Low alt performance of Big Planes in AH

[g00bd0g]

There are so many aerodynamic factors that aren't taken into account in this thread, it makes my head hurt. I'm surprised that no-one mentions airfoil data anywhere. The top speed speed algorythm posted by badboy is pretty decent. But as far as roll rates and acceleration and such I haven't seen much usefull input. Roll is affected not so much by wingspan or aspect ratio, but by how the weight is dispersed around the c/g. Also the size, location and aerodynamics of the control surfaces themselves play a huge part in how quickly you can roll(pitch and yaw as well). I think the biggest problem I see here is a lack of accepted real data, both actual flight test data and design data(C/L, horsepower, weight, airfoil, prop efficiency, etc...) I believe if we could see the actual data AH uses for the aircraft we could pinpoint problems in the FM much easier. Untill then it's all pointless isn't it  

[Badboy]

 

Originally posted by F4UDOA:
Badboy,
I was just looking at your last post and I was hoping you could do the same calculation and show the math for the F4U-1D.
Thanks
F4UDOA

Hi F4UDOA,

Hope you don't mind if I try and answer several posts in one go.

Firstly I'd like to clear up the confusion about the aircraft weight. It is true that weight is an important factor when you consider sustained and instantaneous turning ability and climb rate for example, but it is not so important when considering top speed. Weight will of course have an influence on the top speed, just a very small one. Weight has a much greater impact on acceleration, which influences how long it takes for an aircraft to reach its top speed, but if other things remain equal the weight has an almost negligible influence on the top speed itself. So for example, the difference in top speed for an aircraft with a full load of fuel, and one nearly empty, is often less than a couple of knots and almost always results in less than 1% error. However, that is providing the difference in weight is internal, because external stores change the drag, and that does have a significant influence on speed.
 
So, regardless of the weight, can an aircraft travel at 360mph at sea level?

I will answer that, but perhaps not in the way you might have hoped. What I will do is explain what that would require. Exactly how much power is required to push an aircraft through the dense sea level air at a specific speed?

I've placed a graphical surface at the end of this message which shows the relationship between the brake horse power, the speed and the equivalent flat plate area for any aircraft at sea level with a prop efficiency of 85%. There is nothing contentious about that surface, it is simple aerodynamics and a little math and could apply equally well to any aircraft. The only compromise being the assumption about the prop efficiency.

So, suppose you want to know if an aircraft can reach 380mph at sea level with an engine delivering 2000hp? Follow the red line up from 380mph until it reaches 2000hp and then follow it down to see that it would require an equivalent flat plate area of 5 ft^2 or less to travel that fast.  Basically, any aircraft with an f value less than 5 should be able to do it. For a speed of 360mph with the same power, any aircraft with an f value less than 6 ft^2 would be ok. So for the F4U providing it had a Cdo less than 6/314 = 0.19 it should be able go that fast. The chart should allow you to check other combinations.

The big question of course is did any of the aircraft you have been discussing really have f values that low? Almost every version of the F7F is claimed to be faster than 360mph at sea level, with the claims for the fastest reaching as high as 394mph. The F4U-4 is quoted at 381mph at sea level and the F2G2 (Goodyear) an amazing 399mph. Of course I can't defend those claims, because like everyone else, I'm at the mercy of my sources  

Hope that is helpful, here is the graph…

 

Badboy

[Badboy]

 

Originally posted by Badboy:

So, suppose you want to know if an aircraft can reach 380mph at sea level with an engine delivering 2000hp? Follow the red line up from 380mph until it reaches 2000hp and then follow it down to see that it would require an equivalent flat plate area of 5 ft^2 or less to travel that fast.  Basically, any aircraft with an f value less than 5 should be able to do it. For a speed of 360mph with the same power, any aircraft with an f value less than 6 ft^2 would be ok. So for the F4U providing it had a Cdo less than 6/314 = 0.19 it should be able go that fast. The chart should allow you to check other combinations.
[/B]

Oops, sorry guys, I can't read my own chart  

I've misread the f values, 5 should be 4.5 and the 6 should be 5.5 giving 5.5/314 = 0.0175... fumbled but not dropped  

Badboy

[Badboy]

 

Originally posted by wells:
All other things being equal, roll rate is only dependant upon wingspan.  You can have a wing of any area or aspect ratio, but the higher span will roll slower.  The thing with the Spitfire and P-47 with their elliptical planforms, is that the ailerons have to be 'inboard' a tad and the hinge line is at an angle, both of which reduce the rolling authority.  The elliptical planform is good though, for lower roll inertia.

If memory serves, it is inversly proportional to the fourth power of the span, which is why they clipped the wings of the Spitfire, the small reduction in the span had almost no effect on the lift but resulted in a dramatic increase in roll rate.

Badboy  

[wells]

DOA,

The F4u's ailerons deflected 19 up, 14 down.  It's roll rate at 300 mph was 90 deg/sec, right?  Compare that to the P-51, where the ailerons deflected only 10 up and 10 down for a very close to equal roll rate.  The P-47, while having similar span to an F4u, the ailerons only deflected 16 up, 12 down.  That's why I said, everything else being equal.

Badboy, the relationship is direct (inversely)...no powers.  The wingtip on a wing that has twice the span has to travel twice the distance for the same helix angle.  

[fire_ant]

 

Originally posted by funked:
Fw 190A-5 and all Me 109 variants in AH will out climb and out accelerate the P-47D at 5k.  In my experience they can out turn the Jug too.  (edited 08-11-2000).]

I was outrun by P-47's in AH while flying various Me 109 types, including once the G-10 but I was out of WEP...  it also blows the macchi c205 away in speed and accel which seems absurd to me too....

DB

[funked]

fire_ant, if that happened at 5k then they must have started faster or higher than you.

[StSanta]

WROOOOOOOOM

<sound of G10 engine>

Awww <in love>

And how's this for a *real* 109 engine start: http://www.geocities.com/stsantasatan/engstart.wav

Listen to it, in awe  

------------------
StSanta
JG54 "Grünherz"
"If you died a stones throw from your wingie; you did no wrong". - Hangtime

[This message has been edited by StSanta (edited 08-12-2000).]

[SnakeEyes]

 

Niklas said:  The 109 was constantly improved.

Perhaps you're from Venice and feel that adding gondolas to an airframe constitutes an improvement?  

------------------
SnakeEyes
o-o-o-
=4th Fighter Group=

[This message has been edited by SnakeEyes (edited 08-12-2000).]

[Fishu]

 

Originally posted by fire_ant:
I was outrun by P-47's in AH while flying various Me 109 types, including once the G-10 but I was out of WEP...  it also blows the macchi c205 away in speed and accel which seems absurd to me too....

At least P47 seems to accerlate alot faster than Typhoon and also maintain speed better.
in Typhoon you turn just a tiny bit and speed is gone, while in P47 you can turn without much fear of getting too slow on tiny turn.. (if you get, you will anyway accerlate enough quick)

Though, I must admit this is the best P47 I've ever flown in any game.
P-47 is sooo fun plane.

[SnakeEyes]

It's got to be that *nasty* Tiffie wing design Fishu bleeding all of the E in turns... it's not terribly efficient.

------------------
SnakeEyes
o-o-o-
=4th Fighter Group=

[This message has been edited by SnakeEyes (edited 08-12-2000).]

[Badboy]

 

Originally posted by wells:
DOA,
Badboy, the relationship is direct (inversely)...no powers.  The wingtip on a wing that has twice the span has to travel twice the distance for the same helix angle.

Sorry, I was a bit vague in my last post, it was late. When you compare the rolling performance of aircraft it makes sense to relate it to the stick force because your average pilot could only reasonably be expected to apply about 50lbs laterally, in any case it is common to assume equal pilot physiology, so equal stick force is a valid assumption in that respect. The calculations for the time to bank through a given angle, for a given stick force varies with the fourth power of the wing span. Also there is a damping effect that depends on the aspect ratio and the rate of roll. For any given aspect ratio the difficulty of providing light ailerons also varies as the fourth power of the span so that during WWII the problem of aileron ballance was very delicate. Aileron hinge moments are very sensitive to small proturberances on the control surface as well as to the curvature of the profile. Since (in the UK and Germany any way) the standard of worksmanship deteriorated as time went on, there was often a large variation in aileron heaviness between aircraft of a given type.

So for example, the clipped wings of the Spitfire that reduced the span by a little more than 11%, increased the roll rate from 105dps at 170kts to 150dps.

As a further example, the Me109E had very good aileron control upto about 170kts, above that speed the ailerons became rapidly heavier so that by about 260kts, they were almost solid. Specifically, the Me109E took 4 seconds to bank 45 degrees at 350kts (11dps) which for a fighter is excessive. The later Spitfires rate of roll at 350kts was 60dps, and the Fw190 was even higher.

I think many pilots would agree that these issues are very important from the perspective of air combat. In many ways, a good roll rate, or more importantly, good acceleration into the roll, was considered more important than turn rate and second only to the ability to hold a high speed dive with precision. The ability to break rapidly, is not only a life saver, but has very strong tactical implications in air combat. A good roll rate, properly applied can be converted directly to angular gains in a turning engagement. I think Andy has an explanation of the OODA cycle on the web? I have one somewhere if anyone is interested in the details.

       

[funked]

Fishu, if we are still talking about 5k, the P-47D-30 should accelerate a little better than a Typhoon in level flight at low speeds.  It's got a better power:weight ratio as evidenced by the climb rates at 5k on the HTC charts.  

At high speeds (above 250 mph or so) I would expect the Typhoon to accelerate better though.  Typhoon AFAIK is the fastest accelerating plane above 250 mph and below 7,000 feet.  P-51 and G-10 are pretty fast in that regime too.

I already did a lot of Typhoon acceleration tests, so I'll do a P-47D-30 test to compare.  

[This message has been edited by funked (edited 08-12-2000).]

[This message has been edited by funked (edited 08-12-2000).]

[This message has been edited by funked (edited 08-12-2000).]

[Badboy]

 

Originally posted by Badboy:
 When you compare the rolling performance of aircraft it makes sense to relate it to the stick force because your average pilot could only reasonably be expected to apply about 50lbs laterally, in any case it is common to assume equal pilot physiology, so equal stick force is a valid assumption in that respect.

As an afterthought, one of the most impressive applications of that principle occurred during the Korean conflict when the F86, with its hydraulically powered ailerons, was able to use that advantage to defeat the superior turn rate of the MiG15. It turns out that the main proponent of the theory, (Colonel Boyd USAF) was instrumental in having the F86's ailerons so equipped. I feel confident that it was the roll rate advantage (without wishing to play down the skill and courage of the pilots involved) that was largely responsible for the high kill ratio achieved during that conflict. I'm not sure offhand what US aircraft had powered ailerons during WWII, I think the P-38 did, even though its roll rate was not particularly impressive. I'll have to check. But it is easy to see a strong correlation between the W.W.II aircraft that had light ailerons at high speeds and those that were most successful.

Badboy

[Westy]

Great thread to read. Thanks guys!

-Westy