Moronic Monday | TheaterFire

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MalarkeyJack@reddit

Is it unreasonable to ask for 6-8am scheduled flight training for the duration of my PPL? Discovery flight this weekend with a school, who after talking to the chief flight instructor says this isn’t a problem, but looking at flight scheduling I don’t see any instructors with availability at those times? The earliest I see is 7am.

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AlexJamesFitz@reddit

Ask specific instructors to find one who's willing.

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jtyson1991@reddit

It's not unreasonable to ask, but it's probably unreasonable to expect that no matter what the chief pilot said, unless the chief pilot said something specific like "[so-and-so] here, they're happy to work with you then, don't be late".

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ScathedRuins@reddit

what exactly is V_mc? i know it is the minimum controllable speed. i know below this speed in the event of an engine out the aircraft cannot maintain controllability. my question is more so why, what happens at lower airspeeds that prevents this controllability? is it just a lack of enough rudder authority?

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usmcmech@reddit

Vmc too high, need bigger rudder.

Bigger rudders create problems though. Drag, weight, CG, overcontrolling, .......

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ScathedRuins@reddit

I fear I'm not following, or rather unsure how that answers my question :D

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N546RV@reddit

The vertical stabilizer is an airfoil just like the wings. When you deflect the rudder, you create an angle of attack with the stab and ask it to generate "lift." Since this "lift" is in a horizontal direction, and since it's positioned at the end of the aircraft, the result is a yaw moment.

Now think about the wings. You already know that they can't just produce as much lift as you want, there are limits. You also already know that as airspeed decreases, AoA must increase to counter. And if you keep decreasing airspeed while trying to maintain level flight, eventually you exceed the critical AoA and lift drops off abruptly.

Now apply those same principles to the vertical stab. You have an engine out, resulting asymmetric thrust. You need a certain amount of "lift" (yaw moment) from the vertical stab to counter this. As airspeed decreases, you must ask for more yaw moment, which requires adding more rudder. Eventually, as airspeed decays, one of two things might happen:

You simply run out of rudder authority. You have no way to ask the vertical stab for more AoA, so you're not getting any more yaw moment. As airspeed further decays, so does yaw moment. You can no longer counter the asymmetric thrust.
Instead of benignly running out of rudder authority, you exceed the critical AoA of the vertical stab. Yaw moment drops off abruptly, asymmetric thrust suddenly becomes a big deal, and Bad Things happen.

I used to just think of the first case, and I wondered how a Vmc roll could be such a bad thing, assuming you were slowing gradually. Seemed like it'd be an equally gradual realization that you needed to get some airspeed back.

But when I watched a video that talked about stalling the stab, I understood - that's not going to be a gradual thing, and so it makes sense that it could get out of control really quickly.

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ScathedRuins@reddit

oh wow. excellent explanation. basically I can think of Vmc as the “stall speed” of the vert stab, if i understood correctly. that maked a lot of sense, i’ll check out the video too!

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swedishlightning@reddit

It’s not so much the stall speed of the rudder. The rudder likely has not stalled yet. Instead, it’s the point at which the rudder just doesn’t deflect enough air to counteract the yaw from the good engine.

This video by PrettyFlyforaCFI has some good diagrams explaining it. If you like it, he does several other videos on the nuance of Vmc.

https://youtu.be/bWt_lPtiT04?si=Inyggz7Q1nJiwMQE

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N546RV@reddit

And a bigger rudder won't necessarily save you from stalling the vertical stab.

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ScathedRuins@reddit

Starting my MEP this week and we are using a plane with Rotax engines. I find their RPM values are upwards of 5500 RPM, over double the Lycoming and Continental's I've flown til now with max 2500-2700 RPM. Purely out of curiosity I would like to know why that is? Is that a design choice? I mean I know they spin faster so they have to use a reduction gearbox instead of being direct drive like the lyco/contsm, but I'm left wondering -- why?

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N546RV@reddit

Spinning an engine faster is about the simplest way to get more power out of it. If you assume a flat torque curve, then doubling the RPM gets you double the horsepower. Of course in reality torque curves aren't flat, but that's something you can control through engine design.

Most aviation piston engines turn pretty slowly so they can take advantage of the simplicity of a direct drive system. Reduction drives for aircraft can be surprisingly difficult to engineer, so there's a tradeoff to consider when you want to take advantage of higher engine RPM.

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SensualPuma@reddit

would reliability have to do anything with that as well? constant higher ROMs i assume also mean more/faster wear and tear?

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Lord_Giles@reddit

With all else being equal... if the rpm is doubled wear on piston rings should double... but all else isn't equal.

The water cooling reduces the operating temperature range and reduces hotspots so there is reduced thermal expansion, and peak temperatures are reduced. This reduces wear from parts changing shape/size and the cooler metal is slightly stronger.

Unleaded fuels wear the pistonrings/cylinders less from less lead oxides scratching things. Better (modern synthetic) oils can be used with unleaded fuel too (less wear, less friction, and slightly better cooling)

Electronic fuel injection can reduce fuel dillution in the oil by running leaner (and potentially cooler) because of more even fuel distribution between cylinders.

Higher compression ratios boost power and efficiency, but increase wear. Higher rpms increase power and wear. Efficiency tends to start to drop exponentially above the engine's most efficient rpm (which will vary based on conditions)

Rotax engines seem to balance the various tradeoffs to target a TBO of 2000h (similar to the popular lycoming 360 engines).

Engines run often and at low power settings (and preheated when ambient temperature is below freezing) tend to wear the slowest.

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DesignBuildFlyJump@reddit

I was flying into a busy class D after transitioning over from B. The controller vectored me around (not complaining at all, it was busy). Once I established on long final, the traffdic he asked me to maintain current altitude (TPA) and just fly on upwind and he'll bring me around for a right downwind as the spacingt wasnt working out. A few seconds later he asked me to do a right 360 and then cleared me to land.

This is all good, no issues, always happy to work with the controllers especially when its busy AF. My question is that in the initial scenario where there is someone on final ahead of me slowing down to land and I'm asked to maintain TPA and speed and fly runway heading to do a lap around the pattern, do we not have a safety issue if the landing traffic goes around and climbs straight into me?

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N546RV@reddit

That would certainly be a potential conflict. In this case you'd be relying on the controller to continue working with you to maintain separation from the other aircraft.

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randombrain@reddit

Note that it sounds like at least one aircraft (OP) was VFR, and in Class D airspace there is no official "separation" between a VFR and anybody else.

Except that long-standing truth is going to change this October, if the FAA's proposed notice is implemented as expected.

Except the separation standard will only apply if the VFR is receiving radar service, and many/most Class D tower controllers do not provide radar service.

It's a mess.

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DesignBuildFlyJump@reddit

but he cant ask me to turn left, we got traffic and a full pattern on the parallel runway and then there was another aircraft on the downwind on my side as well so can't turn right. I guess he can only ask me to climb out?

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Flavor_Nukes@reddit

If you fly a Localizer with your aircraft inverted will you get reverse sensing?

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tempskawt@reddit

Yes

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randombrain@reddit

Hmm... maybe it depends on how the instrument is gimbaled? My initial response was "yes," but I'm not a pilot so I don't know how the instruments are installed. It might be different for different aircraft.

Imagine Runway 36 so that the "fly left" signal is received when you are East of the centerline and the "fly right" signal is received when you are West of it. Those signals exist in space all the time, whether there's an aircraft there or not. If there is an aircraft to the East of the centerline, it will receive and display a "fly left" signal. Always.

If the instrument is fixed in place relative to the panel then a "fly left" signal will actually point to the pilot's left, and when you're inverted the pilot's left is a regular pilot's right. So that would be reverse sensing.

But if the instrument is somehow able to rotate through 360° so that the instrument's "down" always references the Earth rather than the sky, then the "fly left" signal would correctly pull toward the inverted pilot's right.

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Flavor_Nukes@reddit

Localizer radio signal is detected via a fixed antenna. The display instrument itself doesn't move.

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randombrain@reddit

The antenna is irrelevant; the "fly left" signal always exists East of the localizer, and the antenna will receive it because there's no other signal to receive.

If the instrument is fixed so that "down" always means the pilot's feet and "left" always means the aircraft's left wing, then yes, if you're flying inverted you should treat the localizer as reverse sensing.

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Flavor_Nukes@reddit

Hmm this makes more sense.

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MultiMillionMiler@reddit

Why does aviation have the most absurd mixing if units imaginable?

Altitude in feet, speed in knots, weather stuff in celsius, fuel/weight/balance in metric or imperial depending on the type of calculation/specific context, lessons logged in metric time (1.3 hours..etc), like, why??

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tempskawt@reddit

Americans inventing manned flight followed by international standardization.

The stuff that we'd benefit from metric-izing is done, like temperature being reported in celsius. We'd really not benefit from converting altitude measurements into meters because, while feet is not an ideal measurement, we aren't converting altitude feet into inches or miles, so there's really not a problem there. Nautical miles are a minute of latitude, so they're the best measurement for long distance flight unless you also want to reinvent maps.

1.3 hours isn't metric.

Now for my soapbox: aircraft that can fly at greater than 100 knots should not have airspeed indicators that have miles per hour on them, even if they also have knots. It's cute in a Piper Cub, it's misleading/dangerous in an Arrow.

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stikshift@reddit

How does flying into a small airport work? Airports with FBOs is pretty straight forward, sign in and out, pay the landing fees and for fuel, etc., but do small airports usually have someone on site? What if you come back too late and are locked out and can't get to your plane?

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carl-swagan@reddit

Most small airports that aren’t attended 24/7 will have a gate code posted that can be used to access the ramp after hours. If you need additional services you can typically pay a call-out fee for line crew to come help you out.

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N546RV@reddit

Sometimes there isn't even a gate to worry about.

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usmcmech@reddit

Sometimes, there isn't even a gate

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Joeyheads@reddit

Yeah, this is how our small home field is. Just drive on 🤷

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TxAggieMike@reddit

Fuel is frequently self serve.

Some are attended during business hours.

An after hours phone number is posted.

When planning a trip to a small municipal airport, I look up the contact information in the Chart Supplement and call to obtain answers so the questions you pose.

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Computerized-Cash@reddit

For a LOC with secondary fix minimums, do you level off at the published step down fix altitude then continue to to the secondary, lower minimums after or, just level off at the lower minimums at the step down fix?

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KCPilot17@reddit

Have you passed said secondary minimums fix? That's when you can go down to that altitude.

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iPhones_cameras_suck@reddit

Has anyone flown into a NASCAR race before day of the race as a regular ticket holder? I'd really like to go to Atlanta this summer or Talladega in the fall, but not sure if they even allow general aviation traffic on race day for attendance (or if they basically shut it down or make prohibitively expensive for non-VIPs)

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FL060@reddit

It's been several years, but I flew into HMP for an Atlanta race the morning of and left that afternoon. They set up a temporary tower to manage everything. IIRC there were instructions available through the airport for expected traffic pattern, have a discreet squawk, etc.

Walking from the FBO to the track and back was a really cool feeling though.

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An after hours phone number is posted.

When planning a trip to a small municipal airport, I look up the contact information in the Chart Supplement and call to obtain answers so the questions you pose.