rmh

gee -I started with Spike Jones compositions - so I just can't resist the chance to tweak noses .
But on another parallel - I also had a classic music education from age seven -till sixteen - when girls and cars suddenly upset the the cart.
My home spun technical background really served me well -I had a few very successful technical patents - two dealing with fail safe pneumatic circuitry.
So when I state the patently absurd - I look to see who understands the subject - If they really do understand it - they see the gag .
You obviously saw it.
Some did not ---
I really do not understand all the reasons why the flat plates work so well but the fact that they are tnin- means that they can be stalled at low speeds -and these can be commanded to do very precise snap rolls - yet they are very docile.
I have a friend who, along with his son - live in Merseyside are active club members and he also acted as a Team Cap. at the prior Polish World Champs
both he and his son fly my designs in competition
An EMC2 and an Ariel FAI aerobatics and a Staudacher I whipped up for scale aerobatics.

davidfee

Yes, the main problem very low Re airfoils have is laminar boundary layers and the fact that this laminar boundary layer can't support large pressure gradients without separation. In layman's terms, fat airfoils don't work at low Re because the airflow can't stick to a really curved surface. An extreme example would be a ball.

Curved plates work well, but real airfoils work better. Often times, a turbulator will be used to energize the boundary layer to prevent separation at high Cl. This turbulator can be as simple as a length of thread glued to the upper surface of the wing, at about 15% chord. Attached is a pic of a couple airfoils suitable for the Re = 40k-80k range. Less camber is normally used at lower Re.

-David

rc flylow

Hey Dick! You must be an F4 pilot. That plane proves that if you got enough thrust and have a large, government-sized reserve of JP4, a rock will fly.

toy264

Yeah, and the F-101 too. Standing joke at Vandenberg AFB was that with those J-57's a barn door would fly!

rmh

Yes!!!
Vectored thrust is a real part of today's aircraft design.
I pulled a few tails to see how many guys actually flew stuff (models or biggies ) using this method of flying.
I think I also stepped on a few tails --
I said early on " If the thing is light enough -cg doesn't
matter -and if it is too heavy -it still doesn't matter".
Watch a close up of an F16 tailplane as the craft takes off - it is wiggling to keep the craft from going ass over teakettle .
OR fly a tiny flate plate wing aerobat with wing loading measured in a few ounces and 2-3 x thrust from the motor.
With a proper computer (or some quick thinking) and these parameters , you can rethink the old rules on flying.
The flate plate wing has a characteristic of going from low drag (at a low AOA) to instant high drag at a fairly low AOA. (predictable also)
on a very low wing loading - this provides a wing that will fly fast -then instantly snap on command.--OR if slowed and power is increased - it allows you to steer the model around like a surfboard.
Low wingloading and high power loading means everything on these designs.
The cg - -oh somewhere convenient -further aft the more fun.

Hal deBolt

Hi ya'll,
Boy what a go around this outing has and is seeing. Creates a desire for everyone to get
his 2 cents into the mix, however I don't have the 2 cents, but>
When you have been there, did it al and learned you find certain things are for sure and as
a result most necessary
In that respect I would suggest that one never forget that BASIC AERODYNAMIC LAWS apply to any and all aircraft. Details can vary but performance is always asociated with the basics.
As Dick has said at extremes it makes little difference what is what but we surely do not
work even close to extremes so must not go beyond he basics, OK?
Good luck,

Hal [email protected]

95tequesta

My Feedback: (4)

Ah, banktoturn you contradict yourself. CG is dependent on speed. The faster a wing travels through the relative air the more lift it attempts to create. Therefore, a fast pylon racer can utilize a cg farther forward of the center of lift. While a slower flyer will benefit more with a CG farther aft than that of a pylon racer. By the way, I understand the points that dick hanson was trying to make. I also respect his opinions (whether correct or incorrect). Calling them absurd is harsh. Reading his threads, his opinions and theories come from personal experimentation. He understands what he is doing and it works for him. Just because his logic is not traditonal doesn't mean it doesn't work. dick you should thank banktoturn for the criticism, for it will motivate you to be more thought provoking. dick you provoked my thinking with the threads in this forum.


Quote from banktoturn

“The effect of CG placement on stability, which is what I was commenting on, does not depend on the speed at which the plane flies.”

“You've pointed out the critical distinction between wing loading and speed. While the stability of a plane with low wing loading is dependent on CG placement, a plane which flies slowly enough can be flown even if it is moderately unstable. The Wright brothers demonstrated this with their unstable flyers. A plane with light wing loading, if flown fast, would be just as hard to fly with an unstable CG location as a plane with high wing loading at the same speed.”

“Your absurd comments are a poor way to "give some other lines of thought". As an alternative, you might consider simply articulating some "other lines of thought" directly, as the absurd comments are simply inaccurate, not thought provoking.”

banktoturn

95tequesta,

Maybe, but I don't think so. What did I say that contradicted something else I said? I didn't find any such contradictions in my postings in this thread.

You claim that "a fast pylon racer can utilize a cg farther forward of the center of lift. While a slower flyer will benefit more with a CG farther aft than that of a pylon racer". This does not make sense to me, contradicts what I have learned about stability, and, I think, is a false statement. Can you explain it to me in more detail so that I can understand it? I'd appreciate that.

Dick's claim that I disagreed with was that "1- If the plane is extremely light - the CG does not matter". This is not untraditional logic that works for Dick, it is simply untrue, and is an absurd statement. I'm sorry if that seems harsh to you. I may not have made the comment, except that this thread is in the context of offering aerodynamics advice to beginners. In that context, claiming that CG location does not matter for a certain type of aircraft is not an appropriate thing to do.

banktoturn

95tequesta

My Feedback: (4)

If you would have read the thread I posted you would have seen the quote that I copied and pasted from your own words. Yes, your correct in that these discussions got away from the intended subject. Your attitude resembles that of a crusty old military person, that takes information presented to them as the gospel, but rarely thinks for themselves or questions "theories" or opinions. I believe you would argue with a brick wall!!!!!!!!!!!!!!!!!!!

You pick and choose information out of the posts. Before I mentioned the pylon racer I said, "The faster a wing travels through the relative air the more lift it ATTEMPTS to create." "Therefore, a fast pylon racer can UTILIZE a cg farther forward of the center of lift. While a slower flyer will BENEFIT MORE with a CG farther aft than that of a pylon racer." Read the small words!

banktoturn

95tequesta,

I am sometimes a bit argumentative, a fault that I struggle with. For some reason, I seem to be having that problem today, in particular.

I think I see the apparent contradiction you were referring to, but it is not really a contradiction. There is a difference between saying that CG location does not matter for a light plane, and saying that a slow plane may be flyable even if it is unstable. CG location DOES matter, at any wing loading, in the sense that it can determine whether the plane is stable or not. The fact that one could decide to fly a very slow plane with an unstable location of the CG does not in any way contradict this. In particular, one would not want to send the message to a beginner that stability, and hence CG location, does not matter. If Dick had made the observation that a sufficiently light plane could fly slowly enough to be controllable despite static instability, I would not have taken issue.

Your comment about the faster wing generating, or attempting to generate, more lift is not relevant to the topic of CG placement's effect on stability. I read all the small words.

It's interesting that you accuse me of not questioning theories or opinions, while the cause of this little exchange is the fact that I questioned Dick's. Is it only well established, proven theories that I should question?

banktoturn

95tequesta

My Feedback: (4)

OK banktoturn,

lets get on a friendly note. I realized what I wrote after I sent it and you are correct and I am wrong in that you did enter this debate questioning hanson's theory. However, I am still correct in saying that speed does play a part in cg location. If you are flying a fast plane you would rather have the cg more forward than aft. However, we are getting into a totally different realm. A more forward cg for a fast plane in relation to a slow plane would be more desireable than an aft cg. Especially if we are trying to make a sport airfoil (which tends to have better lift characteristics than an aircraft designed and built for speed) fly faster. Most of the RC pilots out there are sport pilots and find ways of increasing performance on the sport planes they are already flying. If I wanted a aircraft that would fly balistic I would build one for that intended purpose and nothing else. In this case the cg would be factored into the overall design of the plane and would resemble the % of most other planes in the different categories.

banktoturn

95tequesta,

I'm all for a more friendly note. Generally, a faster plane (a pylon plane for example) will be set up with a nearly neutral CG location (just a little ahead of the main wing's aerodynamic center), because this minimizes the load on the horizontal stabilizer, which reduces drag. A sport plane, whose pilot is less concerned with drag, would usually opt for a more stable CG location, or further forward.

banktoturn

rmh

I fly a lot of models - and some are extreme in their power to weight and wingloading
So to explain to those who don't fly models and /or lots of different stuff- or who are new to all of this:
Here is my silly postulate

"if the plane is light enough -CG does not matter
If it is too heavy -it still does not matter."

Why would I say that?
Imagine a fixed wing aircraft that is so light that it is almost bouyant.
Add an engine -
It is still a fixed wing powered craft.
Power applied and control surface applications will do all of the controlling.
The CG is of little or no importance.
Stall is not going to happen.
Ludicrous craft?
perhaps
Now make the craft too heavy - If it is too heavy to fly , the cg is again, of no value.
Silly?
maybe to you -You fly it.
What I see - over and over is some poor newcomer who has a plane that is too heavy to perform and when asking why, he gets all kinds of theories and rules and worse yet - formulas presented to show why the model does not perform as expected.
The real problem typically -It is just too durn heavy.and or underpowered
the CG can be moved to place the crash site further down the road - but tell it like it is .
All of the model flying I have done shows that "the critical nature of the the CG increases with wing loading."
Be honest - the same thing is true with a 1940 DC3
On racers - we always kept it forward- to prevent easily increasing the AOA past safe limits
On aerobatic stuff -such as designs we did for pattern, or for the TOC ( and they were good enough to place and win ) to little foamies which are grossly powered feathers --I find that weight and power are far more relevant than CG
CG is of course important but first the weight and power must be addressed.
Then place CG parameters for that situation.

h-ray-RCA

Guys, Guys, Guys, (Any Gals here?),

You're ALL missing the basics: Airplanes (R/C, glider, full scale, rotorhead, etc) don't fly because of CG, Thrust, airfoil, etc.

They fly because of $$$$$$$

No bucks, no Buck Rogers...

MikeMc

I thought it was a joke... or sarcasm...

Not only doesn't CG matter but engine, structure, controls, tail, aerodynamics, etc don't matter either. Any minor wind will make it crash and/or blow away. Start thinking about your next plane and stop chasing it.

Same thing but put all the pieces in the trash can before you leave the flied.

If neither of these cases are true, it (CG) matters.

rmh

If you guys don't believe that light loadings increase usable cg range - I guess you don't do much flying with light , aerobatic models .
I did offer a tongue in cheek look at CG-
Why?
If you don't look for the absurd in a situation - you probably don't really see the limits of the plausible.

banktoturn

Dick,

Lower wing loadings increase the usable CG range only in the sense that a slower flying plane can be successfully flown with a smaller static margin. That is much different than saying "1- If the plane is extremely light - the CG does not matter". I have no problem with people using exaggerated, or otherwise absurd, statements to make a point. I personally was not able to pick up on the fact that you were using absurdity in this way. To me, it simply looked as though you were making an incorrect statement. Presumably, a beginner, looking for some basic aerodynamics advice, would be more perceptive, and would not be at risk of trying to fly an unstable plane based on your post.

banktoturn

rmh

YES- my comment was intended to arouse some thought about what typically is wrong with models which don't fly as expected.
I test a lot of models -for others as well as my own junk.
The top of the list for problems is
1 - too heavy
2- poor control set ups
The models which are too heavy won't become good flyers -no matter what you do to the CG/controls-add flaps (no help anyway)- whatever.
The only fix is to increase speed - Then they really become an unguided missile .
The very light models can be soooo screwed up in controls/CG power etc., you could cry.
But the light wing loading saves em
If the cg is too far aft - -you just slow down and the control responses soften.
If it is way too far forward - -just hold a a fair bit of UP and if it is toooo far forward - it never takes off - so that problem is resolved----
CG is down on the list of critical factors for most aerobat models of decent wing loading.- typically a good working envelope is 25-35 percent of MAC.
The flyer can and does adjust control response to get the stability and/or agility desired.
In working with full scale stuff that is measured in square yards -or furlongs --the power to weight is a whole different ballgame
full scale stuff such as flown by the latest unlimited airshow guys -is more like a TOC model than like an Aeronca Champ.
The ol co ordinated turn simply is not part of the ballgame.

adam_one

Sorry, but the problem is still not resolved... because one still has a problem:
it never takes off

banktoturn has indeed some points here.
As far as a flyable aircraft is concerned the CG location does affect how the aircraft reacts to the pilot's controls even if the influence maybe more or less critical depending on the actual speed and wing loading.

A tail-heavy aircraft will be more unstable and susceptible to stall at low speed
e. g. during the landing approach.
Whereas a nose-heavy aircraft will be more difficult to takeoff from the ground and to
gain altitude and will tend to drop its nose when the throttle is reduced. It also
requires higher speed to land.

In order to achieve a good longitudinal stability, the CG should be ahead of the
Neutral Point (NP), which is the Aerodynamic Centre of the whole aircraft.
NP is the position through which all the net lift increments act for a change in
angle of attack.

rmh

Yup -all true --but
drop the wingloadings to almost nothing and add a high power loading - it all gets pretty interesting.
The hard and fast rules get pretty soft.
I get the very firm impressions that no one one his forum tries these types .
No offence!
I just hoped more readers were into this weird stuff.

adam_one

Then you'll get an aircraft that's almost nothing as well…
But Ok Dick, I understood your point.
Have you ever flown such a masterpiece?
Could you show us a picture with details?
Now I'm curious...

davidfee

Dick,
I too would like to see some examples of these very low wing loading models with very high power loading where CG is no longer so important. I think the trouble most of us are having with your statements is the fact that, regardless of the magnitudes of the forces involved, they all still must sum correctly to keep the model in the correct attitude. The laws of physics still apply.

We had this discussion months ago and we understand that as the model gets lighter it can fly slower... giving the pilot more time to respond... but that does not equate to an insignificance of CG. I told you of my indoor rubber models with miniscule wing loadings and lots of power (relative to weight). If the CG is wrong on those, they will not fly.

-David

rmh

OK here is a setup - remember you drop the wing loading to zip -then add 2-1 power capabilities -the result is a model which will fly at about any attitude.
the SPEED is so low and the angles of flight are so high that flight is basically thrust with guidance by the ailerons etc..
These are really crossbreed copters and fixed wings.
at low speeds they are still very controllable, in level flight --but they ain't freeflights -by any stretch of th inagination.
It is a bit like some full scale fighters - where the computer keeps em from "departing".
There are thousand of these types out there now and the market is really growing.
The CG can have a very broad usable range.
The more one goes to high angles (vectored thrust) -the furher aft it can be located.
They are goosey but they do fly .
The model here has under 5 oz loading per sq ft and power is at 30 ozs thrust -for a 13 oz model.
Not calculated - tested
Note the control setup under the wings-with the radio used, I can instantly choose sensitivity or mix of aileons and elevators etc., to give slight trim changes ailerons (droop or raise) to flaperons or add flapperons on a fully integrated basis.
Sound complex but it really isn't.
These integrations are pre programmed and one switch selects combos.
a momentary push switch , adds trim in small increments .
you can do all this easily.on the "fly"

adam_one

Well, and there are autogiros and balloons too, but I supposed we were talking about plain aircraft not just things that hover around…

The computer is necessary just because they are too unstable to be controlled by the pilot only.

How broad? From the tail to nose?
Does that mean that CG location is totally irrelevant for a stable flight?

Hmm…

But thanks for the pictures anyway.

rmh

You asked -
I have an idea what you feel is a "plain " aircraft--fits a more conventional profile -
I also consider a computer controlled aircraft to be - an aircraft .
This concept is also computer controlled ----
The CG -FYI, typically produces decent results over about the first 50% of the chord.
Tricky -yes -
A good friend saved a model one day when the prop exploded and the engine wrenched from the airframe - He landed it .
It took full down elevator control and the flight path was anything but sedate BUT- it was flown to the ground-the model had big control surfaces and lots of throw.
we checked the CG -just to see what happens when a few lbs flies off the nose.
The CG was just AFT the trailing edge.
You might try being less judgemental and try something new - it really can be eye opening.