and is typically easier to recover if it does (there are exceptions ... ask Piper) 2. If the vertical stabilizer is swept, it moves the horizontal stabilizer back further (more tail power). Some airliners put fuel back there to move the CG further aft for more efficient cruise. The vertical stabilizer has to be beefier to handle the horizontal tail loads, though. 3. Drag is reduced (less intersections in smaller boundary layer). 4. Vertical stabilizer can be smaller because it is end-plated on both ends. 5. On smaller airplanes a T-tail is bad for takeoff because there is less ground effect for rotation ... And then when it does rotate the airplane it is lowered into stronger ground effect when the pilot doesn't need it. Prescott Pusher is a great example. Also tip of the iceberg.
  3. So many things to say, but I'll break it up by topic ... and keep them short. I hope. Mooney tails versus v-tails (the original topic) There are pros and cons (tradeoffs) with all tail configurations (as with all design parameters). The original thought on the V-tail design was lower drag due to lower interference drag due to less intersections with the fuselage ... but this is minor ...especially so far aft where the boundary layer is thicker. There are many, many other things to consider, though, too. 1.Effective aspect ratio of the stabilizer surfaces (not geometric aspect ratio). A V-tail has a higher geometric aspect ratio, but a conventional vertical tail is end-plated by the horizontal surface (and vice versa). 2. Flutter modes are different due to the mixing of flight controls AND the higher aspect ratio movable surfaces. IOW, the balance weight on a ruddervator puts a significantly higher torsional load on the ruddervator. The free play on the Bonanza is in the torsional direction (i.e. bad). One can look at this by moving one ruddervator, the other one will move in the opposite direction. 3. Two surfaces are typically heavier than three surfaces because the two surfaces are larger with larger loads, requiring thicker materials. 4. Ruddervator control travels have to be significantly larger than conventional surface to be able to handle both motions. Look at the appropriate TCDS for actual numbers. The travels on the Bonanza are in the non-linear range (if not separated) of the CL versus surface deflection curve. 5, Yaw significantly changes the local AOA (due to the high dihedral) between the left and right surfaces. This in turn adds to the torsional issues when an "elevator" input is added. Tip of the iceberg. There is A LOT more. With today's CFD, it would be much easier to analyze than in 1945-47. PS. There was not ONE failure mode of the tail. There were several. Each "fix" cause the next.
  4. @EricJ Great observation ... made by few! A good yaw damper can take care of the issue. An autopilot may or may not handle the maneuver as it is very subtle. A yaw damper would need to be tuned well to handle it if the motions are small. PS. It not a Waltz (1..2,3) but rather a Somba with a figure-8 motion of the hips
  5. Yaw-Roll coupling does get very complicated ... especially when airplanes have rudder-aileron interconnects, big engines and Charlie weights in the tail, and long wings with fuel ... that moves . It's kind of an oxymoron to call it Stability & Control. It should be called Stability versus Control. A classic example is Langley versus the Wrights. Langley thought the airplane should be stable at the cost of control (the pilot would need to control less). The Wrights on the other hand wanted less stability so they could have more control over the direction of flight ... and hence not stall what their thought. It's a compromise. Dutch roll is the uncoordinated, yaw-roll motion of the airplane. In small GA airplanes it is typically well dampened due to the "straight" (not highly swept) wings. On highly swept wings, Dutch roll is very much the dominate mode. So, the tradeoff here is Dutch roll stability or spiral stability. In other words, if we let go of the yoke, our airplanes will eventually spiral downward. The airplane will try to return to trim airspeed, but once the bank is over 45 degrees, the natural nose up tendency of the airplane will simply tighten the spiral. Think base to final turn (probably not a stall but rather a spiral). The yaw and roll by definition of Dutch roll are out of phase, but they will never, by themselves, get in phase. We actually perform control input frequency testing for the simulators to try to decouple the yaw and roll modes ... it's not easy. I like that you mentioned forces and accelerations. Unlike a car, an airplane is always reacting to force with an acceleration. Unlike an automobile that is displacement-based.
  6. Not a materials issue. V-tails had a ruddervator flutter issue initially (Beech/Textron will say outside of the operating envelope ... or balance specification). The C35 and on have an additional spar added to the ruddervators to stop the torsional flexing from aero-elastic issues. They can't be made from aluminum (or composites) because they would be heavier and require more balance weight ... which there is not physical room for (or torsional stiffness to allow for). That is without a complete, new, flight test flutter program. On a good note, Textron is making magnesium skins again ... for $8K+/side.
  7. @PT20J nails it again! Sweep is defined at 25% chord. As aircraft AOA increases, the vertical stabilizer/rudder 25% chord gets closer to being perpendicular to the local airflow, making it more effective. In addition, the Mooney rudder effectiveness is greatly increased by the forward sweep of the hinge line. It's going to get a little technical here, but ... all y'all will get it. In other words (and when looking at the pressure side of the vertical/rudder (the side the rudder is deflected toward), the local airflow wants to go DOWN the hinge line, but it can't because the pressures are higher there (larger chord). As a result, the flow goes straighter, back over/around/across the rudder. This makes the rudder more effective. Note: the flow also can't easily go UP the hinge line because that is forward (against the main airflow). Someone also mentioned control effectiveness with airspeed. The ailerons should stay more effective than the tail surfaces because the dynamic pressure (airspeed, Qc, etc.) over the ailerons remains close to the airspeed indicator. The tail surfaces on the other hand are seeing lower dynamic pressure (airspeed, Qc, etc.) because the wing, flaps and propeller are slowing it down. FYI, this is why Mooney aircraft have a down spring (low speed, longitudinal stability). Additional FYI, the rudder-aileron interconnect doesn't know (change with) airspeed. In this case, force is force ... not dynamic pressure (airspeed, Qc, etc.) dependent. PS. Hoping to have some really, freaking cool video for Oshkosh!
  8. Although I laughed at that comment, leave that fuselage alone . The fuselage is an F-5 fuselage ... and that's my mistress.
  9. As @A64Pilot mentioned, we match cowing to spinner ... but we design the spinner, too. On a piston airplane it cannot be as tight as shown on the turboprop above as a piston engine moves a lot more (there are are actually design gap minimums. Gaps hurt aerodynamic performance a lot. Cooling drag and efficiency is actually changed by the spinner and inboard (hub) end of the propeller design. In other words, Hartzell and McCauley propellers will not cool the engine the same. BIG spinners are good; propellers get in the way (and move the flow slightly). Another point most people don't realize is that cowlings are not symmetrical. Engines are typically offset about 2 degrees right and 2 degrees nose down to account for cruise torque, etc. and aligning thrust in pitch more in cruise. The first several inches to a foot of the cowling are not symmetrical. Sometimes inlet openings are slightly different sizes. Different airplanes will also change where the cant angles are made from. Most OEMs today will center the front face of the propeller hub on the centerline of the airplane ... but not all. This also means the engine mount is not symmetrical either . The list of little things goes on and on and ...
  10. @carusoam Good observation! As you pointed out, my educated guess is that this chart would look strange being in IAS. In addition, I think that there is an AOA factor on the static ports. At the higher AOAs and with power, the curves are unique. Maybe the static ports should have been lower and/or further forward. They didn't have the CFD that we have today.
  11. The table used for the article has both airspeeds (VX, best angle, and VY, best rate) versus altitude) identified. See table below. These values are for gear UP (enroute). Takeoff distances for small, single-engine, GA airplanes are always gear DOWN ... until clear of the 50' obstacle ... especially for electric gear. Note: The airplane will be above 50' before the gear is fully up. The chart is somewhat confusing in that boxed columns 1, 2 and 4 go together as VY, best rate of climb, information. Column 3 is VX, best angle of climb airspeed. Wind will not change VY information (airspeed to fly or rates of climb), nor will it change the VX airspeed to fly. VX rates of climb are not published because they change a lot with multiple conditions/factors. The VX angle (gradient) will also change with those conditions/factors ... especially wind. Hope this helps. If not, email me at solutions@blueontop.com or call (316) 295-7812. I'd be glad to help. PS. If this chart were to be updated, column 3 should be removed and that information should be added as a general note below.
  12. @HankIt's been changed now to ODA (more than a decade ago). Maybe they got the hint. :)) It's Organization Designation Authorization (ODA) now.
  13. @Hank The C, E and F manuals I looked at are the same way - those same sections are FAA/DOA approved in my versions. Btw, DOA stands for Delegation Option Authorization. This means that the FAA had given Mooney the authorization to act on their behalf.
  14. I have to say that @Hank is nailing this one! My "The Mooney Flyer" article this month (March) is on this exact topic. Thanks for the great idea MooneySpace!. On a strange note, the takeoff and landing data are NOT in the FAA/DOA approved sections in the manual I used.
  15. Thanks for the call in @PT20J All y'all are making this way too complicated. All the information above is great, but ... Vy is best RATE of climb speed, maximum EXCESS (horse)power and minimum sink speed when the fan quits cooling. This speed is NOT FAA approved. Vx is best angle of climb speed and IS FAA approved. It is the best speed to clear an obstacle at the end of the runway. The Owner's Manual/Pilot Operating Handbook/Airplane Flight Manual/etc. provides data for the shortest takeoff possible over a 50' obstacle. The manual will state takeoff performance when when the airplane is configured for takeoff, the brakes are held until full power is achieved, the airplane is accelerated to Vr, rotated and pitched to Vx until 50'. The data ends at this point. Bonus Data: Yes, Vx is a very nose-high attitude. IF the engine quits, pitch down to minimum sink (Vy, Vbg). As mentioned above, add safety margin. PS. Yes, All of you should be able to meet (or exceed) book performance. PS2. If I'm not too late, this would make a good "The Mooney Flyer" article.
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