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View Full Version : Ground Effect? PART TWO



blairgowrie
05-16-2010, 08:47 AM
Continued from :http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/3121062458?r=8631002268#8631002268

Kettenhunde
05-16-2010, 09:21 AM
I don't believe that the "mirror image" thing is more than an analogy, any attempt at a proof or complete explanation of vortex behavior.

Absolutely. It is no different than the thrust formula.

Thrust = (Thrust Horsepower * 325)/ velocity in knots

At 0 kts we have zero thrust mathmatically.

However, this is not the case. Every fan company would be out of business if this was true.

Instead, to describe the physical behavior we have set the usable thrust at zero for zero velocity. In reality, that thrust force is met by ground friction and braking force.

It the same as the concept that Bill was trying to get out of Holtzauge.


The question of Infinite Thrust at zero velocity was the question I posed to help you understand the difference between Net Thrust in the THp equations and Total Thrust (max) available as measured, at rest, for the system. Net Thrust will then decrease as velocity increases from zero up to max V.

So, answer the question - when does the equation for Thp relative to Thrust and Velocity become valid in your workd Holtzauge? Relative to total positive Force in the horizontal plane for level flight?

10kts? 30kts? 100kts? - and why doesn't it apply in deriving a Force vector on the system at zero to low speeds? What law of physics makes it valid at higher speeds? (The correct answer for industry standard practice is 105 kts) but remember it is for Net Thrust.

When do you arrive at a Force value to equate to Force Available - Force Reguired to overcome Drag and accelerate?


http://forum.12oclockhigh.net/...=70663&postcount=111 (http://forum.12oclockhigh.net/showpost.php?p=70663&postcount=111)

Holtzauge
05-16-2010, 10:00 AM
AndyJWest: You have no idea how happy I am to find a fellow pastafarian here! May you forever bask in the benevolent light of his noodliness!

However, Beware of the wayward pastor of creationist aerodynamics who lurks in this forum. Do not fall for his tricks. He has yet to see the light and to be touched by his noodliness.....

PS. Loved the picture. How can anyone doubt when his noodliness manifests himself so clearly?

JtD
05-16-2010, 10:54 AM
Wow, x/0 = 0. That's new.

p.s. And http://forums.ubi.com/images/smilies/88.gif regarding the flying pasta picture! That's proof!

Bremspropeller
05-16-2010, 11:14 AM
Well, it all depends if it's spirelli, spaghetti or rigatoni...

Holtzauge
05-16-2010, 11:24 AM
Beware ye blasphemers or his noodliness shall strike ye down with a bolt of tagliatelli!

M_Gunz
05-16-2010, 04:23 PM
Originally posted by Kettenhunde:
Thrust = (Thrust Horsepower * 325)/ velocity in knots

At 0 kts we have zero thrust mathmatically.

Ummmmmm?

WTE_Galway
05-16-2010, 06:31 PM
The apparent division by zero just means mathematically it needs to be approached as a limit case.



First note that:

T =P/v

is a simplified case assuming a stable system where no acceleration takes place.

hence in our instance:

v (velocity) = 0
and dv/dt (aceleration) = 0
and d^2v/dt^2 (rate of change in acceleration)= 0

now, rearranging and solving for P:

P = Tv

If v=0, then the propulsive POWER of the propeller/engine as a system is ZERO.

Getting back to T =P/v.
Given P = 0 it can be easily shown that for
the limit case as v->0 then T=0
(in non mathematical terms - regardless of how small v gets P = 0 and hence P/v is zero and THRUST remains ZERO)



HOWEVER even from commonsense, if its a stable system where v is constant at zero their can be no EXCESS thrust and the total EXCESS thrust vector must be zero.

Kettenhunde
05-16-2010, 09:29 PM
WTE_Galway

http://forums.ubi.com/images/smilies/25.gif

Wurkeri
05-16-2010, 10:46 PM
Originally posted by WTE_Galway:
The apparent division by zero just means mathematically it needs to be approached as a limit case.



First note that:

T =P/v

is a simplified case assuming a stable system where no acceleration takes place.

hence in our instance:

v (velocity) = 0
and dv/dt (aceleration) = 0
and d^2v/dt^2 (rate of change in acceleration)= 0

now, rearranging and solving for P:

P = Tv

If v=0, then the propulsive POWER of the propeller/engine as a system is ZERO.

Getting back to T =P/v.
Given P = 0 it can be easily shown that for
the limit case as v->0 then T=0
(in non mathematical terms - regardless of how small v gets P = 0 and hence P/v is zero and THRUST remains ZERO)



HOWEVER even from commonsense, if its a stable system where v is constant at zero their can be no EXCESS thrust and the total EXCESS thrust vector must be zero.

Actually this kind of thrust formula is not intended for zero speed situation, there is other kind of formulas for that. And the proper form of it is actually:

T = P*n/V

Where and n is propeller efficiency which of course have to reach zero when the speed reaches zero while the power remains constant. If one wants to calculate out the propulsive power ie thrust horsepower (THp), then it would naturally be P(Hp)*n.

Note here that in the quoted TOCH thread Bill was originally arguing that thrust does not decrease when the speed increases later in thread he changed his mind... read it all if you are interested (some 15 pages).

AndyJWest
05-16-2010, 10:56 PM
... all of which has b****r all to do with ground effect, either in real life or in the sim.

JtD
05-16-2010, 11:05 PM
Originally posted by WTE_Galway:
The apparent division by zero just means mathematically it needs to be approached as a limit case.

No, it doesn't. Not necessarily.

thrust hp = engine hp * prop efficiency

For all situations where neither engine hp or prop efficiency (so basically all situations where engine is on and prop is mounted) thrust hp > 0.

So,
T = P/v with P > 0 and v = 0, so
T = n.d. or, if you want to use a limit case,
T -> infinite

That's basically all there is to it, but I'll be going on ranting a bit.


First note that:

T =P/v

is a simplified case assuming a stable system where no acceleration takes place.

No, acceleration may or may not take place. That's not part of the equation.


now, rearranging and solving for P:

P = Tv

If v=0, then the propulsive POWER of the propeller/engine as a system is ZERO.

Yes, and no matter how large the thrust is, your P from that equation will always be 0 (i.e. T from P/v = n.d.).


Getting back to T =P/v.
Given P = 0 it can be easily shown that for
the limit case as v->0 then T=0
(in non mathematical terms - regardless of how small v gets P = 0 and hence P/v is zero and THRUST remains ZERO)

So, basically you're calculating:

T = P/v, P = Tv so T = T*v/v so T = T. That's all you've done, and it leads nowhere.


HOWEVER even from commonsense, if its a stable system where v is constant at zero their can be no EXCESS thrust and the total EXCESS thrust vector must be zero.

Excess thrust was not the point. Total thrust was.

I'm used to seeing physics getting raped on this board, but now not even math is spared any longer. That hurts. http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif

JtD
05-16-2010, 11:08 PM
Originally posted by AndyJWest:
... all of which has b****r all to do with ground effect, either in real life or in the sim.

Nothing. Sorry. The point where x/0 = 0 should really be a point where I leave a topic because it is getting too stupid. I'll do so now.

M_Gunz
05-16-2010, 11:09 PM
If the v in T=P*n/v is the velocity of air moving through the prop disc and not the plane itself...

AndyJWest
05-16-2010, 11:13 PM
Originally posted by M_Gunz:
If the v in T=P*n/v is the velocity of air moving through the prop disc and not the plane itself...
... it still has b****r all to do with ground effect.

M_Gunz
05-16-2010, 11:13 PM
Originally posted by AndyJWest:
... all of which has b****r all to do with ground effect, either in real life or in the sim.

And the discussion had not weaved around to the use and validity of mathematical models, which has to do with?

Kettenhunde
05-16-2010, 11:19 PM
thrust hp = engine hp * prop efficiency

WTE_Galway got it right.

Power by definition is force x velocity. If our velocity is zero then our power is zero.

Its just basic physics.

http://www.ajdesigner.com/phpp...n_velocity_force.php (http://www.ajdesigner.com/phppower/power_equation_velocity_force.php)

The rest is a clown fest.


And the proper form of it is actually:

T = P*n/V

For example, Thrust Horsepower by definition is:

Shaft Horsepower x n and the 325 is a conversion factor for using Knots in the BGS system. It is not what some were taught to parrot and without understanding the definition of Thrust Horsepower it does not fit their mold.

http://forums.ubi.com/images/smilies/25.gif

AndyJWest
05-16-2010, 11:32 PM
Actually, I started the thread after a question was asked about whether, and how accurately, IL-2 modelled ground effect. This involved attempting to answer two questions: (a) how IL-2 models GE, and (b) what are the effects of GE in real life. Without measurement, mathematical models tell us precisely nothing - they can only be a statement about how reality is expected to behave if the maths and the underlying assumptions are correct. It is noticeable that this thread contains (a) some data gathered from attempts at measuring IL-2 GE, and NO verifiable data about real-world GE. On this basis, almost anything IL-2 does might be right, wrong, or just plain irrelevant. In order to simulate something, you need to know what it is that is being simulated. On the evidence presented so far, I could argue that real-world ground effect was caused by proximity to earthworms...

Kettenhunde
05-16-2010, 11:56 PM
NO verifiable data about real-world GE.


That is not true.

I gave you a simple method to estimate the effect that agrees with real world results very well in the first few posting on the subject.

AndyJWest
05-17-2010, 12:19 AM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">NO verifiable data about real-world GE.


That is not true.

I gave you a simple method to estimate the effect that agrees with real world results very well in the first few posting on the subject. </div></BLOCKQUOTE>

A 'method to estimate the effect' isn't the same thing as 'verifiable data' though, is it? Given the contradictory explanations of GE I've seen, I see little reason to attach any particular credence to estimates.

I think that the IL-2 GE model is wrong. I've still not got much idea about what it would look like if it was right.

Kettenhunde
05-17-2010, 12:27 AM
A 'method to estimate the effect' isn't the same thing as 'verifiable data' though, is it?

You get a estimation of what it should be for the Ju88 at a given height and go verify it to see if your game approximates it.

You wouldn't be floundering around wondering if your game is correct you had done that.

Stop mucking around with the Wind and Turbulence too as that will effect your GE results in the real world too. It just clouds the progress at this point.

AndyJWest
05-17-2010, 12:46 AM
Stop mucking around with the Wind and Turbulence too
No. I've already demonstrated that it has significant influence on results - and not just in the ways that might be expected if wind and turbulence were all that was being modeled - look at my results. I'm not 'floundering around' in any case. I've demonstrated that W & T do this, and am now in a better position to exclude these effects, and look at how the sim models GE in their absence. What I can't do, however, is state that the model is wrong, based on 'estimations' that may rely on false assumptions. I'm more or less convinced that the model is wrong (based not just on my results, but on other evidence), but I'd rather base any criticisms of the model on evidence than estimates based on assumptions that may not be true.

M_Gunz
05-17-2010, 02:25 AM
So we have THP which is power and we have T which is force as in T - D unless Drag is now power?

Let's have it then.

Wurkeri
05-17-2010, 05:23 AM
Gunz,
You don't have to deal with THP nor conversion factors, just use the Si-units and everything is logical and simple.

But this is off topic. Over and out.

M_Gunz
05-17-2010, 08:29 AM
I thought that thrust is a force and that would be independent of units. I still do.

Kettenhunde
05-17-2010, 02:55 PM
I thought that thrust is a force and that would be independent of units. I still do.


Thrust and drag are both forces and not powers.

AndyJWest
05-17-2010, 03:01 PM
Is anyone actually interested in my attempts to explore ground effect modelling in IL-2? Or would they rather this thread continued as an experiment in nit-picking and pedantry?

I happen to believe that it is possible to test the sim, rather than just spout endless unverifiable 'facts' and off-topic clever-d1ckery. I'm not sure there is much point though...

M_Gunz
05-17-2010, 03:50 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I thought that thrust is a force and that would be independent of units. I still do.


Thrust and drag are both forces and not powers. </div></BLOCKQUOTE>

And is the T in the parrot formula T = P * n / v the force T or the power THP?
Because I used that formula (awk, awk!) and then it was T = thrust as a force.
Was I wrong to to do that and should I never do so again?

And you were precisely right bring it up as an example of a limited mathematical model.

M_Gunz
05-17-2010, 03:59 PM
Originally posted by AndyJWest:
Is anyone actually interested in my attempts to explore ground effect modelling in IL-2? Or would they rather this thread continued as an experiment in nit-picking and pedantry?

I happen to believe that it is possible to test the sim, rather than just spout endless unverifiable 'facts' and off-topic clever-d1ckery. I'm not sure there is much point though...

I think that you guys have gotten a lot of really good data and ran good tests.
As I have seen is often the case, the interpretation is the sticky part which does involve a lot of speculation and
subjects from outside a narrow range. In my 12 years experience as part of the FS community, this thread has been
pretty tight compared to the majority!

Just roll with it and ignore what bothers you. Some of us need an "oh yeah" moment and only if enough agree can there
be a consensus. Would you want people agreeing to what they don't understand or hasn't been communicated?

na85
05-17-2010, 04:42 PM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I thought that thrust is a force and that would be independent of units. I still do.


Thrust and drag are both forces and not powers. </div></BLOCKQUOTE>

And is the T in the parrot formula T = P * n / v the force T or the power THP?
Because I used that formula (awk, awk!) and then it was T = thrust as a force.
Was I wrong to to do that and should I never do so again?

And you were precisely right bring it up as an example of a limited mathematical model. </div></BLOCKQUOTE>

T is thrust, a force.

n is dimensionless, and in general Power = Force * velocity, so if you divide power by velocity that leaves you with force on both sides of the equation. Therefore it is correct to use T = thrust not THP.

WTE_Galway
05-17-2010, 05:18 PM
Originally posted by M_Gunz:
I thought that thrust is a force and that would be independent of units. I still do.

Thrust is a force and measured in Newtons for SI (which cashes out to kgm/s) or "pounds force" for imperial (where pounds force equates to the force exerted on one pound of mass by one standard gravity).

As always the metric units make more sense and are easier to use.

AndyJWest the fact that the topic has gone to PART TWO suggests an inteerest in what you are doing regardless of going off topic.

Kettenhunde
05-17-2010, 09:29 PM
And is the T in the parrot formula T = P * n / v the force T or the power THP?
Because I used that formula (awk, awk!) and then it was T = thrust as a force.
Was I wrong to to do that and should I never do so again?

It is the force of thrust. Na85 and others have explained it well.

You are still using thrust horsepower in T = P*n /v

Shaft Power * propeller efficiency <P*n> is the definition of thrust horsepower.


And you were precisely right bring it up as an example of a limited mathematical model.

It is good illustration. Thrust certainly is not infinite either as some people have said. Otherwise I would be buying a new hanger every time I started the airplane.

Divided by zero does not mean the value is infinite as some people mistakenly think.

It means the answer is undefined with an infinite number of answers unless we define it.

AndyJWest
05-17-2010, 09:57 PM
...and yet again, Kettenhunde considers his opinions on the meaning of x/0 as of more importance than the topic of this thread. As far as I'm concerned, you can say it is equal to zero, infinity, or the faint traces of an aroma of Pythagoras's farts that may still hang around the subatomic vortices of the Mediterranean atmosphere to this day. I don't care. It is irrelevant.

na85
05-17-2010, 10:21 PM
My finely attuned senses detect hostility.

AndyJWest
05-17-2010, 11:01 PM
Originally posted by na85:
My finely attuned senses detect hostility.
My somewhat alcohol-dulled senses detect another irrelevant post...
http://www.pointlessinternetargumentforums.com/

ggb123
05-17-2010, 11:06 PM
I know some versions of Pro/E are capable of doing fluide dynamic simulation. it may also allow you to reverse some formulas out from its.


http://www.ptc.com/products/proengineer/


pro e enterprise

AndyJWest
05-17-2010, 11:22 PM
Originally posted by ggb123:
I know some versions of Pro/E are capable of doing fluide dynamic simulation. it may also allow you to reverse some formulas out from its.


http://www.ptc.com/products/proengineer/


pro e enterprise
Yes, thanks, ggb123. I'm not sure this helps a lot though. I'm not really interested in simulating ground effect myself, but in comparing IL-2 GE with 'real-world' GE. What I'd really like to see would be actual data from real tests. Though modern fluid dynamics may model GE with commendable accuracy, I've still got no way to confirm this.

deepo_HP
05-17-2010, 11:37 PM
Originally posted by AndyJWest:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by na85:
My finely attuned senses detect hostility.
My somewhat alcohol-dulled senses detect another irrelevant post...
http://www.pointlessinternetargumentforums.com/ </div></BLOCKQUOTE>then let me add this, so it makes three.

M_Gunz
05-17-2010, 11:38 PM
Originally posted by Kettenhunde:
Divided by zero does not mean the value is infinite as some people mistakenly think.

It means the answer is undefined with an infinite number of answers unless we define it.

All I wrote was 'Ummmmm'? Zero is defined, btw.

X/0 = undefined was the understanding I was given in 4th grade but you look at the curve....
Took until 12th grade before we learned to work with infinities.
Math geeks? More like people who have learned to see as opposed to just look.

Andy, how about throwing in some of the kind of content you want? There is no rule that you can't.
What more you want to say about GE or IL2 or GE in IL2? Something besides "awww guys, cut it out!".

You guys have posited all kinds of things, many beyond the scope of IL2 however real they are.

We including you have been running on interpretations for pages and that's what lead to this:
Is circulation real and how does that affect GE? And there is no consensus.

Find anything new? You want to change the direction then go ahead and LEAD. No one is stopping you!

ggb123
05-18-2010, 12:03 AM
Ah! Question!


Shouldn't you got a bit more Ground Effect when the flape is lowered down? http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Kettenhunde
05-18-2010, 04:30 AM
Though modern fluid dynamics may model GE with commendable accuracy, I've still got no way to confirm this.


I have to ask, just what are looking for? Everyone who tries to help you gets the same answer...it is not good enough.

Yet you are unable to perform any of the data analysis yourself. That is not my fault or anyone else's.

I gave you a method and one that is easy to construct a spreadsheet with that does the analysis. I think you will find the software cost prohibitive but if it does CFD it will work.

Why isn't any analysis tool good enough for IL2 gamer AndyJWest?

AndyJWest
05-18-2010, 05:32 AM
Right, Kettenhunde, let's see the context of that sentence. I wrote this:

I'm not really interested in simulating ground effect myself, but in comparing IL-2 GE with 'real-world' GE. What I'd really like to see would be actual data from real tests. Though modern fluid dynamics may model GE with commendable accuracy, I've still got no way to confirm this.

What part of 'actual data from real tests' don't you understand? Actually, don't bother answering that. I've had enough of your know-it-all posturing. You clearly don't post anything on this forum except with the intention of demonstrating how clever and knowledgeable you are, and how ignorant the rest of us are. And yes, you can call me an 'IL2 gamer', I don't consider it an insult, I'd say that being an IL2 gamer is preferable to being an IL2 game forum troll.

Kettenhunde is on ignore.

M_Gunz
05-18-2010, 08:17 AM
Maybe you could ask Team Daidalos to let you use a copy with the GE code removed and look for differences?

Or... make approaches at fixed power settings and keep those (as opposed to reducing power or shut off) in a
low skim over concrete strips (because they're longer and easier to see) then check the data? On approach you
should be low enough power to not maintain level flight so if you do level out then you know something's up.

AndyJWest
05-18-2010, 09:38 AM
Originally posted by M_Gunz:
Maybe you could ask Team Daidalos to let you use a copy with the GE code removed and look for differences?

Or... make approaches at fixed power settings and keep those (as opposed to reducing power or shut off) in a
low skim over concrete strips (because they're longer and easier to see) then check the data? On approach you
should be low enough power to not maintain level flight so if you do level out then you know something's up.

Viikate has tried the 'GE off' thing, which confirmed that the relevant code was doing something. I know roughly what the code is supposed to do, but not how much effect it is likely to have - I should really try it over a range of speeds and altitudes. AS JtD pointed out some time ago, ( http://forums.ubi.com/eve/foru...283/m/3121062458/p/2 (http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/3121062458/p/2)) the effect seems to work differently at different speeds:

The ground effect appears to give you a some speed advantage, at higher AoA's. I haven't measured it exactly, but in the data from the above test I was eventually using lower throttle setting when I was 2m above the ground then when I was 50m above the ground to maintain the same low speed.
I know from earlier testing (couple of years back) that the top speed at 2m is lower than at 10m, so here you have a disadvantage.

AndyJWest
05-18-2010, 09:50 AM
Originally posted by ggb123:
Ah! Question!


Shouldn't you got a bit more Ground Effect when the flape is lowered down? http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

'Flape'? http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Sorry ggb123, I shouldn't laugh at spelling mistakes and typo's - I make more than enough myself...

Thinking about it, I should probably test in the takeoff and landing configuration - flaps and wheels down - since this is where GE is most likely to be significant anyway. I could make myself an extra-long test runway by combining several FMB 'stationary runways', which will simplify things.

Kettenhunde
05-18-2010, 01:19 PM
I thumbed through the AIAA library for reports on GE. I found 9 that might of interest but that was only in the first 4 pages of over 200 pages of reports.

PM me if you guys want them.

ggb123
05-19-2010, 12:39 AM
Originally posted by AndyJWest:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ggb123:
Ah! Question!


Shouldn't you got a bit more Ground Effect when the flape is lowered down? http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

'Flape'? http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Sorry ggb123, I shouldn't laugh at spelling mistakes and typo's - I make more than enough myself...

Thinking about it, I should probably test in the takeoff and landing configuration - flaps and wheels down - since this is where GE is most likely to be significant anyway. I could make myself an extra-long test runway by combining several FMB 'stationary runways', which will simplify things. </div></BLOCKQUOTE>


I am planning on setting up the aileron flap on my .40 rc plane to see how it does on take off and landing (also under GE). I afraid it would simply just crash for the kind of plane I am using, as far as I know when flap is being use it shifts plane's CG (center of gravirty). when flap is being use (in full down), the plane's CG would move toward the rear, makes it "the" head heavy plane. as the head heavy plane tends to perform a dive, you must use elevator to maintan a level flight. but even the elevator is used, the plane's CG is not without a limit.

ggb123
05-19-2010, 12:49 AM
I really admire Amp (the person that invented/discovered electric current) but I have problem in spelling his name in full. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif Sorry, but that doesn't mean I don't respect him!

M_Gunz
05-19-2010, 01:53 AM
Ampere, same as the full word except the name has accent grave over the first e.
Coulomb, Ohm and Watt are other names you should like too.

ggb123
05-19-2010, 03:23 AM
scientical way of apporach thing, needs more than just Hypothesis, you need data to support it.

Ampere does a great job in backing up his mathematics through restrictly controled environment to accurately demostrate what 1 unit of amp really is. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

I beleive even Coulomb, Ohm and Watt are also important... but the real father is Ampere. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

There is a programe(show) from PBS. tells the stroy of Ampere. a really worth watching peice. http://forums.ubi.com/groupee_common/emoticons/icon_cool.gif

AndyJWest
05-19-2010, 06:49 AM
I am planning on setting up the aileron flap on my .40 rc plane to see how it does on take off and landing (also under GE). I afraid it would simply just crash for the kind of plane I am using, as far as I know when flap is being use it shifts plane's CG (center of gravirty). when flap is being use (in full down), the plane's CG would move toward the rear, makes it "the" head heavy plane. as the head heavy plane tends to perform a dive, you must use elevator to maintan a level flight. but even the elevator is used, the plane's CG is not without a limit.
Lowering flaps on a plane will only have a very minor effect on the centre of gravity, ggb123. The CoG is only defined by the distribution of mass in an object - the effect you are talking about sounds much more like a pitch-up caused by the changed wing aerofoil (possibly affecting airflow over the tailplane). Trying to use ailerons as 'flaps' without having conventional flaps as well is probably a recipe for disaster too - I'd do a bit of research on the subject before you try it. Ground effect will apply to an RC plane in the same way that it will a larger one, but remember it is related to the size of the plane, so you won't get much effect until you are pretty low. If you want advice on this sort of thing, I'd find a RC aircraft forum to ask questions - this is all rather off topic.

I agree with what you say about the need for experiment though:

scientical way of apporach thing, needs more than just Hypothesis, you need data to support it.
A few of the forum regulars would do well to remember this...

M_Gunz
05-19-2010, 06:22 PM
Originally posted by ggb123:
scientical way of apporach thing, needs more than just Hypothesis, you need data to support it.

Ampere does a great job in backing up his mathematics through restrictly controled environment to accurately demostrate what 1 unit of amp really is. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

I beleive even Coulomb, Ohm and Watt are also important... but the real father is Ampere. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

There is a programe(show) from PBS. tells the stroy of Ampere. a really worth watching peice. http://forums.ubi.com/groupee_common/emoticons/icon_cool.gif

You need to watch a good one on Isaac Newton then....

AndyJWest
05-19-2010, 06:53 PM
Just to demonstrate that ground effect isn't an artefact of my autopilot, here's an experiment you can all try. On the Crimea map, select a Ju-88 with 50% fuel, ensure 'wind and turbulence' is off, then fly out low over the sea, slowing until you are almost stalling (about 90% up trim), adjust engine power carefully, so you can drop down to a low altitude. If you are really brave, you can get it to sit in the ground effect like this:
http://i958.photobucket.com/albums/ae65/ajv00987k/il2fb2010-05-1915-18-52-54.jpg
http://i958.photobucket.com/albums/ae65/ajv00987k/il2fb2010-05-1915-19-23-71.jpg
This is at 42% throttle - it will actually just stay airborne on 41%, but the tail is almost in the water. You may have to use slight aileron inputs to keep it straight, but it maintains height on it's own - bobbing up and down over maybe a metre or so.

ggb123
05-19-2010, 10:51 PM
Following the same setting as yours AndyJWest, plus Unlimited Fuel, Radiator position - Closed, Tail Smoke - On


All Pics Shown Max AoA before Stall, Level Flight

1.http://img168.imageshack.us/img168/5687/grab0002.jpg
Engine Power: 40%
Targeted Altitude: Sea Level (closest to ground it could get)


2.http://img411.imageshack.us/img411/8652/grab0008.jpg
Engine Power: 43%
Targeted Altitude: 100M

3.http://img249.imageshack.us/img249/3125/grab0012.jpg
Engine Power: 43%
Targeted Altitude: 500M



Data analyze:

Assuming Ground Effect provides power as "Lg"

Engine Power = Total Drag + Ground Effect power (Lg)

Engine Power figure. 2 - Engine Power figure. 1 = Lg (in assuming figure 2 has completely left the effective range of the ground effect)

While figure 2 and figure 3 have the same among of AoA, Engine Power. Even though TAS are different, they have not effected by Ground Effect

Total Drag = AoA, Airspeed... (it's incomplete, do help me complete it)

AndyJWest
05-19-2010, 11:09 PM
Nice pics, ggb123. http://forums.ubi.com/images/smilies/25.gif

I think I had rads open, which makes a slight difference.

Were you using LesniHu or something similar - You indicate a 'targeted altitude'? I was flying with no AP at all - just trimmed for slow flight, with rudder trim for minimal slip, and minor aileron corrections to keep it straight (this should probably not be needed with a more accurate GE model - it should be self-correcting in roll).

Anyway, it shows that GE is there, though it isn't much use except when you are almost on the deck.

I'll have another go with wheels and flaps down.

deepo_HP
05-19-2010, 11:33 PM
hi andyjwest,

i think, what ggb123 wanted to point out: why do you think, it is ground-effect you have demonstrated?

ggb123
05-19-2010, 11:34 PM
But Please Not So yet!

Look Closer to the figure 1 's AoA reading! it shows lower value than figure 2 and figure 3 to affect induced drag. So, Ground effect do exist but it's not really in a form to provide power. It rather changes plane's AoA... hummm...

someone need to explain that more http://forums.ubi.com/groupee_common/emoticons/icon_rolleyes.gif

ggb123
05-19-2010, 11:40 PM
I want to use the Targeted Altitudes to make a reference chart for furher testing. it is just too hard to flight it in exactly value.

deepo_HP
05-20-2010, 12:07 AM
Originally posted by ggb123:
But Please Not So yet! sorry if i didn't understand...

well, then it is only my question:
why do you think, it is ground-effect you have demonstrated, andyjwest?

AndyJWest
05-20-2010, 12:16 AM
I see what you are getting at, ggb123, now you've edited your posting. Yes, GE isn't doing quite what you'd expect, though it does seem to allow you to maintain height at a lower power setting than you'd otherwise require. This basically confirms that the GE code in IL-2 is flawed, which I had gathered from what I'd been told. More to the point, it shows that this flaw has practical consequences, which wasn't immediately apparent.

I think there is a case for suggesting that TD might look at revising this, as Viikate indicated some time ago. It seems to be a bit more complex than was initially evident though, as my tests with 'wind & turbulence' enabled indicate. A simple request to 'fix ground effect' isn't likely to achieve much in a situation where there are many interacting factors. And realistically it isn't that important a priority compared to some of the issues being addressed by TD in patches. Maybe something to consider for the future...

deepo_HP
05-20-2010, 12:23 AM
Originally posted by deepo_HP:
why do you think, it is ground-effect you have demonstrated, andyjwest?

Originally posted by AndyJWest:
... it does seem to allow you to maintain height at a lower power setting than you'd otherwise require. rgr, missed that i think - sry.

AndyJWest
05-20-2010, 12:36 AM
Yes, sorry, deepo, I'd rather missed the question you were asking. Actually, it is a bit more complex than I'd indicated - you should be able to maintain height over a (small) range of power settings - reducing power results in a lower stable altitude. This is only true over a very limited altitude though.

ggb123
05-27-2010, 01:04 AM
Originally posted by deepo_HP:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ggb123:
But Please Not So yet! sorry if i didn't understand...

well, then it is only my question:
why do you think, it is ground-effect you have demonstrated, andyjwest? </div></BLOCKQUOTE>


Well... from what I been testing from the game. there is quite strong ground effect up to 5 meters, anything higher than that is a bit hard to take notice. I want to say the feel of the effect is quite "linear", without much "exponential" change on the effect with higher AoA.

AndyJWest
05-27-2010, 09:08 AM
If you are testing with 'wind and turbulence' off, that pretty much concurs with what I've found, and with what I expected to find. It has speed-related effects too, and the aircraft size is also relevant.

With 'wind and turbulence' on it all gets more complex, and I suspect this may be of more practical consequence, at least to the online community. Most servers I've flown on have this option selected, as is apparent from the 'bumps' you feel when flying over rivers etc.

WTE_Galway
05-27-2010, 07:13 PM
Originally posted by AndyJWest:
If you are testing with 'wind and turbulence' off, that pretty much concurs with what I've found, and with what I expected to find. It has speed-related effects too, and the aircraft size is also relevant.

With 'wind and turbulence' on it all gets more complex, and I suspect this may be of more practical consequence, at least to the online community. Most servers I've flown on have this option selected, as is apparent from the 'bumps' you feel when flying over rivers etc.

I am having trouble seeing how this effect makes any difference at all to tactics in online combat ? What would you do differently online based on your results ?

AndyJWest
05-27-2010, 08:36 PM
In online combat? Probably any difference would be marginal, though it might under some circumstances (with W & T on) be beneficial if you are forced to try to escape at low level, to get down to 10m rather than 100m for a slight speed increase (lower and you risk hitting the 'true' low level ground effects, which can actually slow you down). It is also worth at least bearing in mind that the 'bumps' you get when crossing from land to water may also affect your pursuer, and hopefully spoil his aim, so following a river bank might theoretically help - this is desperation though really. Otherwise, the minor performance differences caused by terrain are unlikely to be significant. Otherwise, you are more likely to notice the consequences when one would normally expect them to be evident - during takeoff and landing. With or without the effects though, you need to ensure you have excess speed after takeoff before attempting to climb, particularly with a heavy load - but I think most of us know this through experience anyway. Likewise, when landing, it may affect handling slightly, but shouldn't significantly alter your technique - use elevator (preferably by trim) to establish a safe speed, and then use throttle to establish a safe rate of descent.

To sum up, the effects are slight, and they don't require any special tactics, but they are there. Given some of the apparently minor techniques sometimes applied in the sim to improve performance, it is perhaps useful to know that the effects demonstrated are relevant too.

(please bear in mind I'm talking about GE as modelled in IL-2, not the 'real world' - this is more complex, or at least different. IL-2 seems to get parts of it wrong, but at least it has a crack at it)

rfxcasey
06-03-2010, 07:50 AM
http://www.youtube.com/watch?v=IgtaeRZjWNc