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XyZspineZyX
10-13-2003, 06:34 AM
So I'm flying the planes in this game and I wonder how to properly control prop pitch. I've read on mud movers for example the faster you go the lower the pitch so that you can maintain your speed. I'd understand this if we actually controlled the propellers angle, but what we control (in my theory) is really the RPMs, the propeller will change its angle to keep that RPM on its own. Is mud movers saying the prop will have a lower angle to the air so it has less RPMs, but this will actually make the a/c fly faster than a higher RPM which might be at a higher angle thus causing more drag and in theory slow the plane so its not as fast as the a/c with lower RPM? Wouldn't teh high RPM require a lesser angle so the blades can move faster?

So I have some questions:

1) How do you overspeed the prop? I watch rpm meter and its stable as a rock in a screaming dive with 100% pitch in P-47 at 850 kph.

2) Can we overboost the engine?

3) How should we control the aircraft? With throttle control mainly, adjusting prop pitch for flying conditions (climb, cruize, combat)?

4) What a/c don't have a propeller that changes the pitch on its own to correllate with the RPM?

XyZspineZyX
10-13-2003, 06:34 AM
So I'm flying the planes in this game and I wonder how to properly control prop pitch. I've read on mud movers for example the faster you go the lower the pitch so that you can maintain your speed. I'd understand this if we actually controlled the propellers angle, but what we control (in my theory) is really the RPMs, the propeller will change its angle to keep that RPM on its own. Is mud movers saying the prop will have a lower angle to the air so it has less RPMs, but this will actually make the a/c fly faster than a higher RPM which might be at a higher angle thus causing more drag and in theory slow the plane so its not as fast as the a/c with lower RPM? Wouldn't teh high RPM require a lesser angle so the blades can move faster?

So I have some questions:

1) How do you overspeed the prop? I watch rpm meter and its stable as a rock in a screaming dive with 100% pitch in P-47 at 850 kph.

2) Can we overboost the engine?

3) How should we control the aircraft? With throttle control mainly, adjusting prop pitch for flying conditions (climb, cruize, combat)?

4) What a/c don't have a propeller that changes the pitch on its own to correllate with the RPM?

XyZspineZyX
10-13-2003, 06:46 AM
Try it in a Dive in a 109k4 in a dive @ 800 with 100 PP LOL

then youll get the Idea.

its kinda complex but theres lots of old threds here about it just search this forum for Prop Pitch

<CENTER> http://www.onpoi.net/ah/pics/users/ah_109_1065290873.jpg </center>

XyZspineZyX
10-13-2003, 09:18 AM
What it basically is the engine has a certain RPM where it put's out most of it's power. You produce less power when you over rev the engine, and less when the rpm's drop.

So the purpose of propellor pitch is to keep the engine at the same rpm's. Which in doing so will increase it's overall performance.

Example at 100% pitch the engine begins accelerating the aircraft. You eventually reach a terminal speed however nosing over will cause you to gain speed. Yet the engine rpm's will increase. So you pitch down to bring the rpm's back into the "power band" of the engine. Now if you level out it will hold the new speed depending on the aircraft.
You can keep doing it to a point where the aircraft will have reached it's maximum level speed it can maintain.
However it's higher than the level speed had you not used CEM or been using a fixed pitch propellor.

A good example is you can use the prop pitch in a dive with a 109 and when you level out at the bottom at around 700km/h you can actually maintain that airspeed for a good while. Although it slowly begins to drop back down.

Which is why in game except for a couple of allied aircraft nothing can catch a 109 if he decides to dive away, and run.
Even if that aircraft is normally faster than the 109. Simply because most of them cannot dive as fast as the 109 or simply not as aerodynamic, and able to hold the airspeed once they level out.

Every take-off is optional, but every landing is mandatory!

XyZspineZyX
10-13-2003, 09:38 AM
Hopperfly22 wrote:
- What it basically is the engine has a certain RPM
- where it put's out most of it's power. You produce
- less power when you over rev the engine, and less
- when the rpm's drop.
-
Actually it produces more power when you over rev the engine, only that the engine blows up this way.

Honestly, a search on Prop Pitch will help.

XyZspineZyX
10-13-2003, 09:54 AM
If the RPM remains constant despite pitch and power changes then you are flying behind a constant speed prop. In that case there is a prop governor that will automatically change the blade angle to maintain whatever RPM you selected, hence the name "constant Speed". To be honest though I haven't found this to be the case in FB, even in the aircraft that had constant speed props a power change results in an RPM change. (which it should't in an aircraft that actually has a constant speed prop). Some aircraft modeled in the sim simply had an adjustable blade angle that did not maintain RPM, but the pilot could attempt to maintain a certain RPM by frequent adjustments of the RPM/Prop lever (this is the way the 109s, and most of the aircraft work in this sim)
EDIT: as far as how to set things for various aspects of flight, this will depend on which aircraft you are talking about. I deally you want to have the maximum thrust available at all times, without harming your engine. This means having the maximal RPM that allows your engine to run continuously, and at the speed that you are flying, this is an over simplification of course, but that is the basic objective. An aircraft with a constant speed prop is a wonderful thing for a dogfight because you simply adjust the RPM to the combat setting, and leave it alone. This RPM will be a bit higher than the cruise and descent setting, and about the same as your climb setting. In a non combat cruise/descent situation the minimal engine speed that allows you to maintin flight speed is the goal,
though you do not want to use a high power setting an really low RPM as this stresses the engine as well.

S!
TX-EcoDragon
Black 1

Reserve Pilot Aircraft #2 of Gruppo 313
Pattuglia Acrobatica Virtuale
http://www.pav-amvi.it

http://www.calaggieflyers.com/

Message Edited on 10/13/0301:01AM by TX-EcoDragon

XyZspineZyX
10-13-2003, 10:44 AM
That's not true at all.

Two good examples are my Ninja EX500 and my father's Harley Davidson.

My Ninja hits it's power band (where it puts out it's max torque) at 6500 rpm's. From there it's torque begins to fall off while it's HP increases. However at redline or 11,000 rpms it's putting out less torque than at 6500-8000rpm.

Horsepower doesn't really matter anyway torque is what counts.

Now my father's Harley with a 1200cc V-twin put's out 100% of it's Torque at around 2500rpm. From there it begins to fall off all the way up to 5000rpms redline.

However just like in cars, and bikes, the airplane propellors tip speed is what makes it either fast or slow. So long as it's thrust is able to overcome the drag of the aircraft.

However unlike ground vehicles aircraft lack flywheels so for them Torque is really important. Which is why low torque high horsepower engines such as Rotax engines require a reduction drive, and high torque low hp engines like a VW (yes they use them in aircraft) do not.

So while overreving an aircraft engine may increase it's speed it doesn't mean it's generating more torque or horsepower. It simply means it's either reached it's maximum pitch speed, or has not reached the point where it's thrust no longer can overcome the drag on the airframe.

Which is why using prop pitch to keep the engine at it's optimal RPM's will allow a 109 to tear it's wings off in even a shallow dive. However you typically reach a point where the engine is no longer able to overcome the drag on the propellor.

Yet it's almost impossible to describe anything pertaining to the physics of flight in a simple and understandable manner without being off on something else.

Hence the old saying "A little knowledge is a dangerous thing."

I also don't need to look anything up as I've flown both fixed pitch, and adjustable pitch aircraft.

Every take-off is optional, but every landing is mandatory!

XyZspineZyX
10-13-2003, 11:37 AM
Hopperfly22 wrote:
- That's not true at all.
-
- Two good examples are my Ninja EX500 and my father's
- Harley Davidson.
-
- My Ninja hits it's power band (where it puts out
- it's max torque) at 6500 rpm's. From there it's
- torque begins to fall off while it's HP increases.
- However at redline or 11,000 rpms it's putting out
- less torque than at 6500-8000rpm.
-
That's what I was saying: power (call it HP if you like, but power is the proper name while HP is the unit for it) increases with rpm. I didn't say about torque anywhere.

- Horsepower doesn't really matter anyway torque is
- what counts.
-
Generally, HP=rpm*torque (as "power = angular_velocity * torque", put in the necessary unit conversions yourself), so for a given rpm talking torque is really talking horsepower (and vice versa).

- Now my father's Harley with a 1200cc V-twin put's
- out 100% of it's Torque at around 2500rpm. From
- there it begins to fall off all the way up to
- 5000rpms redline.
-
Does the Harley reach its max speed at max Power or max Torque?

- However unlike ground vehicles aircraft lack
- flywheels so for them Torque is really important.
- Which is why low torque high horsepower engines such
- as Rotax engines require a reduction drive, and high
- torque low hp engines like a VW (yes they use them
- in aircraft) do not.
-
At a steady rpm, a flywheel has zero effect on torque or power. Steady rpm is what we're talking about: steady at 2800 or 3000 creates more torque or horsepower...

- So while overreving an aircraft engine may increase
- it's speed it doesn't mean it's generating more
- torque or horsepower. It simply means it's either
- reached it's maximum pitch speed, or has not reached
- the point where it's thrust no longer can overcome
- the drag on the airframe.
-
It does mean it's generating more horsepower. Go check.

- Which is why using prop pitch to keep the engine at
- it's optimal RPM's will allow a 109 to tear it's
- wings off in even a shallow dive. However you
- typically reach a point where the engine is no
- longer able to overcome the drag on the propellor.
-
- Yet it's almost impossible to describe anything
- pertaining to the physics of flight in a simple and
- understandable manner without being off on something
- else.
-
- Hence the old saying "A little knowledge is a
- dangerous thing."
-
- I also don't need to look anything up as I've flown
- both fixed pitch, and adjustable pitch aircraft.
-
You need some literature on physics.

- Every take-off is optional, but every landing is
- mandatory!
Well said.

XyZspineZyX
10-13-2003, 11:52 AM
TX-EcoDragon wrote:
- "constant Speed". To be honest though I haven't
- found this to be the case in FB, even in the
- aircraft that had constant speed props a power
- change results in an RPM change. (which it should't
- in an aircraft that actually has a constant speed
- prop).
The prop governer needs time to respond to a sudden RPM change. Give it a few seconds and the RPM should (as does in FB) return to the set value.

Some aircraft modeled in the sim simply had
- but the pilot could attempt to maintain a certain
- RPM by frequent adjustments of the RPM/Prop lever
- (this is the way the 109s, and most of the aircraft
- work in this sim)
I'd say the prop pitch lever "is like" glued to the throttle lever in the 109. The 109 really has a constant speed prop system. It can be verified by doing a constant throttle zoom climb. As the speed goes down, RPM remains fairly constant at all times.

But why does RPM go down when throttle goes down? It seems to me that the prop governer is set at a lower RPM when at lower throttle, hence I say the pitch lever "is like" glued to the throttle lever.

Feel free to share any insights.

XyZspineZyX
10-13-2003, 01:05 PM
Aircraft engines differ from car engines in that they are designed to deliver max hp and max torque at the same RPM. Thus, beyond that RPM both drop off.

Yes, the RPM control was linked to the throttle in the Bf109s.

Cheers,
Fred

Message Edited on 10/13/0312:07PM by effte

XyZspineZyX
10-13-2003, 01:20 PM
Automotive analogies are really a poor tool here. Why?
Because the drive wheels are DIRECTLY coupled to the road. An aircraft is operating in a fluid. (air) So any "gear" analogies dont work.

A closer approximation would be the different props used on speedboats.

And no, land vehicles don't hit their top speed at their torque peak. Operating at the torque peak will give the most efficient operation in terms of fuel mileage. Hence the tall top gears on economy cars, and the short top gears on performance cars.

<center><FONT color="red">[b]BlitzPig_EL</FONT>[B]<CENTER> http://old.jccc.net/~droberts/p40/images/p40home.gif
</img>.
"All men dream, but not equally. Those who dream by night in the dusty recesses of their minds, wake in the day that it was vanity:
but the dreamers of the day are dangerous men, for they may act on their dreams with open eyes, to make them possible. "
--T.E. Lawrence

XyZspineZyX
10-13-2003, 01:29 PM
Lol my ex yamaha fzr 600 beats the shiate of your dads HD.
And when i get Aprilia RSV Mile it will beat the shaite times two.
/i/smilies/16x16_smiley-very-happy.gif

XyZspineZyX
10-13-2003, 02:15 PM
ElAurens wrote:
- And no, land vehicles don't hit their top speed at
- their torque peak. Operating at the torque peak
- will give the most efficient operation in terms of
- fuel mileage. Hence the tall top gears on economy
- cars, and the short top gears on performance cars.

Thanks for the nice lead in to why we have variable RPM on aircraft to begin with: Lower RPM means better fuel economy, while higher RPM means more power within the torque limitations set by engine and propeller assembly.

Cheers,
Fred

"If we are an arrogant nation, they will resent us. If we are a humble nation, but strong, they will welcome us."
- George W. Bush, during his campaign. No comment.

(Quote brought back by popular demand - RBJ missed it so much he mailed me about it)

XyZspineZyX
10-13-2003, 02:25 PM
VK_Dim wrote:
- Lol my ex yamaha fzr 600 beats the shiate of your
- And when i get Aprilia RSV Mile it will beat the
- shaite times two.

Yeah, but the majority of people will agree: his dad is much cooler than you.

<font face="Courier New">

â â â â â â _____ | _____
â â â â â â â _\__(o)__/_
â â â â â â â â â â ./ \.

</font>

XyZspineZyX
10-13-2003, 05:38 PM
The words "Harley Davidson" and "performance" are mutually exclusive.

/i/smilies/16x16_smiley-very-happy.gif

<center><FONT color="red">[b]BlitzPig_EL</FONT>[B]<CENTER> http://old.jccc.net/~droberts/p40/images/p40home.gif
</img>.
"All men dream, but not equally. Those who dream by night in the dusty recesses of their minds, wake in the day that it was vanity:
but the dreamers of the day are dangerous men, for they may act on their dreams with open eyes, to make them possible. "
--T.E. Lawrence

XyZspineZyX
10-13-2003, 07:09 PM
To answer your questions directly (good explanations above by Effte and Ecodragon), I will assume you are refering to Cosntant Speed Props (not Bf109's or TB-3).

1: Constant Speed Prop (P47, FW190, La etc) will not overspeed in FB, this is not actually realistic. Over-rev should occur in very high speed dives when the props hit their physical adjustment limits, when they are no longer able to 'coursen'. Currently this isn't modeled.

2: Manifold pressure is a very complex system, it is currently incorrect in FB, though it is on the list to be fixed, it is likely impossible to model all of its 'quirks' but expect the next addon/patch to have a better system model (imho)

3: This is a complex one, and dificult to give a general answer, but, generally speaking, use both throttle (manifold pressure) and prop governor (engine RPM).

4: The TB-3 (bomber), which uses a fixed prop (1 blade angle), and the Bf-109 series (in FB 'Manual Mode') which uses a pilot adjustable variable pitch prop ('auto mode' uses some sort of apparatus, retrofitted to the Bf-109e, that adjusts prop pitch automatically for current flight regime). American aircraft, most Russian aircraft (debatable), and the FW190 use a constant speed prop (similar/same as modern aircraft). The FW190 also has an 'auto' system (historically known as Kommandergerat) that conrols/links manifold pressure and engine RPM.

IMHO Mudmovers is incorrect in saying that 'lower rpm' increase speed (if they actually say this, I haven't read the article). This is not realistic, and it is debatable whether it holds true in FB (it may have in Il-2, again debatable). Aircraft engines produce maximum power (or thrust, or horsepower) at their 'max' RPM, and thus their maximum speed (this holds only for constant speed props, fixed props may be a different story). In the Bf-109, using manual control, the pilot (as opposed to the constant speed governor device) controls the prop pitch to maintain maximum engine power at a give flight regime (speed).

Buzz_25th
10-13-2003, 07:21 PM
Since nbody seems to have said it yet.

Just leave the P-47 prop pitch on 100% for the best performance. All constant speed props work best this way in FB.

------------------------------------------------------------------------------------------
25th_Buzz
<center>
http://www.elknet.pl/acestory/foto1/anderson3.jpg

XyZspineZyX
10-13-2003, 10:05 PM
Questions on the 109 series in manual mode:

1) Does the variable pitch prop have the "trim cheat" handicap enforced on it? (# seconds to go from 100% to 0%)?

2) Do you use the RPM meter in congunction with prop manipulation to hold a RPM for best speed, or with the onset of higher speed lower the RPM for "less drag"?

3) How many seconds will the 109 hold 700 kph?

And finally, a question on you rig, what is the best stable HOTAS system? I have a X-45 but its very twitchy and it is impossible for me to hold level flight (I always have to correct one way or the other), even if theres no wind.

P.S. Someone posted the mudmovers on another CEM thread and I read it Fri and it just didn't sound right because I have a vague grasp of constant speed, variable pitch, and fixed pitch systems (just forgot the jargon when I posted originally).

XyZspineZyX
10-14-2003, 01:11 AM
Actually, aircraft generally do make max thrust right around redline rpm, and keep in mind that unlike the vehicles which you mentioned, this is usually around 2,500 to 3,000 instead of 6,000-11,000 for sports cars and bikes (which typically make their best power at some value less than redline). And tipspeed has nothing to do with speed of the aircraft. In fact, accelerating to around Mach 1 at the blade tips will decrease performance quite significantly. Tipspeed will be dependant on blade length and RPM, add more blades=lower tipspeed=more efficiency=less noise=more thrust with most props. The torque of the engine coupled with blade angle is what determines the flying speed. RPM is also not an indicator of engine output in an aircraft equipped with a constant speed prop in the same way as it is in ground based vehicles, Manifold pressure is the power indicator. The RPM is used to maintain the optimum flat blade angle where low speed climb thrust is needed, or high speed thrust at cruise, or a drag decrease (or increase) in dives. Once the aircraft accelerates the aircraft speed will be limited by the distance that the blade tips move/revolution, and you will need to increase pitch to increase speed. Otherwise, the only real reason for this control is to decrease fuel consumption, engine heat and wear, oil consumption, and noise particularly at cruise where flying speed is high enough that power would need to be reduced to prevent engine overspeed damage, and super critical prop tips in a fixed pitch aircraft.

Generally there is no real need to fuss with the prop in any allied aircraft, leave it 100% and it doesn't seem to be any problem. This benefit is there, but the performance benefit of a constant speed prop is also not there. For now I just hope that these systems are reworked and made more true to form. . . then this discussion will be more worth while. The 109 would be pretty mean if you could dial in an RPM, and that would be held constant as you manevuered and made power adjustments as happens in real constant speed prop equipped aircraft.

The P-47 does seem to make a poor attempt at modeling this, though RPMs do vary around +/-300 with attidue and power changes. (though there is no apparent problem just leaving it at 100% in the US aircraft so who cares, I just pretend it works!)

S!
TX-EcoDragon
Black 1

Reserve Pilot Aircraft #2 of Gruppo 313
Pattuglia Acrobatica Virtuale
http://www.pav-amvi.it

http://www.calaggieflyers.com/

Message Edited on 10/13/0304:29PM by TX-EcoDragon

XyZspineZyX
10-14-2003, 05:22 AM
Bump

XyZspineZyX
10-14-2003, 06:21 AM
1. Are the RPMs listed (combat, cruize, econ.) in the FB advanced manual pdf correct?

I just flew a 190D9 late with manual prop pitch and the thing is a whole different bird! Where scissors use to suck and stall, now it whips back and forth with E to spare! My god, now I can fight in the verticle!

XyZspineZyX
10-14-2003, 09:42 AM
When I reffering to tip speed I wasn't talking about the velocity of the blade tip, but rather the efflux of the air from the tip.

Higher RPM's or more pitch will create a higher efflux. A good example is this...

Just a random example to give you an idea the figure are not correct. If a prop turns 3,000rpm's, and say has a blade pitch of 4 degree's lets say it generate's 100lbs of thrust, and an efflux velocity of 80mph.

Now if we simply increase the RPM's we'd see an increase in both thrust and efflux velocity. Yet if we maintain the same rpm's, and increase the props pitch. We'll see the same increase in thrust and efflux velocity without over revving the engine. Although the engine will still be working harder to maintain it's rpm's due to increased drag, and disk compression.

So point in being why over rev and engine if you can simply increase the pitch?

Also unlike turbines when it comes to in-flight airspeed. The above prop on an aircraft at 40mph will not be producing 100lbs of thrust. It's thrust will have dropped relative to the airspeed and will continue to do so until a speed has been reached where it's available thrust is not longer able to overcome the drag of the aircraft.

Why because it's in-flight thrust which is directly related to it's pitch speed or efflux velocity has dropped off substantially.
So we increase the pitch which increases the efflux velocity of the air being pushed by the prop, and allows it to further accelerate the aircraft. Much like shifting gears in a car.

Simply because even if a prop was producing 10,000lbs of thrust with an efflux velocity of 100mph. 100mph air pushing against 100mph air = 0 lbs of thrust.

So the simple purpose of an adjustable pitch prop or a automatically adjusting prop. Is too allow the engine to run at optimal rpm's (which is near redline on most aircraft as well as just about all high performance engines) while providing it with a larger flight envelope.

Which allows an aircraft to accelerate well, climb well, and have a higher speed. There are also points on the spectrum where a prop is stalled in flight, and on the ground.

Hop in the cockpit, and set pitch to 75% and see how well she gets up off the runway. She probably won't at all.

So anyway all this said and done.

If you can over rev your engine you are gaining no advantage over simply changing the pitch. Your simply hurting your engine. The prop pitch has reached a point where it's efflux velocity is not enough higher than the aircrafts airspeed. So the load on the prop or disk as some call it has decreased allowing the engine to further accelerate. Which will increase the props efflux velocity, but you'd have to really overspeed your engine to any definite improvement.

Every take-off is optional, but every landing is mandatory!

XyZspineZyX
10-14-2003, 10:04 AM
Yes. . . I remember the old days, back when I was stuck flying 1PG (who I just called miss piggy) or the other fixed pitch aircraft that new pilots spend most of their time it. With that fixed pitch prop I was always pulling power back to keep out of redline (unless I was over 8,000 MSL), and a major change in RPM did little to increase speed because of that climb optimized prop was pulling as much air as it could, the engine making tons of power, tons of heat, and tons of noise, with most of its power being lost as heat, and not thrust. . . being able to select the proper blade angle is nice, but even nicer than that, is not bothering to adjust blade angle, but rather adjusting RPM, and letting the prop governor do the adjusting to whatever extent is needed to maintain that RPM.

I have heard that the 109 didn't have a true constant speed prop. . . and if that is in fact correct, then my complaints about it's modeling may be in error at least with respect to the 109. (the way that it is done in the aircraft that do have constant speed props is not perfect, but its much better than the 109) If the pilot could manually select an RPM for the automatic prop control that would basically be the same as having a constant speed prop. . . and would make the current game version of the 109 a far more capable aircraft than it is. Getting the ebst power out of it requires fixation on the tachometer, which you can't do in a dogfight. . . so you must use your ear, and keep a buffer zone of RPM so that you don't fry the engine. . . all it takes is one slip up and then your toast.

S!
TX-EcoDragon
Black 1

Reserve Pilot Aircraft #2 of Gruppo 313
Pattuglia Acrobatica Virtuale
http://www.pav-amvi.it

http://www.calaggieflyers.com/

Message Edited on 10/14/0311:59AM by TX-EcoDragon

XyZspineZyX
10-14-2003, 11:16 AM
Sorry, someone mentioned an article on CEM/prop pitch on Mudmovers.com. i seem unable to find it. Can you post the exact link? Ty.

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XyZspineZyX
10-14-2003, 09:11 PM
Howdy

I can't help you there Abraxa, but here is a little one I threw together a while back.

S!
TX-EcoDragon
Black 1

Reserve Pilot Aircraft #2 of Gruppo 313
Pattuglia Acrobatica Virtuale
http://www.pav-amvi.it

http://www.calaggieflyers.com/

Message Edited on 10/14/0312:12PM by TX-EcoDragon

XyZspineZyX
10-14-2003, 09:38 PM
http://www.mudmovers.com/Sims/FB/fb_cem.htm

I have more questions:

1) What type of pitch control does the 190D employ?

2) Of the mentioned bugs in here and those not mentioned, is CEM going to get patched in the upcoming updates? Any mention of specific a/c?

XyZspineZyX
10-15-2003, 07:53 AM
Ty Elfunko /i/smilies/16x16_smiley-happy.gif
S! Ecodragon my friend, I'm always happy to meet you. Long time since we don't fly together. I always appreciated your skills and gentleman style since il2 days /i/smilies/16x16_smiley-wink.gif . Hope we will meet soon.

Cheers

<FONT COLOR="yellow">BBB_ABRAXA</FONT>

<center>http://ourworld.cs.com/Abra772/mc205_3.jpeg </center>

<marquee> <FONT COLOR="red"> Si vis pacem, para bellum</FONT></marquee>