PT20J

Anthony, I have no idea of the actual control forces involved, but the CAR 3 requirements were to raise and lower flaps and apply takeoff power with the following requirement: During each of the controllability demonstrations outlined below it shall not require a change in the trim control or the exertion of more control force than can be readily applied with one hand for a short period. Raising flaps causes a nose up pitching moment. Adding power causes a nose up pitching moment. In the landing configuration, a lot of nose up trim is set. So, with 300 or so hp it doesn't make a lot of sense to jam on full power and raise the flaps simultaneously. A go around should be a simple matter of smoothly adding power and trimming and then raising gear and flaps and trimming. Where people get in trouble is rushing the whole process and trying to do everything too quickly. In the second example, I'm not sure if you are talking about a runaway electric trim or the more serious stuck trim. In a runaway trim, pull the breaker and trim manually. If something mechanical jams full down then you have to find a configuration and speed that minimizes the control forces. It should be flyable, but it won't be fun and having gone to the gym regularly would be helpful. Skip

I think it's important to define terms so we all know that we are talking about the same thing. The FAA has refined it's definition of stabilized approach (when referring to piston GA planes -- not jets) several times over the years. I think they've finally got it right: "A pilot is flying a stabilized approach when he or she establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway." https://www.faa.gov/news/safety_briefing/2018/media/SE_Topic_18-09.pdf A stabilized approach does not require a constant airspeed -- in fact there are lots of cases where a decelerating approach makes a lot of sense so long as you are controlling the airspeed to make the airplane do what you want. A stabilized approach doesn't have to be three degrees. Lot's of airports have obstructions that require a steeper than 3 degree glidepath. You can change configuration on final and still have a stabilized approach. But, it is very difficult to arrive on speed at the spot of your intended landing consistently if you let the glide angle wander during the approach. Skip

Jeppesen has always maintained their own proprietary chart databases and, for the US, updates them with information published in the National Flight Data Digest. Garmin starts with FAA data, but they do extra processing. For instance, they have to make sure that only approaches that can legally be flown within a particular navigator's capabilities are included in that navigator's database. They probably do a bunch of other stuff too, and I'm reasonably sure that the file format used by their navigators is proprietary no matter where the data might originate. Skip

Thanks, Clarence. How do you center the nose wheel? Do you set it to be halfway between the stops? Skip

You mention that your limit marks are painted. There is a decal for that. Anyway, it's easy to check everything when it's up on jacks if you have the rudder travel board since everything starts with getting the rudder stops set correctly.

I'm sure you are correct in your observation. The question is: How do you know your nose wheel steering is rigged correctly? The stops you are feeling are adjustable and the steering idler linkage is adjustable. From your description, it sounds to me like the idler needs adjusting to center the nose wheel.

Not sure about that. There's nothing in my M20J service manual about the steering being asymmetric. The rudder is supposed to be set with a 1 deg right offset when the rudder pedals are centered, which would actually give you 1 degree less travel to the right if you adjust the nose wheel to be centered when he rudder pedals are centered. The manual is unspecific about how to set the nose wheel steering, but I would think that it would be set for the same deflection left and right before hitting the rudder stops. Perhaps @M20Doc can tell us how he does it? Skip

Well, let's check before we start another Mooney Myth. Here's a page from the TCDS for the M20F (I chose the F at random). Really, if you think about it, why would Al, with all his aerodynamic prowess, design an airplane that asymmetrical crosswind capability? In my instructing experience, I've noticed that most pilots, when flying aircraft with side-by-side seating, prefer left crosswinds. It seems more comfortable slipping with the left wing down because of improved visibility to the side and over the nose. The airplane doesn't care. Skip

Thanks, Paul. I didn’t know that — and I’ve a lifetime EAA member (also AOPA and Seaplane Pilots Assoc.) for years. Skip

I’d have it inspected by someone who specializes in vintage wood and fabric airplanes. Our vintage aircraft museum received a donation of a beautiful Mite that I was hankering to test fly until the annual inspection revealed that bugs had gotten into the spar. This airplane is more of an antique/vintage plane than just an old Mooney. The FAA shows only 71 with current US registration. If you are buying it as a rare vintage airplane, and it is in good or restorable shape, then go for it. If you are buying it because it seems cheap, you may be disappointed down the road. Skip

You ask a couple of very reasonable questions. First, when you break in a new cylinder on the airplane (i.e., no run in a test cell) there is a lot of extra friction as the rings mate to the cylinder walls. This creates the high CHT. You want a rich mixture, open cowl flaps and high airspeed to keep the CHT as low as possible while keeping power at around 75% so as to keep combustion pressures high to seat the rings. The high CHTs should drop after a few hours, and this is an indication that the break in is largely complete. Second, the engineers designed the heads with a lot of extra metal. A few hours at 450 deg isn’t going to hurt anything. It is long-term running at high power and elevated temperature that causes problems. Every combustion event causes a peak pressure much higher than the BMEP, and that causes the head to expand and then contract. When it is hotter, it expands and contracts more. Just like bending a piece of aluminum sheet back and forth repeatedly, it will eventually fatigue and fail. Heads do wear out, and that’s why it is best to use new cylinders at overhaul. So, keep temps below 400 most of the time and don’t sweat a few minutes over 400 during a climb if that’s necessary for a safe climb out. Skip

I guess we have to have something to stress out over, or flying would be all fun . It used to be shock cooling. Then it was lean mixtures frying valves. Now it seems to be CHTs. The origin of the curve for aluminum cylinder head yield strength is an old P&W manual (The Aircraft Engine and its Operation -- a good read, BTW) that John Deakin used in the APS courses. Note that the vertical axis is not scaled. The bottom could be zero. It could just as well be 90% of yield strength. The point was just to show the shape of the curve to illustrate the origin of CHT limits. As pilots, we don't really need to know the exact values -- the engineers at Lycoming, Continental and Pratt & Whitney figured that out for us. Skip

Had fun today: got to fly a friend’s 1963 M20C. It’s been a lot if years since I flew a C with manual gear and hydraulic flaps and the first time I remember using the Johnson bar from the right seat. That took a few tries to get right. Had it worked out by the fourth takeoff. The ailerons aren’t bevelled on this one and they do feel stiffer at small deflections than my J, but not a lot different at higher deflections. This is in line with what I’ve read in the old NACA reports about the effect of bevelling. I confirmed that the elevator is streamlined with the stabilizer in cruise unlike my J which trims elevator slightly trailing edge down. Others have reported that long bodies trim slightly trailing edge up. Skip

And remember, Roy was just going after the low hanging fruit, drag-wise. He was part engineer and part marketeer. His goal was never to get the most speed possible -- it was to get >200 mph on 200 hp. A source of irritation at Mooney was that Lopresti got the credit for the speed improvements when most or all had been designed (but not implemented) before he came on board. What Lopresti did was to design a well-instrumented flight test program to figure out the most cost effective way to meet his marketing goal, and then promote it (kind of like Iacocca and Chrysler). Skip

Hinge line position, leading edge shape, balance weights, span-chord ratio, gap seals, trailing edge thickness/shape. Lots of variables. Makes my head hurt. I wonder how you guys ever arrive at a design. And of course, sometimes things don't work out during flight test and fixes get added. The engineers probably would like to go back and correct the design with the new knowledge, but the accountants will declare "good enough." Here's an example I ran across a while back: https://aviation.stackexchange.com/questions/32960/what-is-the-purpose-of-this-aileron-trailing-edge-strip Skip

I find it fascinating to look at various designs and try to figure out what was in the mind of the designer when various design choices were made. And, Mooney's have a lot of interesting choices. The nemeses of control systems from a handling qualities standpoint are stick forces/gradients, friction and lost motion (slop, play, etc). High stick forces cause obvious issues. Stick force gradients affect perceived stability. Friction causes high breakout forces and poor centering (the control doesn't return to the original position when released) and any slop makes precision flying difficult. The Mooney aileron system has a lot of rod ends and a little wear over the years leads to lost motion. (Keep your rod ends lubed with Triflow -- it forms a dry teflon film that doesn't attract wear-causing grime like oil-based lubricants). The Mooney aileron design leads to fairly heavy aileron forces, especially before the beveled ailerons were incorporated. (Not much you can do about that-- it's part of the price you pay for the very effective wide-span flaps) The push-pull tubes run through greased guide blocks that add friction. In some Mooneys, you can hear a "groan" within the wing during preflight when you move the ailerons full up or down. The sound is the tubes rubbing the guide blocks and it happens near the extreme range of motion due to a slight eccentric motion of the outboard bellcrank. (Keep the blocks lubed). There is low pressure on the top relative to the bottom of the ailerons and this tends to make them want to float up in flight and put the control tubes in compression. The tubes are long and thin and will flex slightly in flight increasing the friction especially as the airspeed increases (remember, dynamic pressure increases with the square of TAS). Back in the early 1990's, Mooney cobbled together a M20-based entry for the JPATS competition (Beech finally won the contract). An engineer told me that at high speeds the flex was enough to bind the ailerons so that the stick would stay pretty much wherever you put it. (This isn't a problem in normal Mooney flight since you are not flying that fast or doing aerobatics at cruise speeds, but it does point out that all designs have limitations). So, the push-pull tubes are great when everything is lubed, and new, and if you don't fly too fast. Skip

Well, that was really my point. They told me that this is the same AHRS they use in lots of stuff. A G5 might have similar failure modes. Skip

Well, at least it was still under warranty. Garmin is sending a replacement unit to my avionics shop.

If you search the NASA Technical Reports Server for old NACA reports on beveled ailerons, you will find a lot of reports of wind tunnel and flight test results. Generally I believe the conclusion was that beveling reduces aileron effectiveness, decreases the section lift curve slope and reduces hinge moments. Here’s one example: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093563.pdf Skip

Mine were $225 + shipping in late 2018. Kit includes die cut baffle seals, pop rivets and barrel screws -- everything you need. The original seals are attached with hardened staples. You need a Dremel with a cutoff wheel to remove them. Guy supplied a couple of cutoff wheels also. His SCEET tubing is double wall and much better than SCAT. With the finished ends, they should last at least to TBO. Skip

I recently practiced using the Foreflight synthetic vision display on my iPad (Bluetooth linked to a Garmin GTX 345) as a backup in case my Aspen PFD failed. I quickly lost control of the airplane. Fortunately it was VMC and I just as quickly recovered. It turns out after some investigation that the attitude part of the AHRS in the less-than-a-year-old Garmin transponder had failed (the heading part works fine). I have had mechanical gyros fail and the failure is pretty evident because, after various erroneous indications, eventually they just stop indicating. But, I learned from this that the AHRS can fail in a way that it appears to be working -- it's just not displaying anything like the correct pitch or bank angles. I took some video of the AHRS indications in a standard rate turn to the left and a standard rate turn to the right. The iPad display is Garmin Pilot, but Foreflight does the same thing with one important difference: Foreflight never flags whereas apparently Pilot figures out that the AHRS input doesn't make sense and flags DEGRADED as shown in the video. So the moral to the story is that digital devices can fail, their failure modes are not simple or obvious, and they will kill you unless you quickly recognize the failure, and you need a backup that is in your scan to detect the failure. Garmin tells me that the AHRS used in the GTX 345 is the same as used in their primary flight displays. Skip IMG_3409.MOV

You’re going to have to have it up on jacks for an extended time. I would get a pair of real aircraft jacks with safety locking collars and make a tail weight (there are kits available). Skip

Got to love Mooneyspace where a question about how to replace a $200 gauge turns into a recommendation to spend tens of thousands on new equipment. Skip

I understand, but that's why I compared the Mooney and Comanche -- because they are about as similar as two different airplanes can be. Similar airfoils, almost the same wing area, same MAC, same wingspan, dihedral within 1/2 degree, same forward sweep, essentially the same fuselage length. Hmmm. I hadn't thought of that. Maybe that's one reason for adding the aileron rudder interconnect. I wonder if the Comanche has one? Skip

Somewhere around the mid-1960s, I believe, Mooney beveled the trailing edges of the ailerons. I've heard it said, but do not know for certain, that this was done at the time of introduction of Positive Control to lighten the control forces for the roll servos. I've found lots of references describing beveling the trailing edges as being a method of aerodynamic balance used since the 1940s to reduce control forces, but I've yet to find a good analysis of exactly how it works. My understanding comes from some fairly cryptic comments in an old NACA report that I can no longer lay my hands on. The general idea is that increased hinge moments are caused by flow separation and thickening and beveling the trailing edge increases the camber at the trailing edge which reduces the adverse pressure gradient so that the flow can remain attached. Ron @Blue on Top, did I understand this correctly, or is there a better explanation? Skip