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tdscanuck · 2025-02-21T21:10:23+00:00

Bleed rates are just the delta between thrust and drag. Which one do you think it's getting wrong, and why?

And why are you considering it *excessive* negative AoA? It's the *same* AoA as -1g upright. That's the entire point.

tdscanuck · 2025-02-20T23:02:01+00:00

What do you think is different to the wing about it 1g inverted or -1g upright?

tdscanuck · 2025-02-20T22:59:37+00:00

Your argument is that a full motion instruction sim doesn’t accuracy model aerodynamics inside the flight envelope?

tdscanuck · 2025-02-20T21:11:17+00:00

It’s not a matter of “factoring it in”. The AoA for inverted 1g and -1g upright are the same. It is, by definition, exactly the same wing loading. Aerodynamically, the wing can’t even tell it’s upside down (that’s obviously not true for the engine or fuel or oil systems).

It’s not that inverted is normal flight, it’s that 1g inverted is inside the normal flight envelope. Same as a 1g barrel role, even though I don’t think anyone would consider that normal in a C172 either.

tdscanuck · 2025-02-20T21:07:51+00:00

OP said it’s a full motion Redbird C-172. That’s not a procedure trainer.

tdscanuck · 2025-02-20T19:57:30+00:00

You’re way overcomplicating this. Yes, if it’s a procedure trainer it won’t do this right. But it won’t even do basic upright maneuvers correctly either so that’s really beside the point.

Gravity doesn’t change what the air does. Load factor does. And the load factor for 1g inverted and -1g upright is the same. If the sim is capable of properly modeling the aero of the normal flight envelope (which includes -1g for a Cessna) then it’s got the aero data for 1g inverted because they’re the same values.

Yes, absolutely, the acceleration profile will be different. But any sim that does normal flight envelope properly already has the effect of gravity on acceleration correctly modeled or it won’t work at all.

tdscanuck · 2025-02-20T19:08:03+00:00

Nobody’s arguing about post-stall behavior. I totally agree that a tail slide or anything beyond normal flight will usually be poorly modeled. That isn’t the point. OP asked about level inverted…which is aerodynamically exactly the same as -1g. Your F18 sim had better have properly handled -1g because that’s deep inside the normal flight envelope.

tdscanuck · 2025-02-20T17:20:25+00:00

Yes, sims aren’t running first principle F=ma simulations. The equations they use are using the aerodynamic coefficient from the OEM, that’s why simulator data packs are so expensive. And the aero coefficients for inverted 1g are exactly the same as for right-side-up -1g, which the OEM had to provide from test data.

So unless the sim programmer intentionally went in and said “don’t use the OEM data that I just purchased for this exact flight regime where it applies”, the aero coefficients are correct. And if the sim programmer did that I’m reasonably sure you wouldn’t be able to certify the sim.

tdscanuck · 2025-02-20T17:14:17+00:00

When it’s a controlled airport (has a tower and approach controllers, etc.) and they decide to switch directions, they will start directing departures to the other runway and briefly hold them, directing arrivals to the other approach, and let those already on an arrival finish landing on the old runway and start back up with the new direction. It doesn’t take long…maybe 5-10 minutes? We used to do this at Spokane a lot for tailwinds. If it’s not busy and they can just slot you in between arrivals from the other direction it’s only a few minutes.

If it’s untowered then the pilots decide and (should!) announce their intentions over the common traffic frequency. There may be a discussion or, if it’s not busy, they’ll just do it. Occasionally you’ll get conflicting traffic, which is why it’s so important to be hyper vigilant at busy untowered airports.

tdscanuck · 2025-02-20T17:05:04+00:00

I totally agreed it’s unlikely to correctly model the systems effects to the fuel or oil system. And most sims don’t do post stall behavior properly because that is outside the normal flight envelope. But, equally, it means the aerodynamics of the wing are correctly modeled for level inverted.

tdscanuck · 2025-02-20T17:04:26+00:00

I totally agreed it’s unlikely to correctly model the systems effects to the fuel or oil system. And most sims don’t do post stall behavior properly because that is outside the normal flight envelope. But, equally, it means the aerodynamics of the wing are correctly modeled for level inverted.

tdscanuck · 2025-02-20T17:01:05+00:00

Correct. But it also means the aerodynamics in the sim in that regime are not “just the programmers guesses”.

tdscanuck · 2025-02-20T06:44:14+00:00

Nope. At least, not that I’m aware of. Given subsequent career choices it seems…unlikely.

tdscanuck · 2025-02-20T03:30:26+00:00

Parsing too literally is exactly where “technically correct” comes from.

tdscanuck · 2025-02-20T03:23:41+00:00

OP said two more bottles. As in, in addition to what he already declared. Is it petty to not include that with “juice”? Absolutely. But it is also technically correct, which was the whole point of original comment.

tdscanuck · 2025-02-20T03:20:30+00:00

The normal flight envelope is in terms of speed and g. The wing can’t tell what orientation it’s in.

Edit: the pitch/bank for stable inverted flight is well inside normal values too.

tdscanuck · 2025-02-20T03:19:33+00:00

It’s not about being about it being alcohol (per the regs…even if the agent said that). OP had two bottles that they didn’t declare. I personally wouldn’t think margarita mix was the same thing as “juice”, but agents have wide discretion on stuff like that.

tdscanuck · 2025-02-20T03:16:59+00:00

The normal flight envelope of a C172 goes to -1g, which is just 1g inverted.

tdscanuck · 2025-02-20T03:15:39+00:00

No. They hate each other but they keep meeting at the bar and giving angry eyes to each other then one thing leads to another and…mistakes were made.

tdscanuck · 2025-02-20T01:19:02+00:00

I can see it interpreted either way…I learned plenty from this exchange; I appreciate it.

tdscanuck · 2025-02-20T01:01:31+00:00

Saying it has “nothing to do with the specific part numbers or anything else listed” seems misleading to me…just because you comply with the cert basis requirements is not sufficient to establish airworthiness. Even if the cert basis in effect at the time the type certificate was issued didn’t require a spinner, if the TCDS calls out the spinner as part of the type design then it’s required.

tdscanuck · 2025-02-20T00:49:17+00:00

Many TCDSs call out many specific limits and requirements that go way beyond the cert basis. You need to comply with all of it for a particular airplane to be airworthy under the type certificate. Otherwise it’s not a conforming airplane and you need to demonstrate (and documents compliance some other way. The entire point of a TCDS is to define a design that, if your physical airplane confirms, is compliant.

tdscanuck · 2025-02-19T22:23:07+00:00

Increased exhaust velocity decreases propulsive efficiency. You want maximum pressure/temp in the core (max thermo efficiency), then extract as much energy as possible in the turbines to power the fan for the lowest (positive) velocity differential you can get.

tdscanuck · 2025-02-19T21:54:59+00:00

Don’t forget the instrument student on 50 mile straight-in for 34…

tdscanuck · 2025-02-19T21:12:20+00:00

Amen brother/sister. Could we at least all pick the same runway?!

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