I think there is lot of confusion about these ECL model weights.  It almost appears that guys are trying to match their old IC model weights with the ECL INCLUDING THE BATTERY!!!

I mean maybe this is obvious, but I am starting to wonder.

If you can match your old IC engine weights with an ECL is it much lighter...

Take Dave Fitz's WC airplane.  620" wing at 64 oz, burning 8 oz of fuel.  That is 72 plus oz at takeoff.  72/620 won the world championships.

There is another thread where the fellow is building a Geo XL that he says is going to be 55 oz...  that is finished weight...  no fuel weight.  That means he is really building a Geo that would weigh in the 48 oz range with a PA?  That is crazy light.

Jason and Brad:

If it helps, I posted a table of power system weights on this subsection about 2 months ago, comparing several IC systems (including fuel weight) and several ECL systems. I used my PA61 which is probably very close to the PA51.

The comparison of weight is tricky because of the fuel burnoff, of course. But using the moment and weight table it is clear that the ECL systems, even keeping full takeoff weight through the entire flight, can equal or exceed the IC system as far as CG and overall weight. My China Clipper with a Turnigy 42-50 (a 9-oz motor) and 15-oz battery will have the same CG and overall weight as the same model with the PA in it and a full tank. The E-motor is lighter than the IC engine so the moment is less, while the heavy battery is closer to the CG, somewhat ameliorating its larger moment compared to tank + fuel. The total moment favors the E setup! And using a 7-oz motor (such as 2826) would be even more favorable.

Slightly off subject, but this is a good opportunity to congratulate Brad on the T-Rex. I have only seen pictures and followed the building threads, but very impressive! This looks like a great leap forward for factory-built models.

Brad,

Couple your findings with the fact that an ecl model can be built lighter as it doesn't have to take the vibration loads and you see a major advantage of ECL.  Not to mention the airframe life span increase as it isn't exposed to oil and fuel its entire life. 

Congrats on giving ECL a chance.  You won't be disappointed.

Archie Adamisin
Muncie, Indiana

Guys,

Be careful not to go to light in the front end/motor mount area. Even though there is no pounding vibration we do have torque that is equivalent to IC power plant. Also, the nose does need to resist side loads that could  cause cracking. It seems that a good approach is to use at least hard balsa for the doubler then add a 1/8" lite ply cross plate that forms a stiffener either as a glued in or bolted in.

Best,               DennisT

Thanks!!!  I am still excited to hear flying reports.

Doug and I always used 22 oz for PA 65/header/pipe/spinner/CF prop/Sullivan 8 oz tank.  I think you will find that is a good number.

Add a PA 75 (larger heavier case) and 8 oz of fuel and you get something like 32 oz wet...  You can get a pretty beefy ECl setup for 32 oz...

ummm NO you don't  a  PA 75 is only 1\2 ounce heavier than a 51 61 or 65,(not 10 ounces) and is the same  weight as a OS VF 40

Randy

You're right.

My new plane will be 62 ounces (takeoff weight) at 650 in^2. The power will be equivalent to a 75. I have flown an electric Impact at this weight and it was GREAT. It is in fillet cutrrently, and is below the weight limit to see 62 ounces.   

That is light brutha...

I dunno, I think the target weight should always be LESS.  SO why is it that my birds always end up weighing MORE???      

"What is ALARA ?
ALARA is an acronym for As Low As Reasonably
Achievable. This is a radiation safety principle for
minimizing radiation doses and releases of radioactive
materials by employing all reasonable methods.
ALARA is not only a sound safety principle, but is a
regulatory requirement for all radiation safety programs. "

I guess that quantum stuff keeps you from using fixed numbers like we do.