RE: relationship of ground effect and wing chord
 

according to the dictionary of aeronautical terms 2nd edition, published by asa in the late 80's early 90's. ground effect is an increase in lift of an aerodynamic flying machine (airplane or helicopter) flying very near the ground. this additional lift is caused by a distortion of the airflow that produces an increased angle of attack. grond effect disappears when the flying machine is about a half a wingspan or half rotor span above the ground.

RE: relationship of ground effect and wing chord
 

“bouyancy” buoyancy?? Whatever floats your boat I guess but we were talking about airplanes. If my point by point responses to mikenlapaz questions in post #18 are incorrect or misleading please explain my error/s and provide references to creditable data sources.
Dick,
I’m new to this forum and have just read some of your over 10,000 posts on other threads. You’re a very prolific poster (average 100+/month) and obviously intelligent. I’m not sure which worries me most, that anyone that asks a serious question believes your inane responses or that you believe your responses. I understand that you want to “provoke thought out of the box” but it is irresponsible to do so in this or any other serious thread. I think you do the person asking the question, this forum, the RC community in general and yourself a disservice when you do this. Start your own thread titled RC extremes or how I can fly my plane with every thing crammed in the tail if you like. I’ll participate in that. Most of the rest of us mere mortals fly in the real world. If you wish to fly your plane that weighs nothing in a fantasy world using a liberal application of pixy dust and levitation, have fun.

RE: relationship of ground effect and wing chord
 

“bouyancy” buoyancy?? Whatever floats your boat I guess but we were talking about airplanes. If my point by point responses to mikenlapaz questions in post #18 are incorrect or misleading please explain my error/s and provide references to creditable data sources.

RE: relationship of ground effect and wing chord
 

You need data to understand that pressure differences are what keeps planes in the air ?
What do YOU think ground effect is ?
and please - no links to archiac archives
I find that type of non responsive "reply", to be of little or no value.
BTW, boats n planes share all the laws of nature

RE: relationship of ground effect and wing chord
 

I've made no references to "archiac archives" as you put it, in the last post. You have not responded to the original thread. I repeat: "If my point by point responses to mikenlapaz questions in post #18 are incorrect or misleading please explain my error/s"

RE: relationship of ground effect and wing chord
 

Let's discuss the issue, not each other.

And let's leave off telling each other what you'll accept as proof or what you think of theirs.

RE: relationship of ground effect and wing chord
 

Again I apologize.

RE: relationship of ground effect and wing chord
 

This is a pretty darn good explanation of ground effect.
The bouyancy I mentioned is simply any increase in pressure caused by a large body passing by and "gathering up" air as it goes
If the air is disturbed -it HAS to go someplace and if it can't equalize before the "body" passes by - there is a pressure build up .
We call that condition,
ground effect.
Not really much different than watching a large piece of plywood fall to the ground - the final part of the fall is cushioned by the air which simply can"t equalize pressure with the surrounding air.

RE: relationship of ground effect and wing chord
 

U.S. Department of Transportation
Federal Aviation Administration
Regulatory Support Division, AFS-600 dated September 28,2007
Subject: Learning Statement Reference Guide for Airman Knowledge Testing

13. PLT131 CFI
It is possible to fly an aircraft just clear of the ground at a slightly slower airspeed than that required to sustain level flight at higher altitudes. This is the result of
A) interference of the ground surface with the airflow patterns about the aircraft in flight.
B) a cushioning effect of the air as it is trapped between the ground and the descending aircraft.
C) ground interference with the static pressure system which produces false indications on the
airspeed indicator.

Glossary definition from Pilot’s Handbook of Aeronautical Knowledge
2008
U.S. Department of Transportation
FEDERAL AVIATION ADMINISTRATION
Flight Standards Service

Ground effect. The condition of slightly increased air pressure below an airplane wing or helicopter rotor system that increases the amount of lift produced. It exists within approximately one wing span or one rotor diameter from the ground. It results from a reduction in upwash, downwash, and wingtip vortices, and provides a corresponding decrease in induced drag.

I rest my case.

RE: relationship of ground effect and wing chord
 

Quote "I rest my case. Quote

Not so fast______
"The effect begins to be noticeable when the aircraft's altitude is within 1-1.5 times the length of its own wingspan and, when the altitude is within about half a wingspan of the ground, the effect can increase lift by as much as 40%."

Yet another source, ______ yours is NOT conclusive____merely familiar to you.
There are MANY others and they do not all agree with one another.

RE: relationship of ground effect and wing chord
 

Ground effect is something I never argue about with other people, I simple use this to keep the retractable mains underneath my planes and to get the planes in the air, also because of the wind gradient.
(29,5 Oz/sq ft!)

Cees

RE: relationship of ground effect and wing chord
 

You are perfectly correct. Mine is not conclusive. It is however the current knowledge required to obtain an airman certificate from the FAA. The 2nd edition asa source from the late 80's early 90's may no longer be correct. The asa dictionary of aeronautical terms is currently in its 4th edition and I'd be willing to bet that the definition has been updated. The quote "within about half a wingspan of the ground, the effect can increase lift by as much as 40%" is correct by all the sources I've read. All the sources I have read indicate one wingspan above the surface. Could you provide that source that clains 1.5?

BTW the asa news release for their New Forth Edition dated February 7, 2007 cites the same sources that I cited, as its sources. "All specific to the aviation industry, the terms have been gathered from the regulations, the Pilot/Controller Glossary from the AIM, and glossaries from government handbooks and manuals."

RE: relationship of ground effect and wing chord
 

That's a nice looking plane in your post. Is that your own design?

RE: relationship of ground effect and wing chord
 

Frank,

Sideview, my Orion, design Ed Kazmirski world champion 1960 pattern, but a view procents bigger and some modifications to make a “sport plane” of it. The plane is aerodynamic the same.

30 years old inverted ENYA 60 4 C engine, span 69”, weight 10 lbs.
In my thread "Redesign and reconstruction of the Oldest Taurus on Earth" you found some pictures of the modification of the cooling of the engine.
Classic Pattern Flying page 9 post 203.
http://www.rcuniverse.com/forum/m_79...mpage_9/tm.htm

I think the plane would not fly so easy without ground effect.
My advice, use an old REAL taildragger with as short as possible mainlegs, when you want to fly on grass with retracts, so you have profit of the ground effect.

Cees

RE: relationship of ground effect and wing chord
 

Your answer BEGS the QUESTION rather than answering it.
Why would you quote a full scale source as definitive for this discussion?!!?

Your profile states that you have been building/flying for 30 years. Surely then you are aware that model aerodynamics are NOT the same as full scale, in each and every case.
Reynolds numbers are a classic example of this as in full scale there is a raft of data to be referenced; while in model scale there is virtually none.
We KNOW the Reynolds numbers for our models are quite low but there it ends.
NO further data. That leaves us with assumptions and ???????????

Ever see a model Heli fly inverted??? How about full scale?
How about extended inverted flight (and maneuvers) with an undercambered airfoil??
Models yes. Full scale??????

SOME of the "rules" apply (perhaps even most) but a long, long way from all.

I consider your quotes as interesting but off topic. They apply to a SEGMENT of full scale flight. That's it.

Many of us on these sites are "ex-" about any level of any subject you care to mention, including military, civilian, commercial.
NOW, if you can quote Michael S. Selig I WOULD take notice as he is BOTH full scale and model experienced.

RE: relationship of ground effect and wing chord
 

Mikenlapaz,

When you did read my posts and understand, look to the distances between wing / ground and stab / ground of the Orion.
When these distances are the same and the airplane is right in balance (also downwash wing on the stab) it isn't important anymore on what level you experience the ground effect.

That is the reason I did tell, use a conventional real taildragger because when you take a tricycle and make it a "taildragger" it does not work. Then the stab is too low and the wing is too high normally. Think also on wind gradient if the wind blows!

Also the position of the CG has to be on that location that, because of the forward point of liftforces of the A-symmetrical airfoiled wing with high AOA, the stab is "loaded" and the total plane is your speed brake during landing. Look to the position of the elevator nearly horizontal.

During start, the situation is the same, I can accelerate on the moment the wheels do not touch the ground anymore before climb even retract the gear first.

I can make a full speed fly by on very low altitude and one times hit the ground with the propeller, after that I did make a belly landing on a distance of about 80 m in the next field without damage!
This is because with the real taildragger in high speed the wing gets the influence of the ground effect before the stab!!!!
Ground effect, try it yourself. I think the effect starts between a half and a quart span.
Picture to show the dimensions and fly by lower as on this picture!

Cees

RE: relationship of ground effect and wing chord
 

Regarding the chord issue, no expert here, but my understanding of ground effect is that it primarily results from interfering with the wing tip vortex. It reduces the loss of lift that ordinarily occurs at wing tips because of high pressure air on the bottom spilling over to the top of the wing at the wing tip, which creates the vortex.

Soaring gliders have high aspect ratio wings in order to minimize the proportion of the wing that is affected by this loss, so conversely, a low aspect ratio wing (wide chord in relation to span) will lose proportionally more of its lift to wing tip losses.

If the ground effect explanation above is correct, then obviously ground effect will will be greater on a low aspect ratio wing than on a high aspect ratio wing, because the low aspect ratio wing loses more to wing tip vortices, so preventing that loss should have a proportionally greater effect. The longer aspect ratio wings will still glide best, but the improvement from ground effect should be greater with a low aspect ratio. Anyone have a Slow Poke 40? That should have a pretty poor glide that improves noticeably close to the ground.

I'm not sure if that addresses the original question. As to models experiencing ground effect, like several others, I have witnessed this effect on some of my own models.

Jim

RE: relationship of ground effect and wing chord
 

That makes sense to me, the biggest improvement in glide will be seen by the non-glider types. The gliders are already doing such a fine job that any improvement won't seem too dramatic.
Those Q-500s can skim along for a freakishly long time, especially the low wingers.

RE: relationship of ground effect and wing chord
 

Jim,

Look to the picture, my most simple explanation.

Daniel Bernoulli (Dutchman), higher speed of air lower pressure.

The air underneath the wing is forced through a narrow space, so pressure will be lower near the TE of wing and stab.

Above the wing the air is divided over a greater space, so higher pressure.

The pressure difference will give you downwash (blue arrows), (Newton) is equivalent for lift.

The dihedral is important to get a stabile flight, this will give a better pressure distribution and less loses near the wingtip, third picture.

Cees

RE: relationship of ground effect and wing chord
 

We land in such a ROUGH & FAST sinkrate that we are thru the ground effect before it is noticed.

Land a Jumbo jet the way most people land & there is no ground effect either.

No plane left also.

The pilots of the East River ditching knew ALL about ground effect & how to use it.

My opinion, not great, is that the Deltas are the true kings of ground effect. Why? Because they FORCE the fuselage to BECOME part of the wing area and go into higher AOA. Saab Drakens had tailwheels & tail skids in the 1950's because of the high AOA on their HIGHWAY AIR STRIP landings.

RE: relationship of ground effect and wing chord
 

cyclops2

That was the reason I did start with, see first message.

Cees

RE: relationship of ground effect and wing chord
 

I agree.
But It was hard to leave it out as I rambled on. Everything I say is stolen from someone elses statements.
How many really new ideas are created in aerodynamics each year ?

Rich

RE: relationship of ground effect and wing chord
 

Deleted

Cees

RE: relationship of ground effect and wing chord
 

New ideas ?
not many but there are many interpretations of basic laws of nature. (think of four blind men examining an elephant)
In this case , ground effect, it is simple -

when the moving body is close enough to a stationary body to cause a pressure increase between them
the bouyancy of the moving body is increased . The size and speed and shape of the moving body directly affects the pressure and distance of this occurrance..

no aerodynamic mumbo jumbo required.

RE: relationship of ground effect and wing chord
 

I used that line on a lot of girls. :D