SIX SIMPLE STEPS TO BUILDING A "TECHNICALLY SPEC"
USRA RACING AIRCRAFT
Well, the1999 racing season is over and we are
in the heart of the building season. This is a convenient (if not a bit late)
time to review our
"technical responsibilities" when choosing, designing, building and racing an
aircraft in the USRA Series. Keep in mind, this is only a guide - you can always do more
than the minimum requirement in order to get the job done - advantageous in most
Before I begin, I will review our current hierarchy of
rules and specifications. It is not just a sheet of specs for a particular aircraft. (I
know you already knew that!) The following chart shows, in very simple form, our current
rules and specifications hierarchy:
Most of us are well aware of the specs pertaining to a
particular class of aircraft. But if you decide to build an aircraft (different than any
you have in the past) it would be prudent to go over all the required specs before you
"cut some wood" (or carbon). As you can see, for a particular aircraft to race,
it must meet the "Common Rules and Specifications", its own particular
"Class Common Rules and Specifications" and finally the "Specific Aircraft
Specifications", i.e. the minimum aircraft measurements we are most familiar with
All aircraft racing in our series must comply with these
requirements in order to pass tech. That is not to say that there are not exceptions -
currently there are probably still some aircraft that are grandfathered under past rules.
However, this is the exception and not the norm. When those aircraft eventually go to
"re-kit heaven" we should all be racing legal aircraft under our current specs.
Also, please note that there are blank boxes in the chart above in the Specific Aircraft
Specs. That is because there may be aircraft not on our current "approved" list
that are legal to race.
If you know of one, please let us know so that we can
update our list and eventually get around to determining what its particular minimum
measurements should be. However, if you know of an aircraft that is not on the approved
list and intend to build it to race, then you will need to follow these six
simple steps to "get it on the list" so you can race it. Please do not show up
at a race with an aircraft that is not on the approved list and expect to race it. That
scenario puts our tech inspectors "on the spot" with regard to allowing you to
race and it simply is not fair to do that to them. It borders on unprofessional. We are
all good friends and enjoy the camaraderie and professional aspect of our sport - so lets
be professional, do our homework and enjoy this fantastic sport we love.
So.... you found this great aircraft that no one else is
flying and you know it will be a certain winner, but its not on the "approved"
list for its particular class. How do you get it there? Here goes!!
- FIND AN ACCURATE 3-VIEW OF YOUR AIRCRAFT - This is not as easy as it may sound,
but it must be done. Many racing aircraft are heavily modified from the originals and in
the case of Thompson Trophy, Formula 1 and Biplane, it might be nearly impossible to find
a 3-view. Find pictures, research the internet and museums, call the owner, whatever - you
must come up with the outline of the aircraft in order to build it, even if you have to
draw it yourself from measurements taken from pictures (not an easy task, but not
impossible). Some racing aircraft, like Strega or Rarebear, began as a stock WWII aircraft
and were modified. With pictures of the aircraft and a "stock" 3-view drawing,
you can incorporate those modifications to the 3-view to produce a 3-view for the
particular racing version of the aircraft. Do thorough research - it will make getting the
aircraft approved much easier later on.
- SIZE THE AIRCRAFT TO MEET THE "CLASS COMMON
SPECS" - Determine what size the aircraft must be in order to meet its
particular Class Common Specs. These may include wing area, wingspan, airfoil thickness
ratios - whatever. Read the class common specs and make your aircraft conform to those
minimums. (You can, of course, exceed those minimums) Remember, we are talking
about just the Class Common Specifications. Additionally, it would be a good idea to call
or email your district representative to make sure there are no upcoming rule changes for
the class. There shouldn't be, but why take the chance? If you are going to go to all this
trouble, you will want the aircraft to race for more than one or two seasons, right?
(Disregarding, of course, that the average life span of a racer in our series seems to be
about 30 heats). Now, look over a typical Aircraft Specification sheet and compute all of
your aircraft specific measurements (wingspan, tip chord, root chord, stab span, rudder
height, etc.). Make sure that none of these measurements cause a problem with any current
- ENSURE THE AIRCRAFT MEETS THE "COMMON RULES & SPECIFICATIONS" -
There really are not any specific aircraft issues in the Common Rules, but read through
them anyway just to make sure. It never hurts to cover all your bases. There are
some specs pertaining to wing root thickness and wing tapers, etc. They apply to all of
our aircraft, so they must be incorporated into any new aircraft.
- THE 3-VIEW TO USRA FOR APPROVAL - Once you have a three view with all of the SUBMIT
measurements annotated, send a copy(*) of it and any documentation pictures, etc. to
the USRA so that we may go over your numbers and look for any errors. If everything checks
out, we will approve it and add it to the list with our absolute minimum measurements
(unless you were already there!) and you are free to design and build your aircraft. This
step can sometimes take an iteration or two, as many "behind the scenes" issues
are addressed with regard to a new aircraft. Some of the things being looked at are
fidelity to scale (yeah, I know, not a scale contest - but we still have to look), airfoil
thickness ratios that would limit structural integrity based on the aircraft's intended
speed, complexities of the aircraft that could cause inherent weak points for the size and
speed of its class and so on and so forth. As always, safety is our primary concern.
Please don't be offended if you have to resubmit the 3-view for some reason - our USRA
Board and race promoters have to deal with things like insurance (yuck!) in order for us
to race - not only that, making a 3-view drawing and getting it right the first time with
no errors is not an easy task for anyone - be patient!
*(Please keep in mind that when
making a copy on a copy machine, the copy may not be accurate to the original. Some copy
machines copy horizontally at 100%, but vertically at 98%-102%. Just make sure that 5
inches on your original is 5 inches on your copy (horizontally and vertically)
or we will have a heck of a time scaling from your copy.
- DESIGN AND BUILD YOUR AIRCRAFT - Now the fun begins! You now get to put all of
your knowledge of aerodynamics, engines, structures, etc. to work and come up with a
finished product. Many of us have quite a bit of knowledge about building RC models - but
step back for a moment here and make sure you really do know if this is just an RC model
or a 200mph RPV. Keep in mind the forces at play on one of these "models" are
real. "G" loads, flutter, servo stall, engine vibration, carbon fiber
conductivity, stress induced delamination - everything comes into play when this bird goes
airborne, so you need to do your homework again and be sure that the aircraft you produce
is airworthy prior to coming to a race. Consult every expert you know about
everything you don't know. We are all learning at an incredible rate in this sport and it
would be foolish not to look for advice at every corner - you'll be a better racer for it!
When in doubt, ASK! A bruised ego is forgotten over "post race cocktails", but
(knock on wood) an aircraft into the spectators will be remembered for a long time to
come. Think safety, safety, safety!!! Then go for it!!
- SUBMIT YOUR ACTUAL AIRCRAFT MEASUREMENTS TO THE USRA - All of this work you have
done has helped our sport tremendously! We all have a new aircraft approved to race
(thanks to you!), the tech guys are armed with a 3-view and the aircraft specific model
minimums (thanks again to you) and, if you can before the race, the tech guys would
appreciate you sending them a copy of your actual aircraft measurements. This will make
their job of "teching" you even easier. If you have adhered to your 3-view and
all the specific aircraft minimum requirements, Class Common Specifications and Common
Specifications, you will sail through tech, get that logbook you've been waiting for and
have a great time racing your beauty to the Gold finals! Piece of cake!
I hope this guide has helped those of you who are
contemplating building an aircraft from scratch that is not currently on the approved list
or is an aircraft on the list that has just not been modeled yet. It probably seems like a
lot of work, but it really does help to standardize our aircraft and avoid the hassle of
not passing tech - in that way we will all compete as fairly as possible. As our sport
continues to evolve and grow, our rules and specs will probably evolve and change somewhat
too. But we try to keep changes to a minimum - that makes your job easy and it certainly
makes our job easier too. In closing, if you have any comments, suggestions or ideas,
please let your district representative know. Also, if you have a 3-view of any of our
current approved racers, I personally would greatly appreciate a copy of it - I am
creating a file of all of our current "approved" aircraft 3-views for the USRA,
so that if somebody needs one for building purposes, they can get a copy. Thanks in
advance for your help.