Vance Harral

While it's true that power+attitude directly influences AOA at the wing, I can't agree with this statement. I'm going to link to the BruceAir video again. The pilot specifically says he is "bringing back the power" prior to demonstrating the spin from a slipping turn. The nose appears level or slightly below the horizon for most of the turn (though I admit it's difficult to tell). But it looks to me like the aircraft enters a spin from a descending, power-off turn, in direct contradiction to your statement above. Now, this is an aerobatic airplane specifically designed to snap and spin easily, and it's fair to point out most GA airframes don't behave exactly this way. But I still think your blanket statement is confusing and not really correct, and that the video demonstrates as much. To be clear, I'm not arguing a power-off slipping turn is a risky maneuver. I see them done all the time in taildraggers without incident. I practice and use forward slips in my Mooney, too, though I choose to wait until the base-to-final turn is complete before doing so. I'll also say my experience with stalls from slipping turns is limited to a few iterations in a couple of airframes, and always involved prompt recovery rather than allowing the spin to develop. That's not a broad experience base, and I can easily believe some airplanes - e.g. a fat, straight-wing Cherokee - might do nothing worse than mush and wobble in a stable, descending, power-off, slipping stall. But that would be a characteristic of the airframe, not a blanket statement, so I feel obliged to disagree with the gist of your post. I'm always learning, comments and rebuttals are welcome.

No, that's not correct. A slipping stall still results in an incipient spin. It's just that the incipient spin rolls you toward wings level instead of away from wings level. Therefore, application of prompt recovery technique results in you breaking the stall about the time the wings are level with the horizon, This makes it easier/faster to level the wings with the rudder, and you don't lose as much altitude. But if you don't apply prompt recovery technique, you'll continue the outside snap roll and wind up in a spin opposite the direction you would spin from a skidding turn. Here's a video that shows a one turn spin from a slipping turn. The airplane snap rolls left, away from the right turn:

Tough to ballpark, we didn't take data and the training was several years ago. I can tell you I remember it wasn't necessary to get right up to the hairy edge of a straight ahead stall with buffeting, etc. before kicking rudder. The instruction I got was to reduce power to idle, raise the nose smoothly to maintain altitude until hearing the stall warning (this particular Citabria was so equipped), then kick the rudder. So the "margin" was at least as much as the difference between the stall warning and the actual stall speed. Given the ease with which we entered spins, I suspect I could have initiated the spin with rudder-only input even several knots faster than stall warning speed. It's helpful to do some guestimate math to get a feel for the numbers. Based on my recollection and looking at some spin vidoes online, the yaw rate in a spin in the Citabria appears to be about 180 degrees per second. It's probably fair to guess the yaw rate you can induce by stomping on the rudder is in the same ballpark as the spin rate, which suggests you can (temporarily) accelerate the wings about 180 degrees per second with a rudder stomp. With a wingspan of 33.5', that means the wingtips have a relative differential velocity of about 53 feet per second when you kick full rudder, i.e. the outside wing is suddenly moving 53 fps faster than it was before, and the inside wing 53 fps slower, for a difference of about 100 fps. 100 fps is 68 mph. That's a dramatic difference in velocity between the inside and outside wing tip at GA speeds, with a commensurate difference in lift. Now, the yaw doesn't cause critical AOA to be exceeded by itself. But the significant differential lift on the two wingtips induces a significant rolling moment, and the resulting drop on the inboard wing is, I'd guess, the main factor which causes the inboard wing to stall. Blanking of the inboard wing by the fuselage as the yaw is established is a contributing factor. And if you try to correct the rolling motion with aileron, it just stalls the inboard wing worse. The video linked to above also discusses the swept wing effect causing the center of pressure of lift to move outboard on the outside wing and inboard on the inside wing. On that, I'll just have to take the gentleman's word. But the point is there are multiple factors which cause the inboard wing to stall deeply and the outboard wing to stall lightly (or not at all). The discussion reminds me of left-turning propeller effects, which are not due to a single factor, but rather caused by a combination of P-factor, spiral slipstream, and in some cases torque and gyroscopic force. I'd guess this is the reason PTK and jetdriven have contrary evidence with respect to evidence of buffeting: there are a lot of factors at play, and you may or may not feel buffeting during spin entry, depending on the airplane, the conditions, and the spin entry technique. I just don't think you're going to get even a ballpark number for this. Too many factors at play: rudder size, travel, shape, rudder moment, how fast/hard your control inputs are, whether you're subconciously inputting aileron as well, your current CG, etc. I certainly don't think you can develop a numeric rule of thumb like "an extra 11 knots of airspeed speed protects me against a skidding stall". Hence the focus on teaching coordinated turns. No disagreement from me on this. Both airspeed and AOA indicators are proxies for "true" AOA (which may vary at different points along the wing). An AOA indicator is a better proxy. But whether this difference in accuracy can actually reduce the stall/spin rate across the fleet is a more complicated question. My guess is that as with motorcycle helmets, anti-lock brakes, airbags, and full airframe parachutes, the safety improvement is undermined to some degree by the human tendency for risk homeostasis.

Concur this isn't a one-axis problem. I'm sure there's some variation in indicated stall airspeed during a stable, constant rate coordinated turn vs. a stable, constant rate skidding (or slipping) turn. But as the linked video discusses, the event that causes the stall may be the movement of rudder or aileron controls at a critical moment, rather than increasing pitch input and/or reducing airspeed. The effective change in AOA caused by the rudder and/or aileron input triggers the stall in these cases. The most obvious demonstration of this to me was my spin training. We performed spin entry in the Citabria by slowing to MCA, then simply pressing one rudder pedal all the way to the floor to trigger the stall and resultant spin, with no additional backstick. In other words, the stall/spin was initiated entirely with yaw input, not pitch input. It generated a nice, crisp entry that I'm sure looks good in competition aerobatics, and was certainly sufficient for learning spin recovery. But I'm not sure it was a good demonstration of the inadvertent spin entry we worry about as instructors. Sure was fun, though! Anyway... this discussion of how much "sooner" a stall occurs in a skidding turn isn't meaningful, IMO. It seems to assume you're in stable skidding turn, with a specific, constant amount of crossed aileron and rudder input, then you ease back on the yoke to the break. You can run that experiment, and in fact that's the way my instructor had me perform cross-controlled stalls. But I don't think that's how most stall/spin accidents happen, at least not in Mooneys. In particular, the amount of elevator backpressure required to induce the stall under those conditions is enormous (I'd estimate 20+ lbs of force, and that's based on being trimmed for a stable 500 fpm descent). You'd think would be a huge clue you're about to cause something bad to happen. On the other hand, if you start out in a coordinated turn, then kick in a bunch of ill-advised rudder and simultaneously apply opposite aileron and just a little bit (or no) of backpressure, I can see a surprise snap roll occurring. Because of this, I'm not enamored of using a steep turn to final to bleed off energy. I understand the aerodynamic argument, and believe it's technically "correct", especially with respect to a descending turn at relatively lower load factor. But much like inducing an accelerated stall from rapid pitch input, one can induce a stall from rapid uncoordinated roll/yaw inputs over a wide range of indicated airspeed and G load (i.e. the fact that you're not "loading up the wing" doesn't necessarily protect you). Not an issue if you "never" fly uncoordinated, of course. But we all make mistakes, and those mistakes are more likely at steeper bank angles. As a specific example from my own bag of experience, I've learned that a coordinated turn in the pattern with a healthy crosswind can give the appearance of a slip or skid, based on ground track. I caught myself applying inappropriate rudder under those conditions once. I was genuinely making an attempt to stay coordinated, but using the wrong reference (my eyes, instead of my butt and the slip/skid ball). It was night time, which aggravated the visual illusion, but I make no excuses. It was a mistake worth noting. I agree with 201er's point that airspeed is an error-prone proxy for AOA. But lest anyone get too enamored of AOA technology, note that an AOA indicator may very well let you down in a slip/skid scenario too. There are a couple of different GA AOA sensor technologies, and I don't know which one 201er has. But to my knowledge, none of of them are designed to account for sudden aileron or rudder input. I'd wager any of the GA AOA devices would be "late" in going yellow/red during a spin initiated by rudder or aileron input.

After a lot of thought and consultation with the person giving the training - including discussing Don Kaye's negative experience with uncoordinated stalls linked to above - I chose to take the calculated risk of executing slipping and skidding stalls in our M20F during my CFI training. I've only done this a few times, always at 5000+' AGL. The setup was based on what an inexperienced student might do in a base-to-final turn. In the slipping case, the scenario was that you're already slipping to lose altitude, you overshoot the runway centerline, and get too aggressive with a steep turn in an attempt to get aligned. In the skidding scenario, the concept was a student who executes a shallow turn due to fear of bank angle, uses rudder to horse the nose around to the centerline, and pulls back on the yoke to counter the resulting nose-down behavior. I wouldn't call these cross-controlled stalls "benign", but with prompt execution of appropriate recovery techniques I don't think they're dangerous, per se. In a slipping turn, the stall rolls the aircraft to the outside of the turn, i.e. toward wings level. As you might guess, that's not particularly scary. A skidding turn is more of an E-ticket ride, as the stall rolls the aircraft to the inside of the turn, i.e. away from wings level. On executing the first one, it felt like the airplane rolled nearly knife edge. But the instructor demonstrated that was nowhere near the case. On executing a second one and really paying attention, I found the wings did not exceed 60 degrees of bank. What's surprising is not the total bank angle, but rather the speed at which it rolls to that bank angle. A skidding stall is, by definition, the entry portion of a snap roll. I didn't pay much attention to the airspeed indicator during these maneuvers. Stall speed was higher than the bottom of the white arc, of course, but I don't remember it being way around the dial. Let's say it was closer to 70 MIAS than 100 MIAS. But I'm not sure it's an interesting number anyway. The pitot/static system has some degree of error in slipping/skidding turns, and we know it's AOA rather than airspeed that matters anyway. Recovery is no different from coordinated stalls: immediately reduce the angle of attack with forward pitch, use the rudder (not the ailerons) to level the wings, then execute an appropriate return to climbing flight. I was primed for an immediate recovery since the maneuver was intentional, and that's contrary to the way it would go down in real life. But with a nod to Don's experience, neither the instructor or I had any desire to "really get into it". Unlike counting to three when you pull the power on a simulated engine failure, we didn't attempt to model the disbelief delay in recovery. Even so, the altitude loss in the skidding case is several hundred feet, i.e. probably more than the margin you have on a base-to-final turn (that demonstration being one of the main points of the maneuver). I'm not advocating anyone else do this, and respect those who may argue it's not a good risk/reward tradeoff. But cross-controlled stalls are part of the CFI curriculum, and I didn't want to do them in an aerobatic airplane with different characteristics than the aircraft I mostly teach in (we did use a Citabria for the spin training). If you choose to explore these maneuvers, recommend you do it with an aerobatics-capable instructor with 1000+ hours in your specific make and model of Mooney, like I did. Also, be aware of potential differences in the different Mooney airframes. In particular, our mid-body model with the full-span rudder in the back and "only" the IO-360 motor up front has as much or more rudder leverage as any other Mooney model.

The nuts in question go on the studs that attach the propeller to the crankshaft. If you believe in "Jesus nuts", these would qualify. They're much larger than the ones you see on fuel caps, control linkages, etc. The part number is a specific Hartzell part, not a generic. Spruce doesn't list the A2069, but Skygeek has 'em at $8.29 plus shipping. They have the A-867 split keeper listed at $63.75, which is actually more expensive than the prop shop charged. I don't really see any evidence of gouging here.

Robert, as explained earlier in the thread, the only prop shop in the state (at the time) declined to do an IRAN. Our options were to ship the prop out of state for an IRAN or do an overhaul locally, and we chose the latter. The exact reason(s) the local shop won't IRAN a prop past calendar TBO aren't clear to me, but it's their business, their choice. They've been around for decades, and their policy doesn't seem to be hurting their business.

Thanks for the info, Cody. Our bill is mostly labor, which I'm sure is dramatically higher than an IRAN/reseal due to all the mandatory operations that go with an overhaul, especially blade reprofiling. The shop didn't break out the labor per hour, but I'd guess here in the Denver Metro area, the going retail rate is around $85/hour. That would make for about 24 hours of labor on the full overhaul job, three full man-days. Again, that hourly rate is just a guess, though.

My method for an airport at 5000' MSL where DA approaches 8000' in the summer: advance throttle to 2000 RPM during the runup as normal, lean for peak RPM, then nudge the mixture forward a half inch or so from there. On the takeoff roll I might make a quick adjustment based on EGTs, but I don't devote a lot of time or attention to it. If that sounds imprecise, it is. It should be. If the difference between clearing the trees or not is a few tenths of a GPH in your mixture setting, you made a serious judgement error attempting to take off in the first place.

The $2500 quote included parts, but was "approximate". I never had any illusion the final bill would be that number exactly, nor that there was any chance at all it would be less. Attached is a copy of the invoice wither personal info removed. $742.10 parts, $1980 labor. Big-ticket items in the parts list include new mounting studs and nuts, bearings, and something called a "split keeper". I'm not a propeller expert, and not in a position to quibble over whether every single part in the list is legally required to be replaced per the Hartzell overhaul manual. Happy for everyone here to discuss the bill, but opinions that some parts might not have had to be replaced, or that the labor rate was expensive, aren't going to make me question the decision.

Reporting back here as promised. Reinstalled our prop today after full overhaul. Looks great, worked fine on the test flight, and no drama with the shop. But a little over $2700 all in on the final bill - about 10% more expensive than quoted. Seems to match up with Cody's main complaint about shops running up cost on parts. I spoke with the technician about our blade margins after reshaping. He said after this overhaul, which is the second on the blades, they have about a half inch of margin remaining on the chord, and about 50 thousandths of margin remaining on thickness. His opinion was the blades will almost certainly tolerate another overhaul, and if it doesn't get too dinged up in the field, would likely pass even another overhaul after that. So it seems our particular Hartzell prop is good for about 3-4 iterations of blade work from a responsible shop. That's 24 years of service life even if you reprofile on the extremely conservative 6-year schedule, and only get 3 iterations of blade work. Much longer on our 10-ish year overhaul schedule - essentially a lifetime. I'm still a fan of IRAN/reseal instead of overhaul where practical, by the way. But I don't think a full overhaul is a huge mistake/risk, if you're working with a reputable shop. Might be the most practical option in some cases.

12 years and counting is really impressive, Marauder, I thought we were doing great at 7. But with an RG-35a running $300, our amortized cost over the 7 years was only $43/year. Pretty cheap on the AMU scale, and avoids having another gizmo associated with maintaining the airplane. I'm sure once you get over the hump of the initial wiring, it's trivial to plug in a Battery Minder when you leave the hangar. I don't mean to imply it's a lot of trouble, and I'm not really arguing against their use - I understand why they're beneficial. I just think some owners get the idea via forum lore that our batteries are more fragile than they really are. Trying to provide a real-world data point from the other side.

For what it's worth, our '76F frequently goes a couple of weeks between flights, and has for over a decade. We've never bothered with a battery charger, and haven't had any trouble. No failed starts, no short battery life (last battery went 7 years). The airplane does have an analog clock that runs all the time, so there's always a small load, but that doesn't seem to be an issue. Climate-wise, we have low humidity here, but it frequently gets over 90 in the summer and well below freezing in the winter. The airplane lives in a hangar, but not an insulated one. I confess I don't understand the fascination with Battery Minder and similar products for people who fly at least once a month. I can see it being helpful if an airplane is going to sit for several months. But I just don't think a healthy battery needs help holding a charge for a couple of weeks, in any reasonable climate. For what it's worth, we've run Concorde batteries for many years, which have a stellar reputation. But even the old Gill held up fine for weeks at a time. Not trying to denigrate anyone's good experience with the Battery Minder. I completely understand every situation is different, and maybe we're just a tad lucky. But I'd suggest skipping the cost and wiring of a Battery Minder until/unless you've had an actual weak start.

Makes sense to me, glad you have that shop as a nearby option. Good luck with your choice. I'll try to remember to report back here when our work at RMP is complete.

$1800 does seem like a remarkably good price for a full overhaul. If you feel comfortable with the shop and want (or will accept) the blade work that goes with a full overhaul, I'd take that deal. You might ask them how they manage to do it for so much less than other shops, though. The shop we're using is Rocky Mountain Propeller. They have a video explaining how they overhaul props (see link below). Maybe you can compare what you see in that video with the tools and facilities available at the $1800 shop.

Yes, there's always a chance a shop can $crew you. All you can do is ask for opinions and research reputation, and balance that against the convenience and (limited) control you have with a local shop. Best as I can tell, the only complaint about the shop we're using is they don't do IRANs past the manufacturer's TBO recommendations. Other than that, plenty of good reports, and no stories about destroying hubs or blades without prior discussion.

From the other side of the coin... we just delivered our prop on Monday to a local shop for an overhaul. Pretty much the exact symptoms you're seeing: 10 years since last overhaul (got a new hub at the time on the Hartzell half-price deal), throwing a little grease. In our case we also have numerous nicks filed out over the years, which are a bit ugly though I'm sure only cosmetic. Why an overhaul instead of IRAN? Almost entirely because the number of prop shops in Colorado had dwindled to one when we made the decision - though a second has just recently (re)opened. We wanted a local shop, and as in your case, the shop won't do an IRAN on a 10-years-since-last-overhaul prop. Why is anyone's guess. Maybe liability, maybe lack of interest in dealing with economy-minded customers, or maybe what they legitimately believe to be safety reasons. The point is, our options were to overhaul locally or ship the prop out of state for IRAN. We chose the former. It avoids shipping costs and risks. It also means if they call us next week and say there's corrosion, or the blades need to be condemned, or whatever... we can say, "OK, I'm on my way right now to look at it. I want to see the corrosion, blade measurements, etc. They know we're local, and I like to think that helps keep them honest. Not that they couldn't still grind the blades into oblivion if they were incompetent or malicious, but at some point you have to trust a shop based on their reputation, and this particular one has been in business over 30 years. Assuming no issues, the overhaul will run about $2500, which is more expensive than some of the quotes I'm seeing here. But we have money in the partnership kitty for stuff like this. Even if it were 100% out of pocket, it's not so bad divided by 4 partners. If there are issues, we'll deal with them then. I'll report back here on Mooneyspace if anything interesting comes of it.

I'm interested.

As everyone notes, cabin width, length, and height numbers are comparable or better to the competition. But there are some things that legitimately make the cabin feel smaller to a lot of people. First, the Mooney fuselage is rounded at the top, unlike the square roof of Brand C and the less-rounded roof of other brands. This gives at least the feel and in some cases the actual reality of impingement on the shoulders and heads of tall guys, despite cabin width at the hips and elbows being comparable to the competition. Second, the seating is low with your legs stretched out further, whereas other brands tend to have higher seats and a more upright seating position. Some people really like the "sports car" seating design in the Mooney, but not everyone. I'd be 100% OK with it if it weren't for the way my calf and knee rub on the nose wheel well, which is a minor annoyance I don't get in other airplanes. Finally, and IMO most significant, with the seat positioned to reach the rudder pedals, the instrument panel is closer to you than other brands. I like the way this makes even instruments on the far side of the panel easily visible. But I can understand why a close instrument panel feels "cramped" to some, especially if they're the type to worry about banging their head on the panel in an accident. Whether you're affected by any of the above or not, I think we can agree cabin comfort is a personal thing that varies a lot among individuals. People who have only heard about "cramped" Mooneys without sitting in them are often pleasantly surprised, but complaints from people who've actually climbed in and made their own judgment shouldn't be dismissed.

That's a good question, and I'm sorry to say I don't know the answer. I'm fixated on the IO-360 series since that's what's in my airplane, and forgot C and G models are carbureted. The service instruction relates to detonation margin, which perhaps is only a concern in the 200hp IO-360s in the E/F/J.

There is a Lycoming Service Instruction which recommends changing the timing on the Lycoming IO-360 series from 25 BTDC to 20 BTDC. There's a lot of debate about whether it's a good idea to follow the service instruction. That's up to you. But the most likely explanation for your timing being "significantly off" is that it was deliberately set for 20 BTDC the last time it was adjusted.

Just make sure you actually use the "backup" switch from time to time. If you don't, the contacts tend to oxidize, such that the backup will fail you when you really need it. Some folks argue a single DPST switch is a better solution than two SPST switches for exactly this reason: both sets of contacts are exercised every time the switch lever is operated. It's a good theory, but you're unlikely to notice when/if one set of contacts goes. That effectively puts you back to having a single SPST switch.

All switches designed for high current and/or inductance are spring-loaded, whether they're relays or hand-operated switches. The typical non-relay avionics master switch has the same "quick" open/close behavior as an avionics master relay.

Careful, not all avionics master switch installations use relays. In older airplanes, sometimes an avionics shop will simply wire a large, high-current switch (or two) directly between the main bus and the avionics bus. There are pros and cons to this approach vs. using a relay. I won't get into that debate right now, but if you're debugging an avionics master issue, you really need to get behind the panel and see what the switch is connected to. There may or may not be a relay.

That looks like a backup avionics master switch, given that it's immediately adjacent to the regular avionics master. The idea is that two switches are wired in parallel, and either one can enable the avionics bus. If one switch fails, the other one may be used to keep the power on. Typically used in an installation where a high-current switch directly connects power to the avionics bus (as opposed to systems where the avionics master is a low-current device that controls a relay).