Motors Thrust Calculation for twin engine

[Mohamed Emam]

Hi friends,

If we install one engine, it is easy to match its thrust with the plane's weight. But if we install 2 engines, how should we calculate the thrust and should we put in consideration that one engine might break down while flying and the other one should be able to land the plane in that case?

Also, why should we install Gyro for twin engine planes?

 

[breeze400]

I use what's called a twin sync. On my multi engine planes. Sold by Troy built plains. Look it up on you tube. Plenty of videos out on it. Without it a twin will spin out if control if you loose an engine. Before you can react to it.

 

[Mohamed Emam]

Okay,

How should I calculate the thrust?

I use what's called a twin sync. On my multi engine planes. Sold by Troy built plains. Look it up on you tube. Plenty of videos out on it. Without it a twin will spin out if control if you loose an engine. Before you can react to it.

 

[Tony]

One thing to remember, if you lose an engine in the air, you will have to use a LOT of rudder to keep it tracking in a straight line. IMO, by calculating thrust and everything, you are over thinking this. The same motor, same ESC, same battery, same prop, will have the same thrust. If you notice it starting to yaw, then you need to look at what way it's yaw'ing and replace that slow motor.

 

[Mohamed Emam]

I give you an example to explain what I mean:

If I have a motor with thrust 1 KG, and I need to install 2 engines in a 1 KG airplane, should I get 2 engines with thrust 1 KG too, or should I get 2 with thrust 500 G?

MOe

One thing to remember, if you lose an engine in the air, you will have to use a LOT of rudder to keep it tracking in a straight line. IMO, by calculating thrust and everything, you are over thinking this. The same motor, same ESC, same battery, same prop, will have the same thrust. If you notice it starting to yaw, then you need to look at what way it's yaw'ing and replace that slow motor.

 

[Tony]

I see what you are saying. It all depends on if you want the minimum amount of thrust, or if you want enough thrust to get you out of a hairy situation. If I was going to build this plane, I would opt for the 2:1 thrust to weight ratio rather than the 1:1. I like knowing that I have power on tap to pull me out of something.

 

[pvolcko]

If you're going for scale here, you can figure out the actual plane's thrust to weight and use that as a guide, too. A 727 has a thrust to weight of something like 1:3.7. It isn't capable of vertical climb. If your model has 2:1 you'll be able to vertical climb it like crazy. While it may be nice to get out of a jam, it is also not at all scale. You can always setup your throttle curves to be scale for most of the range but unleash crazy power at the high position range. Or use flight modes for different curves.

 

[Mohamed Emam]

Tony,

Regarding losing an engine in the air, to avoid that, should I install a gyro?

-Moe

One thing to remember, if you lose an engine in the air, you will have to use a LOT of rudder to keep it tracking in a straight line. IMO, by calculating thrust and everything, you are over thinking this. The same motor, same ESC, same battery, same prop, will have the same thrust. If you notice it starting to yaw, then you need to look at what way it's yaw'ing and replace that slow motor.

 

[Mohamed Emam]

While goggling found this link, it might help.

http://www.radiocontrolinfo.com/RCcalculator/index.php

-Moe

 

[Tony]

IMO, the best thing to do if you lose an engine in the air is to just bring it back in dead stick.

 

[murankar]

Flite Test did a video about adding a gyro to the rudder. All thats going to do is assist with straight line flying if your doing scale. For 3D it will assist with tail correction so you can learn at a slower pace. lets say you want to learn how to hover a plank, with the gyro in Head Hold you would not have to make as many corrections to the rudder since the gyro will do that for you. You could add a gryo to almost any surface an a plank but its not really useful.

 

[Tony]

One thing I have learned, if you run a gyro on a plane, you do not want to run in HH mode. It will ultimately cause you to crash. Not sure what it is about it. I have never actually tried running a gyro on a plane, this is just what I have read.