PT20J

OK, you win!

I'm looking for a good abrasion resistant tape -- either white or transparent -- to use on the gear doors, cowling, flaps, etc. I have used the teflon tape from Spruce in the past https://www.aircraftspruce.com/catalog/cspages/teflonantichafetape.php but it doesn't stick very well and is pretty expensive. I was thinking of using uhmw-pe tape, but the 3M 54XX tapes are not listed as UV resistant and, unless treated, uhmw-pe material breaks down under UV (per Emco Plastics, manufacturer of uhmw-pe plastics: Sun without protection – depends on thickness and location. The thicker the better. In Florida, Arizona, New Mexico, and other desert areas – less than one year.) Of course, many areas are no continuously exposed to the sun, so maybe the UV resistance doesn't matter. Anyone found anything good? Skip

Here’s a way to think about it. Assume the engine is producing no power and the plane is gliding and the prop control is at the highest rpm position. Spinning the engine at this rpm requires a certain amount of power which creates drag. As you pull the prop control back the power required to rotate the engine at the lower rpm decreases and so does the drag. If you could pull back all the way to feather, the prop would stop and drag would be minimum. For a stopped prop, the first order approximation of the drag is the flat plate area of the blades which obviously depends on the blade size, shape and number. Skip

The transducer is made by Floscan which was purchased by JPI last year. The transducer spec for flow rate accuracy is +/- 0.5% @ 16 gph. It should be good enough if you set the JPI K-factor to match the K-factor written on the transducer which should be around 29K.

Correct. As I now understand it, the fuse pins are designed to shear under excessive load most likely during impact. My original discussion (long ago) with my Boeing friend related to the DC-10 that lost an engine in flight due to maintenance damage to the attachments during engine installation. I may have confused the two issues. The engines are designed to separate but not under the conditions I originally stated.

Clarence has a really good point here. I realize that I don't really know that the eyebolts are designed to break away. I just noticed how easy it was to pop one and assumed that, so my apologies for stating something I didn't know to be fact. BTW on my '78 J, we repaired my goof with a helicoil and noticed that the other side had been previously helicoiled, so that one had probably been popped, too. I was just trying to make the point that we should be circumspect when selecting parts and making modifications to airplanes. Someone mentioned static thrust, and I'll throw in that Rob McDonnell, who was Mooney chief engineer at the time, sent me some data way back in 1991 and it includes an estimated static thrust for the M20M of 1000 lbs. The example of the jet engine attachment is absolutely true. The engines are mounted with fuse pins designed to fail in shear under excessive load. I first learned about this from a friend who is a powerplant flight test engineer for Boeing, but you can easily find references to this with Google. Here's a quote from https://reports.aviation-safety.net/1992/19921004-2_B742_4X-AXG.pdf "1 .6.3 .1 Pylon to Wing Attachment Design. The design of the engine nacelle and pylon incorporates provisions that preclude a wing fuel cell rupture in case of engine separation, by means of structural fuses . A clean breakaway of the nacelle and/or pylon from the wing is ensured when the shear loading of the fuse pins exceeds the design load conditions. The structural fuse concept utilizes hollow shear pins at the four wing attachment fittings between pylon and wing. The wing support structure and fittings have been designed sufficiently stronger than the fuse pins thus safeguarding the wing from structural damage in case of an overload condition . The nacelle and engine are attached to the pylon bulkheads through forward and aft engine mount fittings . The pylon is essentially a two cell torque box containing three bulkheads: a forward engine mount bulkhead, an aft engine mount bulkhead and a rear closure bulkhead . Pylon to wing attachments are made at the aft end of the upper link, the aft end of the diagonal brace and at the two pylon midspar fittings . The fuse pin at the forward end of the upper link, the aft end of the diagonal brace and at both midspar fittings are the primary fuse pins. The fuse pins at the forward end of the upper link and the aft end of the diagonal brace are designed to fail at a slightly lower load than the fuse pins at the other ends in order to assure a controlled separation of the pylon from the wing." Skip

Same stuff was on my '78 J and again on my '94 J. Pretty sure it's just clear vinyl tubing yellowed by oil and time. When we had to remove it, we used a heat gun and it softened just like vinyl. Whenever I've needed to know what material Mooney used for a particular part, I've had good luck emailing the part number to technicalsupport@mooney.com and asking. If that doesn't work, call LASAR or Maxwell -- they have access to the Mooney Parts Portal.

I talked to Bendix-King today regarding the KFC 230. They are still working on the Bonanza certification and have no date for Mooney.

All engineering is a trade off. There really isn't that much force on the eyes when the plane is tied down. They probably won't hold in a hurricane or tornado, but by reducing the break away force they can protect the spar against the more likely occurrence of taxiing away with the wing tied down. Lot's of airplane structures are designed that way; for instance, the engine mounts on jets are designed to break away and let the engine fall if it goes out of balance enough to risk structural damage to the wing. My point is that airplanes incorporate many non-obvious design decisions, and you need to be careful when making changes. Skip

If you look at the 1933 data, you'll notice that the drag difference between prop stopped and engine at idle is pretty small. The researchers also noted that what's behind the prop has an influence. So it is possible that some airplanes may have more drag with the prop stopped and for some the opposite may be true depending on the shape of the fuselage and the specifics of the prop, but the difference will be relatively small. So, to summarize: 1) It doesn't make much difference in glide ratio whether the prop is stopped, the dead engine is turning, or the engine is turning at idle. 2) In all cases, the prop is creating drag, not thrust. Skip

Yep, there's a little pop sound and they come right out.

They tested a variable pitch prop at different blade angles. There's more data in the report -- I just pulled out the part that seemed most apropos to the current discussion.

Careful about nuts and other mods - these are designed to be breakaway so you don't damage the spar if you forget to untie.

It takes energy (which creates drag) to windmill the prop on a dead engine, and it takes energy (drag), but slightly less energy, to windmill the prop on an idling engine. That's really all I've been saying and I think we agree on that point. The point about zero thrust was simply to help everyone understand that a prop attached to an idling engine on a gliding airplane produces drag and not thrust. The more interesting question is whether a stopped prop has more drag than a windmilling prop on an idling engine. This has been long studied and here is a link to a NACA report from 1933: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091538.pdf The results were, drag in pounds, at 100 mph airspeed: Stopped: 94.4 Windmilling, dead engine: 101.0 Windmilling, idling engine: 100 Skip

The energy goes into turning the prop at 600 rpm or so (ground idle rpm). Windmilling at higher than ground idle rpm requires additional energy and this is the source of the drag.

A propeller attached to an idling engine creates thrust at zero airspeed. As the airspeed increases, the thrust decreases and goes through zero and then becomes negative when the prop starts driving the engine ("windmilling"). You can see this effect clearly with a fixed pitch prop -- as you increase the airspeed in a dive, the rpm increases. With a constant speed prop, the governor changes the blade angle and masks the rpm change. But the prop is still driving the engine at flying airspeeds. The Beechcraft Duchess POH states: ZERO THRUST (Simulated Feather) Use the following power setting to establish zero thrust. 1. Throttle Lever - SET 8.0 in. Hg MANIFOLD PRESSURE 2. Propeller Lever - RETARD TO FEATHER DETENT (The feather detent is the highest pitch position before feather) In the DC-3, we use 15" and 1500 rpm. There's a good discussion of this in: https://www.avweb.com/news/pelican/186778-1.html Skip

A windmilling prop with an idling engine creates drag. It takes a small amount of throttle -- usually around 12" MAP -- to get zero thrust. This setting is what we use in multi-engine training to simulate a feathered prop at low altitudes (where we might want to bring the engine back on line quickly so that a simulated emergency doesn't become a real one).

A few points to keep in mind: Best glide occurs at the angle of attack (AOA) for L/Dmax which occurs at the point where total drag is a minimum and induced and parasite drag each account for half the total drag. It is not dependent on weight. The speed for best glide does depend on weight, of course. Perhaps the easiest way think about this is to remember that in unaccelerated flight, Lift = Weight and Lift is proportional to TAS2 and AOA. If you keep AOA constant for best glide, then the best glide airspeed varies as the square root of the weight. At higher altitudes, the required TAS increases due to the decrease in air density, however this is compensated by using the same indicated airspeed as at sea level. The descent angel will be constant at best glide, but the vertical speed will vary as the TAS. A stopped prop will always produce the best glide performance regardless of the number of blades. If you keep the prop turning, the best thing is to pull it back to minimum rpm as others have mentioned. A windmilling three bladed prop will theoretically have more drag than a two bladed prop and should reduce the best glide speed a little. If the STC doesn't mention it, the effect was likely pretty small. Vy is the speed where there is maximum excess power available above the power required. Vx is the speed where there is a maximum of excess thrust available above the thrust required (drag). In many high performance aircraft it occurs very near the stall speed in which case a higher (safer) speed will be listed in the POH. Since Vx and Vy depend on the characteristics of the propulsion system as well as aerodynamics, they are not strictly determined by AOA. Skip

The Aspen patent has more details... US20160298985A1.pdf

The coaxial panel connector is standard for JPI. I got tired of dragging my laptop out to the hangar and bought the USB download box which works great. https://www.aircraftspruce.com/catalog/inpages/jpiusbdownload.php Skip

Mooney seems to have moved the VR around a lot over the years. My '78 J had it mounted on the cabin side of the firewall behind the circuit breaker panel -- I haven't found it in my '94 J yet, but I think it's behind the center console. It was a long time ago when I had the VR out of the '78. It was an OECO and it went bad so I removed it and replaced the power transistors and set it to the correct voltage on the workbench. I don't remember if it would have been possible to get to the voltage adjustment without removing the unit. I do remember that it was really, really hard to get it in and out.

In my attempt at brevity, I oversimplified and apologize for creating potential confusion. In a long pipe made up of pipes of varying cross sections, or in a pipe with multiple restrictions, of course all contribute to the flow rate. I was simplifying to the case apropos to the current thread where there are multiple restrictions, but one is considerably smaller than the others. In this case, the smaller restriction will dominate. Precision Airmotive lists the ID for the line to the nozzle as 0.085 to 0.090. The lines are supplied by Lycoming. There are only two part numbers for an IO-360-A3B6(D): LW-12098-0-140 for cylinders 1&3 and LW-12098-0-210 for cylinders 2&4. There are not options for different IDs. Lycoming SI 1275C lists the nozzle flow rate as 32 lb/hr at 12 psi under specified test conditions. From this you should be able to calculate the effect of the lines relative to the nozzles.

Fuel injection systems and carburetors are based on a couple of principles: 1) The flow rate across an orifice is a function of the pressure change across it. 2) In a pipe having multiple restrictions along it's length, the flow rate is determined by the smallest orifice. The fuel flow rate to the engine is determined by the main jet. The fuel injector measures airflow and controls the pressure across the main jet to match the fuel flow to the air flow. Equal distribution to the cylinders is determined by the nozzles. The rest is just plumbing. Bendix RSA fuel injectors are based on design principles from Bendix-Stromberg pressure carburetors used on the big radials. A great explanation of how these work (written by the man that designed them) is found in Aircraft Carburetion by Robert H. Thorner.

Things don’t add up here. Engine roughness is caused by the cylinders delivering unequal power. Conversely, if it runs smoothly, especially LOP, the cylinder power, and thus the fuel flows, are balanced. The lines from the flow divider to the injectors are much larger than the injector nozzle and are not a factor unless severely clogged. It is possible for the valve in the flow divider to be damaged or hang up and cause unequal flows, but this should cause roughness or shut down issues. It seems your engine operates normally, but you are concerned about what your instruments (EGT & FF) are telling you. Perhaps it’s an instrumentation issue. You could eliminate one source of confusion by cleaning and re-installing the stock injectors and rerunning the bottle test. Skip

I notice that Precise Flight says to remove them annually for inspection and lube. Does anybody actually do that? Also curious how much others use their speed brakes. I find that I rarely use them unless I’m helping out ATC or I screwed up my descent planning. But then my previous ‘78 J which I flew for seven years, and the C I flew before that, didn’t have them. So, maybe I’m missing something. Skip