Ah good so both you and that report agree with what I allready said, i.e.

S!

Sadly, any real-life pilot can confirm it. The MsFS is very excellent on-board systems, avionics and instrument flight simulation. But the flight model is a large pile of xxxx...

I've done the A2A FSX Spitfire MkIa with the DH 2 pitch prop and will post results soon but the CoD DH5-20 isn't modelled properly. It should be possible to obtain variable pitch in the mid-range of the prop control (which should be a plunger btw not a lever) making it effectively a variable pitch prop although not intended to be be. In fact using the variable capability became an official recommendation and it could deliver almost the same performance as the Rotol in expert hands with the pilot being the 'constant prop speed' governor.

Bottom line is I'll have to use the Rotol set to 2600 rpm which is the prop speed I manually maintained in the A2A FSX model. As the 2 pitch props were capable of being converted to CSPs in the field I am assuming they used the same blades.

Climb speed will never be constant with altitude. Any pilot or first year aeronautical science students knows this....

Climb rate without speed is useless information. All aircraft performance occurs at a specific point on Power required curve and is fixed by the design of the aircraft.

If speed is held constant, the aircraft is not maintaining the best performance point on the Pr curve.

http://home.pcisys.net/~aghorash/Why...h_Altitude.pdf

http://aerosrv.cls.calpoly.edu/dbiez...20and%20Vy.pdf

http://www.pprune.org/tech-log/343259-vx-vy.html

http://williams.best.vwh.net/smxgigpdf/mfly2.pdf

Yes, and in second year they learn that there always are exceptions to the rule, and thus it's "hardly ever" and not "never". An example for an exception has already been given in this topic, so feel free to educate yourself.

Baloney. To achieve Vx or Vy, velocity must change with altitude. There are no exceptions to that no matter how much you tap dance.

Gentlemen!

So many of these arguments seem to based on interpreting an slightly ambiguous statement to make it wrong.

Well this is pretty clear and supported by the reference. the Spittie pilots doing that test climbed at constant IAS mostly and recorded climb rate.

Obviously the pilot can choose to climb at constant IAS if aircraft capability permits. I take it, this statement should be:

Vx (IAS for best climb angle) and Vy (IAS for best rate of climb) will never be constant with altitude."

This is true enough but I know a flight instructor that had it a bit confused :). So climb tests at constant IAS (such as that Spittie one) may not be capturing optimum rate of climb at each altitude? Interesting.

There seems no real disagreement at this point, just an imaginary one

A clearer statement now it is expanded from just "climb speed".

It is quite hard to write unambiguously in technical detail, and anyone's forum posts are likely to fall down on this now and again regardless of their aviation knowledge. But instead of jumping on it as evidence of moron, why not have a lovely big glass of wine? Of course that is what I am doing AND writing this post, so maybe you can do both if you really want to ;)

2007 Reisling, camber

Oh, an educated voice of reason with good manners, what a refreshing sight. I sure hope to see you around for a long time!

The funny part is Crumpp is saying the same thing

He just appears to be a little confused with regards to 'vector math' (what he called correct physics).

That being the resultant (single) vector that is the equivalent of a set (more than one) of vectors. Where is is possible to have a resultant vector with constant magnitude as it changes direction.

In this case the 'resultant' vector is IAS, that is the equivalent of the Vx and Vy set of vectors

From the spitfire test data we can see it maintained a constant IAS for most of the climb, but at the same time the ROC changed as the spitfire climbed.

Mathematically speaking, the resultant vector (IAS) 'direction' changed to maintain the resultant vector (IAS) 'constant magnitude'.

In the case of the spitfire ROC test the 'climb angle' changes which in turn changes the direction of the resultant vector (IAS). Which in turn changes the magnitude of Vy and Vx.

Note in this case Vy is equal to the ROC, the vertical component and Vx is equal to the horizontal component (i.e. earth frame of reference aka coordinate system)

At this point I think it would help those having trouble with vector math to check out the following link..

Comparing Two Vectors

Paying special attention to Example #2, vectors with same magnitude but different directions, i.e.

http://www.grc.nasa.gov/WWW/k-12/air...s/vectcomp.gif

And just to be crystal, allow me to say this again, the 'constant' climb speed statement was more of a test pilot term.. It did not mean they kept it constant down to three decimal places, that is just humanly impossible. What it meant was 'when' you change the IAS during the climb as required, the change should be made as smoothly as possible such that the change in acceleration was kept as small as possible.

Spitfire I Pilot's Notes state:

Hurricane I Pilot's Notes state:

Climb speed refers specifically to Vx or Vy. It is not common to split hairs on it having it mean anything but Vx or Vy without specifying the condition of flight.

http://www.experimentalaircraft.info...imb-speeds.php

All aircraft can climb at a constant IAS. If you do that however, you are not at Vx or Vy.

There is no reason for a huge involved, "Gee Whiz, I wish I was smart" discussion on this topic.

It is a simple fact, an airplanes climb speeds or Vx and Vy, are not constant with altitude. No amount of tap dancing or splitting hairs will change the physics.

In practical terms for flying an airplane it is easier to remember a few speeds for Vx and Vy that get you in the ballpark or just hold it constant so you only have to remember 2 numbers.

Read your Hurricanes notes....

Optimum for what???? Is that best rate or best angle???

It is actually because of the fixed pitch propeller but lets not get ahead of ourselves and get all confused on the correct principles for climbing speeds.

Well flight instructors are only human!

But re-reading your reply I noticed something..

But first some definitions

In pilot jargon terms (read not math terms)

Vx best angle of climb 'airspeed'
Vy best rate of climb 'airspeed'

Put another way

Vx is the 'airspeed' that produces the most altitude in the shortest ground distance
Vy is the 'airspeed' that produces the most altitude in the shortest amount of time

For example

Vx is the airspeed you would want to climb at if your goal is to clear an obstacle at the end of the runway
Vy is the airspeed you would want to climb at if your goal was to intercept the bombers

The point to notice here is both Vx and Vy are 'airspeeds', be it indicated (IAS) or true (TAS).

Which should not be confused with the Vx and Vy I used in my previous (mathematical) example on the resultant vector! Where the Vx and Vy velocity tied to the x and y axis frame of reference. These pilot jargon terms Vx and Vy are actually the resultant vector, i.e. airspeed.

Not likely..

They were more than capable of determining the airspeed that produced the best ROC. With regards to WWII they would do several test and different airspeeds to determine which one produces the best ROC.

One thing to take note of, with regards to WWII test data, most WWII fighter aircraft didn't have TAS gauges, which explains why most WWII ROC data gives airspeeds in IAS, and most if not all of those WWII test reports that do provide TAS, TAS was calculated (post test processing) from IAS.

So most WWII references are in terms of IAS. Where as today TAS gauges are more prevalent, and therefore most modern pilot discussions on Vx and Vy are talking in terms of TAS, where most make note of how Vx (TAS) and Vy (TAS) airspeed changes with altitude.

We also know that TAS changes with altitude relative to IAS, So even with a constant IAS, TAS is changing.

In WWII they typically referred to the airspeed that produced the best ROC as the 'best climb speed', which in todays pilot jargon equates to Vy (best rate of climb airspeed).

Therefore with regards to the WWII ROC test reports jargon vs modern pilot jargon, the constant indicated airspeed (IAS) in the WWII ROC test is the same as saying Vy indicated today, convert both to TAS and this WWII story will match those of today, where Vy changes with altitude.

+1

I did, it still says constant IAS to FTH and linear reduction above optimum climb.

Best rate of climb.

This is not propeller related. There are performance tests with Rotol propellers show that the same applies to Hurricanes or Spitfires with CSP.

It is a pretty simple concept to grasp. Climb speed changes with altitude.

That is it and all you need to know!!

If it does not change with altitude or is a simple linear then for practical pilotage it is simpified to get the pilot in the ballpark!

Again, very simple concept that does not require in depth discussion.

Are you talking about IAS or TAS? If you mean TAS I'm absolutly with you.

Of course it's an pratical approximation. In a theoretical discussion there is no direct relation between IAS and climb rate.

It is a very simple concept that does not require an indepth discussion.

Climb speeds change with altitude.

It does not matter if we are talking Indicated or True airspeed, they both change.

In fact, Indicated airspeed for Vy decreases with altitude and Indicated airspeed for Vx increases with altitude.

Where they meet is the aircraft's absolute ceiling.

http://aerosrv.cls.calpoly.edu/dbiez...20and%20Vy.pdf

There is a definite fixed by design relationship between airspeed and climb rate based on excess power or thrust depending on whether we are talking rate or angle of climb.

Again ... you are talking about TAS and I asbolutly agree about the relation between TAS and climb rate. However IAS is influenced by installation and instrument errors and density of air. The "design relationship" cannot take these factors into account, hence there is no direct relation between IAS and rate of climb.

TAS and climb rate are in relation.
TAS and IAS are in relation.
But there is no direct relation between IAS and climb rate. For example: IAS changed becaused by a frozen pitot tube, but this will not change the climb rate.

I want to make clear that I do not want to say that IAS is mathematically constant for a theoretical maximum rate of climb. I absoluty agree with you that theory says is is decreasing. However what I want to say is that there are pratical references that indicate that for a specific aircraft the IAS for maximum rate of climb can be near constant over a certain altitude range.

Bingo!

Which was stated prior to crump stating it so he actully agrees with what was allready said, yet his replies thus far seem to be ingnorant of the fact that it was allready stated prior to his statement.

Who told you it was "near constant"??

The rule is Vy will be reduced 1 KNOT IAS per 1000 feet altitude. Vx will increase 1 KNOT IAS per 2000 feet altitude.

From sea level to 20,000 feet...

Vy changes 20 KNOTS, 23mph, or 37kph.....

Vx changes 10 KNOTS, 11.5mph or 18.5kph....

See above post......

There is no theory to it. We are not talking quantum physics. Get a pilots license or go to school to learn about airplanes. Stop getting your information from these gamer discussions about virtual planes from folks who have never even smelled avgas.

It is a very simple concept that does not require an indepth discussion.

Climb speeds change with altitude.