While reading the 2013/2014 rules, I found this under Safety:

2.5: Models shall weigh no more than 20 pounds ready for flight, except for fuel.

2.6: Maximum total displacement of the engine(s) will not exceed 1.25 cubic inches. Electric motors of any size may be used to power the model.

It is obvious that the weight of fuel does not count towards total weight of a model and therefore a model equipped with an IC engine can weigh more than 20 lbs ready for take-off.

In the case of electric motor powered models there is no size limit so, one can use a motor that develops 10 hp or more?! Also - nothing is said about the batteries. Does the 20 lbs limit include the weight of the batteries or not? If not - in the case of very large airplanes the batteries can easily weigh an extra 5 lbs if one uses a very large motor.
What do you people in the know think? I am very curious.

Joshua

The reason for bringing up this question is not to stir up the pot, nor challenge or change any rules. I have known for awhile that electric motors offer a way broader power band than IC and in fact have constructed a reduction gearbox that when coupled with a Hacket A60-18L motor was swinging a 31.5 X 31 scale propeller at around 2,500 rpm. I am very serious about this, and, if the batteries weight does not count towards the 20 lbs weight limit, than in my humble opinion some very amazing things can be accomplished in scale competition.

The blatant lack of safety in these rules is appling.

Obviously, ALL weight limits, line sizes and pull tests need to be based on the worst possible case.  Thus, the model weight ALWAYS needs to be the total weight at takeoff.  In Scale the G factors and line sizes are extremely LOW compared to all other control line events. 

For example, think of a 4-pound Corsair or Bearcat that could legally fly in either Class II Carrier or Fun Scale.  In Carrier it would pull 25G's or 100 pounds.  In Scale (I don't have a rule book handy) the same plane would pull 5, 8 or maybe 10 G's, in any case no more that 40 pounds.

A piston engine is limited by its ability to dump liquid fuel through the combustion chamber.  An electric motor can discharge a battery at much-higher rate and achieve more horsepower in the short run.   This might cost the competitor some motors and batteries, but we all know guys will spend the bucks to win.

Gee, I don't know Joshua, it might be that sudden snap, when regaining line tenson, they may be concerned with.   

Ever been there!?   

Charles

Joshua
The maximum model weight for Control Line Scale competition in FAI F4B Scale is 6 KG single engine or 7 KG more than one engine.  For AMA Control Line scale events the limit is 20 Lbs ready to fly less fuel.  For electric power to be ready for flight the batteries must be installed therefore the battery weight is included in the 20 Lb limit.  

The reasoning is that an IC engine burns the fuel in flight lightening the model but discharging the batteries does not change the weight of the model.

Note also that the Pull Test and Line Size chart does not go above 20 Lbs.

Clancy

"2.5: Models shall weigh no more than 20 pounds ready for flight, except for fuel."

Clancy is exactly right.  The C/L Scale rules allow a maximum ready to fly weight of 20 pounds.  Key words ... "No more than"  "Ready for flight"

For electric models that includes the batteries, which are as much a part of the power system as a fuel tank in an IC model.  The model cannot fly without the batteries, so it is not "ready to fly" unless they are included.  (how much do the electrons in the battery weigh?)

For IC, not including the fuel in the ready to fly weight is an inherited clause in the rules that dates back to the 60's, if not the 50s.  It is the same in aerobatics and carrier, and any other control-line events that have a weight limit ... weight is with an empty tank.  

For scale, when you get up near the upper limit in weight, the weight of the fuel is actually a pretty small percentage of the total.  Plus, as Clancy said, the model is seldom flying with a full tank.  Personally, when I competed I always measured my fuel.  I didn't fill the tank, but put in only enough to get through the maneuvers I had planned, plus a little more.  Why carry around the extra weight?  Not including the fuel in the weight limit for IC power has been around for decades in control-line events and has served us well.  I see no need to change it now.

Besides, why would anybody want to fly a C/L model that weighs more than 20 lbs.??  I've flown a 12 lb. airplane.  It's brutal.  You are concentrating so much on turning the circle and not being pulled over, that you can't do any real precision flying.  I just say this, if someone sees some kind of competitive advantage in entering a 20 lb. IC model carrying another 1/2 lb. of fuel, go for it.  Good luck.

Mike Gretz
AMA Scale Contest Board Chairman

I am not a competitor so obviously not speaking from hands-on experience, however it seems to me that requiring a 5G pull test on a 20 lbs model (that is 100 lbs pull) is grossly overreacting. Think about it: most people don't feel comfortable flying a model that pulls more than perhaps 30 lbs, therefore, with adjustable guides I would think that one will adjust the pull to where they are comfortable.

The pull test isn't there for normal flying.  It's there for when s**t happens.  Presumably, the expectation is that scale flights will just be more sedate than competitions involving lots of maneuverings.

And if you don't think the pull test is demanding enough for safety, you can always ask for a stronger pull on your model.

Is there a forward limit as to how far one can move the lead outs to reduce pull?

Ah, I would think that when the airplane turns in on you and attacks you in the center of the circle that you have moved the leadout guides too far forward.

Seriously, if you have a heavy airplane, it is going to pull hard when it is at any flying speed.  The problem with moving the leadouts forward to reduce line pull when the airplane is at flying speed is that when the airplane starts its takeoff roll, there is no mechanical means for the airplane to maintain desired orientation at the end of the lines other than the leadout position.  Basically, the leadout guides should ideally be positioned somewhere around 2 or 3 degrees aft (maybe 4 degrees at most) of the longitudinal CG of the model.

For a scale model where aerobatic flight is probably not a requirement (particularly a 20 pound model) and if excessive line tension is a problem, then rudder offset to reduce line tension might be a solution if that offset is not made excessive.  Rudder offset has little effect at low speed so the takeoff will not be affected too much.  That rudder offset becomes more effective as the airspeed is increased.    This adjustment should be approached incrementally and cautiously.

I saw a well known builder/pilot have a harness around his shoulders so that a helper could help restrain him at the center of the circle while flying his 4 engined (ST 29's I think) Lockheed Electra.  It was a big airplane.  Without the restraint, it would literally drag him from the center of the circle with feet firmly planted.  I do not think rudder offset or leadout positions would have improved the situation very much.

I would recommend that rudder offset or leadout adjustments should be NOT be used to reduce the tremendous pull that results when flying a heavy model at the end of control lines.

Keith

Keith

Thank you so very much for the splendid explanation. Now, from all that was said so far by Clancy, Mike, Tim and yourself I sorta get a picture that CL Scale is not fun, rather it is kind off - we have to sweat the few minutes of an official flight and of course practice to do a good job at it but that's it. Here is a calculation of centripetal force for worst case scenario: a 20 lbs model flying at 50 mph on a 70 ft lines will produce 47 lbs of pull! I want to enjoy taking a nice scale model to the flying field on a routine basis. Am I missing something? I have seen pictures of Grant Hiestand’s Precision Scale 1/3 Scale Spacewalker 103” span, Astro Flight 90 Geared Electric Motor, 18 lbs, 1993 & 1995 Nationals Precision Scale winner, 1995 NASA Flight achievement award winner (source: Fred Cronenwett book). From all that was said it would appear that this would be a bear to handle! Am I correct? I have seen a guy flying a big B-29 and C-124 at Brodak last year, and, it looked like he was in pain. So, what can be done than to make CL Scale enjoyable? Or, perhaps it is most about the joy of building a scale model and flying is secondary?

Joshua

I can only speak from my own experience .. flying a 8-10 pound C/L scale model is a blast!
Mike

Clancy
Your generous sharing of your vast experience is much appreciated, and, advice well taken.
Thanks a bunch
Joshua

Jim

"The selection should not only be of a subject that one really likes, but also of a subject that has a lot of detail information available and has the right anticipated weight/wing area ratio. Have fun."

You nailed it right on the head my friend You see, my problem (well not really) is that the airplane on my mind (for over 30 years now) is going to be 102" span, 103.5" long, 1908 sq.in. wing area and flown with a scale propeller (31.5X32) at 2,200 rpm. Now, it's ok if every one will write me off as a nut case  - I am used to it. I can only say that I have already validated the Motor/Speed Reduction/Propeller combination, and, the main unknown right now is IF the model can be built to 15 lbs ready to fly. Clancy and I discussed the issue and he felt that it can be done - I trust his opinion 100%. You said that the speed will probably not be as high as 50 MPH - very possible, however: 50 MPH would be scale speed for this design. Here are pictures to clue you in.
Thanks for chiming in, I appreciate your contribution.

Joshua

Fred

Thanks for your input. Do you know if Grant built his model straight from a Sig kit or did he substitute competition grade balsa? Also, how fast would you say his model flys? I am talking about 18 oz/sq.ft. with my proposed model.

Joshua

If Grant had followed the Sig plans the model would have been well over 20 lbs, but he changed the wings and fuselage and made them much lighter than the kit called out. Flying RC vs CL has different loads so some of the structure was changed. Most kits are overdesigned and are overbuilt.

The model flies slow, maybe does a lap every 8 or 9 seconds (at guess from memory) much slower than a comparable stunt model.

Fred