View Full Version : is there any ideal speed to climb?

11-25-2004, 07:04 AM
i was wondering if in 3.01 they solved this problem of previous versions

11-25-2004, 08:22 AM
No, the best climb speeds are in a very wide speed range, as in the past. Instead of having a Best angle of climb or a best rate of climb, you have a 'best angle of climb speed range' and a 'best rate of climb speed range'. It ususally is about 30 or 40 Kph wide for both, in just about every plane. For example, I just found that the best rate of climb for the P-40C is from 220kph to 260kph, with no discernable difference from the low end to the high end.

11-25-2004, 09:45 AM
If there's a speed range, it is as it should be.

The best speed will vary too, depending on first and foremost altitude.

11-25-2004, 11:46 AM
Remember it may also depend on enemy aircraft, if you are in combat. At similar speeds, one aircraft may handily outclimb yours, but at higher speeds your aircraft may handily outclimb theirs. In short, your best climb speed (or range) may not be your best alternative in combat. Just because 'anecdote x' says that 'aircraft y' can easily excape 'aircraft z' in a climb does not mean he is climbing at his best climb speed; he is climbing at his best relative climb speed.

11-25-2004, 02:57 PM
This iss'na gonn'a be much help....

Best rate of climb occurs where there is the best thrust vrs. lift over drag ratio. The wing has an INDICATED airspeed at which it produces the best ratio of lift over drag (L/D). This gets a little complicated as the rest of the plane produces drag as well, which more or less increases with the square of speed. Powerplant propulsusive effecency also is some what speed related.

Take all of that stuff together for a WWII fighter and best RATE of climb (and glide) occurs somewhere around the L/D max. The value of L/D max remains constant with weight change, but the airspeed at which it occurs does not! An example of this is the glide ratio for a configuration does not change with weight, just the speed at which it occurs!

For, say an F4U, somewhere around 140-160 knots might give best RATE of climb. Maximum angle occurs at a lower airspeed, perhaps 15-20 knots slower. Max angle is just that, maximum rise for a given distance. The altitude gained in a unit of time will be less, but the distance covered shorter.

Experiment with this, remembering it is weight related.

11-25-2004, 11:57 PM
Also remember that best climb speed will vary with fuel/munition load and temperature (it will be different on different maps and in different seasons).

11-26-2004, 12:19 AM
only real way is to test

there is a fastest time to 8K , & its gotten by holding a certian speed

NOT a certian speed range , like another poster stated , this is a value that is different for virtually every A/C

11-26-2004, 06:56 AM
Maximizing rate of climb or climb angle and maximum L/D are not at all related.

Here€s something I posted over at SimHQ ( http://www.simhq.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=114;t=001095;p=2):

€you can pull back on the stick all the way to that peak in the Cl curve which will give you the peak INSTANTANEOUS climb rate for whatever airspeed you are at€

No. This will give you the maximum load factor and minimum radii on the transition into the climb. Specific excess power, SEP, (and climbrate) will not be at a maximum at max L/D or maximum lift. Nor will the climb angle. I€ll try to explain why.

If we assume thrust to be parallel with the direction of flight, the force equation parallell to the flight path vector becomes

T-D-W*sin(gamma) = 0,

where gamma is the flight path vector angle (climb angle) measured from the horizontal. This gives

gamma = arcsin((T-D)/W)

In other words, maximize the specific excess thrust (SET) and you have maximized the climb angle. This is not the same as maximizing L/D!

For a jet, where thrust is largely independent of airspeed, the velocity for maximum climb angle (Vx) will be close to the velocity for L/D_max. This will hold less and less true as the climb angles increase. Take a look at the vertical climb case without acceleration (T-D=W, gamma = pi/2 = 90 deg), where the optimal AoA will be the zero-lift AoA. This is far away from L/D_max. Any other AoA will mean a lower climb angle.

For propeller aircraft, where the thrust available varies quite a bit with airspeed, things are rather more complicated.

Climb rate is the SEP. Both are measured in m/s. The SEP is specific excess thrust (excess thrust divided by weight) times TAS. This will move even further from L/D_max.

€œif you slow below the Lift over Drag max speed (the trough in the above Lift/Drag graph) then over the long haul you will actually climb on average slower than if you had just started at L/D max, added full power and stayed there.€

As seen above, this is not true.

€œ(which is why vectored thrust aircraft are so rare...because it's so much harder to oppose weight with just an engine than with a wing)€

Which is why VTOL is rare. The main use of vectored thrust is manoeuvrability. But your conclusions are correct. With enough power, you will be able to climb in just about any part of the envelope (including beyond the stall). It will not be putting all that power to effective use, but it can be done.


A few online references:

http://www.erau.edu/er/newsmedia/articles/wp6.html (Note that the editor got the climb angle equation all wrong by omitting the inner parentheses)



As for drag from cowl flaps:


Second to last post by myself.

11-26-2004, 07:03 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by CV8_Dudeness:
there is a fastest time to 8K , & its gotten by holding a certian speed

Nope. The speed for best RoC will vary with altitude, both in TAS and IAS. Typically, the best ROC speed for WWII aircraft will be given as a fixed IAS in a few altitude segments.

Thus, you cannot test the climb performance by climbing from SL to e g 8,000 feet. You have to use smaller test blocks and create a chart of SEP as a function of airspeed and altitude.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
NOT a certian speed range

As the SEP curve reaches a peak, it levels off. This means that for a certain speed range, you are so close to max RoC that there is no noticeable difference. Within this speed range, you are free to optimise your flight for other purposes.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
this is a value that is different for virtually every A/C <HR></BLOCKQUOTE>

Agreed. The best RoC speed curve will vary hugely between different aircraft.

11-26-2004, 08:58 AM
Anyway .. ideal speed for gaining altitude was common part of aircraft flight manual and such thing is missing in IL2. There should be card with instructions for each plane .. minimum speed, max speed, best climb, guns load etc.

11-26-2004, 10:44 AM
Well gee whiz....

I fly jets for a living, and Thrust is definitly related to speed! It is somewhat less true with modern FAN jets, but very true for any pure jet (such as the P80, ME 262 etc) where almost all of the thrust comes from jet reaction. For them to work properly they have to be mated with an airframe optimized for where the engine is efficent (high speed). The original jets were worthless till they got some speed up.

I am in the Mid East (not Ohio) at present and a bit far from my reference library, but anyone with a copy of HH Hurd can read his disertation on this and a few other subjects.

Remember you only have maximize excess power (for climb) when you minimize drag. Weight changes the airspeed value at which max L/D occurs, but not it's angle of attack. At heavier weights the speed will be higher and the climb rate lower. Temperature variations from standard are not modeled in this GAME. External loads will, because of parasite drag cause both best rate and angle airspeeds to decrease.

As one approaches the operational ceiling of an aircraft, the best rate and best angle speeds start to merge. At the absolute cieling they are the only speed that will keep you aloft! Quite a few years ago I flew a (unsupercharged) Supercub over Mt McKinley (20,320'), which IS at it's ceiling with carefull airmanship. Two days ago we flew nonstop from the South Eastern US. to Hong Kong, a 17hr.59min. flight. We only got there by very carefull attention to maximizing the efficency of the aircraft for the changing weights and condition encountered.

A sucessfull airplane optimizes it's airframe and powerplant, in combination.

Try load combinations for ONE plane you will fly, try these vrs airspeeds and see what works best. You are the test pilot, since no information has been supplied by the "manufacturer".