Zoom Climb

[spicmart]

Often read about zoom climb. Most prominently in the British comparison of P-51, Spitfire, Fw 190A and Me 109G.
Noticeably the Fw 190A was mentioned to have inferior zoom climb (out of a dive or horizontal flight).
What features make a plane better or worse in this aspect of air combat?

 

[GregP]

A clean, heavy airframe has a good zoom climb, after which you go to sustained rate of climb. It likely has a high top speed.

A light airframe has a better sustained climb and better acceleration. Top speed depends on drag and power much more than weight.

So, rate of climb is tied closely to power-to-weight ratio, among other factors.

Top speed is usually tied to more to total drag than to power to weight ratio.

A lot of power on a P-47 didn't make it fast as low altitude. A low drag coupled with medium power made the P-51A very fast down low.

 

[Ascent]

Effectively Zoom climb is trading kinetic energy for height, those with a lot of kinetic energy to convert tend to do better in this regard, so all else being equal, the heavier aircraft will have a better zoom.

 

[Civettone]

Would it be right to say that a fast diver will be a good zoom climber?

 

[Ivan1GFP]

Effectively Zoom climb is trading kinetic energy for height, those with a lot of kinetic energy to convert tend to do better in this regard, so all else being equal, the heavier aircraft will have a better zoom.

I don't believe this would work from a physics standpoint. It is true but the weight / mass is in both the kinetic energy equation And the potential energy (altitude) calculation and cancel each other out.
I believe the difference is really how relatively streamlined the aircraft is. This streamlining would be in the AoA that the aircraft would be in for Zero G. I am also thinking that an airframe with a higher Reynolds number would have a better zoom because the air is effectively less "viscous".

 

[Shortround6]

Well, when you run out of kinetic energy you are back to 'normal' climb, (hanging off the prop in the mid/upper 150-200mph range)

Ability to zoom climb for very long depends on initial speed, weight and low drag. Using speed from a dive (higher speed/energy) than max level speed gives the energy for a "zoom" climb, yes it stops being a zoom climb once you restore the potential energy of the height minus the drag of moving through the air. Other wise we have perpetual motion

"Zoom" climb tends to be noted in heavy airplanes that couldn't climb very well to begin with, like P-47s as an extreme example. P-47 also has a fairly high dive speed.
Or at higher altitudes (over 20,000ft) it may be 30-60mph faster in level flight than an opponent and can trade some speed for a quick pull up.

Light weight, high drag planes are not noted for good zoom climb. Of course a lot of them have better climb rates to begin with the difference isn't as marked.
Something that is rarely (never) noted is what kind of angle the "zoom" climb is done at.
An early P-47 at max climb rate is doing just under 200mph while climbing at about 2500fpm. Plane is climbing at just under 7ft horizontal for ever 1 foot it climbs.
P-47 that is doing 360mph at low altitude (10,000ft) has some energy to trade for increased climb angle while the speed bleeds off.
P-47 that is doing 450mph (coming out of a dive) at low altitude has more energy to trade for increased climb angle while the speed bleeds off.
Now the steeper the climb angle the sooner the kinetic energy bleeds off.

 

[gumbyk]

I don't believe this would work from a physics standpoint. It is true but the weight / mass is in both the kinetic energy equation And the potential energy (altitude) calculation and cancel each other out.
I believe the difference is really how relatively streamlined the aircraft is. This streamlining would be in the AoA that the aircraft would be in for Zero G. I am also thinking that an airframe with a higher Reynolds number would have a better zoom because the air is effectively less "viscous".

I think you're over-thinking it. streaming, etc all affect the speed, which has the effect on the zoom climb.
During a zoom climb you're trading energy for altitude (potential energy). Energy is 1/2mv2 so the only real items which affect it are weight and speed. Given that there is a minimum speed for the aircraft to fly, the aircraft with the greatest span between cruise speed and stall speed effectively has the most airspeed to trade for altitude.

 

[GregP]

Definitely favors a heavy P-51 or a Navy fighter with a much lower stall speed than a USAAF aircraft. A Hellcat, F4U, or FM-2 come to mind for decent zoom climb for a Naval fighter. Moreso the F6F and FM-2 than the F4U. which had a higher stall speed than the F6F or FM-2. But, the F4U-4 made up for it in sustained rate of climb over the other two, so maybe it didn't matter much in practice. I notice in airshows the F4U-4 doesn't seem to lack for ability to go vertical.


View: https://youtu.be/Gy9t8tK5yq8

 

[Ivan1GFP]

I think you're over-thinking it. streaming, etc all affect the speed, which has the effect on the zoom climb.
During a zoom climb you're trading energy for altitude (potential energy). Energy is 1/2mv2 so the only real items which affect it are weight and speed. Given that there is a minimum speed for the aircraft to fly, the aircraft with the greatest span between cruise speed and stall speed effectively has the most airspeed to trade for altitude.

I don't believe you are correct.
The speed at the end of the zoom climb often is irrelevant as was the case with world absolute altitude records.
The stall speed didn't matter because the aircraft really wasn't "flying" by the time it reached maximum altitude. Typically they were so high, there wasn't enough air for the engines to operate any more.

The reason why mass / weight is not terribly relevant in the absolute sense is that the formula for the potential energy gained in altitude in the zoom is Mass * Gravity * Height. In theory, in an absolute vacuum, the cotton ball Cessna and the P-51 would have the same altitude gain at the same rate if they started at the same speed..... If there were no air resistance.

So basically the idea is that the difference in zoom climb is a combination of how slick the airframe is (streamlining) and how much thrust is being added during the zoom climb. Part of the streamlining is how little effect the air has to slow down this particular aircraft and that is where I believe the Reynolds number comes in.

 

[GregP]

Airplanes don't fly in a vacuum and they don't fly in the absence air resistance ... unless they fly so fast and high and to get into orbit.

And no, the potential energy is not the same, nor is the momentum, nor kinetic energy. A toy car hitting you at 5 mph won't do much damage if you are against a solid wall, but a real passenger car most certainly will. The real car will also hold it's speed a LOT longer than the toy car will.

Potential energy is: PE = Mass * acceleration due to gravity * Height.
Kinetic Energy is" KE = 1/2 Mass * Velocity^2.

With equal velocity, both potential and kinetic energy are only equal if the two masses are equal. You seem to have completely forgotten about the "Mass" part.

An 8,000-pound F8F Bearcat at 150 mph has a lot more energy than a 3,000-pound Cessna 182 at the same speed. Literally about 2.667 times as much energy for both PE and KE. Gravity and Height might BE the same, but the mass isn't.

If the two masses ARE equal, then yes, the two zoom climbs will be nearly identical with the lower-drag aircraft being a bit better.

Mass is not irrelevant.

 

[Ivan1GFP]

Airplanes don't fly in a vacuum and they don't fly in the absence air resistance ... unless they fly so fast and high and to get into orbit.

And no, the potential energy is not the same, nor is the momentum, nor kinetic energy. A toy car hitting you at 5 mph won't do much damage if you are against a solid wall, but a real passenger car most certainly will. The real car will also hold it's speed a LOT longer than the toy car will.

Potential energy is: PE = Mass * acceleration due to gravity * Height.
Kinetic Energy is" KE = 1/2 Mass * Velocity^2.

With equal velocity, both potential and kinetic energy are only equal if the two masses are equal. You seem to have completely forgotten about the "Mass" part.

An 8,000-pound F8F Bearcat at 150 mph has a lot more energy than a 3,000-pound Cessna 182 at the same speed. Literally about 2.667 times as much energy for both PE and KE. Gravity and Height might BE the same, but the mass isn't.

If the two masses ARE equal, then yes, the two zoom climbs will be nearly identical with the lower-drag aircraft being a bit better.

Mass is not irrelevant.

Airplanes don't "Fly" in a vacuum, but we aren't talking about "Flying". We are discussing a Zoom climb.
When the F-15 Streak Eagle hits the top of its flight path, it really isn't doing a whole lot of flying. Same applied to a bunch of other aircraft that needed reaction controls to maneuver because there wasn't enough "airflow" over control surfaces by the time they made it to the peak of their zoom climb.

The reason I stated that Mass / Weight was irrelevant was because I thought it was clear what I was responding to.
If the Mass is in both the Kinetic Energy equation and in the Potential Energy equation, then the Mass really doesn't matter if we are talking about the zoom climb for a particular aircraft because we don't expect the Mass to change significantly.

If your Bearcat and Cessna are both at 5000 feet altitude, the Bearcat will have the same 2.667 times the potential energy which is the point I was making. The conversion from kinetic to potential energy for a particular object has the mass in both calculations, so essentially can be ignored for discussing zoom climbs.

 

[pbehn]

Airplanes don't "Fly" in a vacuum, but we aren't talking about "Flying". We are discussing a Zoom climb.
When the F-15 Streak Eagle hits the top of its flight path, it really isn't doing a whole lot of flying. Same applied to a bunch of other aircraft that needed reaction controls to maneuver because there wasn't enough "airflow" over control surfaces by the time they made it to the peak of their zoom climb.

The reason I stated that Mass / Weight was irrelevant was because I thought it was clear what I was responding to.
If the Mass is in both the Kinetic Energy equation and in the Potential Energy equation, then the Mass really doesn't matter if we are talking about the zoom climb for a particular aircraft because we don't expect the Mass to change significantly.

If your Bearcat and Cessna are both at 5000 feet altitude, the Bearcat will have the same 2.667 times the potential energy which is the point I was making. The conversion from kinetic to potential energy for a particular object has the mass in both calculations, so essentially can be ignored for discussing zoom climbs.

The weight of an aircraft like a Bearcat only matters when accelerating in to a dive, very quickly other laws of physics take over. A P-47 accelerated into a dive more quickly than a Spitfire but the Spitfire had a higher maximum dive speed. Due to compressibility issues a plane like the P-38 was uncomfortably close to its maximum dive speed when flat out in level flight. WW2 aircraft could not be just dived without thought, they quickly became uncontrollable and started to fall apart. Horsepower and residual thrust is important in accelerating into a dive but these also become redundant at high speed because a propeller cant provide thrust, the Spitfires which set records in dive speed had fully feathering props to avoid blowing the engine, as it was they wrecked the prop and deformed the wings. P-38s and P-47s were fitted with dive brakes to keep them controllable.

 

[Ivan1GFP]

The weight of an aircraft like a Bearcat only matters when accelerating in to a dive, very quickly other laws of physics take over. A P-47 accelerated into a dive more quickly than a Spitfire but the Spitfire had a higher maximum dive speed. Due to compressibility issues a plane like the P-38 was uncomfortably close to its maximum dive speed when flat out in level flight. WW2 aircraft could not be just dived without thought, they quickly became uncontrollable and started to fall apart. Horsepower and residual thrust is important in accelerating into a dive but these also become redundant at high speed because a propeller cant provide thrust, the Spitfires which set records in dive speed had fully feathering props to avoid blowing the engine, as it was they wrecked the prop and deformed the wings. P-38s and P-47s were fitted with dive brakes to keep them controllable.

Gravitational acceleration affects all objects the same regardless of their weight. Without other factors such as additional thrust or aerodynamic drag, Acceleration is a simple 9.8 M/s^2 or 32.16 Ft/s^2.
A heavy object doesn't fall any faster but for the aero drag having less of an effect on an equal sized object that is heavier.

 

[GregP]

Airplanes don't "Fly" in a vacuum, but we aren't talking about "Flying". We are discussing a Zoom climb.
When the F-15 Streak Eagle hits the top of its flight path, it really isn't doing a whole lot of flying. Same applied to a bunch of other aircraft that needed reaction controls to maneuver because there wasn't enough "airflow" over control surfaces by the time they made it to the peak of their zoom climb.

The reason I stated that Mass / Weight was irrelevant was because I thought it was clear what I was responding to.
If the Mass is in both the Kinetic Energy equation and in the Potential Energy equation, then the Mass really doesn't matter if we are talking about the zoom climb for a particular aircraft because we don't expect the Mass to change significantly.

If your Bearcat and Cessna are both at 5000 feet altitude, the Bearcat will have the same 2.667 times the potential energy which is the point I was making. The conversion from kinetic to potential energy for a particular object has the mass in both calculations, so essentially can be ignored for discussing zoom climbs.

No F-15s and no reaction-based control aircraft flew in WWII, and this question was ostensibly about WWII fighter aircraft zoom climb.

I believe the OP mentioned P-51, Spitfire, Me 109, and Fw 190A, not X-15s or Eagles, Streak Eagles or otherwise.

Again, mass / weight is not able to be neglected when considering zoom climb within the bottom 45,000 feet or so of our atmosphere. And if you want to GET up to where it CAN be neglected, you can't neglect it on the way up as you try to climb your heavy airplane up there with heavy fuel.

Even at 100,000 feet, there is mass in the PE and KE equations.

 

[gumbyk]

And, like every performance discussion, the caveat here is that pilot input has such a huge impact that the actual numbers are a very rough guide.
e.g. I have pulled up from a buzz and break and busted circuit altitude, and on the same flight not even made circuit altitude simply because I pulled too hard.

 

[GregP]

Sounds like you need more buzz practice!

 

[pbehn]

Gravitational acceleration affects all objects the same regardless of their weight. Without other factors such as additional thrust or aerodynamic drag, Acceleration is a simple 9.8 M/s^2 or 32.16 Ft/s^2.
A heavy object doesn't fall any faster but for the aero drag having less of an effect on an equal sized object that is heavier.

That is what I posted, you cant quote a principle that applies in a vacuum when discussing aircraft that need air to fly and for their engines to work. Physical size is only part of the discussion, Concorde could cruise at a speed that would tear apart any WW2 aircraft, despite being much bigger. An aeroplane isnt just an "object" it is a device that contains a human who would like to live until tomorrow. With various aerodynamic effects, aeroelasticity and aileron reversal some aircraft quickly became impossible to control in a dive, and killed the pilot, sometimes this happened in level flight.

 

[gumbyk]

Sounds like you need more buzz practice!

Trying to avoid breaking over a group of people watching! Second one I did the break after passing the group, went much better, and they didn't have to see the filthy bottom of the aircraft.

 

[Ivan1GFP]

That is what I posted, you cant quote a principle that applies in a vacuum when discussing aircraft that need air to fly and for their engines to work. Physical size is only part of the discussion, Concorde could cruise at a speed that would tear apart any WW2 aircraft, despite being much bigger. An aeroplane isnt just an "object" it is a device that contains a human who would like to live until tomorrow. With various aerodynamic effects, aeroelasticity and aileron reversal some aircraft quickly became impossible to control in a dive, and killed the pilot, sometimes this happened in level flight.

You CAN quote the laws of physics pretty much until you get close to relativistic speeds and we are certainly not there in regards to any know aircraft or even spacecraft. They don't really chance much as we might want them to sometimes.
Everything else affecting a zoom climb is "part of the discussion". I was pointing out that weight canceled itself out as far as KE to PE conversion. The difference had to be aerodynamic effects such as streamlining and the relative effects of air on the vehicle, thus the mention of Reynolds number as a possible factor in the calculation.

 

[Ivan1GFP]

No F-15s and no reaction-based control aircraft flew in WWII, and this question was ostensibly about WWII fighter aircraft zoom climb.

I believe the OP mentioned P-51, Spitfire, Me 109, and Fw 190A, not X-15s or Eagles, Streak Eagles or otherwise.

Again, mass / weight is not able to be neglected when considering zoom climb within the bottom 45,000 feet or so of our atmosphere. And if you want to GET up to where it CAN be neglected, you can't neglect it on the way up as you try to climb your heavy airplane up there with heavy fuel.

Even at 100,000 feet, there is mass in the PE and KE equations.

Hello GregP,
Of all the people in this discussion, you and Shortround6 are the two that I would have expected the least argument for this line of thought.
The point I keep trying to make is that Mass is in both the PE and KE equations and therefore cancel each other out.
A WW2 aircraft flying to a hammerhead stall isn't behaving a whole lot different than the Streak Eagle.

Let's consider THIS situation:
We have two identical P-47 Thunderbolts.
One has a full load of fuel and ammunition. The other has no ammunition and much less fuel.
Figure one is 1500 pounds heavier than the other.
Both pull into a zoom climb at same angle and from the same initial level speed.
Which one will go higher?
Why?

Yes, one will have a bit more induced drag, but..... The additional weight should give it an advantage.
What do you really think?