RE: PATRIOT AT 170 MPH !!!!!!!  
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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 1:28:38 AM   
LGM Graphix



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Status: offline 		Ed, I beg to differ, the mathematical speed from RPM and pitch does not take into account the lift (in this case forward motion) generated by the airfoil on the prop.

I posted this quite a while back from MAAC magazine, for the same reason our airplanes fly with an airfoil it stands to reason that the airfoil of the prop creating "lift" will propel an airplane faster than the mathematical speed.

http://www.rcuniverse.com/forum/m_3028682/anchors_3028682/mpage_1/key_theoretical%252Cspeed/anchor/tm.htm#3028682

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 1:37:24 AM   
freakingfast


 

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Status: offline 		The math says 22600 rpm true pitch(8" ) with a zero drag plane to do 170 mph. However the prop is a lifting airfloil so add about 2 degrees there and there's a bunch of drag on the plane so take some speed there. So off the top of my head best GUESS, I don't think the engine needed to go much over 20,000 to do it. Not an unrealistic number.

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 1:41:48 AM   
SpeedBoy



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quote:

ORIGINAL: Ed Smith
To reach the speed you mention with an 8" pitch prop the rpm would have to be approximately 24,000.

Ed S



WRONG !!!!!!

I don`t know too , but remember rpm is not all , many factors are involved to obtain the result .

One fact is an eagle2 plane , with 16,000 rpm 10x7 and another is a magnum with the same prop and the same rpm , I can assure to you that the difference of speeds would be infinite . That is a fact .

< Message edited by SpeedBoy -- 12/23/2007 1:44:03 AM >

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 1:45:31 AM   
Mike Connor



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Status: offline 		Gravity is another thing not considered by the pitch rpm formula. This speed was achieved by diving.

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 2:11:02 AM   
Flyboy Dave



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Status: offline 		....the prop creates a certain amount of thrust. In a dive the speed of the plane will reach
the theoretical top speed of the rpm/pitch calculation very quicky. According to this "calculation",
the plane cannot exceed this speed. However when this theoritical top speed is reached, the
thrust of the prop begins to offset the drag of the airframe because the plane is in a dive.

When you take away the drag of the airframe the speed can be increased past the theoretical
maximum rpm/pitch calculation because good ol' gravity comes into play.

Look at some of those gliders that fly on gravity alone....the ones that "slope soar"in a circle
....they go over 200 with zero thrust.

FBD.

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 2:22:17 AM   
combatpigg



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Status: online 		This thread has proven to be most interesting. It has pointed out that even if you think you already know it all, there are always new lessons that can be learned. I don't think Hector and Mike Conners teamed up in advance to create a hoax here . This thread has turned out to be a great sales pitch for the Patriot and Rossi .53.......I think Hector has done a super job to get the most out of this combo. What a great set up for club racing!

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 6:47:19 AM   
HighPlains


 

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Status: online 		Great video Speedboy, it did appear that each time the dive got steeper and steeper from watching the angle the radar was held during each approach. Have you got a radar speed without a dive? I'm estimating that you would see around 135 mph, but an actual number would be useful in figuring out how much power is from the engine, and how much from gravity. Would also need the actual weight of the aircraft too.

Your flying site has a great background looking at the mountains in the distance.

I believe my analysis on post 14 holds up.

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 7:01:57 AM   
SpeedBoy



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quote:

ORIGINAL: combatpigg

This thread has proven to be most interesting. It has pointed out that even if you think you already know it all, there are always new lessons that can be learned. I don't think Hector and Mike Conners teamed up in advance to create a hoax here . This thread has turned out to be a great sales pitch for the Patriot and Rossi .53.......I think Hector has done a super job to get the most out of this combo. What a great set up for club racing!


Thank you combatpigg again !!!!

And I do not have commission for that jejeje

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 7:33:21 AM   
SpeedBoy



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quote:

ORIGINAL: HighPlains

Great video Speedboy, it did appear that each time the dive got steeper and steeper from watching the angle the radar was held during each approach. Have you got a radar speed without a dive? I'm estimating that you would see around 135 mph, but an actual number would be useful in figuring out how much power is from the engine, and how much from gravity. Would also need the actual weight of the aircraft too.

Your flying site has a great background looking at the mountains in the distance.

I believe my analysis on post 14 holds up.



You right !!!!!!! the more recent result without a dive and against the wind is at 215 kmh (133mph)

Unfortunately I do not have the real weight of the airplane, yet ...... but I promise I´ll do and posted


HighPlains I believe in your analysis too and tank you for explanation , it was better of I which had been able it to explain .

Thank you again !

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 8:50:43 AM   
vasek



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quote:

ORIGINAL: SpeedBoy

If one day I want less drag, I apply wax of car all to my airplane , this it is another extra work, but it is worth the trouble , it works very well to my



Hector, as strange as it may seem, waxing the plane will only increase the drag. It is a well known phenomenon that a "slightly" rough surface will generate less drag than a polished one. It has to do with a "protective" air layer trapped on top of the surface THUS making the layer of air molecules sort of a ball bearing effect to the rest of the air flow. I am not an expert, but wanted to wax my plane also and found out this principle through the forums here. Do a search.

I now believe that slightly sanding your wings with a 100 grit sandpaper would have a better effect than polishing or waxing

Cheers, Vasek

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 1:52:22 PM   
Ed Smith


 

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quote:

Ed, I beg to differ, the mathematical speed from RPM and pitch does not take into account the lift (in this case forward motion) generated by the airfoil on the prop.

I posted this quite a while back from MAAC magazine, for the same reason our airplanes fly with an airfoil it stands to reason that the airfoil of the prop creating "lift" will propel an airplane faster than the mathematical speed.


LGM Graphix,

Not so. How one calculates lift and in what units I do not know. As I am sure you are aware the lift, in whatever units, generated by an airfoil is different for different airspeeds. At 2mph will an airplane get off the ground? Gliders lose airspeed and sink to the ground. An engine at idle will not move the airplane along. The weight and drag of the airplane overcomes the forward lift of the prop. This same wieght and drag will also hamper top speed. When using the mathmatical formula certain figures have to be accepted. The pitch of the prop has to be exactly that specified at any rpm, knowing full well that assumption will give optimistic results at certain rpm.

For those of us that commonly fly at the speed claimed here, 170mph is no great achievement. The past 30 years of my Pylon Racing has been a 30 year search for more speed. In the later years the claimed speed here is quite common on a Pylon Racing course. I have also found that the mathmatical formula I used is not that far removed from reality. The comments I offer are based on many years of actually doing it, comparing notes with other "Doers" and comparing theory with reality at the speeds we commonly fly at.

Ed S

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 3:31:03 PM   
Mike Connor



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quote:

ORIGINAL: Ed Smith
I have also found that the mathmatical formula I used is not that far removed from reality. Ed S

The fact that the formula can be anywhere close to the actual speed of an aircraft at 170 is proof the airplane is outrunning the pitch/rpm formula. The tremendous drag at those speeds, if your theory was correct, would produce a much much slower speed.

The interesting part of LGM Graphix example is that the slower you are going the more you are out running the formula. This shows how much influence that drag has. If it was possible to get rid of drag I suspect the aircraft speed would be about 1.5 times the formula speed.

Over and over I see evidence that speed is much more complicated then a simple formula. Seeing is believing and I believe I see.

< Message edited by Mike Connor -- 12/23/2007 3:36:49 PM >

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 4:52:42 PM   
Ed Smith


 

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quote:

Over and over I see evidence that speed is much more complicated then a simple formula. Seeing is believing and I believe I see.


I agree with that.

The theory is not mine. I would guess it has been around since the birth of aviation. I offer the following. Our current Q40 Pylon Racers fly at or near the speed claimed here regularly. They fly on a closed course with turns. For most the course pattern flown is kind of egg shaped. One lap is 1/4 mile. The airplanes weigh 4# and are powered by a racing .40 engine turning an APC 7.4 x 8.0 prop at around 25K. Those are the facts.

Do the calculation and see if the result is acceptably close to theory taking into account drag, prop slippage, etc, etc.

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 5:46:09 PM   
combatpigg



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Status: online 		"for those of us that commonly fly at the speed claimed here, 170mph is no great achievement".


Why does there always have to be "one"?

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RE: PATRIOT AT 170 MPH !!!!!!! - 12/23/2007 5:55:02 PM   
Ed Smith


 

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