190A5 vs 190A8

[PJ_Godzilla]

I actually would love to have something like that for my RC planes... describe them in some virtual 3d format and see how the should perform before I build it... that would be cool.

Call a CFD house. This kind of stuff is done all the time. We used to even do some WT sims using ADAMs.

Depending on the guts of HTC's FM, who knows, it might be a genuine cross-sell opportunity.

[PJ_Godzilla]

    The mitigating factor here is that closer to the spinner axis the backward movement is less than at the prop tip: I hear blade center of thrust was at 2/3rds the height, but max height is only in the center of the rotation in profile view, so the "scientific" way of doing this would be to calculate how high the ENTIRE 4000 lbs center of thrust is displaced into the upper disc half, as is accepted by PJGodzilla as being what actually happens on stick pull, and that height of the 4000 lbs center of thrust will then give us the leverage applied by the prop at full power against the wing's center of lift.

    But then you have to take into account the leverage-increasing effect of the prop being at a right-angle to the lenght of the nose, creating a right-angle stress-riser that increase somewhat the actual leverage, given the forward direction of the thrust...

   The FW-190A is advantaged, like all radials, by having less upper disc half leverage agains the wing's center of lift due to the shorter nose, and, by extension, less leverage compared to the elevator's tail lenght leverage...

Okay, I'll accept the scaling argument for now. Suffice it to say that the disk will resist rotation in pitch, both for the blade alpha and rotational inertial effects I've mentioned before.

Let's also be clear that you can resolve the resultant thrust + torque to a single force above the prop axis - thus admitting the change in center of thrust of which you speak. This is simply physical shorthand and is easily done.

The torque resulting from this CofT change, regardless of how far out you move it radially along the prop blades, acts on a pitch lever arm that is perpendicular to the long axis of the a/c - indeed should be something like the distance from the CofT to the a/c CG and will tend to pitch the a/c nose down. I see zero reason for the "close-couple" f-dub to realize any advantage or freedom from this effect that the Spit would not also have, this distance likely not being significantly different b/w the two. I.e., I think you're using the wrong moment arm in your mental model.

As for that "close- coupling" again, I'd say it's real advantage is a minimized pitch inertia. However, the ability to rotate the a/c in pitch is dependent on both this and the ability of both wing and elevator to generate a pitch moment - and we know the max lift of the wing per unit mass is compromised due to this a/c's higher W/A.

I don't think we get there from here with the 190.

[gripen]

I actually would love to have something like that for my RC planes... describe them in some virtual 3d format and see how the should perform before I build it... that would be cool.

There actually is some good design software for the RC-planes, my favorite is the Profili2.

http://www.profili2.com/

[Gaston]

Okay, I'll accept the scaling argument for now. Suffice it to say that the disk will resist rotation in pitch, both for the blade alpha and rotational inertial effects I've mentioned before.

Let's also be clear that you can resolve the resultant thrust + torque to a single force above the prop axis - thus admitting the change in center of thrust of which you speak. This is simply physical shorthand and is easily done.

The torque resulting from this CofT change, regardless of how far out you move it radially along the prop blades, acts on a pitch lever arm that is perpendicular to the long axis of the a/c - indeed should be something like the distance from the CofT to the a/c CG and will tend to pitch the a/c nose down. I see zero reason for the "close-couple" f-dub to realize any advantage or freedom from this effect that the Spit would not also have, this distance likely not being significantly different b/w the two. I.e., I think you're using the wrong moment arm in your mental model.




   -I understand what you mean: That the distance from the wing's center of lift to the prop on a Spit is not necessarily different than that of the FW-190A's... I don't claim to know for sure WHY the FW-190A performs better at low speed than would be expected: I just observe that it was preferred to the Me-109G as a low-speed sustained horizontal turn fighter at medium-low altitudes while the Me-109G was preferred as a Boom and Zoom vertical fighter... This is why Rall said they "complemented" one another and that the FW-190A was a "Sabre" (curved), while the Me-109G was a "floret" (straight)...

  Maybe it is the distribution of drag due to the broader nose, the distribution of mass compared to the tail lenght to nose-lenght ratio: It could be any number of things... I do not say a downthrottled Spitfire will not out turn a downthrottled FW-190A... I do not even say that the Karhila Me-109G's 160 MPH best sustained turn speed will beat the sustained turn rate observed at 220 MPH by the Fins: I say the sustained turn rate is the SAME PLUS the advantage of a smaller radius...

  It could be that for very obscure unintuitive reasons the FW-190A gains more from downthrottling than other aircrafts... The critical point is that we agree that the purpose of downthrottling here is NOT to wait for a lower speed but to reduce IMMEDIATELY the nefarious effect of the prop's pull on the tightness of the radius, at the same time succeeding in MAINTAINING the SAME sustained turn rate, or even potentially improving it, while reducing the radius to a greater extent than the speed is reduced...

   This would explain why the Corner Speed is found in Il-2, and in actual tests, to be near 400 MPH, despite calculations putting it at around 280 MPH on a P-51D Mustang: The negative effect of the prop disc load at these middle speeds is what delays the ability to pull the maximum G on most types to such a high speed, meaning as you go down from 400 MPH to 300 MPH your ability to pull Gs is REDUCED, to a low around 260-300 on most types, getting no better but MUCH tighter if you downthrottle from there to sustainable turn speeds much below those: On Il-2 the best sustained turn rate for the P-51D at full power is 240 MPH, for the Me-109G the Fins found it at 220 MPH, but on both downthrottling would probably allow an slight increase of sustained turn rate combined with a BIG increase in turn radius reduction, so that the best combination is actually 200 MPH on a P-51D and 160 MPH on the Me-109G-6, as narrated by Karhila...

  As for high-speed fighting in the FW-190A, again theory is found wanting, but this time for aerodynamic behaviour reasons that have nothing or little to do with the prop disc load......

  True, Kurt Tank did say 7Gs with minimal stick forces at high speeds, but I think these included the typical tail-down pull-out deceleration that the Russian observed made a nose-level FW-190A drop a further 660 ft. on dive pull-out, this AFTER the nose was level! These were in part DECELERATION Gs in high-speed stick-pulls, horizontal behaviour adding snapping out because of assymetry in loads, but could include sideway "sinking" also, and the lack of elevator competitiveness of the FW-190A above 250 MPH is laughably obvious from all sources, and can only be ignored because it does not match people's intuitive expectations...


  I hope I covered some of the wanted points...

  Gaston



   

[hitech]

Gaston: Repeat after me.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

HiTech

[hitech]

Hear is a picture of our FW in a sustained turn about 180mph. The blue vectors are the thrust vectors.

[Angus]

Gaston, try as well:
Top speed in level flight will not decrease with less weight.
Or:
Top speed will decrease with less throttle.
Or:
Climb rate will increase with less weight.
Or:
Sustained turn rate will increase with less weight.
Then:
Climb rate will decrease with less throttle.
And:
Acceleration from stall in level flight will decrease with increased weight.
While bearing in mind that ROC, acceleration and sustained turning are.....not in different corners given the same thrust....

[FLS]

Hear is a picture of our FW in a sustained turn about 180mph. The blue vectors are the thrust vectors.

Cool picture.


Can you post an mp3 when the pig finally sings?   

[thorsim]

could you describe/define the other numbers ?

Hear is a picture of our FW in a sustained turn about 180mph. The blue vectors are the thrust vectors.

[PJ_Godzilla]

could you describe/define the other numbers ?

Or even the thrust numbers. It's hard to see how the vectors are distributed and what their magnitudes are. Are they generally lower thrust on the faster portions oF the "disk" (outside/lower)? One thing that IS clear is that it is not a uniform thrust centered at the hub. You've discretized it to 4 or 6 nodes.

BTW, Hitech, you are THE MAN. I go a little Chris Matthews (that bought-and-paid-for shill) everytime I hear the default "check 6".  Now about my special 410, that I ALONE will be enabled to fly...

[hitech]

I may be in a slip Godzilla, but the numbers are just to get a feel for the magnitudes, they are LB's thrust. I have no Idea where the ball was, and because PFactor will have much more of an effect then Inside/ Outside curve would. 

No mater what the outside tip would travel about 75 ft more per circle. So 180mph and 20 sec circle
1.46 * 180 * 20    = 5256
(5256 + 75)  / 20 / 1.46   = 182.19178082191780   
would be about 2 mph difference. I.E. about 1.2% difference in thrust so in the fw it would be in the range of 20lbs.

HiTech

[PJ_Godzilla]

I may be in a slip Godzilla, but the numbers are just to get a feel for the magnitudes, they are LB's thrust. I have no Idea where the ball was, and because PFactor will have much more of an effect then Inside/ Outside curve would.  

No mater what the outside tip would travel about 75 ft more per circle. So 180mph and 20 sec circle
1.46 * 180 * 20    = 5256
(5256 + 75)  / 20 / 1.46   = 182.19178082191780   
would be about 2 mph difference. I.E. about 1.2% difference in thrust so in the fw it would be in the range of 20lbs.

HiTech

I take your point but, since blade lift goes like v^2 and the relative V magnitude of inner and outer is (vtangential^2 + vforward^2)^.5 ... it's still small - even though the local blade Cl will be slightly different due to the alpha diff (something like blade pitch off horiz less atan(vtangential/vforward) - the diff in vforward dictating that this ratio diff too will be small. Thus, so diminishes the torque on the hub due to a/c pitch or - the movement in Center of Thrust. Since that displaces off of hub only slightly, Gaston's power-on pitch moment difference disappears with it.

Yet, my suspicion is, he'll continue to cling to this argument.

I wouldn't mind losing that 90 gals of fuel weight equivalent, mind, on the F-dub. And I do want the 410BeauKi43g55re2005pe2fulmar swordfishdevastatorvengeanced efiantp63rocskuabattlebarracu daraidenyak3...

[Gaston]

Gaston: Repeat after me.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.
Sustained turn rate decreases with less throttle.

Sustained turn rate decreases with less throttle.

HiTech

  -That is simply not the case below 250-300 MPH on most types... Plenty of anecdotal accounts make this perfectly clear, though on some types it is likely the turn rate stays the same and the radius decreases, an advantage of itself... Gaston

[thorsim]

we got any real world data on turn rate over speed range? and radius over speed range?

so we can look at the relationship, i'm not all in on gaston's point, but it could easily make sense that a pilot could see an decrease in radius without much of a decrease in rate as a "better turning" state for an aircraft and therefore prefer a slower turn speed ...

[Karnak]

  -That is simply not the case below 250-300 MPH on most types... Plenty of anecdotal accounts make this perfectly clear, though on some types it is likely the turn rate stays the same and the radius decreases, an advantage of itself... Gaston

That is physically impossible, therefor the anecdotes are wrong.  If you reduce your throttle you will go slower and if you are going slower you will take longer to complete a circle.  You do not tighten the circle enough by going slower to make up the difference.