Quick question about stall horns?

[morfiend]

Re gear not down. Lavochkins had a red pin that was pushed out (proud of) the wing when the gear was down. It was activated by a cam off the gear hinge point. The pilot had to look out across each wing to see if that gear was fully down or not. Cockpit indicators merely stated whether the gear down activators (hydraulics) were under pressure or not.

 IIRC the early mig jets used this same system.

   

[Ruah]

the Japanese used a similar pin system in their planes too - I believe the design was originally American, with the right sold to the Japanese Empire in the mid 30s but I can't be arsed to check now.

[Chalenge]

P-51 Mustangs would experience elevator  buffet as they approached a stall with a faster speed at stall meaning a more violent buffet. The Mustang also has an audible horn (as well as the warning lights) when the gear is up and the throttle is reduced to minimum and this can be cleared with a cut-out switch but anytime the throttle is moved forward again the horn is also reset.

[bagrat]

just curious but as stated earlier, since the wing root stalls first before the tips and ailerons. once stall speed is reached would not this result in the mushy or violent nose down effect instead of the roll which occurs some times... it was even said that a p-51 would stall so violently nose down at a stall that the pilot would bang there head on the canopy (not sure where i saw this). however it seems a barrel roll to inversion with slight nose down effect afterward will generally be the outcome of a stall here... curious

[Chalenge]

According to the manual:

A stall in the P-51 is comparatively mild. The airplane does not whip at the stall but rolls rather slowly and has very little tendency to drop into a spin. When a complete stall is reached a wing drops. After that if you continue to pull back on the stick the airplane falls off into a steep spiral.

When you release the stick and rudder the nose drops sharply and the airplane recovers from the stall almost instantly.


There is more but thats the basics... HTC is about as spot on as anyone could get.

By the way your supposition is incorrect about the root stalling first. It is true of wingforms like the Spitfire that the tip stalls very early which is why it has washout. In the case of the P-51 the tips stall first with the rest of the wing quickly following but in cases where the wing is even more rectangular you can get root stalls.

[Serenity]

just curious but as stated earlier, since the wing root stalls first before the tips and ailerons. once stall speed is reached would not this result in the mushy or violent nose down effect instead of the roll which occurs some times... it was even said that a p-51 would stall so violently nose down at a stall that the pilot would bang there head on the canopy. however it seems a barrel roll to inversion with slight nose down effect afterward will generally be the outcome of a stall here...curious

My guess as to the roll is the way the wing stalls matched with the torque. The way the aircraft reacts, i.e. roll vs drop is plane specific. IIRC, the F4U was known to have a NASTY snaproll when stalling (Based on what I can recall of the F4U training video I have) where one wing just drops, whereas the P-47 just drops straight down without any tendency to roll (based on a similar P-47 training film).

[RTHolmes]

Re gear not down. Lavochkins had a red pin that was pushed out (proud of) the wing when the gear was down. It was activated by a cam off the gear hinge point. The pilot had to look out across each wing to see if that gear was fully down or not. Cockpit indicators merely stated whether the gear down activators (hydraulics) were under pressure or not.

are they modelled on our LAs like they are on our spits? iirc all our spits have these pins, although I'm pretty sure anything with a C or E wing shouldnt have them. not sure about the flap indicators.

[colmbo]

By the way your supposition is incorrect about the root stalling first. It is true of wingforms like the Spitfire that the tip stalls very early which is why it has washout. In the case of the P-51 the tips stall first with the rest of the wing quickly following but in cases where the wing is even more rectangular you can get root stalls.

If the tips stalled first the airplane would be very wicked at the stall.  Designers always want the root to stall first.  There is more than wing planform that effects how the wing stalls.  Washout (the twist in the wing putting the tip at a lower angle of incidence than the root) prevents/delays wingtip stall.

[colmbo]

According to the manual:

A stall in the P-51 is comparatively mild. The airplane does not whip at the stall but rolls rather slowly and has very little tendency to drop into a spin. When a complete stall is reached a wing drops. After that if you continue to pull back on the stick the airplane falls off into a steep spiral.

When you release the stick and rudder the nose drops sharply and the airplane recovers from the stall almost instantly.

Here is what is looks  like.

[Chalenge]

If the tips stalled first the airplane would be very wicked at the stall.  Designers always want the root to stall first.  There is more than wing planform that effects how the wing stalls.  Washout (the twist in the wing putting the tip at a lower angle of incidence than the root) prevents/delays wingtip stall.

You speak in great generalities and in this case 'wicked' would be correct if the pilot doesnt realize what is happening. All WWII fighters can be wicked if handled poorly. Washout is designed into aircraft to alleviate tip stalls in elliptical wings and in wings that have a tapered leading edge like the Me262.

The reason the P-51 experiences buffeting of the tail during stall is not because of the root stalling first (which doesnt happen anyway) but because the downwash of the wing causes an increase in induced drag. If you were to picture the induced drag of nearly every plane in WWII you could see it as slight turbulent flow above the wing behind about the 60% point on the chord (actual percentage varies by airfoil obviously). In the case of the P-51 you would not be incorrect by picturing that as occuring behind the wing altogether.

This is why when the RAE went looking for a combat aircraft to fight the Luftwaffe above 30k they found all allied aircraft wanting except the P-51. While the luftwaffe was fielding aircraft that could fight at mach 0.75 the P-38 was only capable of fighting up to mach 0.68 and the P-47 at mach 0.71 while the Spitfire itself was too fragile to handle combat at high speeds. But the Mustang saved the day because it could fight at mach 0.78 and because of its design (laminar flow and very low induced drag) it could manoeuvre at high speeds at high altitude very successfully.

[colmbo]

You speak in great generalities and in this case 'wicked' would be correct if the pilot doesnt realize what is happening. All WWII fighters can be wicked if handled poorly. Washout is designed into aircraft to alleviate tip stalls in elliptical wings and in wings that have a tapered leading edge like the Me262.

Even the lowly Cessna 150 has washout built into the wing.

I really doubt your statement about the mustang not stalling root first, do you have anything to back it up?  I doubt that any airplane that reached any level of production had a stall that started at the wing tip.

[Chalenge]

Airfoil stall progression is from trailing edge forward in all cases. Now if you accept that as true (and it is taught this way universally) than you should be able to reason that a rectangular airfoil planform will stall simultaneously from root to tip except that most designs (and particularly in trainers) have a washout/washin design to cause the stall to move from root to tip. In the case of tapered wings however the stall is from tip to root because as the chord decreases (and it does near the tip) the distance also decreases between center of pressure (CP) and the higher pressure at the trailing edge. Because there is a shorter distance there is an increase in the adverse pressure gradient. In a perfect world the washout of the wing would make up for the difference in distance and the entire trailing edge would stall simultaneously. It seldom happens that way and particularly in combat the pilot will have his vectors crossed up (control input) and one wingtip will always (99.99%) stall first.

Laminar flow designs sacrifice low speed handling for high speed performance and so when a laminar design stalls its all stalled at once as in other designs. Just like tapered wing designs 99.99% of the time it is not the entire wing at once but a tip followed by the rest but it is almost certainly never (as close as never could be) the root.

[Karnak]

Post supporting documentation about the Spitfire being too fragile to fight at high speeds, please.  I've never seen anything suggesting that was a concern.

[Chalenge]

The quote was from Capt Eric Brown at RAE Farnborough in his conversation with General Doolittle. In whole what he said was that the Spitfire was too fragile to carry enough fuel to escort bomber groups deep into Germany and fight at the same time. If it was stiffened for the extra weight of fuel it would be too heavy to fight and so it must be relegated to interceptor roles.

The question was concerning what was going wrong with escort duties at the time (December 1943) and why it was the P-38s and P-47s were such a disaster in Germany while the P-38 was doing such a 'marvelous job' in the Pacific? Capt Browns answer was: 'Against German fighters at high altitudes you need Mustangs.'

I am sure there is also an official report out there somewhere to the same effect.

[RTHolmes]

might be a dumb question but why is it better for the stall to start at the root rather than the wingtip?