Brewster Buffalo dive speed and handling

[hlbly]

Brewster at 1k alt 150 to 250 mph ias `22 seconds
FW190a8` at 1kalt 150 to 250 mph ias 25 seconds
Could not figure out how to do it at sea level . Was unable to keep gear on while on the ground at that speed .
Test conducted at 1000 k alt auto level on . E6b used for recording speed . 1k alt was obtained throttled back until speed was 120 ias . Full throttle then applied .2 stop watches started by myself and wife as speed hit 150 ias. watches stopped at 250 ias . Test repeated 5 times . Differences in times below .5 seconds for both watches , each test . AC were augured after each test . Fuel level was 25% no ords and lightest gun package .


http://bbs.hitechcreations.com/smf/index.php/topic,290564.0/topicseen.html Gyrene here is a link to the chart I was referring to it is on the 1st page of the thread .

[Stoney]

Wait, my understanding is that a high wing load has a faster instantaneous turn performance and poor sustained turn capability, whereas a lower wing loading has slower instantaneous turn performance and better sustained turn capability. Angle of attack, airfoil dimensions, drag and thrust affect the coefficient of lift in that the higher the angle of attack, the more drag is produced which requires more thrust to maintain lift.



Brain freeze...          I'm so confused.

Wing-loading is merely a single aircraft characteristic.  With respect to "turn" ability, it should be judged only in its proper aerodynamic context, which is pretty narrow.  It'd be like saying the P-47M is the fastest prop plane in the game, without any other caveat.  High or low wing-loading has no direct correlation to the turn capability of the aircraft taken out of context.  All it really tells you is whether or not a plane will have to generate more or less lift for a given condition of flight.

[dtango]

Brain freeze...          I'm so confused.

Don't be confused .  Let's see if I keep from confusing you even more!

Let's first start with the instantaneous level turn performance case.  That's easier to explain.  A simple way to explain it is this.  When you turn an airplane the lift is used to both support the weight of the airplane as well as turn it.  In a turn the higher wing-loaded aircraft will have to expend more of it's lift capability just to support the weight of the aircraft and has less usable lift to turn the aircraft compared to a lower wing-loaded aircraft.  Therefore the lower wing loaded aircraft has a better instantaneous turn.
 

Here's another way to explain it: mathematically we can express turn rate and turn radius like this:

Turn Radius:


Turn Rate:


where n=g-loading, g=gravity, V=velocity

So to minimize turn radius and maximize turn rate you want velocity as low as you can get while g-loading as high as you can get.  Well n (g-loading) of an airplane is bound by the maximum structural limit the airframe can take.  In AH though there's a structural limit we usually hit a virtual limit of our pilot blacking out around 6g's.

How do we minimize maneuverable velocity of an airplane?  One way is by decreasing wing loading.  Doing a bunch of fancy math we can derive the following equation:



This nice little equation gives us the corner velocity of an airplane as a function of wing loading (the W/S term in the equation - weight / wing_surface_area ).  So corner velocity then varies directly with wing loading (W/S).  As wing loading increases, so does corner velocity.  As wing loading decreases so does corner velocity.  As we've stated already reducing velocity reduces turn radius and increase turn rate thus lower wing loading improves the instantaneous turn performance of an airplane.

Sustained level turns are much more complicated animals to explain.  It'll take more time for me to come up with an explanation of how sustained turns work with wing loading factored in.

Tango
412th FS Braunco Mustangs

[dtango]

Brewster at 1k alt 150 to 250 mph ias `22 seconds
FW190a8` at 1kalt 150 to 250 mph ias 25 seconds

1) I assume you used military power and not WEP for the A8?
2) And is this result wrong?  If so why do you think it's wrong?

Tango
412th FS Braunco Mustangs

[gyrene81]

dtango, I think I'm getting mixed up on the term "intstantaneous turn performance". When I see that term, and from everything I've been busting blood vessels on trying to understand for the past 8 months, that means the ease at which an airplane can enter a turn from level flight at x velocity based on wing load, power to weight ratio and angle of attack. But you're saying based on the calculations the lower wing load can not only enter a turn faster at a higher relative velocity, it can sustain that turn for a longer period? I fully understand the equations as relating to sustained turn and turn rate, but not instantaneous turn performance. Maybe I'm just mixing up the term.




*takes 2 tylenol* 

[dtango]

dtango, I think I'm getting mixed up on the term "intstantaneous turn performance"....means the ease at which an airplane can enter a turn from level flight at x velocity based on wing load, power to weight ratio and angle of attack.

Remove power-to-weight ratio from your definition of instantaneous turn, then that's a better definition of it.

But you're saying based on the calculations the lower wing load can not only enter a turn faster at a higher relative velocity, it can sustain that turn for a longer period? I fully understand the equations as relating to sustained turn and turn rate, but not instantaneous turn performance. Maybe I'm just mixing up the term.

No, that's not what I'm saying .

Working on another response to you on all this.  Use tylenol as needed until then!

Tango
412th FS Braunco Mustangs

[Wmaker]

Just as a general note (And to what Tango was getting at with his questions, I believe. ): if the climb rate is correct, so is the acceleration. Plane climbs with whatever amount thrust isn't needed to maintain the speed it is doing at that precise moment, otherwise it would be accelerating.



Something that doesn't make sense to me is the shape of the curves that depict Brewster's climb rate in both the Pilot's Viewpoint II and AHT (the black curve is from the former book) considering Cyclone has two speed supercharger. Looking at the Cyclones power curves, HTC's climb curves make much more sense in that regard. Are those real life curves averaged out after the first gear. I mean that's how it looks like but doesn't really make much sense to depict them that way IMO?

Any ideas?

[gyrene81]

Remove power-to-weight ratio from your definition of instantaneous turn, then that's a better definition of it.

I get it!!! Because power to weight ratio affects speed and flight, not the ability to enter a turn.    

Thank you sir.





*now to go find my tylenol*

[gyrene81]

Just as a general note (And to what Tango was getting at with his questions, I believe. ) is that if the climb rate is correct, so is the acceleration. Plane climbs with whatever amount thrust isn't needed to maintain the speed it is doing at that precise moment, otherwise it would be accelerating.

(Image removed from quote.)

Something that doesn't make sense to me is the shape of the curves that depict Brewster's climb rate in both the Pilot's Viewpoint II and AHT (the black curve is from the former book) considering Cyclone has two speed supercharger. Looking at the Cyclones power curves, HTC's climb curves make much more sense in that regard. Are those real life curves averaged out after the first gear. I mean that's how it looks like but doesn't really make much sense to depict them that way IMO?

Any ideas?

Wmaker, are you sure you have those horsepower ratings correct? The cyclone engines the B-239s were shipped with were rated at a higher take off BHP than what you have depicted, from what I've seen the 850hp was at 6000 feet.

[dtango]

Just as a general note (And to what Tango was getting at with his questions, I believe. ) is that if the climb rate is correct, so is the acceleration. Plane climbs with whatever amount thrust isn't needed to maintain the speed it is doing at that precise moment, otherwise it would be accelerating.

Yep.  And if hlbly is surprised by what he's seeing in his test between a 190A-8 and B239, wait until he tries his test between the 190A-8 and the I-16 .  EDIT- especially around 4,000 ft.

Tango
412th FS Braunco Mustangs

[dtango]

I get it!!! Because power to weight ratio affects speed and flight, not the ability to enter a turn.    

Thank you sir.

Yep, you're getting there!  We could be much more precise than that but you're getting the idea.  Just adding a little more to your statement to increase the clarity just a tad I would modify it to...

"Because power to weight ratio affects speed and flight, not the ability to enter a turn at that instant in time."

EDIT: ... I like the following even better ...
"Because power to weight ratio affects speed and flight, not the maximum turn ability at that instant in time."


Maybe tequila shots are better than tylenol?

Tango
412th FS Braunco Mustangs

[Wmaker]

Wmaker, are you sure you have those horsepower ratings correct? The cyclone engines the B-239s were shipped with were rated at a higher take off BHP than what you have depicted, from what I've seen the 850hp was at 6000 feet.

Check that speed chart I posted earlier. Never said that it would the all-out output. It's the max. continuous rating. As you can see, the first gear produces 850hp close to 7000ft in practise due to ram.

edited: Corrected the alt as I remembered/read it wrong.

EDIT2: The black graph is actually with the 1000hp MIL setting. When I made the graph I named the power setting according the MAP gauge in AH. But in reality the FTHs match with the 1000hp setting. The probable reson why the MAP gauge displays the 950hp MAP is that I wasn't able to find the MAP-figure for the 1000hp setting. It isn't mentioned in the original docs.

[hlbly]

No tango at 190a8 used WEP in the test . You think this acceleration is correct comparatively ?

[Wmaker]

Brewster's fuel load is much bigger portion of its weight than A-8s fuel load is from its weight. The HTC charts are with full fuel load. Hlbly used 25% fuel loads in his test. My guess is that the power loadings agree nicely with real life figures.

[gyrene81]

Yep, you're getting there!  We could be much more precise than that but you're getting the idea.  Just adding a little more to your statement to increase the clarity just a tad I would modify it to...

"Because power to weight ratio affects speed and flight, not the ability to enter a turn at that instant in time."

EDIT: ... I like the following even better ...
"Because power to weight ratio affects speed and flight, not the maximum turn ability at that instant in time."


Maybe tequila shots are better than tylenol?

Tango
412th FS Braunco Mustangs

Yes the second statement is much clearer. And after re-reading the mounds of information to the point of hairy eyeballs, the whole picture is clearer, and I've been struggling to digest this stuff for months.  


I enjoy tequila a little too much and it makes me stupider than I already am   ...last episode was 15 years ago in a bar in Slidell, La.