Hangar 9 Sukhoi SU-31, Instruction Manual

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Our new 1/3-Scale Sukhoi will blow away almost any pilot wanting
to fly aerobatics. When designing this model, I incorporated
design features and enhancements that I used in several
Tournament of Champions and IMAC competitions. Does this
mean the Sukhoi is only for the serious competitor? Absolutely
not! What this does mean is that the Sukhoi is fine-tuned and
tweaked to excel in both precision aerobatics and wild freestyle
type 3-D, so doing any aerobatics will be easier than it has ever
been. I’ve found the Eppler 169 airfoil used on this Sukhoi to
make the low-speed flight exceptionally good.
Preflight
Before getting to the really fun stuff, flying, I’d like to reiterate
some very important steps that were covered in the assembly
instructions. For those of you who are veterans of large models,
this is old news. But to you new comers to the world of large
models, this is very important information. While many smaller
models are very tolerant of improper control linkage setups and
flying techniques, large models are not. Don’t let that scare you
away from large models; they are truly one of the best flying
experiences in RC that money can buy. However, please pay
particular attention to the following areas:
Seal the aileron and elevator hinge gaps.
This should be considered part of finishing the model and is as
important as installing the fuel tank or battery pack. On large
aerobatic models, this is absolutely necessary. Failure to do this
may very well cause control surface flutter, and on a large model,
this will most likely cause a crash. Putting safety and model
preservation to the side, there are several other reasons to do
this on an aerobatic model. It will increase the effectiveness of
the control surfaces, and the model will track more true and
precise. Hinge gaps sealed? CHECK!
Maintain the proper mechanical advantage on all con-
trol surface linkages.
Same as unsealed hinge gaps, this is often the cause of flutter.
Please follow the control horn and servo arm lengths recommended
in this manual. Shorter arms on the servo or longer control
horns on the elevator and ailerons are fine, but do not try to go
the other way to increase throw. It will cause flutter on the
Sukhoi. The recommended linkage setups are more than adequate
to achieve full 3-D throws. That’s straight off of the prototypes.
Linkages are set? CHECK!
Never attempt to make full throttle dives!
Large models perform much more like full-size aircraft than
small models. If the airframe goes too fast, such as in a high
throttle dive, it may fail. The Sukhoi should be flown like a full-
scale Sukhoi. Throttle management is absolutely necessary. If the
nose is down, the throttle comes back. CHECK!
The Prototype Model Setup
All of the recommended settings in this manual are a result of
the flight-testing on the prototype Sukhois. There are no secrets.
If you follow the instructions and these tips, your Sukhoi will be
set up just like mine.
Although a computer radio is not mandatory, it is preferable in
this model. I use exponential on all controls to soften the feel
around neutral. This makes it easier to fly smooth in precision
maneuvers and also makes it less likely to over-control in 3-D
mode. I use the following expo values: El38% Low Rate,
+70% 3-D Rate. A40% Low Rate, +55% 3-D Rate.
25% Low Rate, +50% 3-D Rate. Note that + expo
values soften the neutral with JR radios. Other brand systems
may require "-" (negative) expo values to soften the neutral.
I have flown Sukhois equipped with JR 8101, JR8231 and
JR 8411 digital servos. While all are excellent choices for the
Sukhoi, I personally prefer the feel with the digital 8411 servos;
with these servos, the model feels slightly more responsive. I
use a 6V Ni-Cd battery pack for maximum speed and torque
from the servos.
The prototype Sukhois were tested on my favorite power plant,
the Zenoah GT-80. I use a Bolly 24 x 10 propeller, which the
GT-80 turns at approximately 7000 rpm, and a preshaped and
balanced Bolly 24 x 10 at 7700 rpm. Both work well, but I feel
the preshaped prop has the edge in hovering maneuvers. This
combination has proven to be totally unlimited and allows
anything imaginable from torque rolls just a few inches off the
ground to multiple vertical snaps. I found that adequate engine
cooling is very important with the GT-80 and strongly recommend
cutting the cowl bottom hole to the size recommended in the
instructions. When this was done, the performance difference
was dramatic. If you aren’t getting this kind of performance,
take a look at the cowl and how well the GT-80 is being cooled.
Performance Tip: Drill eight 5/16" diameter holes through the
internal baffle plate in the GT-80 mufflers. I drilled seven through
the intake opening and one up through the exhaust stack. Just be
sure to flush out all of the metal shavings from the mufflers. This
little 10-minute trick will add 300 rpm to the top end.
Section 18: Setup and Flight Information by
Mike McConville