Climb rate vs descend rate

[HexHead]

Woah, don't take me too literally. Just throwing out a reasonable sketch.

AVG tactics were to dive on bogeys and use the P-40's speed advantage to run away after the diving attack - rinse & repeat.

Diving planes have terminal velocities, also. A lot depends on airframe construction and integrity and the engine - the four vanes of the Jug's prop were not an unimportant feature - pushing more air more quickly. 2000 hp didn't hurt, either.

And I am certainly quickly out of my depth on much of the technical side - just speculating with basic knowledge and a few supposed facts.

[HexHead]

How does having more mass help in turning?

Greater angular momentum? Just a wild guess. Also, greater mass would usually reflect a 'sturdier', more robust airframe.

[HansBolter]

ORIGINAL: HexHead

And, although completely untutored in aeronautical engineering, it should be apparent that lighter masses (e. g., Zekes) can, pari passu, can have a higher ceiling and maneuver better in thinner air densities. Yeah, that seems to be modeled. But I wouldn't expect Claire Chennault to be diving on packs of Zeroes anytime soon.

I was under the impression that light planes with large wings and low wing loading suffered from a high altitude drop off in performance as a result of the resistance of the large wing and the drop off of lift provided by it at high altitude and that planes with small wings and high wing loading performed better at high altitude.

Is this an incorrect understanding?

[HexHead]

Just a technical writer, here, mein Herr. IOW, I don't know what I'm talking about.

Wing loading would deal with design issues, I would say. I was thinking less mass in the four-arrow diagram so beloved of flight instructors.

[Symon]

ORIGINAL: HexHead
And, although completely untutored in aeronautical engineering, it should be apparent that lighter masses (e. g., Zekes) can, pari passu, can have a higher ceiling and maneuver better in thinner air densities. Yeah, that seems to be modeled. But I wouldn't expect Claire Chennault to be diving on packs of Zeroes anytime soon.

Hi, Hexhead.
In the grand scheme of things, that just ain’t so. I fly a 812 lb light sport airplane plane, and I can’t get above 12k to save my life. Wouldn’t want to, anyway, because that’s pretty rarified for me, and performance totally sucks. It’s not the weight, or even the planform. It’s the power plant. Regardless of the exquisite design of the aerodynamic surfaces, one needs a power source to overcome the unfortunate fact of gravity.

Since these power sources are internal combustion types, they need a certain amount of air (O2) to keep running and keep moving the plane forward at a speed that will promote airflow over the lifting surfaces, such that the thing will “fly”. Since air pressure decreases with altitude, there is less Reynolds flow over the surfaces, so you have to go faster to develop enough lift. But lower air pressure means you can’t get the fuel ‘bolus’ right for your power plant to generate the power to keep you up there.

The higher you go, the more power you need to keep you there.
The higher you go, the less power you can develop to keep you there.

Can you say “compensation”? Thus superchargers and their turbo-driven cousins. All devised to get the “right amount” of air into the fuel mixture to get that metal beast pumping out righteous Kw at altitude to keep the bird up.

[HexHead]

Thanks for the clarification. In aeronautics, there are usually a few factors involved at the same time. Thrust, of course, is very important.

[Dili]

Is this an incorrect understanding?

Depends [:)] from what plane you look it. There is an optimal band of wing loading for certain altitudes. For example the Macchi 205 V initial models were with small wing of Macchi 202. This was giving too much wing loading for the thin air altitudes to intercept 4 engine Liberators bombers, the plane was not controllable since it dropped. They increased the wing size and was borne the Macchi 205 N.

This is also depends on maneuverability requirements of the air force, if they only want the purest interceptor then a rocket with guns with almost no wing works for any altitude, obviously it probably only make one pass.

[Symon]

ORIGINAL: HexHead
Thanks for the clarification. In aeronautics, there are usually a few factors involved at the same time. Thrust, of course, is very important.

You are welcome.
Yes. There’s lots of things happening at the same time. Just think about sailing, even sailing a Sunfish. The harder the wind blows, the more tippy you get and the harder it is to trim in your sails. And going faster just means the airflow is going faster past your sail, too. So just think about high velocity speed and pressure, and what do ya get? Makes for serious biceps development, yeah?

Ok, so mass is a factor in dive, but dive ain’t got jack to do with gravity (sorta). Airplanes have this thing called engines that let them “split ass, and power down”. An airplane, under power, can and will go waaayyyy beyond terminal velocity.

Some planes can handle it. Most planes will disintegrate in mid air. Back then it was called compressibility. These days it’s called “flow separation”.

[LoBaron]

ORIGINAL: HexHead

ORIGINAL: Erkki

ORIGINAL: Sieppo

How does weight affect dropping speed?

Because heavier planes tend to have more mass for comparable effective resisting aerodynamic cross-section than the lighter planes.

Two objects of similar size but different mass do have the same initial falling acceleration, but the heavier one will have higher (top)falling speed in same g, air pressure yadda yadda. [:)]

Yes, no, need to rewrite (unclear). Please let me suggest:

The terminal velocity (i. e., in effect, the velocity at any desired time, as is noted immediately below) of a freely accelerating body (note that 'freely accelerating' necessarily implies no other forces acting on the body) is given by:

v sub t = 1/2 (acceleration due to the local gravitational field) (t^2)

in other words, in a vacuum. If one does the work (see Elementary Differential Equations), the result is that when air resistance is allowed for, most objects reach a terminal velocity that is an upper bound.[...]

Excuse me, Erkki is pretty much spot on.

You are correctly quoting Newton´s second law of gravity, obviously, but what you are missing is that in the environment and situation concerned - airborne fighter aircraft initiating a dive - the acceleration of a free falling object in a vacuum is only of minor relevance anymore.

At the speeds we are talking about drag already is the major force to overcome. So given the circumstances, even without taking engine power into account, the relevant variables for the dive are airframe cross section induced drag and aircraft mass.

[HexHead]

ORIGINAL: LoBaron

ORIGINAL: HexHead

ORIGINAL: Erkki





Because heavier planes tend to have more mass for comparable effective resisting aerodynamic cross-section than the lighter planes.

Two objects of similar size but different mass do have the same initial falling acceleration, but the heavier one will have higher (top)falling speed in same g, air pressure yadda yadda. [:)]

Yes, no, need to rewrite (unclear). Please let me suggest:

The terminal velocity (i. e., in effect, the velocity at any desired time, as is noted immediately below) of a freely accelerating body (note that 'freely accelerating' necessarily implies no other forces acting on the body) is given by:

v sub t = 1/2 (acceleration due to the local gravitational field) (t^2)

in other words, in a vacuum. If one does the work (see Elementary Differential Equations), the result is that when air resistance is allowed for, most objects reach a terminal velocity that is an upper bound.[...]

Excuse me, Erkki is pretty much spot on.

You are correctly quoting Newton´s second law of gravity, obviously, but what you are missing is that in the environment and situation concerned - airborne fighter aircraft initiating a dive - the acceleration of a free falling object in a vacuum is only of minor relevance anymore.

At the speeds we are talking about drag already is the major force to overcome. So given the circumstances, even without taking engine power into account, the relevant variables for the dive are airframe cross section induced drag and aircraft mass.

Perhaps I was unclear - if you read my other posts in this thread, it will be seen that I was not discussing free fall per se, and pointed out the distinction mentioned. I was being illustrative for the sake of completeness.

[LoBaron]

In which you are of course correct as far as completeness is concerned.

I might have been unclear as well. What I wanted to point out - and this is what I assume Erkki thought as well - is that the original question by Sieppo already seemed to be posted with the 2nd law of gravity in mind (which on first glance contradicts the assumption that heavier aircraft - always assumed the airframe has a similar cross section - have the advantage in a dive). In that context Erkki´s response was complete.

But maybe I am doing too much guesswork wrt the original question.

[HexHead]

Oh, we're killing electrons by the barn full (nothing like puns about subatomic physics) in this thread. Informative, though.

[Panther Bait]

When a plane is in a dive, there is more than just gravity acting on the airframe. Unless the pilot throttles back on the engine and lets the plane just pick up speed by "coasting", the engine will aid in accelerating into the dive. And since heavier airplanes generally have larger, stronger engines to maintain level flight (or a climb), it makes sense that a heavier plane with a more powerful engine can accelerate faster in the initial stage of the dive. Building up delta v between the two planes quickly at the beginning of the dive can equate to a lot of distance very quickly.

Mike

[crsutton]

ORIGINAL: Symon

ORIGINAL: HexHead
And, although completely untutored in aeronautical engineering, it should be apparent that lighter masses (e. g., Zekes) can, pari passu, can have a higher ceiling and maneuver better in thinner air densities. Yeah, that seems to be modeled. But I wouldn't expect Claire Chennault to be diving on packs of Zeroes anytime soon.

Hi, Hexhead.
In the grand scheme of things, that just ain’t so. I fly a 812 lb light sport airplane plane, and I can’t get above 12k to save my life. Wouldn’t want to, anyway, because that’s pretty rarified for me, and performance totally sucks. It’s not the weight, or even the planform. It’s the power plant. Regardless of the exquisite design of the aerodynamic surfaces, one needs a power source to overcome the unfortunate fact of gravity.

Since these power sources are internal combustion types, they need a certain amount of air (O2) to keep running and keep moving the plane forward at a speed that will promote airflow over the lifting surfaces, such that the thing will “fly”. Since air pressure decreases with altitude, there is less Reynolds flow over the surfaces, so you have to go faster to develop enough lift. But lower air pressure means you can’t get the fuel ‘bolus’ right for your power plant to generate the power to keep you up there.

The higher you go, the more power you need to keep you there.
The higher you go, the less power you can develop to keep you there.

Can you say “compensation”? Thus superchargers and their turbo-driven cousins. All devised to get the “right amount” of air into the fuel mixture to get that metal beast pumping out righteous Kw at altitude to keep the bird up.

Yes, the thunderbolt is a good example. The plane was fairly big and the large cowling created a lot of drag. However, at high altitude where the air was thin and thus drag less of a factor the thunderbolt became an excellent airplane because of it massive horsepower output.

[Erkki]

ORIGINAL: Panther Bait

When a plane is in a dive, there is more than just gravity acting on the airframe. Unless the pilot throttles back on the engine and lets the plane just pick up speed by "coasting", the engine will aid in accelerating into the dive. And since heavier airplanes generally have larger, stronger engines to maintain level flight (or a climb), it makes sense that a heavier plane with a more powerful engine can accelerate faster in the initial stage of the dive. Building up delta v between the two planes quickly at the beginning of the dive can equate to a lot of distance very quickly.

Mike

Actually the other way around - P-47 has compared to other ww2 fighters a fairly lowish power-to-weight ratio(and thus thrust-to-mass), even up high, so it loses in initial acceleration(which is also why P-47 had very hard time winning just about any other fighter in a classic duel). Its weight and raw power overcome most of that defiency at higher speeds though.

EDIT: this is because the higher the speed the larger chunk of the thrust is required to battle the drag and less is available for accelerating the aircraft. Large fighters tended to have more mass for drag coefficient --> dives better(no need to also create the lift to keep the plane level for which a heavier plane needs either more wing area(often means more drag) or more speed).

Someone else can probably explain it better. [:)]

[inqistor]

ORIGINAL: dr.hal

Read books like Wings of Gold, where it is articulated that a major defense tactic of Allied aircraft was the dive to get OUT of an attack. The reason is simple, a heavy aircraft can fall quicker than a light aircraft as both would have engines that can assist, but the advantage goes to the aircraft whose frame is helped by gravity.

It was more because Japanese planes poor integrity. Allies planes could reach far higher speed in dive, during which Japanese planes would already rip their wings off. It was known problem, and later versions of ZERO had strenghtened wings. Also NICKs got better integrity (and extra 100 MPH safe diving speed) from some late-mid-hundreth production model.