Be-1900 Airfoil and mach tuck...

[ppragman]

So, I know this guy who is absolutely afraid of the barber poll in the 1900. He doesn't want to nose over to the poll whenever he starts his descent, and is terrified that he will nose over and enter a "mach tuck." This is rediculous, but there is no way for me to prove it unless I can get some info on the airfoil of the 1900. If I could find out what the critical mach number is I could prove to him that at .48M (Mmo in the 1900c) we are nowhere near the critical mach #. Anyone know where to look?

[tgrayson]

Originally Posted by ppragman

there is no way for me to prove it unless I can get some info on the airfoil of the 1900. If I could find out what the critical mach number is I could prove to him that at .48M (Mmo in the 1900c) we are nowhere near the critical mach #. Anyone know where to look?

The Beech 1900 (C-12) uses the NACA 23018 for the root and the NACA 23012 for the tip. NACA often uses these airfoils for a variety of tests, so you might be able to get the figure from one of their reports (Will take a lot of work.) I have a book at home which might have the data.

.48M would be a very low critical mach, as you know.

[B767Driver]

Your answer won't lie in the horizontal airfoil (the wing) but in the vertical ones (the props). A turboprop is mostly limited to such a low mach to prevent the propellers from going supersonic (specifically the tips). Mach tuck won't be an issue.

On a lot of the racing airplanes you will see shortened diameter propellers that enable the airplane to go faster without losing efficiency to mach effects at the prop tips.

[ppragman]

thanks a lot

[ppragman]

Originally Posted by B767Driver

Your answer won't lie in the horizontal airfoil (the wing) but in the vertical ones (the props). A turboprop is mostly limited to such a low mach to prevent the propellers from going supersonic (specifically the tips). Mach tuck won't be an issue.

On a lot of the racing airplanes you will see shortened diameter propellers that enable the airplane to go faster without losing efficiency to mach effects at the prop tips.

That's pretty useful info. I think it's rediculous worry, but that's why I'm trying to get this info to prove it to him.

[ZapBrannigan]

If it goes any faster all of those ridiculous winglets and vortilons and whatever the heck else those things the engineers stuck on that airplane to make it fly are called might fall off!

[ppragman]

Originally Posted by ZapBrannigan

If it goes any faster all of those ridiculous winglets and vortilons and whatever the heck else those things the engineers stuck on that airplane to make it fly are called might fall off!

[Firebird2XC]

Originally Posted by ppragman

So, I know this guy who is absolutely afraid of the barber poll in the 1900. He doesn't want to nose over to the poll whenever he starts his descent, and is terrified that he will nose over and enter a "mach tuck." This is rediculous, but there is no way for me to prove it unless I can get some info on the airfoil of the 1900. If I could find out what the critical mach number is I could prove to him that at .48M (Mmo in the 1900c) we are nowhere near the critical mach #. Anyone know where to look?

I've been flying the 1900 for about six months.. had a guy set off the overspeed for a second once.

We're still here.

[NJA_Capt]

Originally Posted by ppragman

...terrified that he will nose over and enter a "mach tuck." This is ridiculous, but there is no way for me to prove it unless I can get some info on the airfoil of the 1900.

Technical aspects aside, if it were "theoretically" possible for a 1900 to enter mach tuck, doesn't he understand that certification margins would preclude him from exceeding such a speed under normal operations?

B1900D
Mmo .48
Max Alt FL250

King Air 300/350
Mmo .58
Max Alt FL350

http://rgl.faa.gov/Regulatory_and_Gu...FILE/a24ce.pdf


Please tell me he isn't a PIC......

[falconvalley]

ROFL Some one told him the barber pole was the limit for mach tuck??!!? For your airplane to be able to mach tuck, it needs to not be built like a dump truck!

[ppragman]

Originally Posted by NJA_Capt

Please tell me he isn't a PIC......

No, thank god, he's one of the other FOs

[ppragman]

Originally Posted by falconvalley

ROFL

that's what I said

[WalterSobchak]

Ride the pole like a stripper! Especially on the last leg or min day.

[OldTownPilot]

Mach tuck in a Beech........Not gonna happen. Period.

The speed limitations like were said earlier are to prevent the props from going supersonic. Its the same reason helicopters don't go that fast.

[ppragman]

I know, that's what I said

[#1FMS]

I would ask him how it is that mach tuck could be a risk on a plane that doesn't even go half the speed of sound (.48). Shouldn't it be obvious to an airline pilot that no local flow over any surface of an airplane that goes so slow will get anywhere near supersonic? (Prop tips excepted.)

Ask him to define Mmo.

[tgrayson]

Originally Posted by #1FMS

on a plane that doesn't even go half the speed of sound (.48)

Actually, for airfoils that weren't intended for high speed, critical mach can be quite low. I'm looking at some data indicating .58 or so for an airfoil similar to the one on the Beech, and that's at a low AOA. Put this aircraft into a 60 degree bank and the critical mach would be much lower.

[ppragman]

Originally Posted by tgrayson

Actually, for airfoils that weren't intended for high speed, critical mach can be quite low. I'm looking at some data indicating .58 or so for an airfoil similar to the one on the Beech, and that's at a low AOA. Put this aircraft into a 60 degree bank and the critical mach would be much lower.

Put anything into a 60 degree bank and the critical mach should be lower. Let's just say then that hypothetically, the Mcrit on the 1900 is .58, a full 10% higher than .48. So let's say that you roll it over into a 60 degree bank, if you maintain altitude, then there's no way you'll even be at the barber poll. If you roll over into a 60 degree bank while diving then you might have some issues assuming Mcrit is lowered more than negligibly, but how often are you going to roll into a 60 degree bank in a dive? I'm a freight dog and that's rediculous, we don't even do that to get into dutch harbor.

[I_WANNA_BE_ATP]

I'm surprised no one here asked if this guy went to GIA ???

Did he ??