PT20J

That's a cool simulation. I did not see where it showed that there is a net downward momentum. I believe that Doug McLean addressed that fallacy at the end of his lecture and in more detail in his book. Both McLean's analysis and Lissaman's paper show that there is an updraft before the airfoil and a corresponding downdraft behind the airfoil and each accounts for 1/2 of the lift force. It occurs to me that there can be confusion with the term downdraft. There is downdraft behind even an infinitely long wing just as there will be an updraft ahead of the wing. But that's not the downdraft that people generally refer to when invoking Newton's third law to explain lift. The "Newton explanation" downdraft is the one that is not balanced by the updraft ahead of the wing and it is the source of induced drag, not lift. It is caused by a vortex sheet shed by a finite span wing. Details can be found in any aerodynamics textbook where induced drag is introduced.

Aircraft Spruce buys them from McFarlane. So does Mooney. I doubt anyone keeps them in stock but if McFarlane lists the part number then they should have a drawing for it and can make one without you having to send your old one to them.

It's going to be a Mooney part number and if you buy it from Mooney it's going to be expensive if they even have it. I would contact McFarlane and see if they have one. Worst case, you would send them your old one and they would make a new one to match it.

The important requirement for lift is that the average pressure above the wing be lower than the average pressure below the wing. This does not necessarily mean that the pressure below the wing is higher than the static air pressure.

This actually makes a great point. Camber is not necessary to generate lift. A flat plate will generate lift. The purpose of airfoil shapes is to generate lift efficiently which means minimizing the drag created by the wing. Drag takes on two forms: Parasite drag from skin friction which is reduced by minimizing the wing area thus necessitating so-called high lift devices on the leading and trailing edges in order to get lift at lower speeds for takeoff and landing; and, induced drag which is caused by the production of lift and can be reduced by careful airfoil design.

I am certainly not trying to argue with anyone and none of the ideas I have presented are my own. In fact, I presented two videos, one by a retired senior Boeing engineer and one by a professor of aeronautics, that essentially say the same thing albeit with much more detail and rigor. Here is a paper (for those who might be interested) written by a (now sadly deceased) well know aeronautical engineer. My only purpose in presenting this was to try to point out that a lot of what is presented in instructional materials for pilots is just plain wrong and it's not really that hard to understand what is really happening, at least at a very basic level. But I do understand the law of primacy and what we first learn sticks with us. But, for those with an interest, I think it is a fascinating subject to explore. So many things I thought I knew in my early flying career have been proven to be wrong and one reason I find aviation continually interesting is that there is always more to learn. The Facts of Lift - Lissaman.pdf

Maybe not zero, but not much more at cruise. From the attached curves I got long ago from Mooney, the Mooney wing zero lift angle of attack is -1 deg. So, because of the camber, it generates lift at zero. But, we can easily calculate it: L = 1/2 p V2 CL S Solving for CL and converting to convenient units at sea level on a standard day, CL = 295 W/V2S where, W = weight in lb., V = KTAS, S = wing area in ft2. For a M20J, S = 174.8 ft2. For our example, lets use 2500 lb weight at 150 KIAS: So, CL = 295*2500/150^2*174.8 = 0.1875 According to the attached curve, that corresponds to a angle of attack of about +1 deg. M20K Aerodynamic Coef - Flaps 0.pdf

As I said in my first post, what happens is that the air changes velocity (direction and speed) due to the presence of the wing. A change in velocity requires a force (Newton's second law), which for a fluid, must necessarily be a pressure (force over an area). A change in velocity also causes a change in momentum (mass x velocity). So mathematically, lift can be derived from either the change in momentum or the change in pressure. But this is not the same as saying it is due to downwash and Newtons third law. The problem with that explanation is that downwash has been shown not to be required for lift, and there is no way to describe the physical means by with the action (downwash) would cause the equal and opposite reaction (lift) that is physically correct.

No, the airfoil and pressure distributions around it are the same whether it is a section of a propeller or a wing. Likewise with tip effects: propellers and wings both shed a vortex sheet along their span and a vortex at their tips. The difference is that the propeller rotates normal to the free airflow and a wing passes tangential to it.

Excellent question. The propeller blades rotate in a plane normal to the axis of rotation and direction of flight. Because of this constraint it is often modelled as a permeable disk that imparts energy to the air flowing through it. The disk creates a low pressure area ahead of it and a high pressure area behind it. This has the effect of creating a stream tube along the axis of rotation that "sucks" air in ahead of the propeller and accelerates it out the back side. The motion of air through the propeller disk is thus different than that of a wing.

If you look carefully at the streamlines in the picture, you will notice that the air does not impact the bottom of the airfoil but curves to follow it's surface. There are always physical limitations It takes a force to cause air to increase velocity, so there must be a pressure gradient at work. At true airspeeds less than 200 kts, the atmosphere acts as if it were incompressible.

The airfoil is at a positive angle of attack so the trailing edge is lower than the leading edge.

The point is that there are many fallacies about lift that keep getting repeated and now are so ingrained that we don't give them much thought. If you throw out the incorrect drawings and move beyond a rigid cause-effect mindset, then it's pretty easy to understand what is happening based on simple physics. It only gets complicated when you want to calculate the exact amount of lift, but that's what computational fluid dynamics programs are for.

For those that believe that lift is caused by air being forced downward, consider these questions: 1. How do you explain lift generated by a 2D airfoil (like a wind tunnel model) that has no net downwash? (If you look at @0TreeLemur's wind tunnel picture, you'll notice that the downwash behind the airfoil is offset by an upwash ahead of the airfoil. So, the net downwash is zero.) 2. If lift is caused by forcing air downward, reducing downwash should reduce lift. So, how do you explain the fact that lift is increased slightly in ground effect while downwash is reduced (because the air cannot continue moving downwards due to the presence of the ground plane).

Does it only do this during acceleration or will it do it if you run it up at a steady rpm in the 2200 rpm range? If it does it only during acceleration, it sounds like it is momentarily running out of fuel. The RSA fuel servo does not have an accelerator pump or economizer valve. It simply meters fuel according to airflow. There isn't enough airflow below about 1500 rpm for accurate metering and so mixture is controlled manually by a valve connected to the throttle. So, the first thing to do is set the idle mixture for a 25-50 rpm rise during shut down and then set the idle speed for about 650 rpm. If it still has a problem, I would look to see that the servo is receiving adequate fuel pressure. There are no other field adjustments on the servo.

When researching an unfamiliar airport, it's a good idea to bone up on any special procedures in use: The Chart Supplement A/FD entry for the airport will often have procedural information entered in the Comments section. The Chart Supplement Notices section may have special procedures that are in effect. (Example: PAMR, Merrill Field, Anchorage AK). Any procedures described by Letters to Airmen will be found by searching the FAA NOTAM site for the airport. (Example: KBFI, Boeing Field, Seattle WA). One nice feature of ForeFlight is that it gathers all the available information and makes it available on the Airport tab.

I believe there was also a hardware problem with some units, but those should have been replaced on warranty by now and they were running batteries down pretty quickly so if you had one of those you’d know it.

It’s probably fine. I left my G5 on somehow and ran the battery down to 0 and it recharged fine in about 2 hrs. I don’t notice that the battery discharges much when left for a week or two, so I don’t think there is much current draw when the G5 is off ( there has to be some so that it can wake up on battery when you press the power button.) If you are worried about it you can do as Byron suggests.

Have you tried a snubber?

I believe that the M20J SMM specifies control surfaces to be balanced trailing edge heavy.

A lot of YouTube videos are just wrong. Here’s a good one by a retired Boeing engineer (his book goes into more detail) This one is good also.

The spanwise vortex sheet is a consequence of the tip effects. Lift can be calculated by either accounting for the pressure differences above and below the wing or the momentum changes in the air as it moves around the wing. But the latter is not the same as ‘forcing air down” as the example of ground effect demonstrates. Aerodynamics text books first describe 2D airfoils in order to derive equations of lift and drag and then go on the describe 3D wings in order to account for the effects of planform and span. The NACA catalog of airfoils is 2D wind tunnel data because the wing models completely filled the test section from wall to wall so there were no tips.

The March 2025 AOPA Pilot magazine got me thinking: I wonder why it seems so hard to understand how our wings produce lift? Bernoulli? Newton? Both? Neither? It's not as hard as we make it, but it is not intuitive and trying to make it match our intuition seems to me to be what trips up those that try to explain it in simple terms. Consider Bernoulli. Yes, the air flowing over the top of the wing speeds up and produces a lower pressure. But why does it speed up? It is NOT because the air above the wing is funneled through some sort of half venturi. This is easily shown by the fact that a flat sheet will generate lift at a positive angle of attack, but, since there is no camber, there is no half venturi. Consider Newton. Lift is not created by downwash. Downwash creates drag. Downwash is due to the tip vortices of finite span wings. 2D airfoils generate lift but have no downwash. Ground effect reduces downwash with the effect that drag decreases and lift increases. If downwash was responsible for lift, lift would decrease as we neared the ground and our Mooneys wouldn't float so much. There are two problems that impede our understanding of lift. The first is that many of the drawings of streamlines flowing past an airfoil are incorrectly drawn. An airplane wing actually affects the airflow at a considerable distance ahead, above, below and behind the wing. The second problem is that we are used to simple systems that have discernable cause and effect. But fluid dynamics isn't like that. If the air speeds up, is it because the pressure changed? Or, does the pressure change because the air speeds up? What is really happening is that the wing presents an obstacle that the air must go around. And, there are laws of nature that the air must obey in so doing. The air must change direction to get out of the way. Air has mass so changing its direction requires a force. Force on a fluid such as air is a pressure. So, as the air flows around the wing there will be pressure gradients. And pressure gradients cause the air to speed up or slow down. It's not correct to say that the pressure causes the direction and speed changes or that the direction and speed changes cause the pressure changes because all three parameters are part of one system.

Owner of the museum where I used to volunteer couldn't get the left engine on the B-25 started. Primed the hell out of it leaving a big puddle on the ground. Of course it backfired (well, actually afterfired) on the next attempt and lit off the fuel. Fortunately he got it started and blew out the fire just as the fire guard was running with the fire extinguisher. Ross, I think I'd just inspect everything closely -- too many variables to predict what damage might occur.

Yeah, I got a 1" ratchet box end wrench. I can't get a torque wrench on the filter on the A3B6. I figured out that torqueing a rubber gasket doesn't make a lot of sense anyway and 3/4 turn seems to do it. Never had a leak on the cars or airplanes. Wobbly extensions are useful. The only socket I've had to turn down is the half inch for the Lycoming exhaust nuts.