PT20J

I guess my question is really if it’s typical behavior for most airplanes to stabilize in a descending turn at constant airspeed and bank angle after the spiral begins? Regarding the aileron-rudder interconnect, my thought was that the rudder would tend to streamline and perhaps the springs would act as aileron centering springs. I seem to recall reading an old NACA report years ago where it was found that centering springs improved spiral stability. Skip

If they aren’t stock, they should be able to order them from Mooney.

Not sure about other models, but on a J with the breaker switches located along the bottom of the panel, if you grab the bottom of the panel to pull the seat forward, you and deform the bus bar on the switches and cause a short (don’t ask me how I know this ). Skip

On mine, the hole in the vertical pin in the actuator didn’t align well with the little wire causing the wire to slip out. I put a small cotter pin through the hole and put the wire through the eye of the cotter pin which effectively rotates the hole 90 degrees and this solved the problem. Skip

Excellent!! Minor nit from an old EE -- it's bus, not buss. Buss is a kiss . (Yeah, I know, Mooney gets it wrong in some docs, too.) Skip

Ron, @Blue on Top since we are discussing phugoids ....this early post got lost in other discussions, but I’m still curious if this behavior is common in other airplanes. Skip P.S. I'm wondering if the Mooney might have a more stable spiral than some other airplanes due to the aileron-rudder interconnect and the trim bungees. The former might affect stick-free lateral stability while the latter should increase stick-free longitudinal stability. (I think).

I won't shoot -- it's always good to check. But, yes I did this stick free with only minor rudder inputs to keep the wings level. Here is a very rough time history I did years ago with my '78 J. It appears that the '94 has similar behavior. Just another mystery of the universe Skip

Thanks for the follow up. So often we don’t get “the rest of the story” and don’t get to learn from other’s experiences. Skip

Hey Ron, @Blue on Top, any thoughts on why my M20J pitches up when I lower the landing gear? I would have expected it to pitch down due to drag increment being below the CG, the airspeed stability effect of deceleration and the fact the nose wheel doesn’t weigh enough to move the CG very far forward. Skip

Sounds pretty obvious now that I read your comments -- but you're smarter than me Thanks for the tips !!! Skip

I interpreted that to mean the male threads on flare fittings since there is a separate paragraph for tapered thread fittings. But...I agree with you

Good point!! The TCDS defines the manual requirements. The Mooney TCDS Note 13 states that "From 1976 model year and ON "Pilots Operating Handbooks" have replaced "Owners Manuals." The flight manual provisions in CAR 3 paragraph 3.777 would seem to require more of the manual to be FAA approved than the language of Part 23, but the FAA may have made exception for "Level 2" aircraft. That was before my time . However, Mooney made it pretty clear what is FAA approved in the AFM/POH by including FAA APPROVED in the footer of the Limitations section. No other sections contain this footer. Mooney TCDS 2A3 Rev 52 dtd 9DEC10.pdf CAR-PART3.pdf Skip

Byron, how did you locate the snap positions from above so you weren't drilling into anything important underneath? What snaps did you use? Skip

Clarence, you got me curious since I recall Mooney installed the pipe fittings on my standby vacuum pump using teflon tape (which I believe the vacuum pump manufacturers caution against). According to this excerpt from the Service Manual, that's what Mooney says to use for all tapered pipe fittings. Personally, I think teflon tape is for plumbers not aircraft maintainers. I had a plumber doing some work at my home a while back and asked him what he used on tapered threads and he said, "Three wraps of teflon tape and pipe dope." I asked why he used both tape and dope and he said, "Because I don't want to come back." So, it appears that even plumbers don't trust teflon tape. Personally, I've had issues with it on gas and water pipes if the threads are not cut perfectly. I've come to prefer the dope for home plumbing jobs, and I don't think I'd use teflon tape on an airplane for fear that a shred might get loose and cause trouble. But, that's just me. Skip

I used SEM on my previous M20J and it held up very well. I plan to do my current interior this winter/spring. My IA used to be an automotive paint guy and he believes that SEM is the best product for plastic, so I'm going to use that again. The interior panels are ABS plastic. Mooney used pretty thin sheets to start with and the vacuum forming process causes additional thinning at each radius which is why they often crack there. I've had good success taking the thinnest fiberglass cloth I can find and laying it up in three layers on the back side with ABS cement (or you can melt Legos in MEK or acetone -- or buy a kit from Plane Plastics with ABS bits and a small paint can to melt). If you have a plastic store around, you can also buy a small piece of ABS sheet to cut up to make patches to glue on the backside to reinforce flat areas. Skip

I've looked into the Floscan (now owned by JPI) transducers pretty extensively trying to improve the accuracy of the factory installation on my '94 J. Here are a few points I've learned. 1. The transducer is pretty simple and simply emits pulses as the fuel spins a plastic wheel. The K-factor is the number of pulses per gallon (usually around 29,000 calibrated at 16 gph). There are three wires which should be shielded: Ground, Power, Output. The output is an open collector transistor with pretty robust pulses. 2. Transducers can fail because the electronics die (no output), or the the wheel gets stuck (no output, intermittent output, reads low). One fix some have used to get a little more life out of a transducer is to soak it in Hoppes No. 9 or carburetor cleaner. I tried this on my intermittent unit and it worked better for a short while. I ended up replacing it. 3. Your symptom of flow rate sometimes reading unbelievably high seems strange because it is hard to see a way that the transducer could physically put out that many pulses. I'd talk to JPI again because maybe the 450 processor does something weird when it gets intermittent input. Since the transducer is that old, it might be worthwhile to replace it anyway. IIRC, the transducers are rated for 20,000 hours, but a tech from JPI told me that they frequently see them go bad after about 20 years. Or you could try soaking it. Probably not related to your problem, but just for completeness on the subject: 1. On M20J's, Mooney mounted the transducer upside down with a 45-degree ell at the input. I went to some trouble to remount it with the wires up and a straight fitting and it made no difference in accuracy. The only reason to mount it with the wires up is that the vent works properly in the unlikely event that you have vapor bubbles in the input line. 2. JPI recommends using steel fittings (the body is aluminum so aluminum fittings could gall -- especially if assembled dry). Mooney uses aluminum fittings, however. 3. Although JPI warns not to use sealant on the fittings, it's a bit of a crap shoot to get tapered pipe threads to seal without sealant because there is a spiral path around the threads and without sealant, the seal depends on deformation of the threads when tightening. But if you over tighten, it can crack the aluminum case. I couldn't get steel fittings to seal without sealant. If you apply a small amount of sealant to the male threads omitting the first two threads, you should be fine. 4. The Mooney factory K-factor setting on my Shadin miniflo-L did not match the installed transducer K-factor. After I replaced the intermittent transducer, I reset the K-factor in the Shadin to match the transducer K-factor and it was way off. I verified this by substituting a second known good miniflo-L. I reset the Shadin to the original Mooney K-factor and it is closer, but still not within 4%. I'm sure the transducers probably meet their spec of 2% accuracy at 16.0 gph, but I suspect they are less accurate at lower fuel flows and so some tweaking of the K-factor is probably required. Skip

Merry Christmas, Clarence -- and thanks for all the great (free) advice you provide.

Ron @Blue on Top, this is not a Mooney question, but perhaps you can explain how split flaps (DC-3, B-17, C-310) do so well at increasing lift coefficient (I believe they are somewhere between a plain flap and a single-slotted flap). The whole layout seems counterintuitive. And, doesn’t it violate the Kutta condition of circulation theory? Skip

Now I can understand this old Peter Garrison article : Rectangular Wings.docx Skip

Great question. That's where the "Newton third law" lift explanations lead us astray. Downwash is not necessary for lift. What is necessary is to cause the air to follow a curved path (Newton's second law as someone pointed out) which sets up the required pressure gradients. The idea, which appears in a number of aerodynamic texts, that lift is a product of the downward momentum induced by the wing turns out to be incorrect and based on a mathematical error (McLean, Understanding Aerodynamics, p. 433, and also discussed in his talk I posted earlier). Here's a pretty good article that explains lift without a lot of obscure concepts (such as circulation) and obfuscating math. The math is important if you need to calculate lift, but it's not very intuitive for explaining it. howwingswork.pdf Skip

Here's one way to think about it. The flow around a finite-span wing far from the ground produces wingtip vortices and a net downwash behind the wing. As the wing nears the the ground, the ground interferes with the flow in such a way that vortices and downwash are reduced. It is as if the wing gains span. The result is that the aerodynamic force vector tilts forward. If we resolve the AF vector into a vertical component (lift) and rearward component (drag) the forward tilting increases lift and reduces drag. Skip

I think you'll find the answer near the end of this:

@Blue on Top makes excellent points ... again Years ago, Flying columnist Peter Garrison made the observation that even a child understands lift. It's angle of attack. They know this by "flying" their hand out the car window. My private pilot ground school instructor used to say that you could fly a sheet of plywood if you had the right angle of attack and enough power. I've come to the point where I think all the discussion of Newton and Bernoulli and camber and such is not very helpful to pilots. We cannot see the air and we cannot change the wing shape (excepting flaps). But angle of attack is something we can understand, visualize and control. The point of airfoil design is to use that angle of attack to generate lift efficiently my minimizing the associated drag. Skip

Try this one. A bit long and I had to watch parts of it several times to understand it (mostly ;-), but I found it pretty interesting. Skip

I'm glad @Cargil48 brought this up because this is an example of the simplifications that we've all been taught over the years that turn out not to be accurate. Here's a wind tunnel video using pulsed smoke that shows clearly what @Austintatious points out. It turns out that there are a couple of other problems with this explanation of lift. Even if you take a highly cambered airfoil (like the Clark-Y) the difference in path length isn't nearly enough to account for the difference in speed of the air over the top and bottom of the wing. Also, if you look at the Mooney root airfoil, it is curved on both top and bottom, so the path lengths are not that different at all. http://airfoiltools.com/airfoil/details?airfoil=n63215-il Skip