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RE: Suggestion for moderators - 3/21/2006 5:15:05 AM   
Oldbob


 

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Status: offline 		I am relitively new to RCU and have been mostly reading topics that others have posted.How do I go about posting my own topic? any help will be appreciated.

Old Bob

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RE: Suggestion for moderators - 4/17/2006 5:54:13 PM   
Tall Paul



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Status: offline 		At the beginning of the forum, there's a selection at the upper left for "new post". Plunk on that one.

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RE: Suggestion for moderators - 4/17/2006 6:03:02 PM   
Tall Paul



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quote:

ORIGINAL: antter

This thread is going for years and still not getting anywhere.

What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.

And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.

And hot air baloon fly too! No thrust and very lite indeed.

A hot air balloon merely put some distance between the basket and the ground. It's a self-contained thermal. It doesn't really "fly" but just drifts with the prevaling wind.
"Flying", meaning controlled manuvering in many directions, including upwind and crosswind, takes more participation on the part of the device being used.

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RE: Suggestion for moderators - 4/20/2006 7:03:31 AM   
KillerCharlie


 

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Status: offline 		Hot air balloons work on buoyancy. They're so big and light that they float up - just like a ball under water.

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RE: Suggestion for moderators - 7/8/2006 10:34:38 PM   
antter


 

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From: KuressaareSaaremaa, ESTONIA
Status: offline 		I promise this is my last post on this topic, its like discussion about if size does matter, after someone invents extreme argument of zero size, in which case it indeed doesn't matter.

I know well why balloon flies, but doesn't position of center of gravity matters for balloon? Or indeed even for parashute?

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RE: basic aerodynamics - 7/21/2006 2:05:37 AM   
Semi Retired Aviator



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From: Melbourne Victoria, AUSTRALIA
Status: offline
quote:

ORIGINAL: antter

This thread is going for years and still not getting anywhere.

What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.

And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.

And hot air baloon fly too! No thrust and very lite indeed.


You're going to find that a lot said here doesn't relate to the topic particularly, or perhaps even at all, but provided somebody is learning something, who cares.

When I posted the following site, it was intended for beginners to go there to pick up a few tips on 'basic aerodynamics', and hopefully it's worked. That it has diversified from basic aerodynamics is of no real consequnece.

http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html

Somebody made the point a few posts back that model design doesn't relate to full scale, and that's probably right, but one thing you can be sure of is that ALL obey the laws of aerodynamics even though that may be difficult to understand at times.

I enjoy dropping in fromtime to time and seeing how this has and is developing.

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RE: Suggestion for moderators - 9/24/2006 7:04:01 PM   
Crusty



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quote:

ORIGINAL: dick Hanson

OK- you tell me why it works -using wind tunnel data .
Believe it ot not you don't need tunnel data to make something work.
Lots of stuff that was designed by wind tunnel research turned out to be a flop.
NOT because of the tunnel - simply because real world use shows up flaws that paper work and controlled enviroments don't/ can't / never will.
Tunnels beat guesswork - I am not a fool.
I never alluded to any explanation of why the stuff works - simply that it does work-
You have to do actual hands on stuff , eventually .
Where are you going to get a tunnel which runs at 10 mph airflow ?
I guess they exist - I don't kno who uses em tho -
You really don't think light weight broadens usable CG range?
Lower loadings = lower angles of attack needed to provide same amount of lift.
So the craft can maneuver at lower angles of attack and will recover to lower angles of attack that is, recover from departure conditions (stalled ) much more readily.
This is not a true statement?
Take any powered plane - fly it - now add weight - keeping speed the same - and see if you can't find the same effect.
eventually it will stall and never take off.
How does lower loading increase CG range ?
It simply reduces the critical nature of the cg --control can become pretty ham fisted in fact .
Attempts at exceeding stall angle have to be really intentional -as opposed to the typical full scale design which must be carefully kept with in the "envelope".
stability can be traded for maneuverability .


I agree with the thought that lightly loaded aircraft are more tolerant of cg position, tho the trim able speed range reduces greatly..the free flight gliders I flew back in the seventies, were built with rearward cg locations and lifting tail surfaces I think speed range is the key factor in this configuration perhaps more so than actual loading, but I wouldnt dare set up a 20 pound gasser like it to find out if I was right

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RE: Suggestion for moderators - 9/25/2006 6:18:41 PM   
gilbertfh


 

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Status: offline 		I really wish I would have gotten in on this thread a long long long time ago. I am in the Air Force and have been for 14 years one of my primary jobs is that of a load planner. The window in which a center of gravity can be in order for an aircraft to be flyable becomes smaller the heavier the aircraft is and larger the lighter the load is. Pictures are so much easier than trying to explain in terms everyone will understand. Suffice to say the lighter it is the easier to balance.

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RE: Suggestion for moderators - 9/25/2006 11:58:44 PM   
dick Hanson



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Status: offline 		yes -that's a fact - I once noted that if a plane was light enough - the CG simply did not matter - you should of heard the learned replies on that one!
I bet you also found that if the load was too heavy --the CG meant nothing (It couldn't fly -so why bother .)

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RE: Suggestion for moderators - 9/26/2006 12:22:58 AM   
ArCeeFlyer



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Status: offline 		But we're only concerned with real world practical applications. Who cares about the fantasy and the absurd? Of course, if a plane could be so light that air would be like molasses, it virtually wouldn't fall due to gravity, not mention it could hardly move in any direction, thus c.g. doesn't matter (the fantasy) and why would we want to build a plane so heavy that it couldn't fly? (the absurd) I understand what you're saying. It just seems pointless.

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RE: basic aerodynamics - 9/26/2006 1:33:02 AM   
da Rock



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From: western, NC, USA
Status: offline 		Actually, to put the "light enough and the CG doesn't matter" into "real world, practical" context.

I've been messing almost exclusively with 46size airplanes for the last year. And have been instructing. And every student has brought a 46size highwing. And some of them have been HEAVY. And I've built a couple of highwingers. And enough of them have had about the same areas and moments that I'd suggest they were all basically "the same airplane".

And part of the "school sessions" were spent adding nose weight when it was needed. So I've seen the same planes with different CGs.

And when the heavy ones had CGs toward the edges of the envelope, they flew like it. And when the CG moved, you could see it for sure.

And I've got a scratch built of the same size and areas and moments. And have messed with it's CG as a way to teach myself what CG location does. But this scratch one is what anyone would call light. It's better than a pound lighter than the lightest of the student's airplanes. And I'd decided, after the experiments with it, that CG location was overrated. And then this last year, messing with heavy models of this class, I came to the startling conclusion that what Hanson just said is what it is....

In our real world, if the model is light enough (and my old trainer is) the CG don't do as much as you'd think.

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RE: basic aerodynamics - 9/26/2006 2:15:06 AM   
ArCeeFlyer



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Status: offline 		That makes sense. It probably has more to do with wing loading though, than actual weight. But there is still a limit. I bet if you take your light plane and move the c.g. totally off the wing, I'm pretty sure you're going to have a difficult time flying it.

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RE: Suggestion for moderators - 9/26/2006 4:19:34 AM   
dick Hanson



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Status: offline 		unless one looks at effects along boundries of parameters -- you can never have full understanding of the parameters .
It is not silly or pointless, rather ,it increases knowledge .

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RE: Suggestion for moderators - 9/26/2006 4:38:05 AM   
ArCeeFlyer



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Status: offline 		When you put it that way, I agree that expanding one's knowledge horizons is good. So, understanding the extreme brings the practical into better focus. I like that. I've often thought up extreme scenarios in physics, space and time and try to figure out the "what if" of it. In that respect, I see that it's not as pointless as I said earlier.

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RE: basic aerodynamics - 9/26/2006 10:11:19 AM   
da Rock



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quote:

But we're only concerned with real world practical applications. Who cares about the fantasy and the absurd?


quote:

I bet if you take your light plane and move the c.g. totally off the wing, ................................................


Hey, didn't the same guy post these two ideas almost back to back???????

(in reply to ArCeeFlyer)
&nb