PT20J

I agree this is not a particularly good design. The bellcrank at the outboard end causes the push-pull tube to have a fore-aft motion which causes the tubes to rub against the guide blocks and increases friction. On some planes (including my J) you can hear it from outside the airplane if move the aileron through the extremes of travel. I recall hearing from Roger Hoh that around 1990 Mooney thought to enter the JPATS competition and built a prototype for testing. At high speeds, the ailerons floated up and flexed the tubes enough to bind. The stick would stay wherever it was displaced. I’ve often wondered if something was beefed up in the big engine Mooneys (that fly faster than the J) to solve this. Skip

I would expect mis-rigged gear doors to cause a yaw rather than a roll and even at that nothing of the magnitude you describe. The aileron control tubes run close to the gear bellcrank. Should be easy to figure it out if you put it on jacks and remove the belly and observe the gear motion.

Cool. I didn’t know that! I just looked up the specs for my iPad mini 5 and it supports Assisted GPS (evidently this uses the cellular network to provide an initial position for faster acquisition) GLONASS, Galileo, and QZSS. Skip

The OP's M20J tip/lens was a factory installation on later Js. Your C tip is a retrofit -- different part.

One thing that helps me understand airplanes is to look at the features of various designs and ponder why the designer made certain choices. The Mooney flaps are a bit of a puzzlement to me. The J has a clean stall speed of 63 KCAS which is above the CAR 3 max of 61, so clearly a high lift device is called for. The choice of a slotted flap seems reasonable as it gives the best increase in CL with a simple hinge mechanism. The thing I don't understand is the span. Flaps and ailerons compete for wingspan. By allocating so much to the flaps, the ailerons had to be made short and of greater chord (to get the area required for roll authority) which increases the aileron hinge moments. Coupled with the short throw of the Mooney control wheel (stick forces are governed by hinge moment and stick lever arm), the aileron design makes the stick forces high in roll -- so much so that the aileron trailing edges were eventually beveled to improve the situation (I've heard claim this was done in order to reduce forces to accommodate the addition of the PC system or maybe an autopilot). I wouldn't call the M20 roll rate sprightly, but adding more aileron chord to increase the area would have made the stick force worse. So, it seems that the choice of flap span came at a cost of roll rate and stick force. The Mooney flaps do more effectively reduce stall speed than flaps on many other airplanes. From POH data, here are the Vs1/Vso speeds (KCAS) for various airplanes at gross weight: M20J 63/56 PA24-250 62/54 A-36 62/58 C-182T 49/54 C-172S 48/53 PA28-181 59/53 The Bonanza and Cherokee flaps are not terribly effective at reducing stall speed. The Cessna flaps with shorter span but greater chord and some rearward travel (although apparently not enough that Cessna claimed them to be Fowlers) are better, but still less effective than the Mooney flaps. So, apparently span is more important in flap design than chord. The Comanche flaps appear similar to the Mooney flaps, though shorter, and provide the same or perhaps slightly better stall speed reduction while leaving more room for ailerons with (presumably) lower roll axis stick forces. Ron @Blue on Top any thoughts on this? Did Al make the flaps too long, or am I missing something? Skip

OK, so now I have to ask: who makes the oil?

You know, I’m comparing a 25 year old original lens with the new LASAR lens. Who knows what Mooney is currently shipping??? Next time I see a newer plane on the ramp, I’m going to look at the wingtips

Maybe, Paul, but my LASAR lens was noticeably lesser quality than the Mooney lens as I noted. Also, if the drawing in the IPC is accurate, the Mooney lens is already trimmed. But, the LASAR lens was good enough for me and in stock so I didn’t even inquire about the cost of the Mooney part because my mother taught me never to ask a question if you can’t stand to hear the answer Skip

This would be a fun experiment if you had the interior out. Measure TAS by 3 vector GPS test. Remove all the antennas and tape over the holes and see if it makes a speed difference. Then add them back one at a time and record what each one costs. Skip

Did you install one of these? I’m curious how it compares to the LASAR part. Does it require trimming? Also, I found the radius at the extreme outboard point where the lens meets up with the wingtip to be off just slightly on the left side LASAR part and it also isn’t as distortion free as the original. How’s the fit and finish of Great Lakes part. The LASAR part is fine unless you are a perfectionist, but maybe the Great Lakes part is better for the extra cost. Skip

I’m curious what experience others have with the Aspen synthesized AOA indicator. Does it seem accurate? Do you use it? I have a EFD 1000 (PFD only) with AOA installed by the previous owner. Mine seems to be out of calibration as I’m deep into the crosshatch at 65 KIAS, 2400 lb., full flaps in a M20J which seems to provide a reasonable compromise between too much float and enough reserve for a good flare. Also the display is so small that I find it hard to read at a glance. Skip

@donkaye Just type the @ followed by a the first few letters of the username and a drop down list will appear with the closest matches to select from. What approach speeds do you teach for the J? Skip

LASAR has a PMA one that is much cheaper than the Mooney part. You’ll have to trim it to size and drill the mounting holes. There’s a thread somewhere on MS with recommendations on various ways to do that. I used a Dremel cutoff wheel and step drill. Sand the edges smooth after trimming to avoid any stress risers - acrylic loves to crack. Skip

If you really want to get into the details of airplane cooling design, check out resources at EAA. There’s lots of good information there. Homebuilders have two great advantages: engineering time is “free”, and they can optimize a design without worrying about production cost.

The Yak-52 has that setup. Not sure it makes much difference where you put the throttle to control the airflow. Skip

My point is simply that most of the airflow arriving at the cowling is going to go around the cowling (causing a certain skin friction drag) whether there are openings or not. When some of the air is diverted for cooling, there are losses involved which are highly dependent on the cowling design. Now, time to quit before someone brings up Meredith effect.

Take an unopened tin can and hold it under the faucet. Looks pretty much like the opened one with a hole in the bottom. Most of the water flows around the can in both cases. The can is analogous to the airplane and the water is analogous to the air. In the airplane flying along at 160 kts, most of the air is going to go around the cowling either way.

But in the case of the airplane, all that air is going to flow around the cowling anyway.

The air that flows out through the cowl flaps obviously came in through the inlets. The cowl flaps regulate the air flow. “Extra” air does not flow into the cowling and accumulate. Take an empty tin can and punch a hole in the bottom. Hold the open end under a faucet and turn the water on. Water flows into the can and some flow out through the hole. When the can gets full, what happens to the extra water? Air works the same way.

I use (per service manual) Aeroshell 22 for zerks Aeroshell 7 for the guide blocks and trim screws Lubriplate 630AA for the gear ball screw Mobil SHC 100 for the wheel bearings Tri-flow for the rod ends Any light mineral oil such as 3-in-1 for the control surface and other bearings. Clean out all old grease if you are not sure what was used before since some are not compatible with each other. Skip

At the speeds we fly, air is (to good approximation) incompressible, so it won't accumulate. It won't go in if it can't get out.

Many years ago I had an interesting conversation with flight test and handling qualities engineer Roger Hoh (whose most recent achievement is the Heli-SAS for the R-44) about spiral stability. He made a point that the classic graveyard spiral (ever steepening bank and ever increasing airspeed until the wings come off or the ground intercedes) is somewhat mythical and if the airplane has sufficient longitudinal stability, such behavior is more caused by mis-rigging or lateral imbalance than the inherent dynamics of the airplane. At the time I owned a '78 M20J and one day I took it up to about 5000' and trimmed it for 90 KIAS in level flight and let go of the controls. This airplane was rigged properly and it flew pretty straight for long enough that I got impatient and gave it a small poke (impulse I believe the test pilots say) on the right rudder. It slowly rolled off to the right and the nose went down and the airspeed increased pretty rapidly. But then, just as Roger said it would, the longitudinal stability (phugoid) kicked in (just about at the point where the airspeed was getting close enough to redline that I was about to end the exercise) and the nose rose and the airspeed decreased and the roll rate also decreased. The airspeed dropped off until somewhere above stall and then the nose started down again. As I recall, the airplane completed two and a half cycles, each of decreasing amplitude, and ended up in a steady 45-deg banked descending turn at around 90 KIAS. I wish I had tried this in other airplanes, but I never have. So, I'm wondering if Roger was right and this is common behavior, or if there's something about the Mooney that makes this work out. Skip

When I redid my interior years ago in my first J, I just replaced the #4 PK screws with #6 and #6 trim washers. If you don’t like the silver screws and washers, you can paint them.

I can’t understand why anyone would want something that you have to remove to check/replenish the air in the tires. The airplane sits so low to the ground that you can hardly see the wheels anyway. But if you must - LASAR sells stainless steel main gear hubcaps for the CB-pleasing price of $55/pair and nose wheel covers for $45. So for $100 you can have shiny hubcaps. You can paint them if you must. EOT

Thanks for the compliment, but I'm just trying to figure out stuff you probably knew 20 years ago! I never considered the tip effects - thanks for the insight. So, the vertical tail gets to be smaller with less parasitic drag and yet has a longer "effective" span in a sideslip which recovers any loss in effectiveness due to the reduced area. I think that's the idea. Wonder if this would require a larger dorsal fin? Comparing the Mooney and Comanche 3-views, the Mooney does appear to have a larger dorsal, but it's a little hard to tell for sure. Skip