this diagram is wrong , lift always is behind the weight , lift ahead of the weight is a unstable config and can only be controlled using fly by wire ,

oops that was a mistake since we were concentrating on the thrust drag couple I just drew it there. So normally without elevator trim the pushers will be going down where other planes will remain in the same level?

Bingo, that's why easy star is meant for easy flying.

Quote from: augustinev on April 20, 2011, 07:28:56 PM
For a Conventional Aircraft thrust drag couple is nose up and Lift Weight Couple is Nose Down

However for aircraft like easy star or axn floater (Like a sea plane) the thrust drag couple and lift weight both are nose down couple , (Because the thrust line goes above the drag line) that is why thrust line is inclined, inspite of this you will see the trim point of the tail plane is for nose up (tail down).

How does one determine the drag line? In a conventional tractor, it is shown as being directly opposite to the thrust line, so how is it different in a pusher?

thumb rule (1) for a low-winger, between the wing line and the fuselage reference line (See image) (2) for a mid-winger through the aircraft (3) for a high winger , between the fuselage and the wing line. if there is a fixed undercarriage, then it shifts marginally towards the undercarriage

The nose down couple for a Low winger seems to be very similar to the pusher(if the motor is not tilted) ?. Only difference is the starting point of the thrust line. but that causes adverse effect of the plane to be pulled down?

That is why thrust line is so very important. it is just a thumb rule 2 deg down and to the right, actually with controls neutral fly your foamie and small size aircraft vertically while holding the spine as you slowly release the pressure see to which side is it falling adjust motor mount to the opposite side. for big aircraft run in from right to left or left to right, right in front of you pull up and with power on see which side she is falling  opposite side is where your thrust line correction should be. for a low winger thrust drag couple is more nose up than high winger, high winger it is almost negligible.

some people like me are very very finicky of the thrust line, some trim it off or correct it while flying

This maybe a stupid question to ask...but havent tried it ..hence asking

In a brushless setup, is the thrust generated by prop the same in either direction of rotation of motor?

I use GWS props and in tractor setup the markings (eg GWS 11x4.7) are facing you, i.e away from motor (looking from the front side). In other words the convex side of the prop is in the direction of the flight.

Will the thrust generated be same, no matter which direction the motor rotate?

Sorry if its a silly question

 No it wont be the same, think of the blades as wings moving through air.
Also read post #31 on page 2 of this thread.

where is the drag line for the following
1) AXN Floater type pusher which has motor above and behind the wing
2) Pusher jet which has the motor almost level with the wing

slightly below the wing line stubbier the fuselage lower the line

Dear Mr Augustinev,

I am in process of making a flying wing

Here is the plan..

http://www.rcgroups.com/forums/showthread.php?t=497083

I wanted to know, what care should i take to reduce the speed at which tip stall occurs.

I would like it to glide nicely and land at a slower speed without stalling.

Bakya

This wont tip stall, basically because there is a tip fence, this will glide extremely well, at very low speed this will do something called a Falling Leaf as the name suggests will fall like a leaf. this design is proven design . Flying Wings, B1B to name a few.

One thing though only this wing can do and that is inverted spin at very high rate of roll. after you fly it and gained confidence do the following :-

gain height , cut throttle and very low speed push right rudder and move Right stick diagonally to the right and forward(Mode II) now watch the fun,  she will spin like a top. for recovery simply open full power.

PS
my batix is coming real slow, but steady

Thank you sir 

I was doing some glide tests with it without installing the tip fence (by that you mean the stabilizers at the tips right?). I had a attached weight at the nose such that the CG was at the position as given in that thread. I held it above my head and let the glide with a little force. It would travel a little distance very nicely and then the nose would go up and it would fall down. Was this tip stall? If i do the same with the little stabilizers at the wing tips, would it glide better? or was my CG off ?

at stall she should go nose down that is conventional stall, however a delta or a swept back wing wont stall classically , if she was gliding well then CG is not the issue, wing fence also gives it directional stability therefore a must, all the best

BASIC PROPELLER PRINCIPLES - TORQUE REACTION

Newton's Third Law says for every action, there is an equal and opposite reaction. As applied to the airplane, propeller revolving in one direction, an equal force is trying to rotate the airplane in the opposite direction. this reactionary force acting along the longitudinal axis is responsible for torque rolling the aeroplane.  There are many compensating methods for a fixed wing aeroplane, they are :-

(a) Compensation by Rigging This method entails one wing producing more lift than the other , however this method had a drawback, compensation worked only for a particular speed, outside this rigged speed the aircraft flew cross controls.

(b) engine offset method This is more popular method and is used in RC Aircraft too (2 deg right and down)

(c) Compensation by cantering the fin This method is more popular in a transport aeroplane, the prop-wash is a rotating mass of air, by sufficiently cantering the rudder and or the fin provides adequate compensation. (see Image)

Let us discuss an example here All this is clearly visible in a Hover , you can see (http://www.rcindia.org/rc-maneuvers-and-skills/aerofly-pro-delux-sim-videos-enjoy-!!!/), to hold a hover you still need to hold opposite aileron, otherwise she will torque roll. Even this roll is controlled by adequately removing the Aileron Roll offset, some times in some aeroplane you run out of aileron and she no matter how-much ever aileron you hold, still torque rolls, to recover from the situation you open power to get some prop wash onto the aileron (More on 3D Aerobatics later)

The magnitude of this moment is dependent on many variables. Some of these variables are: (1) size and horsepower of engine, (2) size of propeller and the rpm, (3) size of the airplane

Torque Reaction in Heli [/u] However in a heli this torque reaction needs to be controlled by a (a) tailrotor (b) contra rotating blades or by using (c) two separate rotors like in chinook. The reason is pretty simple (See para above) it is to do with the Size RPM of the engine and Size and RPM of the Prop (In this case the Rotor Blade), The MAGNITUDE of the torque force is so high that an aerodynamic surface is not adequate to control this is also contributed by low forward speed at which a Heli is desgined to fly(In Jet engine sometimes you do reach such a situation at very low speeds) That's why when you loose tail rotor you loose control of a heli

Hot and High What is it ?

Aircraft including RC performance is affected by Density Altitude. What is Density Altitude

Density altitude is the altitude in the International Standard Atmosphere (A Standardized Atmospheric tables issued by ICAO) at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. "Density Altitude" is the pressure altitude adjusted for non-standard temperature. (See image where the indicated altitude of the aeroplane is 5000 feet however due to temperature see how its true altitude varies)

Put in a layman terms: - Pressure altitude represents a physical distance above sea level as determined by the weight of the atmosphere, density altitude represents the number of air molecules in a given volume of space.  That space may be the area of air beneath the wings, the volume within the engine cylinders or the area of air surrounding a spinning propeller

Both an increase in temperature and, to a much lesser degree, humidity will cause an increase in density altitude. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude. if the place itself is at high altitude it makes matters worse. That is Hot and High for you (Explanation in Wikipedia sucks)

There are only Four types of altitude you need to know and they are :-

True Altitude  Actual height in feet above mean sea level.

Absolute Altitude  Actual height above the ground.

Pressure Altitude Weight of the atmosphere measured in inches of mercury, millibars, or hectopascals.

Density Altitude  Equals pressure altitude corrected for non-standard temperature.  

what effect does it have on the Aircraft

Fixed Wing
1. Take Distance is more
2. Take off speed is more
3. Braking Distance in case of reject take off is more
4. Take off angle is shallow

Helis
1. IGE Hover power is more
2. OGE to IGE hover transition is difficult
3. AUW for hover landing is less (If it was already overloaded for the said density altitude it wont hover at all, it will sit down like a lump of ...you know what)
4. Hover takeoff collective is more, hover take off load carrying capacity is less

Basically hot and high affects Heli more than Aeroplane and tests pilots skills a lot, including RC heli

Worth a watch 

Simplicity , thy name Bruce

Torque reaction...
Well my scratch built pusher tends to turn right on its own. I have to apply sizable rudder trim to keep it straight. Could this be due to prop/torque reaction?

On a pusher i am assuming you have a small prop, in that case its most probably the thrust angle

well!! I got a 9 inch prop on with a low Kv motor. The motor is mounted straight in the sense the thrust angle is not visible.

9 inch is a big prop, if it turns only when you throttle up then the turning tendency is due to torque reaction which you'll have to correct by giving some correcting thrust angle.

is it happening on ground?