rmh

We don't calculate --
we test -because we find that to bemore accurate.
besides the only numbers I am familiar with are my wife's birthday and Christmas.
Using my little test stand --I measure power in and thrust output.
But - the logic remains - you can't get something for nothing -
of course air resistance is less at high altitudes
of course the EFFICIENCY for a higher speed is better
but you gotta get there first -

adam_one

Sure Dick, but the calculation may be useful for a quick comparasion purpose and to put you in the ballpark, then you may fine tweak with test flights.
Besides, the calculator is cheaper, as you don't need to buy lots of different motors and props to check and compare their performance with different combinations.

Yeah, and it's often difficult because the setup is always optimized for the actual flying site's altitude.

Dick, you could run your nice test stand and compare the values with the calculator and tell me the difference (include barometer pressure and temperature).

rmh

We do that when we test gasoline engines - makes BIG difference.

former spad

Back to the original question ... How does a flat wing produce lift? I stayed up all night thinking about. I finally realized maybe we are asking the wrong question. Since a flat wing does fly, maybe the question should be ... Why don't we understand how a flat wing flies? I was able to think of a comparison with a full flying vertical stabilizer. When heading straight through the wind, equal air pressure on both sides cancel each other out, no lift is produced and the plane flies straight. Change the angle of attack with control input, the presure differential changes, a horizontal force (lift) is produced, and the plane starts to turn. In this simple experiment, the only real difference in how a wing and full flying vertical stabilizer produce lift is the direction of resultant force. I tend to agree with what Dick Hanson said about structural needs dictating aerodynamic designs over the years. No one, except Dick, knew a flat airfoil could fly until foam, brushless motors and Lipoly batteries came along. My guess is they fly because they are so light, and therefore, don't need a chambered airfoil which adds too much weight.

30 years ago, Uncle Sam gave me the opportunity to stand on foreign soil and watch all sorts of his planes fly overhead. I would like to nominate the SR-71 as the first 3D plane. Overpowered with almost flat wing. The only time you could see it was in the pattern. On take off, not straight up, but sometimes it seemed like it. On landing, it would float nose high. It flew a pattern no other plane could even come close to matching.

BMatthews

There's no mystery about it. It produces lift the same way any other non cambered airfoil (id: symetrical) produces lift. By angling the airfoil so it meets the oncoming air or flows through the stationary air with a positive angle of attack. By passing through the air with a positive angle of attack the air flows around the plate and produces a lower pressure above and a higher pressure below and at the same time this produces a change in direction to the air so it's floing down off the trailing edge of the plate. All this is classic stuff that lift is made of.

B.L.E.

I was playing with profile fusilage CL planes that had flat sheets of balsa for wings and a reed valve .049 for power back in the days when L.B.J. was in office. Let's not forget those rubber band free flight stick planes that you could buy for a quarter or so at most 5 & 10 cent stores either. Fred Flintstone probably played with those.

jlkonn

My Feedback: (1)

If I may...
http://www.amasci.com/wing/airfoil.html
[sm=spinnyeyes.gif]
JLK

rmh

I knew about flat wings in 1949- -and flew plenty of em -as a kid
The foamie flat wing was a whole different look at PERFORMANCE and it was thryu experimenting with them as many others did - I saw that much of th supposed "necessary airfoil" info -simply had little or no detectible influence of these ultra light, overpowered models.
I am a firm believer tho in the idea that most of the "why" in aircraft came about because of structural limitations and low power to weight powerplants
I have asked a number of times what would have happened to aircraft design - if "somehow" the power available suddnly doubled --or the materials necessary suddenly were reduced in weight by 50%.
The plodding evolution we have seen would have likely made some important turns .
like perhaps the revolutionary design changes 60 years ago in German arcraft.
Thinking outside the "box" is sometimes extremely productive.

Blue_Moon_

Hi! What a long thread about someting simple like this!

A flat surface can provide lift if you provide the surface with an angle of attack. If the angle is too large, the airflow on the upper side will leave the surface and turbulence is occuring.

The curvature of a wing profile is also in need of a very little angle of attack, how big angle depends on the wing profile. Curvature is a very effective profile (but you dont need it to provide lift, angle of attack is enough) If you provide the curavture with an underside, you will obtain an even more effective wingprofile wich can be used in a bigger spectrum of speeds.

starwoes

seems folks in here DEBATE a lot. Maybe I should open a "DEBATE" thread just for the heck of it. any and everything goes LOL.

Meanwhile, a few threads over, the airplane on the threadmill will fly no question.....LOL

gtmattz

NOW... If we put a helicopter on a treadmill powered by 16,000 hamsters in microgravity.......................


ANYWAY...


Thrust and Angle-of-Attack.. Enough thrust and proper AOA will make a patio block fly.

mesae

I must respectfully disagree somewhat. This debate has been raging since long before I started flying full-scale twenty years ago. In reality, we all know that any time power is adjusted, pitch, descent angle, and airspeed are affected, if we are attempting to maintain a specific glidepath AND airspeed, as in any landing approach.

Consider the case of being low and fast (One cannot assume that the airspeed will not require at least minor adjustments throughout the approach.). Strictly following the above technique as stated, one would reduce power to decrease airspeed, but this would do nothing to bring the airplane closer to the desired glidepath. If the pilot simply increased pitch slightly, the airplane would come up to glidepath, AND the speed would reduce toward the desired value. Then, when the glidepath is intercepted, power could be reduced, and the nose allowed to drop slightly to re-establish descent on glidpath and on speed. This is the way professional pilots do it, because it is the easiest and most effecient way.

In level flight, the only practical way to adjust airspeed (beside drag devices) is with power, and elevator controls altitude. Why should this reverse just because an airplane is descending? Positive transfer is facilitated by keeping the same technique of considering power an airspeed control, and elevator a descent rate control while on approach. One of my check pilots, a retired Air Force tanker pilot, insisted that pilot trainees consider power as controlling airspeed, and pitch as controlling rate of descent on all approaches. He did this because it was how he was trained in the USAF, and how he flew as a corporate and charter pilot, and because it works.

All three companies I flew for insisted that I not reduce power (except to maintain operating limits--ITT, N1, MP, etc.) when initiating a descent, until withing stage-cooling distance. Pitch is adjusted to initiate an enroute descent, unless it is turbulent enough to warrant a reduced-airspeed descent. In a climb, power is usually fixed, so practically speaking, speed is controlled with pitch, unless a constant airspeed AND rate climb is desired. Again, pitch and power adjustments are both interdependent.

Big jets often initiate enroute descents with a power reduction and a pitch adjustment to a target vertical speed, since their airspeed is already very high at cruise.

mesae

The plane cannot fly straight with the wing producing zero lift unless it is pointing straight up or straight down, or hovering. All other flight paths would be curved toward the ground.

rmh

WE once -back in late 60's had a DamnFool land a 727 here - -and he coasted all the way in --till he finally realized his sink rate was too high - a gear went up into the fuselage -and people died.
His co pilot attempted to advance power but the Captain said "who is flying this thing - me or you?"
Now - you have to carry power -- as it should be .
note the cross wind landing videos

starwoes

GT,

thought hampsters had a fear of heights? therefore, they'd underperform intentionally!

mesae -

different schools with different thoughts. i was also told in flt school that since turbines take a while to "spin" up....better to keep the revs waaay up there, (in case you need it in a hurry) and to do other things to stay on glide slope...

mesae

That's true, and nothing I wrote contradicts what you just wrote. Turbines are often reduced to idle power for the clean enroute descent, then brought up again at leveloff (to maintain airspeed and altitude), then brought up still higher for the draggy approach (to maintain airspeed and descent angle). But you still cannot strictly consider either power or pitch as exclusively controlling airspeed or descent angle/rate. Both are interdependent. I'm trying to pull people off the walls on this debate and more toward the factual, physical truth in the middle.

starwoes

I am debating for the heck of it --

decided not to open another thread LOL

Bax

My Feedback: (11)

Actually, what the high-performance pilots are doing is basically setting an AoA for the wing and using the pitch control and power controls to maintain it. So for the landing approach, with gear and flaps out, an airspeed (that's weight-dependent) is targeted. Pitch and power controls are used to maintain that airspeed on the desired approach slope. Holding an airspeed amounts to the same thing as holding a desired AoA. Navy carrier pilots actually have an AoA readout that they use. They target the desired AoA and hold it all the way onto the deck...again using pitch and power to maintain that AoA and the desired descent slope. Everything is moved as necessary to keep the approach stabilized. If you're properly set up, though, control movement should be minimal, given stable wind conditions.

adam_one

Hi,
Since it seems there are some full size planes pilots here, I would like to put the following question:
Are the model planes more difficult to control and to land than the full size ones?

rmh

How long is a piece of string?
Some models , some full sized, are incredibly easy to land -
Some are not.
Having steered only small single engined 4 bangers - and never having gotten a pilot's license, I thought they were quite easy -BUT I never had to fight a wind or foul weather.
The "after the fact" nature of RC flying - can be quite daunting
Having taught a number of guys to fly models , I found the landing to be the most difficult part for some.
The reason is obvious to me .
Many newcomers are introduced by someone who has only recently learned to land in one piece. no real training -just "here -now you fly it" is typical first lesson.
Further , there is typically no training given on how to fly the model at low airspeed so - the landing is simply a necessary evil -which follows chasing the models around at full tilt.
The "trainer" in many cases is an evil handling model - setup in a manner which dares you to do anything smoothly. Why? because basic setup and a bit of groundschool is usually ignored.
My opinion -- full sized craft typically -- are better suited to learning and typically the flier gets far better training in how to land.
The result-- they are eaiser to land

LouW

As an active full-scale flight instructor for several decades and an R/C modeler since the middle 1950’s I will offer my opinion for what it’s worth. There is really no comparison as the skills required are quite different. A model airplane is flown by watching from the outside, while a full-scale airplane is flown using cues from the inside looking out. There is practically no carry over from one to the other. Full-scale pilots often have trouble following what a model is doing and usually must go through the same learning process as any other beginner. On the other hand, I have had opportunity to teach model pilots to fly full-scale aircraft and the same is true. They have to go through the same process, and they have the same problems as any other student.

As to the relative difficulty, flying a full-scale airplane is by far the more difficult of the two. This is obvious by the fact that after a half dozen or so flights on a buddy box a model pilot has reasonable expectations of making a flight and bringing the craft down again in one piece. On the other hand just to takeoff, fly around the pattern and land a full-scale airplane solo takes 15-20 hours of intensive training. To become a fully qualified private pilot requires an average of 80 hours of focused training and experience (and that is really just an entry level of pilot training). (Dick, holding the controls of an airplane in flight gives you absolutely no idea how easy or hard it is to fly.)

Screw up flying a model and you will take home a bag of sticks and may be out a hundred dollars. Screw up flying a full-scale airplane and you will likely be dead.

I love to build and fly my models (I have seven in the shop now). But when I climb into the cockpit of a full-scale airplane I am in a different world. There is really no comparison.

mesae

Well said!

rmh

Low -respectfully --you missed the point-
And in my opinion-based on my experience- the manual dexterity skills required to fly full scale are LESS than to fly a good aerobatic model.
The question wasn't one on judgement - just which is easier .
I have not just "held the controls"- I have even swapped off -flying/ navigating flying coast to coast - but -always with a licensed pilot . I am no fool.
Having worked with a number of full scale fliers -teaching them the skills for model flying - you are right-- there is little or no correlation.
Some knew all of the answers for the correct approach to flying but they "just couldn't get it".
Others get it - first time out.
Training a new flier takes a lot of basic groundwork for most --BUT for some - none required .
I compare learning to fly much like learning a musical instrument - some people have the natural skills and it is only a matter of learning the rules from that point.

old git

In the First World War many pilots had 8 hours in the book when they reached their active service units and indulged in aerial combat. Some survived and I have no doubt that the aircraft were more difficult to fly then. My model trimming skill transferred well when sailing a Yacht (keelboat) less so in a dingy and even less when attempting to fly a full size glider. I think that an aircraft possessed of inherent stability and easy responsiveness invites transfer of skills and leaves time for thought. In my opinion a full blown aerobat would not make for a good trainer.

As to flat aerofoils, it seems that an apprenticeship of Hand Launched Gliders gives a very useful grounding to understand aerodynamics. As a pre teen (just post war, there were no teenagers in that era) I built every configuration of glider imaginable. I built a KeilKraft Achiles as a low wing model to the horror of my father. Low wing models were considered a dark art in those days. Look up KAMLET Knights Aerodynamic Low wing Elementary Trainer to see how difficult it was perceived to design and trim a low winged aircraft.


old git

LouW

In the First World War more pilots were killed in training accidents than by the enemy. Even so the typical time going into combat was more like 20-30 hours. By the time of the Second World War the services had learned a little more about flight training. The first “phase” check in primary training was a solo flight and it was given at about 8 hours. Those not meeting it were given additional training. If they hadn’t soloed in 12 hours they were usually washed out of the program. It was wartime and the pressure for pilots was great. After solo, primary training continued then was followed by “basic”. After basic training, “advanced” training proceeded after which they got their wings. They were then sorted into single engine (fighters) or multiengine (bombers or transport) where they were given additional training for assignment to an operational unit. Pilots reporting for action typically had 100-150 hours flying time before meeting the enemy. The actual process varied somewhat for different services but the times are typical.

I have personally trained many pilots over the past 40 years, and I stick by my statement.