Opinions on my experiement wanted..

[ziomatrixacs]

I am working on a plane, a little different from most. My goal is something 3D capable but a sleek pattern plane frame.
No numbers have been set, everything is still in percents (no weight, no area ,ect) and no structure/material/powwer plant has be decided
This is what I came up with. I have the elevator full flying, with the pivot on the elevators CG. The ailerons are forward swept with autobalancers. The drawing may not reflect the following numbers, im still tweeking them..I tried to make the elevator area 30% the size of the wing area. The ailerons are going to be 27% the wing area. The rudder is going to be around 27-30% the wing area. I am going to put the distance from rudder pivot point to CG to be 2 - 2.5 wing average chords. The distance from elevator PP to CG is 2 "WACs" and the distance from CG to the nose is 1.5 "WACs"

Any feed back on my idear' is much appreciated. Im trying to untangle the laws of physics and aerodynamics on a small scale with no real tools except my mind and a computer.

[gyrocptr]

.... the elevator full flying, with the pivot on the elevators CG. ....
I seem to recall that with a full flying stab, you would want ~25% of the stab area located ahead of the pivot axis. Then, if you want to weight-balance the stab, relative to the pivot-axis, you would add weight to the stab-portion located forward of the pivot axis.

.... rudder 27-30% of the wing area....
That would be huge! Even the whole stab wouldn't that big. 27-30% of the total area of the vertical fin? Typical vertical fin = ~10-15% of the wing area, depending on the amount of fuselage side-area located behind the wing.

....elevator (??full-flying horizontal stabilizer) area 30% the size of the wing area....
Pretty large. Stabilizer area equal to 20-25% of the wing area is typical when distance between AC (aerodynamic-center) of wing and AC of stabilizer is 2.5-3x the mean aerodynamic chord of the wing.

[ziomatrixacs]

Thanks! Ill implicated that advice. I just made a 7" model with movable wings and stuff. I can change an angle real easy by bending the foam with out having to reinforce the plane. I gave it a few good tosses in my room and found some real interesting things.

That design seems to try to flip upside down with full rudder either way. Not sure why, probably an aileron effect from having a rudder too tall.

[Montag DP]

That design seems to try to flip upside down with full rudder either way. Not sure why, probably an aileron effect from having a rudder too tall.Yeah, it looks like most of the rudder area is above the CG. You'll probably want to adjust the shape of the vertical fin and even the shape of the fuselage so that the area is similar above and below.

[ziomatrixacs]

i designed this plane a while ago. I think I had the CG off, because it flew funky. I cant test it again, I "decomissioned" the air frame.

I had alot of the rudder "underslug" of the CG line. Im trying to get that CG line on the thrust line, so it rolls real smooth. That plane I posted above is real skinny compared to this one. Like a pattern plane sorta. But less fuse. side area might make knifes edge harder to do. I was thinking about experimenting with canards on a 3D bird, but its hard to implicate since the distance from LE to nose is short.

[gyrocptr]

Thanks! Ill implicated that advice. I just made a 7" model with movable wings and stuff. I can change an angle real easy by bending the foam with out having to reinforce the plane. I gave it a few good tosses in my room and found some real interesting things.

That design seems to try to flip upside down with full rudder either way. Not sure why, probably an aileron effect from having a rudder too tall.

Perhaps your center-of-gravity location, relative to the top and bottom of the fuselage, is positioned too high above the wing. See if adding weight to the belly helps to keep the plane "upright".

[ziomatrixacs]

That would be huge! Even the whole stab wouldn't that big. 27-30% of the total area of the vertical fin? Typical vertical fin = ~10-15% of the wing area, depending on the amount of fuselage side-area located behind the wing.

You are right, thanks for catching that. I just though about have a wing panel as a rudder. :rolleyes:


Pretty large. Stabilizer area equal to 20-25% of the wing area is typical when distance between AC (aerodynamic-center) of wing and AC of stabilizer is 2.5-3x the mean aerodynamic chord of the wing.


Yeah, im trying to get it to have plenty of authority...:D

The hardest part of my experiments is actually coming up with a question..I see problems but dont really know what the problem is. :confused: Other problem is figuring out what instance you are applying the question to. IE, a low wing trainer isnt as good as a high wing trainer.

I am trying to figure out how the size of the elevator and the distance from the wing changes performance.
-A large elevator near the main wing is basically a flying wing (but slightly more complex since the elevator is directly in the turbulent air flow from the main wing)
-A large elevator far away gives the effect of a tandem wing, which behaves like a weird biplane almost. What does this mean?


-A Small elevator at a long distance can provide equal torque (IE, pitching ability) to as a large elevator at a short distance.
But what is the advantage? Maybe the small elevator at a long distance has less frontal drag and is exposed to clean, undisturbed air so its more efficient but the weight added by that fuselage extension makes the plane heavier, which means you need more weight up front, or a longer nose.

Since a 3D plane is usually tossing and tumbling, its akin to splashing in the water and trying to keep stable. I think it helps to have as much tail surface area exposed to the air even if the air isnt "clean." This should give the tail authority in a lot of situations. Say you are hovering. A small tail far away wont be in the prop wash, so it become ineffective. A large tail close will be right in the prop wash, which gives a lot of authority.

Is an airfoil really that important for a 3D bird? These flat foamies out today made me think. Air molecules do not get scaled up, so a 1/3rd scale cub flys differently than a full scale cub. Smaller scale models can use simpler rules of thumb, like Cubic wing loading, Wind loading and those equations to get a rough idea of how a plane will fly. While a large airplane needs more advance calculations. I kinda feel like its the gap between General relativity and Quantum mechanics. (I know, it makes no sense) The Bernoullian principle and the Newtonian principle when added together equals to lift. The Newtonian principle seems to apply to both Large and Small scale models. The Bernoullian principle seems to have the best result with a larger model than a small one albeit the effect is there. An airfoil does help, but how much does it enhance performance?

I know I will be sacrificing some things for other things and there really is no all purpose trainer, pattern, 3D plane. I am just trying to find a balance that suits my style while learning about airplanes and how things effect each other..instead of paying $100 for an ARF foamie. I have searched the internet and forums for years for a GOOD article or even a post on this stuff, and havnt found any.

[ziomatrixacs]

Perhaps your center-of-gravity location, relative to the top and bottom of the fuselage, is positioned too high above the wing. See if adding weight to the belly helps to keep the plane "upright".

yeah, that is the reason why the first plane is thinner than this one. No heavy plastic canopy to toss the balance off. Im trying to make the fuse roomy as possible, and allow me to mount weights strategically through out the frame to get a balance in all 3 axis. Most people go to just the main CG on the wing which is OK for general flying, but Id also like about tuning the model. Im just worried that the plane I build is inherently out of tune.

[HugePanic]

for comparing elevator/rudder designs you can calculate the elevator/rudder VOLUME!

Rudder/elevator VOLUME = AREA x Distance(to CG)

so it's very easy to calcualte your elevator-surface by comparing it to other planes.

mfg
Ich

[ziomatrixacs]

for comparing elevator/rudder designs you can calculate the elevator/rudder VOLUME!

Rudder/elevator VOLUME = AREA x Distance(to CG)

so it's very easy to calcualte your elevator-surface by comparing it to other planes.

mfg
Ich


Im not sure I understand. What does the elevator-rudder volume do?

I made a 7" foam model of the other plane so I built both of the planes on this thread as 7" models. Oddly enough, when both scaled to the same size. The wings were exactly the same, so was the distance between nose and tail. The new planes rudder was smaller and the fuse. thinner. The elevator was slightly smaller too. I designed both of these airplanes with the TLAR method.. so 2 airplanes designed months apart came out about 80% the same. Is that good or not? :o

[gyrocptr]

I am trying to figure out how the size of the elevator and the distance from the wing changes performance.
-A large elevator near the main wing is basically a flying wing (but slightly more complex since the elevator is directly in the turbulent air flow from the main wing)
-A large elevator far away gives the effect of a tandem wing, which behaves like a weird biplane almost. What does this mean?

-A Small elevator at a long distance can provide equal torque (IE, pitching ability) to as a large elevator at a short distance.
But what is the advantage? Maybe the small elevator at a long distance has less frontal drag and is exposed to clean, undisturbed air so its more efficient but the weight added by that fuselage extension makes the plane heavier, which means you need more weight up front, or a longer nose.

Since a 3D plane is usually tossing and tumbling, its akin to splashing in the water and trying to keep stable. I think it helps to have as much tail surface area exposed to the air even if the air isnt "clean." This should give the tail authority in a lot of situations. Say you are hovering. A small tail far away wont be in the prop wash, so it become ineffective. A large tail close will be right in the prop wash, which gives a lot of authority.

From practical experience, short fuselages and short wings (low aspect ratio) work well for 3D because people have found that the plane reacts faster to the controls. One technical/engineering reason arises from the concept of "polar moment of inertia" (inertia against rotation; harder to start, harder to stop). For example, the longer the tail, the longer the lever and the greater the control exerted by the stab/elevator. However, the polar moment of inertia increases in proportion to the square of the length. For example, if you double the length of the tail (or nose), the inertial resistance to rotation will more than double, even if the weight of the tail (or nose) is kept the same. Thus, a longer tail allows good stability with the use of a smaller stab (if desired), but typically slows the reaction of the plane ("smoother" flight), unless, of course, one increases the size of the moveable portion of the stab.

Is an airfoil really that important for a 3D bird? These flat foamies out today made me think.
A thin flat plate is a fully symmetrical airfoil with zero curvature of the upper and lower surfaces. But compared to symmetrical airfoils with curvature, the flat plate has higher drag at high angles of attack (OK for 3D), and low beam-strength :( . Beam-strength increases in proportion to the square of the wing thickness :). However, weight increases in proportion to the cube of the length dimensions of the wing :(. That's why wings for heavier planes are designed to be "hollow" with the material (spars and sheeting) concentrated at the outer surfaces of the wing.

Air molecules do not get scaled up, so a 1/3rd scale cub flys differently than a full scale cub. Smaller scale models can use simpler rules of thumb, like Cubic wing loading, Wind loading and those equations to get a rough idea of how a plane will fly. While a large airplane needs more advance calculations. I kinda feel like its the gap between General relativity and Quantum mechanics. (I know, it makes no sense) The Bernoullian principle and the Newtonian principle when added together equals to lift. The Newtonian principle seems to apply to both Large and Small scale models. The Bernoullian principle seems to have the best result with a larger model than a small one albeit the effect is there. An airfoil does help, but how much does it enhance performance?

From a practical standpoint, it boils down to the following:
The bigger the wing area (e.g. more square feet), the higher the wing loading (e.g. ounces per square foot) that can be supported while allowing vigorous aerobatics.
The lower the wing-loading, the slower the plane can fly, without stalling, at low power and ordinary angles of attack.
For high-alpha maneuvers you will be targeting thrust-to-weight ratios of 1.5-2, or more.
A single wing with a total wing area is more efficient (for lift) than two or more smaller wings having the same total wing area. Why biplanes? The wing-spans are shorter (lower moments of inertia for 3D); more total wing area in smaller space (good for indoor 3D); higher drag for slow-speed 3D; lower efficiency viz. lift, but the widely spaced apart top and bottom wings with the struts and filament braces in between provides a light wing-structure having very high rigidity and very high beam-strength.

I know I will be sacrificing some things for other things and there really is no all purpose trainer, pattern, 3D plane. I am just trying to find a balance that suits my style while learning about airplanes and how things effect each other..instead of paying $100 for an ARF foamie. I have searched the internet and forums for years for a GOOD article or even a post on this stuff, and havnt found any.

Suggestion: Learn basics with a "trainer" (aileron-elevator-rudder-throttle) set up with generous-sized control surfaces, but small control throws. Progress to the point where you can perform consecutive aileron rolls while maintaining a constant altitude using coordinated elevator-control.
Install larger motor and increase throws on the control surfaces of the "trainer". The plane will be more capable of ordinary "pattern" maneuvers. However, yaw/pitch and yaw/roll cross-coupling will probably discourage maneuvers that require extended flight in knife-edge. Practice slow-flight in where you coordinate rudder and throttle with high angle of attack to maintain constant altitude. If there is a 10-15 mph wind, practice maintaining constant altitude with zero (or backward) ground speed.
When you feel that you are beyond the "trainer" stage, upgrade to a "foamy" plane designed and powered for 3D (note: high powered "fun-fly" planes do not equate to 3D planes). A good 3D plane will have large amounts of side area, and will exhibit no yaw/pitch cross-coupling and no yaw/roll cross-coupling. There are downloadable, free plans located throughout this news group (e.g. search "Nasty", "Regal", "Amos" ...). If you use reduced control-throws, the plane will be capable of all of the "pattern" maneuvers, including point-rolls and extended knife-edge flight (even at partial throttle). With increase control-throws, the plane will be capable of all of the 3D maneuvers. Adjust the plane's CG and control-throws to match your own particular flying "style" and desired level of "twitchiness".

[ziomatrixacs]

Suggestion: Learn basics with a "trainer" (aileron-elevator-rudder-throttle) set up with generous-sized control surfaces, but small control throws. Progress to the point where you can perform consecutive aileron rolls while maintaining a constant altitude using coordinated elevator-control.
Install larger motor and increase throws on the control surfaces of the "trainer". The plane will be more capable of ordinary "pattern" maneuvers. However, yaw/pitch and yaw/roll cross-coupling will probably discourage maneuvers that require extended flight in knife-edge. Practice slow-flight in where you coordinate rudder and throttle with high angle of attack to maintain constant altitude. If there is a 10-15 mph wind, practice maintaining constant altitude with zero (or backward) ground speed.
When you feel that you are beyond the "trainer" stage, upgrade to a "foamy" plane designed and powered for 3D (note: high powered "fun-fly" planes do not equate to 3D planes). A good 3D plane will have large amounts of side area, and will exhibit no yaw/pitch cross-coupling and no yaw/roll cross-coupling. There are downloadable, free plans located throughout this news group (e.g. search "Nasty", "Regal", "Amos" ...). If you use reduced control-throws, the plane will be capable of all of the "pattern" maneuvers, including point-rolls and extended knife-edge flight (even at partial throttle). With increase control-throws, the plane will be capable of all of the 3D maneuvers. Adjust the plane's CG and control-throws to match your own particular flying "style" and desired level of "twitchiness".



I am in a bit of a hurry right now, only a few minutes to type a reply. I have to go to a Commanders Call :(
After reading that, Id just like to add I am not a beginner to flying, just an intermediate to building my own stuff. I started off building my own model airplanes, with absolutely no knowledge except the absolute basic things. (no idea of CG, wing loading, ect.) I just knew you need a wing, motor and tail to fly! (eventually I got better and better) Now I am trying to understand how a certain aspect of a plane effects the overall performance. I am very confident in my flying, and have flown quite a wide variety of planes and helicopters. I like learning new things like this!

[HugePanic]

I am in a bit of a hurry right now, only a few minutes to type a reply. I have to go to a Commanders Call :(
After reading that, Id just like to add I am not a beginner to flying, just an intermediate to building my own stuff. I started off building my own model airplanes, with absolutely no knowledge except the absolute basic things. (no idea of CG, wing loading, ect.) I just knew you need a wing, motor and tail to fly! (eventually I got better and better) Now I am trying to understand how a certain aspect of a plane effects the overall performance. I am very confident in my flying, and have flown quite a wide variety of planes and helicopters. I like learning new things like this!

new proposal:

JUST BUILD IT!!!

your planes look good enough to fly well!
put the CG to 20% and have fun...
later move the CG and find out what happens....

there can't be more damage than a some $ if you build a foamy... :)

[bwalt822]

I don't know if this has been suggested because i havent read all of some of the long posts but,

You would want to put the pivot of the full flying elevator at the aerodynamic center of the elevator. This is where the aero forces would balance and aero forces would be much greater than gravitational forces. It can be thought of as the aerodynamic version of CG.

3D airplanes have shorter tails because of the moment of inertia thing mentioned earlier AND because the tail needs to be in the propwash to work since airspeed is nearly zero. A canard would do almost nothing for a 3D airplane because it wouldn't be located in the propwash.

[ziomatrixacs]

Im back from the meeting. Got a bit of a head ache from nearly getting stranded 1 hour drive away from home. :eek:

new proposal: JUST BUILD IT!!! your planes look good enough to fly well! put the CG to 20% and have fun... later move the CG and find out what happens.... there can't be more damage than a some $ if you build a foamy...

:D I like your thinking! Its winter time where I live, we just got hit with a sleet storm actually. My fingers tend to get real cold while flying. Built one of those Radio heated boxes and my cat started sleeping in it. :o

Thats how I started flying many years ago actually. I remember getting a Humming bird V1 and taking the electronics out to use in my first series of scratch built planes.

#1, the very first one I made was similar in outline to the wing dragon. High wing, pusher with a normal tail. Except mine had a 1/8th solid basswood stab/rudder. 1/16th bass wood fuselage (it was a very thin profile!) and the wing was 3"x9"x36" made from three 3/16th inch dowels in the form of a rough, triangular airfoil. Used trashbags as wing covering. No ribs except one on the tip of each wing half. Of course I knew nothing of wing loading or center of gravity then. I went out in my small city back yard and tossed this bad boy on my very first fly with an airplane. Thing went up at a 50 degree angle and I thought "Oh boy!" then it stalled and came back at me. Nearly lost an eye but I was hooked. :D Turns out a speed 280 wont turn a 9x10 rubber band plane prop (unbalanced of course) and the CG was a tad off.

I have a pretty firm idea of how to get something in the air, im trying to gain a little more knowledge now instead of just "send er' up!" Of course that is THE best way to test something. Just hard to do it with a cat on my radio. :o


I don't know if this has been suggested because i havent read all of some of the long posts but,

You would want to put the pivot of the full flying elevator at the aerodynamic center of the elevator. This is where the aero forces would balance and aero forces would be much greater than gravitational forces. It can be thought of as the aerodynamic version of CG.


I seem to recall that with a full flying stab, you would want ~25% of the stab area located ahead of the pivot axis. Then, if you want to weight-balance the stab, relative to the pivot-axis, you would add weight to the stab-portion located forward of the pivot axis.


Yeah, it was answered in a slightly different way. I was told the % of stab area ahead of the pivot axis, and then to balance the mass. That % I assume is the general rule of thumb to locate your MAC. I bet it will be a bear to do on an odd shaped tail. I had completely forgot about the MAC. I had to look in my 1942 mathematics in aviation book to read up on it again.(no need for wiki!) That makes much more sense than CG.
Does this same rule apply to a standard (part stab and part elevator) tail? It just occurred to me that it might. On the standard everyday tail, there is the part that doesnt move, I call the stab. And there is the part that does move, I call it the elevator. Would you want the pivot of the elevator to be on the MAC? Or does it not matter?



3D airplanes have shorter tails because of the moment of inertia thing mentioned earlier AND because the tail needs to be in the propwash to work since airspeed is nearly zero. A canard would do almost nothing for a 3D airplane because it wouldn't be located in the propwash.

I agree, less weight you have "out there" the quicker it will respond. If you add weight to your wing tips, the acceleration will take longer but it should reach the same speed as the one without the weight (as long as it is internal weight, not effecting aerodynamic properties)
Makes sense you need that tail to be short to stay in your prop wash too. Is the a rule of thumb for prop length to elevator span? Say your prop is 10" and the rule of thumb is you multiply it by 1.7 to get the span of the elevator so your elevator should be 17" wide. I think the distance from the nose would matter too, but its 4:00AM and I dont feel like figuring that one out.



Thanks for all of the help, it has all been very helpful. I noticed some people dont want to read the whole thread, thats fine, just submit some advice. :rolleyes:

[bwalt822]

There arent any rules of thumb that I know of and they would simply be ways to make your plane look like a plane that alreay works. You can make them yourself by comparing proportions of one plane that already works to your plane.

FYI MAC (Mean Aerodynamic Chord (although MAC can stand for Mean Aerodynamic center but I haven't heard anybody use it that way)) and AC (aerodynamic center) are not the same but for a flat plate they happen to be in the same location.

[ziomatrixacs]

Im reading about the MAC now. I did a quick search and I think they are very similar but not quite the same.

Mean aerodynamic chord seems to refer to a point on a wing. Say you have a tapered wing from 10 inches to 6 inches. 8 inchs would be the average chord of the wing. MAC=Chord/4 so you divide 8 by 4 and you get 2. The MAC would be where the 8 inch "rib" would be and 2 inches back from the leading edge. Right?

Mean aerodynamic Center seems to refer to 25% percent of overall area. Although dividing by 4 and multiplying by .25 are the same thing, they have a different meaning. Say you have a wing 100 square inches. 25% of 100 is 25 square inches and the rest is 75 square inches. You would want the 25 square inches between the leading edge and pivot point of the wing and 75 square inches behind the pivot point to the trailing edge. Right?

That is just my interpretation of what I have read so far..


Here is the mini 6.5" model I made. I also gave it a set of canards which aid appear to aid in maneuvers that dont require power or "straight line" maneuvers instead of hovering, torque rolling, ect. I also notice canards are found mostly on planes with a pushing engine than a puller. I think canards on a 3D machine would hurt the performance since its inbetween the motor and the CG of the plane. A full flying elevator seems to be more effective at moving the air, albeit I will have to add a mechanism to rotate the axle for the elevators to connect to.

[ziomatrixacs]

For symmetric airfoils, the aerodynamic moment about the ac is zero for all angles of attack. With camber, the moment is non-zero and constant for thin airfoils. For a positive cambered airfoil, the moment is negative and results in a counter-clockwise rotation of the airfoil. With camber, an angle of attack can be determined for which the airfoil produces no lift, but the moment is still present. For rectangular wings, the wing ac is the same as the airfoil ac. But for wings with some other planform (triangular, trapezoidal, compound, etc.) we have to find a mean aerodynamic center (mac) which is the average for the whole wing. The computation of the mac depends on the shape of the planform.

Taken from a nasa website. Seems a symmetrical airfoiled wing behaves different?

[HerkS]

Mean Aerodynamic Chord (MAC) is different than the mean chord - on a wing like the one on your model it would be a bit inboard of the mean chord. There is no meaningful aerodynamic term "Mean Aerodynamic Center."

If you compute the location and length of the MAC you can begin an aerodynamic analysis of the wing by assuming that the forces on the wing (lift, drag and moment) act at a point on the MAC, 25% of the chord length back from the leading edge of that chord.

[bwalt822]

Bottom line: MAC is based on planform alone and AC is based on the aerodynamic properties of the wing (planform is one of the many variables that affects AC). AC can actually change location for some wings at very high AoA, but MAC never changes location.

Yes I know that AC is defined as the point on the wing where the pitching moment is independent of AoA but this I believe is based on a linearized equation that is only valid near AoA = 0

I think some people could take Mean Aerodynamic Center to mean the same thing as Neutral Point. Neutral point is the AC for the whole airplane including the tail and fuselage. I have never heard anyone actually use this term but if you search for it on the internet it comes up several times so some people may use it.

MAC does not have a lateral location that means anything so MAC cannot be located inboard/outboard of another definition of "mean chord".

[bwalt822]

Your mini model looks like it is proportioned fine. If that is a canard by the plane, it wont do much even if its in the propwash. The moment arm on which it acts will be very short.

[Brandano]

indeed, the reason why canards are usually pushers is because in order to get the CG far back it's easier to mount the motor in a pusher setup, and you need a far back CG to give the canard a big moment arm. On RC models, especially electrics, the CG can be moved backward by shifting other equipment, so a puller canard might be more viable.