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Search: Posts Made By: NJSwede
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02-15-2011, 02:19 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Yes, and add to that the fact that the power...

Yes, and add to that the fact that the power system on such a fast bird is probably capable of letting you fly the plane straight up at a fairly good clip. So the thrust generated by the prop is a...
02-13-2011, 06:15 PM
Replies: 160
Views: 27,728
Posted By NJSwede

You just told me everything I needed to know....

You just told me everything I needed to know. Instead of admitting that you're wrong you're throwing mumbo-jumbo around and treat others as if they were idiots. Let's just stop this before gets ugly....
02-13-2011, 04:27 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Since I'm a nice guy and just got back church...

Since I'm a nice guy and just got back church feeling all godly, I'm going to give you one more chance to prove that you know what you're talking about. Show me that this hypothetical helicopter...
02-13-2011, 03:55 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Yeah, except that you used it to try to prove the...

Yeah, except that you used it to try to prove the opposite of what I'm saying. :)
02-13-2011, 01:20 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Aaaahhh! That makes total sense! I think the...

Aaaahhh! That makes total sense!

I think the easiest way to think about it is to bring out the old pizza analogy again. You want to distribute the tomato sauce (thrust) evenly over the pizza...
02-13-2011, 02:56 AM
Replies: 160
Views: 27,728
Posted By NJSwede

Removed... (Got the numbers wrong and too tired...

Removed... (Got the numbers wrong and too tired to fix it...)
02-13-2011, 12:34 AM
Replies: 160
Views: 27,728
Posted By NJSwede

Uhm... Sorry. That was a little harsh. Sorry for...

Uhm... Sorry. That was a little harsh. Sorry for losing my cool!

I think this ishow my wife sees me:

http://languagelog.ldc.upenn.edu/myl/llog/duty_calls.png
02-13-2011, 12:24 AM
Replies: 160
Views: 27,728
Posted By NJSwede

Of course I'm "hung up" on v-squared! The lift...

Of course I'm "hung up" on v-squared! The lift equation is a MULTIPLICATION! Let's go back to grammar school math: Anything multiplied by zero yields zero!!!!

Now, think of the hub of a rotor....
02-12-2011, 11:57 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Wow! You just proved that helicopters can't fly!...

Wow! You just proved that helicopters can't fly! I have to tell that to my buddy who's a 1:1 helicopter pilot! He's going to get P*SSED!!!! :):):)

Why? Well, the radial speed is zero at the hub,...
02-12-2011, 11:26 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Actually, the helicopter rotor puts the last nail...

Actually, the helicopter rotor puts the last nail in the coffin for the idea that the propeller/rotor has the highest thrust close to the root. Ahve you ever looked at a the rotor of a large...
02-12-2011, 10:12 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Hovering rotors aren't the same as propellers...

Hovering rotors aren't the same as propellers under forward motion. He's talking about how to optimize the twist for hover. I'm no expert, but I think that's a very different problem he's solving.
...
02-12-2011, 07:46 PM
Replies: 160
Views: 27,728
Posted By NJSwede

"Circular area due to v-squared????" You have...

"Circular area due to v-squared????" You have seriously misunderstood the lift equation! The v-squared has NOTHING to do with area. Nothing. In simple terms, the v squared is there because the...
02-12-2011, 06:08 PM
Replies: 160
Views: 27,728
Posted By NJSwede

You're right. They're never designed that way....

You're right. They're never designed that way. But a fundamental difference between a wing and a propeller is that a wing experiences the same airspeed along its entire length, whereas a prop blade...
02-12-2011, 01:35 PM
Replies: 160
Views: 27,728
Posted By NJSwede

It depends on how you defined "at the tip". Any...

It depends on how you defined "at the tip". Any design that tapers off to zero at the tip (such as an ellipse, my parabolic example or a simple triangle) obviously has zero lift at the very tip. But...
02-12-2011, 12:10 AM
Replies: 160
Views: 27,728
Posted By NJSwede

I have no idea what the first sentence is...

I have no idea what the first sentence is supposed to mean. But all my calculations are obviously wrong. I bow to the master and kneel before your superior intelligence. Have a nice evening!
02-11-2011, 10:16 PM
Replies: 160
Views: 27,728
Posted By NJSwede

My guess: Because they can. And because it...

My guess: Because they can. And because it results in a more powerful prop. Since you generate more thrust closer to the tip, it makes sense to have a prop that's wide where it matters most. Z-8 is...
02-11-2011, 09:37 PM
Replies: 160
Views: 27,728
Posted By NJSwede

This topic is just too interesting to leave...

This topic is just too interesting to leave alone!

An elliptic curve ends up with a really nasty integral I couldn't find an algebraic way to solve, so I went with a parabolic curve and...
02-11-2011, 08:04 PM
Replies: 160
Views: 27,728
Posted By NJSwede

BTW, for the effect that z-8 suggests to exist,...

BTW, for the effect that z-8 suggests to exist, the tapering has to be at rate of r^2 or higher. That's clearly not the case for any of the props I showed you. They're essentially twisted rectangles...
02-11-2011, 07:19 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Absolutely. But z-8's point seemed to be that all...

Absolutely. But z-8's point seemed to be that all props are tapered to keep the thrust constant or even less at the tips. That's simply not true. Anyway, I've wasted enough time on this now. :red:
02-11-2011, 07:06 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Are you saying that's true for ALL props? ...

Are you saying that's true for ALL props?

What about this one?
...
02-11-2011, 06:18 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Ahaaa! Maybe you could. The point is that with...

Ahaaa! Maybe you could. The point is that with most props (most notably props with a square or only slightly tapered trapezoid planform) you're going to have something like 80-90% of the thrust on...
02-11-2011, 05:55 PM
Replies: 160
Views: 27,728
Posted By NJSwede

You mean a prop that starts with a high pith near...

You mean a prop that starts with a high pith near the hub and continues like that all the way out to the tip? Or even one that has higher pitch towards the tip? The problem with that is that you'd...
02-11-2011, 05:07 PM
Replies: 160
Views: 27,728
Posted By NJSwede

Here's what it would look like if the twist of...

Here's what it would look like if the twist of the prop was there just to compensate for the difference in wind vectors depending on the speed at which the blade travels along its rotational path,...
02-11-2011, 04:43 PM
Replies: 160
Views: 27,728
Posted By NJSwede

That's exactly why. Think about it: The "side...

That's exactly why. Think about it: The "side motion" (caused by rotation) is very slow close to the hub, but the headwind coming from the movement of the plane is exactly the same. So the majority...
02-10-2011, 01:24 AM
Replies: 160
Views: 27,728
Posted By NJSwede

Well, if you think about it, two interesting...

Well, if you think about it, two interesting things happen around that point:
1) When you're starting to have enough negative alpha, the high-pressure and low pressure zones on the blades trade...
02-10-2011, 12:51 AM
Replies: 160
Views: 27,728
Posted By NJSwede

The exact solution to exactly how much drag is...

The exact solution to exactly how much drag is generated under which circumstances is probably at (or more maybe even beyond) what's possible to calculate today. A lot of the mechanisms around fluid...
02-09-2011, 11:08 PM
Replies: 160
Views: 27,728
Posted By NJSwede

I have to give you a boring answer: I don't know,...

I have to give you a boring answer: I don't know, but I can give you a crappy answer that probably ignores a lot of significant effects.

Given my limited knowledge, I can only give you the answer...
02-09-2011, 10:57 PM
Replies: 160
Views: 27,728
Posted By NJSwede

I WAS WRONG! I WAS WRONG! I WAS WRONG! ...

I WAS WRONG!
I WAS WRONG!
I WAS WRONG!

You *can* have a negative angle of attack. I had the prop turning the wrong way in my head when I thought about it. SORRY!!!
02-09-2011, 09:49 PM
Replies: 160
Views: 27,728
Posted By NJSwede

You're just restating what you just said. Not how...

You're just restating what you just said. Not how it is possible. A diagram or calculation would be nice. But as I said, we have passed the limit of what is a meaningful discussion a while ago. Have...
02-09-2011, 09:47 PM
Replies: 160
Views: 27,728
Posted By NJSwede

And by the way, mathematically speaking, the...

And by the way, mathematically speaking, the chord at the end of the propeller isn't zero. It approaches zero, just as any propeller with a pointed or rounded edge does. If the chord is zero, you're...
Showing results 1 to 30 of 39
 


 
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