PT20J

BEVELED AILERONS (again): Mooney introduced beveled ailerons in the 1960s and they may have been added to reduce hinge moments (stick forces) for the PC servos. Thickening a control surface and beveling the trailing edge is a method for improving aerodynamic balance and reducing stick forces used ever since the later P-51s. For some time, I've been trying to understand exactly how they do this. I thought I understood it a while back, but was never completely satisfied. I finally found a good explanation in Airplane Stability and Control by Abzug and Larrabee. The idea goes like this: Suppose an aileron is deflected down (to raise a wing). The protrusion into the airstream thins the boundary layer on the bottom and thickens the boundary layer on the top. The thinner boundary layer tends to follow the surface contour better, so when the air flowing along the bottom gets to the trailing edge it wants to follow the bevel and deflect upward. Curving the airflow requires a pressure change -- in this case a lowering pressure at the bottom of the trailing edge. The thicker boundary layer along the top surface doesn't follow the bevel well so there is a differential pressure effect that tends to pull the aileron down which is in the desired direction. NACA report 927 (referenced by Abzug and Larrabee) quantifies the effect: Skip

The way insurance companies make money is on what Warren Buffett calls “float.” It’s the timing difference between when premiums are collected and claims are paid. The companies get to invest money that isn’t theirs to keep (it will have to be paid out in claims at some future date). But, they get to keep the investment income. When investment returns are low and losses are high, premiums will rise. It’s basic business economics. Competition ensures that the converse is also true. Skip

Pretty interesting how close the three quotes are for the carriers that would quote the risk.

Both by J’s — one manual and one electric— would cruise @ 70% with the cowl flaps closed at peak EGT with hottest cylinder 380 F or less. Manual one had flat left cowl flap rigged slightly open when closed to make room for the tubes, and electric one has the bulge.

For a K maybe. But for a J, I think they only increase my long-term maintenance costs. .

Actually, according to the BK Installation manual, it was developed in 1980. Mine flies great for 40 year old technology. Skip

Good question. Frankly, I can't see any except increased maintenance costs. My 1978 J was manual and worked fine. My 1994 is electric and it works fine, too. When I first got it, I played around with different settings, but I didn't find any utility in it. Bob Kromer has stated that they fly a bit faster when cracked open, but mine doesn't. At some point Mooney changed the left cowl flap from flat to a bulged shape similar to the exhaust pipe bulge in the right flap. I'm not sure if this coincided with adding the electric motor or not. Maybe if you have electric cowl flaps and the flat left flap cracking makes a difference. Does anyone find the electric cowl flaps very useful and if so in what conditions and on what model? Skip

So, how many carriers are left in the market?

FHP is the HP that is required just to rotate the engine at that speed. It lowers the THP — thrust hp, i.e., the power available to the prop.

Precision Airmotive (current manufacturers of RSA fuel injection systems) has a DVD on troubleshooting that includes this test. Call them and they will send it to you free of charge. @flyer338 didn’t mention whether CHTs are higher now than with earlier higher fuel flows. Concern would be that if fuel flows are now too low, engine may be too lean at full power reducing detonation margin. Skip

Depends on what I am trying to accomplish. Really, when power is available, pitch and power are used in concert. But airplane control is quicker and more precise when manipulating the elevator than by adjusting power. So, I use elevator inputs as the primary control for the parameter I want to control most precisely. For instance, on an ILS, I want to be on the glideslope and I don't care if the airspeed wanders around +/- 5 kts, so I fly the glideslope with elevator inputs and adjust airspeed with power. If I am landing on a short runway, I want my speed to be right on target and I control airspeed primarily with elevator and adjust glidepath with power. This is not the only way to do it -- it's just a technique that I find works for me. Skip

The K is kind of an interesting cross-over airplane. It has the same fuselage as the J, but it has the elevator bobweight and variable downspring trim system used in the long bodies. Bob Kromer told me that Carl Mittag (engineering test pilot on the M20K) told him that they were surprised during flight testing that the M20K had different stability characteristics, stall characteristics and handling qualities compared to the M20J which has the trim bungees used in all previous designs. The change to the elevator controls and trim system was the solution to meet certification requirements. Classically, a bobweght increases stick force per g and a downspring improves airspeed stability. Perhaps @Blue on Top has some thoughts. Skip

Remember to use calibrated airspeed if you are comparing stall speeds to eliminate instrument error which can be considerable at low speeds. I did this a while back in another post. POH stall speeds flaps up/flaps down KCAS M20J 63/56 PA24-250 62/54 A-36 62/58 C-182T 54/49 C-172S 53/48 PA28-181 59/53 Skip

There is something weird here. How would the engine know to only run rough when you are flying versus static? When you did the full power run ups did you let it run for a few minutes to stabilize temps and power? Are you sure your fuel flow measurement is accurate? 19.6 gph seems high. But suppose that number represents the correct flow even if the measurement is not accurate. It would represent a fuel flow somewhere in the neighborhood of 200F ROP. The lower fuel flow that you are seeing now should result in a leaner mixture and higher CHTs. Did it? Skip

Mooney flaps aren't very draggy, as flaps go. This causes some to say that they aren't very effective which is incorrect. Flaps are characterized as "high lift" devices. Their function is not to slow you down, but to allow you to land slower by decreasing the stall speed. Check flap/no flap stall speeds of a bunch of airplanes and you will find that Mooney flaps lower the stall speed much more than most single engine airplanes. For a lot of GA singles, the main function of the flaps is to improve visibility over the nose on landing approach. When I plan a go around in any airplane, I think in terms of getting it into the climb configuration as quickly and efficiently as possible. For the Mooney, my sequence is power, gear flaps. Skip

This doesn't make sense to me. First, how does the airplane know that it is climbing or descending? Aerodynamically, it only knows pressures and shear forces (drag) as it moves through the air. And why would climb or descent or level flight affect the ability to set trim ("hands off" at a constant airspeed is just slang for zero stick force which is the definition of being in trim). But we cannot test this because 100% power in level flight or a descent (unless you are at very high altitude) will exceed the flap speed. I'm clearly not understanding your point. Skip

IO-550 has 4.25" stroke x 2 per revolution /12 in/ft x 100 rpm x 60 min/hr x 2000 hr / 5280 ft/mile = 1610 miles of piston ring travel over engine life per 100 rpm

Mooneys are very sensitive to ground effect. Everyone, I'm sure, is aware of the reduction in induced drag in ground effect -- that, and the slight increase in lift, cause the famous Mooney float. But, ground effect also causes a pitch down moment. We need to raise the nose to flare for landing, and at the same time the airplane wants to pitch down increasing the stick force. Some people deal with this by adding nose up trim during the flare, but that really sets you up for an out of trim condition if you need to go around. So, with the trim stuck full down, it would take a lot of stick force to flare. Mooneys had a problem with stuck trim due to the configuration of the stops on the trim mechanism and there is a fix for that which every airplane with electric trim should have installed. (The problem is usually caused by running the electric trim -- which has lot of torque -- hard to the stop which then jams). Skip

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