LMProd

I wasn't sure where to post this. I also appears in the ARF section.


I am putting together a GP Spacewalker and want to use it to get my feet wet at IMAA events.

The instructions state for IMAA 4-40 rods and servos on for control surfaces to be at least 45 oz. I plan on using two servos on the elevator so that should be legal.

But the ailerons, is that considered one control surface for roll on the longitudinal axis. That would mean a 40 oz JR servo attached to each aileron would equal 80 oz on the control surface.

Would this be legal for IMAA ? Two 70 oz servos seems over kill.

I don't want to drive to an event to be turned away by inspector

cknaack

My Feedback: (1)

I have the same exact airplane. What a relaxing plane to fly!
I used JR 531's on the ailerons. The reason for this is more than just an IMAA rule. I did it for safety reasons. The cost of upgrading the servos is insignificant compared to loosing the aircraft or worse hurting someone due to a servo related issue.
You will also find that the airplane will respond with more authority.

Just my opinion.

Rodney

To often, modelers substitute force for finesse. If the surface is both aerodynamically balanced and statically balanced you can get by with very weak servos. I believer Burt Rutan, a renown designer of both models and full scale aircraft, flew a full scale Varyease with a 40 inch/ounce RC servo driving the ailerons just to prove it could be done. Back in the 50's we flew many models using Mighty Midget motors (probably about 5 inch/ounce at best) but we did pay attention to static balance and good hinging techniques.

beepee

LMProd,

2 things ...

1. IMAA does not require servo sizes, nore do the inspectors check them. At least not in the many events I have attended.

2. Servo loads are influenced by control surface size and maximum deflection, but more by the aircraft flight speed than either of those. Add the influence of counterbalance often found on elevators and rudders and loads are often relatively low. What type of flying do you intend to do?

I agree with Rodney in that servos are often oversized. I have a quarter scale Cub powered by a Quadra 42 with Futaba S-28 aileron servos (rated 42 oz-in) in the wings and I have never had the slightest indication of trouble. I have a couple of hundred hours on this plane spread over 10+ years. I am now replacing them, but out of routine maintenance needs rather than faults.

Have fun!

Bedford

fryfly

My Feedback: (8)

Beepee is right! The only thing that is required for IMAA is SIZE.Monoplanes have to be 80" inches or true 1/4 scale and biplanes need to be atleast 68" or true 1/4 scale,other than that servo's are up to the modeler.Consider what you will ask of your airframe to do in an extreme condition relative to the aircraft and size and go from there.Most applications of sport flying require only basic torque sizes.I at one time flew a 80" midwest extra with a 3w 50 in it with standard JR servo's that came with my radio package! worked well for the 2 years I flew it.I still have the aircraft but have stripped it down and have gone to larger aircraft since.

LMProd

Thanks for all the replies. I also received a reply from Andy Argeino with the IMAA.

He stated about the same as your post. The Safety Code is to help and assist the pilot and not to determine the technical airworthiness of a model. It is the responsibility of the pilot for a safe flight and model.

He stated the use of two standard servos for a 9 lb Spacewalker should be adequate. But I might consider a 6 volt battery. This would up the torque of a JR 527/537 from 43 oz to 51 oz.

I thought that was a great idea, so I went out a bought 6 volt motor cycle battery, not really, but I did buy a 6 volt receiver battery. I also plan on installing pull pull on the rudder with a 70oz torque servo.

Thanks again for everyones help.

Gary