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RE: LR1 servos? - 5/16/2008 3:23:40 AM   
Lomcevak Duck



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Status: offline 		It is possible to fly faster than pitch speed, and this has been proven many times. Props are more than just flat plates and prop manufacturers have invested a lot of time in R&D to improve their efficiency. The idea that pitch speed is equal to airspeed is similar to introductory aerodynamics claiming Bernoulli's principle makes a plane fly.

I think bob27 may have some more info on pitch speed vs. true speed if you're interested in previous numbers.

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RE: LR1 servos? - 5/16/2008 4:40:30 AM   
z06kal


 

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From: Woodland Hills, CA, USA
Status: offline 		Bernoulli's principle perfectly explains how wings work and does not contradict circulation theory or any other popularly used aerodynamic theories in text books to explain how lift works. Bernoulli's equations still perfectly calculate lift and explain how lift works and the behavior of objects traveling through fluids. Just because some people have used his models in a very oversimplified form and applied the equal transit time falicy does not mean his work is wrong. Aerodynamicists apply Bernoulli's equations everyday to calculate lift. The fact that you even mention it as being wrong shows your lack of understanding on the subject.

I am very familiar with how propellers work and the types of modified airfoils APC uses. You are talking about 0 angle lift which is not going to fetch you anywhere near the differences we are talking about here. If anything the little bit of 0 angle airfoil lift allows an airframe to fly a little closer to its pitch speed by canceling out some slippage. I have clocked soooo many planes on the Prospeed CR1K. This includes the most streamlined pylon racers like F5D, Q40 etc. I have yet to see any plane fly faster than pitch speed in true straight and level flight. Not a single one. And certainly not a plane as draggy as an LR1 with its is super wide cowl and fuse and for sure nothing like a 30+mph gain.

< Message edited by z06kal -- 5/16/2008 4:42:01 AM >

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RE: LR1 servos? - 5/16/2008 5:03:17 AM   
Lomcevak Duck



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quote:

ORIGINAL: z06kal

Bernoulli's principle perfectly explains how wings work and does not contradict circulation theory or any other popularly used aerodynamic theories in text books to explain how lift works. [snip]Aerodynamicists apply Bernoulli's equations everyday to calculate lift. The fact that you even mention it as being wrong shows your lack of understanding on the subject.


Hold on here friend, I'm not attacking you in the least, just trying to add a bit of relative fact to the conversation. If you'll reread my above post you'll find that I never said Bernoulli's principle was wrong; you interpreted that somehow. It is similar to the pitch-speed calculations in that it is an over simplified approach if that's all you take into consideration when evaluating possible speeds. If you really want to talk aerodynamics we'll talk, but as far as my 'lack of understanding on the subject'... lets leave the insults elsewhere.

< Message edited by Lomcevak Duck -- 5/16/2008 5:04:15 AM >

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RE: LR1 servos? - 5/16/2008 11:16:50 AM   
airraptor


 

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From: fairfield, CA, USA
Status: offline 		here is a good question on LIFT then and Bernoulli lol how can a fully sysmetrical wing fly then?

I think this Z06 guy like to argue anyway. he may have a valid point on my pitch speed stuff and saying it cant go that fast. I just am going off the radar guns at the field. we have some really fast guys here at my club and i have the fastest lr1. all that matteres anyway is that i am having fun flying and trying to help people out here in the forums. i have been flying for over 29 years so i do know alittle bit. If i would have know my mph posting would have caused this ZO6 guy to want to dispute so much i wouldnt have posted it.

my LR1 is very close to some of the other guys who have miss donna's and ashleys with nelson engine's they are a bit faster in the straights but i can out turn them.

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RE: LR1 servos? - 5/16/2008 1:36:28 PM   
Rudeboy



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quote:

ORIGINAL: airraptor

here is a good question on LIFT then and Bernoulli lol how can a fully sysmetrical wing fly then?




Positive angle of attack....

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RE: LR1 servos? - 5/16/2008 2:03:31 PM   
airraptor


 

Posts: 207
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From: fairfield, CA, USA
Status: offline 		lol rude i know that just trying to see what other think . lift by lower pressure, lift my angle of attack , or combo of each at different speeds

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RE: LR1 servos? - 5/16/2008 2:52:09 PM   
Lomcevak Duck



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Status: offline 		Bernoulli's principle is not wrong entirely with regaurd to a wing creating lift, but it is not the only explanation for lift. Also to consider are Newton's third law which can explain a fully symmetrical airfoil creating lift at a positive angle of attack, and the circulation theory that z06 mentioned which is more of a mathematical method of calculating lift than an explanation for why a wing produces lift.

Like I said, explaining lift using Bernoulli's principle is not wrong in and of itself, but neither the equal transit time theory nor the venturi flow theories are 100% correct if that's all you consider. But for most folks, telling them air passes over the top of the wing faster than under it thus 'sucking' the wing up, is explanation enough. Just like a pitch-speed calculation is a neat way to guess at the speed. But neither are the whole story.

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RE: LR1 servos? - 5/16/2008 2:55:21 PM   
Lomcevak Duck



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Status: offline 		It's also important to keep in mind that neither Bernoulli or Newton published any work describing aerodynamic lift. The work of both is usefull in evaluating lift and aerodynamics, but most people don't think about the fact that neither of them ever heard of an airplane.

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RE: LR1 servos? - 5/16/2008 4:23:38 PM   
bob27s



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quote:

ORIGINAL: z06kal

191mph on a 35LX? I'll believe it when I see. This thing would be lucky to hit 165 with a Qm40/Q500 Jett .40. The fuse is very draggy.


The 35LX is sort of a "small" QM40 engine for lack of a better explaination. Although I have not see all that is behind this or the flight, it is not all that too far fetched of everything is set up correctly.

Keep in mind, the ground peak or launch rpm is one thing.... active flight rpm is another.
And as noted, the prop does "Work". Its not just the effect of pitch x rpm. Mike Conner posted a quite long thread describing the effective pitch of a prop. There is also some excellent prop design documentation by supercool that is worth reading

As a brief example, it is know and repeatable that a TT40 powered Q-500, with a 9x6 APC, turning 16,500 ground peak rpm will indeed exceed 120 mph in level flight. Regress the math from this and you will see what I mean.

as an added reference.....
Current QM40 setup, 7.4x8ish prop pushes over 190 corner entry speed on the race course, and can do better than that in extended level flight.

< Message edited by bob27s -- 5/16/2008 4:35:20 PM >


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RE: LR1 servos? - 5/17/2008 2:13:01 AM   
airraptor


 

Posts: 207
Joined: 1/26/2004
From: fairfield, CA, USA
Status: offline 		i havent tried one of the pylon props yet. every one at the club said i need to run an 8" prop to help with corner speed. the smaler ones would be faster top end but slow down to much in the corners.

i have another one in the box and have been thinking of trying a jett .60lx or a Mb/nelson engine

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RE: LR1 servos? - 7/8/2008 7:20:35 AM   
airraptor


 

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Status: offline 		well do you have a flight report for us?

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