If you had an airforce...

Soren · Aug 31, 2008

Bill,

I noted very carefully where I got all the information from, it's all from FW NACA, and I even told you which reports. Go check them out plz.

Regarding Cd0, well for piston engined fighters it is nearly always in the 0.02 to 0.025 area, you should be able to check that as-well. Now I could imagine that the Cd0 of the P-51H could be as low as 0.019 or 0.018, no problem, the airfoil was like a knife, but again it makes no difference in turning combat as Cd0 has close to no effect here.

And as for the FW190's wing and its stalling characteristics, well Gene has told this many times by now, the vicious stall was a combination of the elliptical lift distribution achieved in turns because of aeroelasticity (lift and G forces increase) bending the wing to the point where this was achieved, and then the already nasty stalling characteristics of the NACA 23000 series airfoil. But I'll contact Gene again and report back when he replies, no problem, but be prepared to get the exact same answer.

But finally there's one thing I really do not understand Bill, why is it you don't contact Gene yourself, then you can be 100% sure that you get your opinion across exactly as you intend it. As an equal nitpicker I'd prefer that myself really.

drgondog · Aug 31, 2008

Soren said:
Bill,

I noted very carefully where I got all the information from, it's all from FW NACA, and I even told you which reports. Go check them out plz.

Soren - I don't have to check anything. You are trying to beat Dave into submission with 'facts not entered into evidence' as the lawyers say. YOU present them and prove your case

Regarding Cd0, well for piston engined fighters it is nearly always in the 0.02 to 0.025 area, you should be able to check that as-well. Now I could imagine that the Cd0 of the P-51H could be as low as 0.019 or 0.018, no problem, the airfoil was like a knife, but again it makes no difference in turning combat as Cd0 has close to no effect here.

High speed drag (dominant Cd0) a huge effect on energy retention. YOU prove that it has no 'effect'

And as for the FW190's wing and its stalling characteristics, well Gene has told this many times by now, the vicious stall was a combination of the elliptical lift distribution achieved in turns because of aeroelasticity (lift and G forces increase) bending the wing to the point where this was achieved, and then the already nasty stalling characteristics of the NACA 23000 series airfoil. But I'll contact Gene again and report back when he replies, no problem, but be prepared to get the exact same answer.

I'll be waiting in breathless anticipation

But finally there's one thing I really do not understand Bill, why is it you don't contact Gene yourself, then you can be 100% sure that you get your opinion across exactly as you intend it. As an equal nitpicker I'd prefer that myself really.

I am in dialogue with Gene frequently, but not in last couple of weeks. I have huge respect for Gene and his opinions, I don't need them to form my Own.

I have documented my opinions and the math behind them. Document your own and publish them - but submit your facts to support your math.

Soren · Sep 1, 2008

Soren - I don't have to check anything. You are trying to beat Dave into submission with 'facts not entered into evidence' as the lawyers say. YOU present them and prove your case

But how can that be true when I've provided references to everything I have put forward ? Seriously Bill.

drgondog said:
I am in dialogue with Gene frequently, but not in last couple of weeks. I have huge respect for Gene and his opinions, I don't need them to form my Own.

Well that's fine, but Gene doesn't say something unless he's confident he is right, that you need to know.

I have documented my opinions and the math behind them.

Ah but you haven't Bill, you haven't yet provided any mathematical proof or confirmation of your opinions at all. All you have done is say that Cd0 has a significant effect in turning combat at high speed. Where is the math, where are the equations to prove that ??

Document your own and publish them - but submit your facts to support your math.

Fair enough Bill, but you'll have to do the same then, that you must understand.

Let me demonstrate why Cd0 has close to no effect in turning combat:

Cl = 1.5
Cd0 = 0.021
e = 0.8

Cdi = (Cl^2) / (pi*AR*e)
Cdi = (1.5^2) / (pi*6*0.80)
Cdi = 0.149207759

So Cd0 only represents 12.8% of the total drag, and considering that the difference in Cd0 between single seat piston engine fighters of the era generally is less than 9% (A Cd0 of 0.019 really wouldn't change things much) I think most people would agree that Cd0 has close to no effect in turning combat.

Now while Cd0 isn't important in turning combat, it is in straight flight, where the AoA pulled and therefore Cl is relatively low.

So now I've provided the math behind what I've been saying, now it's your turn.

Some references for people interested:
The Lift Equation
The Lift Coefficient
The Drag Equation
The Drag Coefficient

Overview:
Index of Aerodynamics Slides

B-17engineer · Sep 1, 2008

Your good at math.......**(clueless)

drgondog · Sep 1, 2008

Soren said:
But how can that be true when I've provided references to everything I have put forward ? Seriously Bill.

I must have missed the references you posted for specific Cd0 for both ships. Where are they again? and do you mean Cd0 as the zero lift drag of the wing or the total parisite drag of the wing body, trim and AoA configuration? You named a NACA report but didn't show the report so nobody can read the same report and conclude or disagree with your numbers?

Well that's fine, but Gene doesn't say something unless he's confident he is right, that you need to know.

I don't either. You made an unequivocal statement that the Fw 190 had a true elliptical lift distribution in a high G turn. Icarefully explained the difference between a mathmatical true 'elliptical' as achievable with zero twist, elliptical planform - then explained 'eeliptical like' on say a trapezoidal planform with twist, Chord ratios around .4 and tip geometry.

I asked you to reviste with Gene what I just said if you don't accept it and you respond with this?

Ah but you haven't Bill, you haven't yet provided any mathematical proof or confirmation of your opinions at all. All you have done is say that Cd0 has a significant effect in turning combat at high speed. Where is the math, where are the equations to prove that ??

I gave you the Parasite Drag equations, the breakout between the AoA dependent factors and the empirical standards for the factors - all preliminary design approaches to be validated in wind tunnel and flight tests - as well as the reference

Thrust = Drag
Thrust = DragProp+DragInduced+DragParasite
Cdparasite = max at highest V.. Cd0 of wing at near constant, other factors vary
Cdi = max at highest AoA

As the ship slows down the DragProp decreases and DragInduced increases

Fair enough Bill, but you'll have to do the same then, that you must understand.

Let me demonstrate why Cd0 has close to no effect in turning combat:

Cl = 1.5
Cd0 = 0.021 Prove this??)
e = 0.8 (Prove this)

Cdi = (Cl^2) / (pi*AR*e)
Cdi = (1.5^2) / (pi*6*0.80)
Cdi = 0.149207759 (if 'e' is in fact .8)

References for .8 as the efficiency factor for Ta 152?

So Cd0 only represents 12.8% of the total drag,

So let us remember CdParasite is comprised of 1.) the Cd0 of the wing (estimated form airfoil chart and validated in wind tunnel and flight tests) and dependent on wing area, plus 2.) trim drag, fuselage drag as AoA increases, friction drag, gaps in flight control surfaces, wheel well, antenna, etc - each with a different reference area. Friction drag and profile drag are function of wetted surface, wake drag at high speeds due to Boundary Layer growth is a function of wing area, trim drag is function of tail area.

and considering that the difference in Cd0 between single seat piston engine fighters of the era generally is less than 9% (A Cd0 of 0.019 really wouldn't change things much) I think most people would agree that Cd0 has close to no effect in turning combat.

You keep using generalities Soren. What IS the exact Cd0 and Parasite Drag for each of these ships?

Most people would agree that at near stall angle of Attack - yes. Turning combat starting at High Speeds at low AoA and is about energy retention as well as the ability to continuously reef the ship in - and increase the bank angle and AoA to retain same altitude in the comparison.

So the equations, if not the values, at high AoA are correct as you have them - as long as you recognize the difficulty in getting an accurate Parasite drag in any position except at equilibrium in the flight profile of a high G turn from beginning to end. Remember equilibrium is not achieved except when paoer available equal power required.

Turning combat is also about Power available - Power required with acceleration continuing until max G in level altitude. Also important is Cl, and the Bhp of that specific engine and boost at that altitude and density versus the adversary.

So tell us us about the characteristics of the ship, as both enter equally at same high speed - one in trail. and lead us through the math as level flight is maintained, bank angle and G forces increase, Cdparasite from my second part of Parasite Drag (dependent on total area of ship and in some cases AoA)as I explained away up above.

Cd parasite will be lower factor, relatively speaking, than CDi at the low end of the energy balance.

I gave you the Math for Cdparasite which has not only the empirical value of level flight in a wind tunnel, but also the trim drag and high AoA factors.

So now I've provided the math behind what I've been saying, now it's your turn.

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You have provided the equations for CDinduced, then intoduced efficiencies not yet proven by reference.

When you plug into the efficiencies not proven you derive a value for Induced Drag.

When you intorduce the force balances, you introduce an Induced Drag effect at the velocities being compared, but introduce Cd0 without sources for both ships. Nor do you explain whether you mean zero lift drag or Parasite drag

You use a propeller efficiency not introduced by reference as fact.

So, let's summarize.

Your force diagram was incomplete with respect to the forces in positive and negative x axis (level flight)

Your drag forces were incomplete. If you say they are 'close enough' then you have to provide sources for Cd0 of the wing as well as the other parasite drag components and further demonstrate the sum is result you say it is - namely between .20 and .25. But proof of the Cd0 of wing as a starting point is required.

And not just at Low Aoa, but also high AoA at max bank angle with demonstrated Power available over power required in that state. To prove your thesis, integrate the Force equation with respect to rate of change with time for those values in your drag forces to determine the rate of change of energy loss in the curvilinear path.

I repeat Soren - your equations are close enough for the max G equilibrium point where you can safely assume you have a correct Induced drag for the Net thrust and Velocity at that Bank Angle and Velocity, or

you have a correct and validated Parasite Drag for the angle of attack and airspeed at equilibrium.

I haven't a.) seen any correct figures for prop efficiency to convert Bhp to Thrust, b.) efficiency factor for each of those two, or c.) any of the parasite drag components published to support your "numbers".

pbfoot · Sep 1, 2008

I think you guys should have a design off . so get your French Curves,T Squares, Compasses and slide rules and go for .

GrauGeist · Sep 1, 2008

Well you know, I was gonna post a list a while back, but got caught up in reading the debate over performances...

I might not be the brightest light on the Christmas Tree when it comes to number crunching, but I can tell they're down to the smallest of percentages, and it kinda scares me.

Hell, just build it and I'll go kill something with it...

Soren · Sep 1, 2008

Bill,

The base figures in the equation were just examplary, they're not connected to any specific a/c. I used a Cd0 of 0.021 as that is in the normal range for a piston engined fighter, and I used an Oswald efficiency factor of .80 because again the wings of most fighters are either closely at or above that.

Now as for the reports here's a chart from one of them;

As you can see trapezoidal wings can have just as high a 'e' factor as a fully elliptical wing without any twist.

Now I don't have anymore time today, so I'll soonest be back tommorrow and then I'll compare two a/c entering a turn at high speed.

B-17engineer · Sep 1, 2008

pbfoot said:
I think you guys should have a design off . so get your French Curves,T Squares, Compasses and slide rules and go for .

Good idea I would love to see that lol

drgondog · Sep 2, 2008

Soren said:
Bill,

The base figures in the equation were just examplary, they're not connected to any specific a/c. I used a Cd0 of 0.021 as that is in the normal range for a piston engined fighter, and I used an Oswald efficiency factor of .80 because again the wings of most fighters are either closely at or above that.

IIRC you started this with a debate with Dave, citing prop efficiencies, oswald efficiencies and Cd0 as specific when you concluded the Ta 152 was "30% better than the P-51H in turn' - or words to that effect?

Now as for the reports here's a chart from one of them;

As you can see trapezoidal wings can have just as high a 'e' factor as a fully elliptical wing without any twist.

They 'can be close' - so, what 'are they' specifically for the Ta 152 (and Fw 190) and P-51H? Also your thesis was that the Fw 190 had a fully elliptical lift distribution in high G", and I challenged that by stating 'possibly close' or 'elliptical like' but not elliptical - and cited the interesting design feature of the Fw 190 that did Not have twist all the way to tip root - stopping at .8 and having zero twist from there to the tip.

You haven't commented on the Ta 152 twist philosophy or figures to support your oswald efficiency thesis?

Now I don't have anymore time today, so I'll soonest be back tommorrow and then I'll compare two a/c entering a turn at high speed.

You would be wasting your time w/o specific Bhp for the boost, the weights of the airfames you compare, the CD parasite, including Cd0. If you dally at altitudes other than SL, you need to introduce density and the Bhp to altitude charts or references.

The latter is my personal stopping point in collaborating with Gene on a semi reasonable model to make such comparisons.

Once again we are hijacking the thread - take it to the performance thread that you started back in the spring?

Soren · Sep 3, 2008

Bill,

I think you're being abit too obsessed with a very small difference in figures cause wether either a/c have a 'e' of 0.80 or 0.85 doesn't really matter, so lets say they're equal in this department, I'd expect them to be.

Cd0 is the coefficient for parasite drag while Cdi is the coefficient for induced drag.

D = Cd * A * .5 * r * V^2

Cd = Cd0 + Cdi

Now you'd really need to be at a very low AoA and Cl range before Cd0 would start to make its presence felt. Cd0 really is only important when it comes to straight out speed.

But just like the parasitic drag the induced drag rises with greater speeds as-well, and it's all about which AoA is being pulled, and in turns it tends to be in the high end of the AoA/Cl curve.

PS: Send a message to Gene regarding our debate

drgondog · Sep 4, 2008

Soren said:
Bill,

I think you're being abit too obsessed with a very small difference in figures cause wether either a/c have a 'e' of 0.80 or 0.85 doesn't really matter, so lets say they're equal in this department, I'd expect them to be.

Cd0 is the coefficient for parasite drag while Cdi is the coefficient for induced drag.

D = Cd * A * .5 * r * V^2

Cdo is coeficient for zero lift wing drag in the total parasite drag equation. Cd parasite includes that but also all the other factors for the a/c including trim drag etc and most of those are impacted at higher AoA/
Cd = Cd0 + Cdi

Now you'd really need to be at a very low AoA and Cl range before Cd0 would start to make its presence felt. Cd0 really is only important when it comes to straight out speed.

Explain that once more?? True for wing Cdo at high speeds and straight levelflight - false for high AoA effects on trim drag and even propeller drag(for example)

But just like the parasitic drag the induced drag rises with greater speeds as-well, and it's all about which AoA is being pulled, and in turns it tends to be in the high end of the AoA/Cl curve.

PS: Send a message to Gene regarding our debate

You send a message - it's your thesis. The last thing he and i collaborated on was the effect of Gross weight on performance and we had fun! While the effect of 5% increse doesn't effect Vmax by the same amount - it is huge in climb and turn and power required - as well as range.

The issue Soren is you are using performzance equations, which correct for one condition in comparing the two a/c is not correct for an integrated solution, in which Power available to Power required is truly impacted by not only hte CL but also the airframe drag considerations, and all are affected by altitude comparisons as the engines perform differently.

I am dropping out of this discussion as a have lost interest in the rigor of the physics and the assumptions

moomoo2 · Sep 5, 2008

The physics are scaring me but i think i get the idea of the original post

Fighter: Mustang
Light/Attack Bomber: Thud or FB mosquito
Medium Bomber: B26
Heavy Bomber: B-29, well it is really the only choice
Transport: ME323 for the fun value

davparlr · Sep 5, 2008

moomoo2 said:
Light/Attack Bomber: Thud or FB mosquito

I think you mean Jug (P-47). Thud is an F-105, which would certainly make a great WWII anything.

kool kitty89 · Sep 5, 2008

I posted a lift for my (more or less) optimized for a large country with extensive Land and carrier forces. (ie the US) (although I omitted listing trainer aircraft)

Something that no one has touched on yet is the spectral opposite of my choice, an airforce for a small country with limited resourses. (and using only 87 octane -or equivelent- fuels)

So what would be the best choices for a country like Finnland for aircraft they could produce domestically?

Juha · Sep 6, 2008

Hello KK
Because our limited industrial capacity but plenty of wood around the simple answer is the Soviet types, at first I-16 then Yaks and La-5FN because plywood and metal tube and fabric construction, Blenheim and Pe-2 as bombers. Mosquito would have been nice but I'm not sure if our industry was capable to produce Merlins. And one dive-bomber type to replace Fokker C.X from 1940 onwards, maybe SBD.
The a limited run of a bomber that could carry heavier bombs, Wellington is out because no use to invest geodetic structures for a limited run type. Maybe Il-4. Ju 88 was excellent for FAF but probably too complicated for production here.

Juha

kool kitty89 · Sep 6, 2008

About the Mossie, I think it would be fair to say that other engines could be adopted fairly easily. In fact it would probably be necessary, as the Merlin's performance realy wasn't too great with lower octane fuel.
So either DB 601 (or later, 605), Jumo 211, or Klimov M-105 engines. (I'd immagine the M-105 would be the easiest to produce, granted performance would be somewhat less) Assuming the Soviet fighter designs were also used, the M-105 wouls also be looking attractive. Though the DB series would be the most attractive performance wise, assuming it would be practical for Finnland to produce.

Another problem though would be the construction. Though made of wood, the Mosquito used a specialized plywood of Balsa sanwiched between layers of Birch. So unless the Finns had access to balsa (or the design could be made using more conventional plywood), it probably was not a practical choice.

More on the Mossie's construction:
de Havilland Mosquito - Wikipedia, the free encyclopedia

The bulk of the Mosquito was made of custom plywoods. The fuselage was built by forming up a plywood made of 3/8" sheets of Ecuadorean balsawood sandwiched between sheets of Canadian birch. These were formed inside large concrete moulds, each holding one half of the fuselage, split vertically. While the casein-based glue in the plywood dried, carpenters cut a sawtooth joint into their edges while other workers installed the controls and cabling on the inside wall. When the glue was completely dried, the two halves were glued and screwed together. A covering of doped Madapolam (a fine plain woven cotton) fabric completed the unit.

The wings were similar but used different materials and techniques. The wing was built as a single unit, not two sides, based on two birch plywood boxes as spars fore and aft. Plywood ribs and stringers were glued and screwed to form the basic wing shape. The skinning was also birch plywood, one layer thick on the bottom and doubled up on the top. Between the two top layers was another layer of fir stringers. Building up the structure used an enormous number of brass screws, 30,000 per wing. The wing was completed with wooden flaps and aluminum ailerons.

When both parts were complete the fuselage was lowered onto the wing, and once again glued and screwed together. The remainder consisted of wooden horizontal and vertical tail surfaces, with aluminum control surfaces. Engine mounts of welded steel tube were added, along with simple landing gear oleos filled with rubber blocks. The total weight of castings and forgings used in the aircraft was only 280 lbs

I hadn't though of the wooden Russian fighters before you mentiond them (though it would seem the obvious choice). I had been leaning toward the Hurricane. (given the extensive use of steel, simple construction, and relatively limited aluminum) it would have to be re-engined though. (this being done historically with the DB 601)

Juha · Sep 6, 2008

Hello KK
DB 601 and 605 would probably have been even more problematic with their injection pumps. So engine choises would have been Mercury, PW Twin Wasp or Russian engines if it would have been possible to got a licence for them, or as in real world, war booty engines with all problems that they brought with them.

Juha

Juha

kool kitty89 · Sep 6, 2008

So the Jumo 211 would be out as well. (injection pumps)

The Pegasus might be a good choice though, a bit larger in diameter than the Mercury but not much heavier and had significantly better performance. (particularly the 2-speed versions, the Mk.XVIII probably being a good all-around choice)
Given the comperable size of the Pegasus to the Wright R-1820 (which the I-16 was developed with, and used a derivative of in producion) it may have been a good fit for the I-16, probably with a significant performance increase at altitude.

Would the Ju 52 be the transport then?

Juha · Sep 6, 2008

Hello KK
Quote: "Would the Ju 52 be the transport then?"

Now if we would have been able to produce say I-16, Yak-1/7/9 and La-5F (I made mistake earlier, -5FN had engine with fuel injection, so probably it also was too complicated to be manufactured by Finns), Blenheims and Pe-2s and some SBDs then there would not have been any capacity to produce transports. So only solution would have been same as in reality, use of planes of our national airliner and old Ju 34s etc.

FAF's Fokker C.Xs had Pegasus engines but those were probably bought from Bristol.

Juha

If you had an airforce...

1st Lieutenant

Major

1st Lieutenant

Colonel

Major

1st Lieutenant

Generalfeldmarschall zur Luftschiff Abteilung

1st Lieutenant

Colonel

Major

1st Lieutenant

Major

Airman

Senior Master Sergeant

Senior Master Sergeant

Senior Master Sergeant

Senior Master Sergeant

Senior Master Sergeant

Senior Master Sergeant

Senior Master Sergeant

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