A fundemental view on Weight and E state and its role in ACM

[mechanic]

Does that not also mean the Nik2j has more potential to use it's energy than the A20, in turn? Or is there a 'sweet spot' for an aircrafts mass thats combines the best of both worlds?
Man, i hated physics class, I suck at it. Nevermind, im going to go get high! (flying for rooks)

[Mace2004]

A couple of thoughts here.

First, not meaning to be critical, but Newton is far more applicable to the physics of aircraft flight than Einstein.  Actually, I'm not even sure how you plugged aircraft speed into E=MC² to arrive at your numbers.  I think that what you're getting at, i.e., an understanding of total energy as being the result of Kinetic and Potential energy is very valid; however, the theory of relativity is more useful when you're considering the transformation of mass into energy and back, speed near the speed of light, and subatomic partical behavior but Newton rules the aviation world.  The problem with the simplification of E as you've done is that it fails to take into account the physical world of aircraft including P_s and aerodynamic factors such as drag.  This is done using Newton's laws plus throwing in Bernoulli, a bit of Boyle (and a quite a few others) and calculus, not Einstein.

As far as "zoom" is concerned, if you take two identical aircraft, one with full fuel (i.e., "ballast") and the other almost empty, the lighter plane will outzoom the heavier one every single time.  It's a common misperception that a heavier airplane can zoom better (usually a point made by Jug pilots) but it's unfortunently just not true.  The heavier weight for the same thrust means a lower P_s (thrust minus drag) and also higher induced drag.  The drag can be reduced if both are unloaded to zero G in the zoom but it still doesn't make up for the differrence in P_s.

Also, if you compare a larger airplane with a smaller airplane, both with the same thrust to weight (something unlikely when comparing a bomber to a fighter), the smaller plane will outzoom the larger one because of the larger plane's greater drag.

Extra weight on an aircraft is always a detrement, it is never a positive.  It always degrades P_s, turn performance, climb performance and energy retention.  Extra weight = bad juju.

Let me add another note.  Look at my avatar.  It's a fully loaded F-14D with four AIM-54C, two AIM-7M, two AIM-9L and two external fuel tanks.  I took the picture from an F-14A with just the external tanks.  Even given the D's much greater thrust to weight ratio (much greater than 1:1 without stores) I easily outzoomed the D with it's extra weight.

[humble]

Mace,

I've got no problem at all with you or anyone being critical. I think "zoom" is the hardest concept for many sim pilots to grasp. The formula itself is perfectly applicable. Mass is weight and velocity speed. I converted the mph to m/s (tmes .45) but now to think of it I left the mass in lbs...should convert to grams I think to get actual joules. But the ratios should be the same....

How this stored E is tranfered to motion and specifically zoom goes beyond a pure measurement. Not only due you have the relative efficiency of the airframe but also the contribution of the engine(s) etc. The physics that the heavier the object the more "stored E" it has at a given speed should be correct. Again certainly open to correction or refinement....

[Mace2004]

Sorry, maybe I'm being dense (a good possibility since math was never my strong suit) but I'm still not seeing where you plug aircraft speed into the equation.  E is energy in Joules.  M is mass (usually Kilograms) and C is a constant (the speed of light).  Where did you plug in aircraft speed?

[df54]

   i always thought       joules was a measurement of heat energy

[humble]

for the theory of relativity yes, but Energy can be viewed as mass x velocity. I think that the formula is correct. A joule is a measure of energy:
 It is the energy exerted by a force of one newton acting to move an object through a distance of one metre. So at a minimum I needed to convert pounds to Kg's. I do think that doing that the formula would be accurate.

So much more comes into play but the thought behind the post was to try and explain why a heavy plane like the A-20 appears to have inexhaustible E vs fighters. If you fly "flat" then its very inefficient and scrubs E much faster then a fighter will (which lets you pull lead at higher speeds). However if your flying it "on the X" then apparently minimal yoyo's offer tremendous conversation of E from potential to kinetic.

I know WW has covered it better and in more depth here and in the TA, but the concept of weight and its application in the zoom is tough to grasp for even good pilots. It happened to come up repeatedly last night so I thought i'd try to explain it within the limits of my capabilities.

[Wedge1126]

   i always thought       joules was a measurement of heat energy

The Joule is a unit of energy. Energy is energy; it doesn't matter what form that energy is in.
We could use calories if we wanted to... it'd sound a little weird, though.

... but Energy can be viewed as mass x velocity. I think that the formula is correct. ...

I think kinetic energy is 0.5 * mass * velocity^2.
Potential energy is mass * height * g.

[BnZs]

Mech:
In an unloaded zoom, both starting at say 400mph, an airplane with for example a lot more internal fuel would indeed out-zoom an identical airplane without the ballast.

But that extra weight would hurt every other area of aircraft performance....instantaneous and sustained turn rate and radius, acceleration, climb, and energy retention while pulling Gs,

That is why, all things considered, the guy who brings 25% fuel to a duel has an advantage over the guy with 100% onboard, despite the fact that the latter will probably have some advantage in a zoom starting co-speed.

EDIT: Mech, the "best of all possible worlds" would be an airframe that had low-drag, a light wing-loading, good power-loading, AND was just a plain massive besides...




 

[dtango]

Hi Guys

Been awhile since I've posted here but I thought I would weigh in on the topic.  Mace is absolutely right about the issue.  Increased weight / mass in the grand scheme of things is a detriment to performance.  If you're looking for a simple explanation for this, I haven't found an easy way to sum the relationship up.  It's embedded in the complexity of the interdependent relationships between thrust, weight, lift, and drag.

If I find the time I'll post some basic modeling to demonstrate.

Cheers!

Tango, XO
412th FS Braunco Mustangs

[humble]

Again this is not "performance" per se, simply an attempt to explain how mass effects zoom. The simple unalterable reality is that no fighter in the game traveling at equal speed can outzoom an A-20....none. This in no way makes the A-20 "uber" but it is a factor that needs to be recognized when fighting one.

[dtango]

I include zooms in the performance category .  And yes increased weight is a detriment to zoom, just as Mace points out.  I realize the A-20 is the airplane you're wanting to address.   Try zooming between a B-17 or B-24 vs. a the A-20 and you'll see.  It's not weight that gives the A-20 it's zoom capability. 

Sorry, I can't explain it any other way because I can't think of any other way to show it without requiring presenting some basic modeling of the physics to demonstrate why.  I'd have to dust off some old spreadsheets and monkey with them to present the data and not sure I want to find the time to do that at the moment !

Tango, XO
412th FS Braunco Mustangs

[SPKmes]

If only I had read this before my cry on 200 last night...oh well.. I always knew but seeing it in plan English helps me understand how these things happen. Nice post

[humble]

No question that drag and other factors enter the equation as well. I can tell you flat out that a B-17 will out zoom an A-20 from an even start....at least at higher alts. Obviously zoom is a relatively short lived event and a lot of factors come into play. Any type of a spiral climb will force a pursuer quickly out of zoom and into sustained performance. This applies to mossie, 110, p-38, jug or any other heavy plane, obviously results will vary but if your going vertical vs anything with zoom you need to be careful in how much you load the airframe....

[humble]

out of curiousity took a up a 100% + 2000 lb (internal) and a clean 25% A-20 off line. Very little difference in zoom (only did 1 of each) {level at 500 pull up at 300 true}. The heavy one held more speed but fell of at higher speed, while the light one topped out at the same alt but was significantly slower. Alt was within 100 ft. I'd say I could wring another 400 ft or so (about 10%) out of the heavy based on airspeed differential...but no question the heavier one was more susceptible to poor piloting. I got it just sightly cockeyed and the control inputs scrubbed speed and it fell off at about double the speed of the "light" A-20.

[BnZs]

Just did a test.

Took up P-47N, 8 guns, 425rpg, 100% internal. Tested zoom climb in my normal way, dive to 100 feet above sea level, autolevel until speed bleeds down to 400, 3g pull up until straight vertical, shift+x to hold it there until it falls off. Got back up to 5,800 feet.

Then I tried with a P-47N with 6 guns, 267rpg, and 25% internal. The result this time was a zoom back up to 6,100 feet before falling off.

So light appears to out-zoom heavy.

Now, in the world of ballistics everyone knows that a heavier bullet of the same diameter and drag coefficient, accelerated to the same muzzle velocity, will retain that velocity better. I had assumed similar principals would apply to two airplanes that are identical except for internal weight when both airplanes are in the unloaded condition. Is the increased E-bleed caused by the extra weight during the pull up to vertical what cost the heavier Jug airspeed and allowed the lighter one to out-zoom it?

And a hypothetical. You have two single engine prop airplanes. They have the same wing-loading. They have the same mass/horsepower ratio. They have the same drag/horsepower ratio (identical top speeds.). One, however, is a bigger and heavier airplane. Will it out-perform the lighter airplane in the vertical?