Why are engines mounted foreward?

[Daravon]

Why are engines mounted usually a good ways in front of the wing?

I build and fly spads, and if I could dispense with the wing dowel (not hard) I could slide the fuel tank under the wing, near the CG, and have the backplate of the engine right in front of the wing. This would let me shave off a few ounces, and get a few more planes out of every section of downspout.

How would flight characteristics change?

In physics we learned that when it comes to producing moments and such, a force can act anywhere along its line of action without changing the net effect.

[Sparky Paul]

The tail weight hasn't changed in your sketch.
So you'll be carrying ballast..useless weight to get the c.g. forward to where it was.

[Daravon]

I'm fairly certain the tail could be lightened to match, in fact with my 46 I usually put both my servos out on the stab and overbuild the tail to get it to balance. Also assume you could slide the engine back to any convenient length for balancing. Or just hang a bigger engine on it! Might as well have the weight that used to be fuselage be engine.

That does explain why they are mounted so far from CG on most planes though. Tails aren't massless. How silly of me.

[portablevcb]

Or shorten the fuselage so the tail is closer to the wing so the CG remains on the same place. That will change flight characteristics a bit with the shorter tail moment. Taken to the extreme you end up with a flying wing :)

charlie

[lockheed martin]

Or keep the tail in the same place and use a larger heavier engine further back.

[perttime]

I have understood that having your weight distributed close to CG is good for aerobatics, i.e. it is easier to start and stop the movement of a light wing or a light tail.

[lockheed martin]

Yes that and also haveing the wieght nearer the COG will help the plane be more axial in rolls and loop tighter.

[Thomas B]

Why are engines mounted usually a good ways in front of the wing?

I build and fly spads, and if I could dispense with the wing dowel (not hard) I could slide the fuel tank under the wing, near the CG, and have the backplate of the engine right in front of the wing. This would let me shave off a few ounces, and get a few more planes out of every section of downspout.

How would flight characteristics change?

In physics we learned that when it comes to producing moments and such, a force can act anywhere along its line of action without changing the net effect.

you can certainly reduce the nose moment as long as you reduce the tail moment, so that things will stay in balance.

What you give up is some pitch stability and quality of handling in that axis.

The shorter moments can make the model react much faster to pitch commands. This is a boon for some, but can be not so good for flyers with slower reflexes.

you end up with a model that is much less damped in the longitudinal axis

Control line combat models have had this arrangement for a LONG time, for the obvious reason. Many of the newer R/C combat only designs have gone to short fuse moments and longerer wings, for instant pitch reaction in battle.

Moments are one of those grand compromises that are made in every aircraft design. More moment is more stable, less moment is less stable, in general. Something is the middle of the bell curve is usually best, overall...:)