Parasite and Induced drag on Su-25/T

[Ironhand]

Andrew, you're cracking me up! :megalol:

 

So, in the end, the -25T isn't as slippery as it seems? Personally, I wish we could throttle back more.

 

Rich

[GGTharos]

Well, captprob said that 'something was wrong' and to be honest, he was quite right.

 

 

While the cause has been identified, well, eh ... :)

I think his instincts win in that he spotted something that wasinexplicably off to him - the drag model on teh 25T is correct, though.

[SwingKid]

So, in the end, the -25T isn't as slippery as it seems? Personally, I wish we could throttle back more.

 

I'm satisified that the AFM Su-25T, with engines off, is about 8% less "slippery" than the miniZAP artillery shell - notwithstanding the comparison against FC's own (artificially "frictionized") bombs.

As long as it satisfies that condition (being less slippery than an artillery shell, instead of more), then I am personally satisfied that the "ballpark" behaviour is approximately reasonable - it's good enough for me.

 

The AFM Su-25T's corrected Cd, as I calculate it now (with engines off), would be:

 

Cd ~= 0.045 (wing planform-referenced)

or

Cd ~= 0.15 (cross-section referenced)

 

The first number puts it in the same ballpark as the other aircraft in the list:

http://www.aerospaceweb.org/question/aerodynamics/q0184.shtml

 

The second number says that the AFM Su-25T is about twice as slippery as a "slippery road car," according to this site:

http://www.insideracingtechnology.com/tech102drag.htm

 

Draw own conclusions.

 

For my part - even if I think the AFM Su-25T may still be a little bit too slippery, I don't think that I will be able to prove a problem mathematically anymore, and my original calculations were still wrong because of idle engine thrust. So, what more can I say? If Yo-yo says the Su-25T airframe is only 8% less slippery than an artillery shell, and a whole 50% less than a road car, what number will I invent? 30%? 50%? 80%? Maybe I would like to see it closer to half-way between the artillery shell and the road car, but that would be just an opinionated guess, no more or less convincing than the current AFM model, even to me.

 

-SK

[SwingKid]

Woah woah woah ... where's the wolf picture? ;)

 

Speaking of pictures - what's in your avatar, a rescue submersible? I've been looking at it for years and never known. :confused:

 

-SK

[Dmut]

Ok - despite how funny that image looks, in order to prevent Yo-yo from exploding, I should admit that that's actually just drama. The problem with that image/trk is not so much with the Su-25T AFM, but rather, the LOMAC bomb flight model is a little bit "tweaked" - LOMAC bombs have helium in them, did you know? ;)

-SK

Exactly. The problem is bomb's FM, which is to be "AFMed" in next project :)

[GGTharos]

Speaking of pictures - what's in your avatar, a rescue submersible? I've been looking at it for years and never known. :confused:

 

-SK

 

It's Macross Zero's F-14 hero pilot looking up through his canopy at a variable flanker about to shoot him down.

[Dmut]

To All: I understand that "your ignorance shocked me" is rather harsh phrase, but two things will excuse Yo-Yo:

a) it's developer-to-tester relations, and Yo-Yo and SK are friends.

b) it's a foreign language issues, when we translate "ignorance" like "not knowing about...".

[Groove]

Could anyone explain to me what is meant by the word "slippery" ?

 

There was a example with cars. I know what this word mean in whole but i cant understand the meaning of a "slippery jet".

 

Thx in addvance !

[Yo-Yo]

Well, then I'm confused. In one message you tell me that I shoulnd't be using cross-section as a reference area, because I should be using wing planform instead.

 

Now you say that in fact AFM doesn't use wing planform, but rather "each element has its own area."

 

Ok, so what is the area used to calculated parasitic drag from the Su-25T main body? And what Cd, does it have?

 

I'm not talking here about the induced drag from the wing, that varies with angle of attack - I'm talking about the parasitic form drag from the aircraft body, that generates zero lift. It seems to have Cd of about 0.05 in Flaming Cliffs, using the body's own cross-sectional area as a reference. Can you show a different calculation?

 

I don't think that we can use the wing planform as a reference for parasitic drag Cd, because the wing planform induced drag changes rapidly with angle of attack, while parasitic body form drag doesn't.

 

-SK

At first I should apologise: I used the word "ignorance" not to hurt you. I mean this word as anthonim for "awareness". I was really surprised that you don't know the standard reference area for the planes. In flight dynamics applications NOBODY and NEVER uses area different from the WING AREA.

Not for helicopters though...

 

In aerodynamics application if you assemble and calculate your future plane from the parts you must calculate each part separately using their own cross-section or planform area.

The main goal is to otain FORCES from each element (at certain dynamic pressure and MAch) and then gather it to ONE FORCE. The AFM does the same. But finally you must reference this FORCE to the dynamic pressure and reference area. This is what we called integral characteristic of a plane - CD, CL.

 

By the way, finally you obtained CD of Su-25 referenced to its cross section as 1/2 of a car. Please take a look at your own picture you posted here - the body and a half-body. Any ideas? :)

[Shepski]

To All: I understand that "your ignorance shocked me" is rather harsh phrase, but two things will excuse Yo-Yo:

a) it's developer-to-tester relations, and Yo-Yo and SK are friends.

b) it's a foreign language issues, when we translate "ignorance" like "not knowing about...".

 

Agreed Dmut...

 

In fact... in the english speaking world, most people think "ignorant" is only an insult and they are really ignorant of it's true meaning... all it takes is a dictionary. :)

[SwingKid]

Exactly. The problem is bomb's FM, which is to be "AFMed" in next project :)

 

It might create a problem, with bomb pipper always falling below the lower limit of the gunsight in Su-25. I thought that was the original reason for putting the "helium" in the LOMAC bombs - to compensate for the reduced Su-25 cockpit downward visibility, and allow the pilot to see the bomb aiming point, that is "floating" higher as a result. Or, it's incorrect?

 

-SK

[SwingKid]

I know what this word mean in whole but i cant understand the meaning of a "slippery jet".

 

"slippery" = streamlined, sleek, slick

 

A "slippery" jet (in our discussion) will be less affected by air resistance. It will glide through air almost without slowing.

 

-SK

[Yo-Yo]

It might create a problem, with bomb pipper always falling below the lower limit of the gunsight in Su-25. I thought that was the original reason for putting the "helium" in the LOMAC bombs - to compensate for the reduced Su-25 cockpit downward visibility, and allow the pilot to see the bomb aiming point, that is "floating" higher as a result. Or, it's incorrect?

 

-SK

 

No, the old bombs was made regardless of pippers, etc. I even don't know what reasons the bomb programmer has... :)

The new bombs (AFMed) already was tested, and I can say that I have no problems dropping them. In both modes. Very interesting business.

 

And the feeling that the virtual bomb flyes exactly as its RL prototype is very amazing. Like the shells in the current beta... :)

[SwingKid]

a) it's developer-to-tester relations, and Yo-Yo and SK are friends.

 

Like family ;)

 

 

-SK

[SwingKid]

In flight dynamics applications NOBODY and NEVER uses area different from the WING AREA.

Not for helicopters though...

 

Not for missiles too.

 

Ok, "nobody," "never.." :rolleyes: - strong words. We're not talking here about StarForce. ;)

 

By the way, finally you obtained CD of Su-25 referenced to its cross section as 1/2 of a car. Please take a look at your own picture you posted here - the body and a half-body. Any ideas? :)

 

I understand your meaning, yes, but I think we should wait until capttrob's ban is finished, maybe he's the only person who needs now to be convinced.

 

The new bombs (AFMed) already was tested, and I can say that I have no problems dropping them. In both modes. Very interesting business.

 

Really, with Su-25? Or Su-25T?

With Su-25, I even have problems to drop the old bombs, in CCIP. :wassat:

 

-SK

[Groove]

"slippery" = streamlined, sleek, slick

 

A "slippery" jet (in our discussion) will be less affected by air resistance. It will glide through air almost without slowing.

 

-SK

 

cool now i understand what this thread was / is all about :D

[Guest IguanaKing]

Agreed Dmut...

 

In fact... in the english speaking world, most people think "ignorant" is only an insult and they are really ignorant of it's true meaning... all it takes is a dictionary. :)

 

But, the point is, in the English-speaking world, the word "ignorant" IS considered to be a derogatory or insulting word. ;) No dictionary can ever provide the psychological/cultural meaning of any word, that's why we have translation errors that may sound like insults to some. The man was banned, however, before this fact was made clear...and if he thought an ED staff member was insulting a paying customer...well, he may have been a little sarcastic about who may or may not be a good company representative with his FighterOps remark. Its a series of misunderstandings, in my view. :smilewink:

[SwingKid]

Yeah, sometimes I think around here, the moderation could use a little moderation.

 

With capttrob unable to reply, I've got no closure! Is he satisifed? Is he sorry? Who knows? It's like after 9/11 - who do you punish, when the terrorists went and killed themselves? (besides Iraq, of course) How come I have to do all the apologizing alone here?!

 

I guess this is the way to punish me, since I would probably enjoy being banned... :)

 

-SK

[Weta43]

He's not a very happy chap - has a big rant in a (now closed) thread over at UBI. Personally I think his behavoiur was worth a PM or a warning, but probably not a banning.

[SwingKid]

He's not a very happy chap - has a big rant in a (now closed) thread over at UBI. Personally I think his behavoiur was worth a PM or a warning, but probably not a banning.

 

He's not happy about the ban, or about the math?

 

Link?

 

-SK

[Weta43]

http://forums.ubi.com/groupee/forums/a/tpc/f/38610606/m/5901033044

[SwingKid]

The nerve!! - he didn't even say a WORD about my mathematics, and whether he thinks he was right or wrong about Su-25T drag!! Just rambling on about female dogs or something now. :mad:

 

Ok thanks, that made me feel better. Let him suffer the judgement of the mods:

 

 

-SK

[Guest IguanaKing]

Well...the guy was not happy about being banned over a misunderstanding/translation problem. The use of the female dog reference was a bit over-the-top, but I think it was used to make a point about the cultural vs. technical meaning of a word. Again, the example was a bit extreme and shouldn't have been applied to any particular person, but the clarifications and apologies came AFTER he was banned and no longer able to say "no worries" or whatever he had to say. If given a chance, he may have even apologized for what he said about Yo-yo that was taken as an insult, since he recognized that Yo-yo had come back to say himself that he meant no harm by his comment.

 

Now, I'm not debating the decision, I'm just sharing my opinion. I think the ban stick was used prematurely here. Just my opinion though. ;)

[Groove]

I was recently one of them. Its rare you come across a thread over there where you dont see someone banned.

 

Sorry but he is telling BS.

[Guest IguanaKing]

Yeah...it was an exagerration. I don't think the post was meant to be scientific, but it does illustrate the tendancy toward overreaction here. ;)

 

OK...and now for something completely different. :D

 

Parasitic Drag- A guy who bums an XC ride from you and then complains because your machine isn't as fast as Charlie's.