Author Topic: Spit 5 (Read 11674 times)

Crumpp · « **Reply #120 on:** August 11, 2004, 01:40:52 PM »

Milo,

I bet you wish you could erase that last post!

Crumpp

Crumpp · « **Reply #121 on:** August 11, 2004, 01:53:03 PM »

If you study Horsepower, it changes considerably not only with altitude but even among the same engine type.

Other than drawing general conclusions, cross referenced by multiple sources. The Horsepower of the Merlin 66, 61, and the BMW-801D2 were extremely close.

Least that is what I discoved after chasing Hp figures on the BMW801 and Merlin engines.

I don't even think HP figures into AH modeling.

Crumpp

Nashwan · « **Reply #122 on:** August 11, 2004, 01:55:12 PM »

Quote

The "induced drag" debate, following the formula, pretty much comes down to the 190's better aspect ratio vs. the "e" factor of the Spitfires wingtip. HTC and the "computer environment" in the end determine the variables we would be squabbling over.

In level flight, a plane has to generate as much lift as it's mass.

The 190 is heavier, it has to generate more lift.

The amount of lift, as Isegrim has said, is dependent not only on the wingloading, but on the CL. Multiply the CL by the wing area to get the lift.

The Spitfire had a much larger wing area, and a fair bit less weight. That means it needs a much lower CL .

The higher the CL, the higher the induced drag.

Big wings and low weight produce less induced drag.

So of the 3 factors in the equation, the aspect ratio favours the 190, the Oswald efficiency probably favours the Spit, the CL favours the Spit by a large margin.

Crumpp · « **Reply #123 on:** August 11, 2004, 02:31:33 PM »

Quote

So of the 3 factors in the equation, the aspect ratio favours the 190, the Oswald efficiency probably favours the Spit, the CL favours the Spit by a large margin.

Again, not according to some of the online aerodynamic programs where you can program in the NACA code for airfoil and it calculates the lift.

Crumpp

Crumpp · « **Reply #124 on:** August 11, 2004, 03:21:46 PM »

Let me add though since Area is factored in both in figuring out Lift and the lift coefficient is squared, I tend to agree Nashwan.

Fluid mechanic modeling though determines how large or small the effects.

And all of this has little effect on the zoom climb of the 190A vs Merlin Spit.

Isegrim, If you have any official data please share it. Thanks.

Crumpp

MiloMorai · « **Reply #125 on:** August 11, 2004, 04:31:27 PM »

Quote

Originally posted by Crumpp
If you study Horsepower, it changes considerably not only with altitude but even among the same engine type.

Other than drawing general conclusions, cross referenced by multiple sources. The Horsepower of the Merlin 66, 61, and the BMW-801D2 were extremely close.

Least that is what I discoved after chasing Hp figures on the BMW801 and Merlin engines.

Was your other post to be included with this post of yours? Why would I want to erase my post? It is my understanding that 'ram' increased hp, among other things. Correction awaited. Indulge me and answer the questions asked in the post, since you are so smart?

How close is close? Is a 160ps difference extremely close? (1680hp = ~1700ps)

Crumpp · « **Reply #126 on:** August 11, 2004, 04:51:32 PM »

Nashwan,

Remember though the Spitfires Cd is greater than the FW-190's.

No matter how small amount of Cdi the Spitfire's wing generates it still adds to the total drag forces. Same goes for any A/C in flight.

I think that in adding the Cd + Cdi the FW-190 will still come out ahead overall.

Charge,

Is this what you are refering too?

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

Cl = Clo / (1 + Clo /[pi * AR])

So we see the higher aspect ratio factored in twice.

Quote

This makes the drag (NOT the induced drag) a very difficult problem.
Compressible, viscos, non-adiabatic, driven air flow on an irregular shape... I want to see this solved analyticaly...

Yes it is a very sticky problem. My source is an article written for "Sport Aviation" magazine. The man who wrote it is an aeronautical engineer and works for a firm which does computer simulations of A/C for the defense industry.

http://www.anycities.com/user/j22/j22/lednicer.htm

http://www.am-inc.com/

Crumpp

Crumpp · « **Reply #127 on:** August 11, 2004, 05:27:31 PM »

QUOTE]It is my understanding that 'ram' increased hp, among other things. Correction awaited. Indulge me and answer the questions asked in the post, since you are so smart? [/QUOTE]

By "RAM" I assume you talking about adjust the Hp for velocity at speed. This has the net effect of lowering the Hp output. It raises full throttle height and lowers Hp output some. It's the "dynamic air pressure gains at equivalent level speeds".

Examine the BMD801D graph on this website. It includes Hp adjust for velocity at speed.

http://www.terra.es/personal2/matias.s/fw190.htm

Isegrims figures seem to be for static Hp and are not adjusted for RAM. I did not take the time to confirm the boost pressure he is using to make sure both A/C are using the equivalent throttle setting.

To truly compare the charts you have to use the RAM line on the BMW-801D chart for 1.32ata @ 2400U/min. I get around 1480hp - 1490hp for the FW-190. I believe he is using the FW-190A5 Speed graph from the same website.

The Horsepower figures are close. The gap widens based on your source and different sources say different things for the same engine for both Aircraft. The Spit and FW-190 seem to trade off with altitude but never greatly outdistance each other in the power available arena.

Don't confuse PS with Hp either. They are close but Hp is just a little less because the unit of measure is larger.
Example - 2100PS is approx. 2050hp.

Crumpp

Charge · « **Reply #128 on:** August 12, 2004, 01:15:42 AM »

No Crumpp, thats not what I meant. The Spits wing has a sort of "torsional twist" which is there to counter the bad features of elliptical wing in high AoA. The tip has some negative angle when compared to the root of the wing so that when the root exceeds its AoA limit and stall,s the tip of the wing still provides lift. This is why Spitfire could be flown in overly stalled condition where the heavy buffeting indicated that the root part of the wing had already stalled but the a/c still flew well under control.

What I tried to point out was that while being a good feature this "washout" it could have a drawback which was that while the root of the wing provided lift at optimum angle the tip was in position where its angle was not so optimal to airflow considering lift creation. Thus the suggestion that when calculating the lift of the wing profile at certain speed the other part of the wing is not in the same AoA and thus does not provide the lift its profile suggests to.

But in turn in certain speeds while it was in "no lift angle" it didn't create much lift related drag either but merely some "plate area drag" which is related to its frontal area.

In high speed I'd imagine that the wing cannot be in optimal angle from almost any part of it as the root forces the fuselage upwards and the tip of the wing downwards. I'd imagine such situation to result in quite a spectacular vortex behind the wing.

But why the washout is there? As far as I've understood the elliptical wing is optimal in terms of providing lift when given a certain wing area minimizing the drag effects. So in that wing plan profile all surface that is not creating lift in level flight is simply left off thus giving that unique elliptic form and thus maximum area with minimum drag. However, in high AoA the elliptical wing is not working on its optimal area where the only thing it has is that very wing area it is designed to provide, and in this region the wing shapes of 109 and 190 work better.

Of course this is not something that is easily accessible via a few generic equations with calculator.

-C+

Crumpp · « **Reply #129 on:** August 12, 2004, 04:00:28 AM »

Well Charge the downwash on NASA's site goes a long way toward explaining why the Cl calculated by the computer porgrams is very different from Gripens.

Crumpp

Crumpp · « **Reply #130 on:** August 12, 2004, 04:20:01 AM »

In fact,

This formula IS the raw Cl.

Quote

For three dimensional wings, the downwash generated near the wing tips reduces the overall lift coefficient of the wing.

http://www.grc.nasa.gov/WWW/K-12/airplane/liftco.html

So When you factor in downwash, the higher aspect ratio of the FW-190's wing becomes important.

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

Crumpp

Charge · « **Reply #131 on:** August 12, 2004, 04:50:03 AM »

I understood the downwash so that it decreases the lift and that mostly near wing tips so Spitfire's wing's long pointy tip takes the vortex inducing component quite far from that part of wing that actually does the lifting in level flight and it also does not suffer from negative lift as badly as a square tipped wing because the vortice induced by the leading edge of the wing does not "hit" the trailing edge, thus not producing a strong down lift component, as there is no trailing edge (from the vortex's point of view).

But higher aspect ratio is considered better in rectangular wings as the vortex has smaller effect because of the lower angle of the vortex versus wingform. So the AoI of the wing tip in Spitfire is to the wrong direction when countering the bad effects of the downwash but the shape manages to counter those effects (but how much?).

SO a bad choice would be a rectangular wing with low AoI?

-C+

Crumpp · « **Reply #132 on:** August 12, 2004, 05:20:21 AM »

Efficiency factor of the wingtip is only used when calculating CDi not the downwash. The "raw" Cl is converted to the true Cl and that is used in all other calculations. Gripen has taken the "raw" Cl and used it without factoring in the downwash. The Cl will be much more evenly matched when entered into the Cdi formula.

According to everything I have read, the higher the Aspect ratio the better for manuverability.

Looks to me like the designers of the FW-190 and the Spitfire took different approachs to try and solve the same problem.

Everybody wants a fighter that is fast and manuverable.

High Aspect ratio's usually generate lots of lift and are found on aircraft like gliders. Low aspect ratio wings are found on speedsters like the F-104 pictured in Bozon's reply.

The FW-190 went with a High Aspect ratio and smaller wing area.

The Spitfire went with a lower aspect ratio and a large wing area.

In lift game, usually the higher aspect ratio wins. However, the Spitfire has a large amount of wing area.

Crumpp

Angus · « **Reply #133 on:** August 12, 2004, 06:58:32 AM »

From Izzy:
"the Spit`s huge wing area only produce a relatively tiny amount of lift. It`s not effective for lift generating purposes, also for the reasons Crummp mentioned, re: washout.

In fact, liftloading of the MkIX was already slightly worser than the 109G, despite having a 41% larger wing area a lower 'wingloading'. "

The Spit wing generates less lift pr sq/ft than i.e. the wing of a 109. However, the whole wing makes it up as a whole, so a Spitty hauling itself upwards with the same power as i.e. a 109 will generate more Newtons in the same time.

The wingloading factor and the shape of the Spitties wing actually start shining under angles and in hard maneuvers. The wingform and loading has the key to the Spitties insane escape maneuver of corkscrewing upwards! The same explains it's ability to turn so well.

An aerobatic wing....

Crumpp: Those chart would be welcomed. Try burns@isholf.is

MiloMorai · « **Reply #134 on:** August 12, 2004, 09:30:46 AM »

Thanks Crumpp.

I didn't confuse hp and ps. That is why I asked for hp > hp or ps > ps.

You might find this interesting. Notice the weight > 4395kg for the A-8(normaljagar)