Dan:

I will weigh in on the whys and wherefores of APRA as opposed to 424 as well as any other rules deviations used.

1st off my credentials: We run at least 10 races a year between Whittier, the Basin and PHX. All races except the PHX Winterfest run three classes: 422, 428 and 424-APRA (the Winterfest runs 428 and 424-APRA. I CD four of these events and am deeply involved with race management of all except PHX. (PHX also puts on monthly APRA races but does not use the 9 lap rule)

Rule deviations are as follows:

422: APC 8 x 7.4 carbon fiber filled molded props permitted:
Rational: We believe use of this prop promotes 422 racing by eliminating a huge variable and added expense.

428: No deviations.

APRA-424: Deviations from the 424 rules are as follows.

1. No composite wings or tails.
Rational:
a.Cost. A competitive Q500 composite airframe cost is prohibitive for an entry-level class. The Vortex, arguably the best quickie around, runs from $400.00 to $650.00 depending on level of completion.
b.Performance. A composite airframe is perceived as being faster. If it is or not I can't say but I don't believe there were any wood and foam quickies in the top 10 at the Nats.
2. Permissible engine list.
Rational: Two samples of all engines permitted are tested both in the air and on the ground using a reference 9 x 6 APC prop. Only those which give no huge advantage are permitted.
3. No RPM limit.
a. The current predominate engine the TT PRO 40 will exceed the 16500 RPM limit specified in the 424 Rules using the mandated APC 9 x 6 prop.
b.It has been our experience in racing classes where RPM is limited it in necessary to check the winner of each heat. This takes 2 to 3 minutes additional each heat which severely impacts the number of rounds we can get in. We see as much as a 1000 RPM difference from the morning to afternoon with the highest RPM during the heat of the day.
4. APC 9 x 6 prop. (Sometimes supplied at the race)
Rational: Levels the playing field. Same size prop as permitted engines are tested with.
5. Engines must be stock except for bearings, bolts, back plate mount (if used) and head gaskets.
Rational: Some sport engine bearings will not hold up under racing conditions. Intended to be the same as 428 engine rules.
6. Novice pilots are permitted to fly 9 laps instead of 10 until he or she meets break out criteria.
Rational: Levels the playing field and encourages new pilots. The break out on the long course is 1:45. A good pilot can beat this in 10 laps but it’s a struggle for most. We consider this a entry-level event and want to give the novice a chance. We generally have a 9 lapper in the top three but almost never have a 9 lapper winning overall. We also award both 9 and 10 lap fast time plaques.


These rules work for us. Our average number of entrants, split between three classes, is between 40 and 50 with 428 being heaviest followed by APRA then 422. APRA turn out has been on the up swing. A couple of years ago when several APRA contestants were flying composite airframes entries had fallen to about half of what they were and are again.


Hope this helps


Barry