Engines, Propellers, and Weights
 

Hey,

I have this inclination to answer yes, but I just want to confirm: a properly built model airplane should ideally take off, even without propellers, right? (It would just land a few moments after being in the air.)

Also, when building a model, which is a better starting point? Choosing an engine and building on its specs or creating a model first and choosing an engine + propeller afterward?

Thanks!

Mark<br type="_moz" />

RE: Engines, Propellers, and Weights
 

I believe your first question means whether or not a properly built and balanced airplane can glide without power, and the answer is yes. Obviously the flight pattern without power very much depends on the air frame, but the answer is yes. If you mean whether or not the plane will remain airborne after "throwing" it - and assuming you are talking about a real RC plane with all the gears built in it - you would find it to be a very short flight! An RC plane with all the gears in it is relatively heavy and will need a certain air speed to remain airborne. You may not be able to impart the proper air speed to it by throwing it, which means the story will not have a happy ending. I am also assuming you are asking this question for educational purposes and not really intending on trying this. If so, you may want to consider free flight planes that are designed for this purpose.

As for your second question, unless you already have an engine that you want to find a plane for, my recommendation would be to choose your plane first, and then match the powertrain to it.

RE: Engines, Propellers, and Weights
 

If you mean can you toss it by hand and let it glide, yes.

If it is going faster than stall speed it will glide until it lands or until it stalls and falls out of the air.
If it is going slower than stall speed it will just fall to the ground.

If this will be your first flying model you should buy a kit and select the engine and other parts based on the kit designer's recommendations. You need to learn to build and fly before you try to do your own design.

RE: Engines, Propellers, and Weights
 

Throwing would make a short flight, but would ground take-off actually be able to get the plane (though only momentarily) into the air?The way I see it, takeoff is just like a person "throwing" an airplane, though now the airplane is doing that throwing by itself. If the airfoil is good, it should get the plane up into the air even just for a moment, running only on the thrust made by the takeoff, right? Or is that nonsense :P

And on the engine, is there some sort of relationship between model weight, for instance, and an appropriate engine + propeller?

RE: Engines, Propellers, and Weights
 

The engine does not drive the wheels. Thrust, from a prop or a fan, is required to make it move.

RE: Engines, Propellers, and Weights
 

Size, weight, and type of airframe determine power requirements.

Here is a listing of trainer plane kits from one retailer.
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=AAB
There are lots of retailers and other choices but the Tower web site is one of the easier ones to use.
The recommended engine size and wing span is listed in the item name.
Example "Goldberg Eagle 2 Trainer Kit .29-.45,63"
Maximim recommended engine is .45 cubic inch
Wing span 63 inches
If you click the links and read the notes you will see the estimated weight of the finished model.
Most trainer type models that recommend a .45 size engine will be similar size and weight.
When you buy an engine, the manual should list a range of prop sizes that are suitable for the engine. You can ask local modelers, or ask on RCU, for specific prop recommendations after you have a plane and engine.

RE: Engines, Propellers, and Weights
 

mjerome,

As long as the wing receives enough air speed, and it is facing it at positive angle of attack (more than zero and less than 12 degrees), the wing will lift the weight of the rest of the airplane.

For a relationship between model weight, engine and propeller, check these articles:

http://findarticles.com/p/articles/m...=rbxcra.2.a.22

http://findarticles.com/p/articles/m...=rbxcra.2.a.22

http://findarticles.com/p/articles/m...=rbxcra.2.a.33

http://findarticles.com/p/articles/m...=rbxcra.2.a.33

Regards!

RE: Engines, Propellers, and Weights
 

Thanks guys! That sheds a little more light now.

One last for now, could you direct me to where I could shop for these engines, maybe online also? It would be nice to see the brands commonly used around. Also, are there engines which run on electric power and not gas? That would be nice.

RE: Engines, Propellers, and Weights
 

I suggest you look at the very first posts in the "Beginner" forum. They are "Sticky", meaning they stay at the top of the list, and they are packed with information on planes, engines, electronics and techniques.

When you have read those posts, look in the Engine forums and the Electric Beginners forums, and you will find plenty of information.

Best wishes,
Dave Olson

RE: Engines, Propellers, and Weights
 

Good information also here:

http://www.gettingairborne.com/

http://www.masportaviator.com/sectionalchart.asp

http://www.rc-airplane-world.com/rc-...-site-map.html

http://www.rcuniverse.com/university...id=0&classid=0

It would be great for you to contact people in your area who have experience with model airplnes.
See the attachment for a list of RCU members that live in Manila.
You can get there by using the Members List button above, and then you can send a PM or e-mail to those people for a first contact.

Regards!

RE: Engines, Propellers, and Weights
 

Thanks for all the help guys, especially<span class="Apple-style-span" style="font-family: verdana, arial; font-size: 11px; font-weight: bold; -webkit-border-horizontal-spacing: 1px; -webkit-border-vertical-spacing: 1px; ">lnewqban!<br type="_moz" /></span>