Ron, et al:
Here's a few data points from a Sport Class knucklehead (ok, addict
)...and Ron, your name is familiar, so we may have chatted before. This is a great way to spread the info tho.
Timing wise, give yourself a lot of lead time...and apologies, but the ship has left the pier this year, as the deadline for PRS (Pylon Racing Seminar) entries was 4/22. That's typical each year. You'll really want to give yourself plenty of time to prepare both plane and pilot. For 2023, I'd say start...hmmmm, well...now (PRS in June 2023 will be here before you can blink...AMHIK!)
WRT to pilot experience, please check out our requirements on our website, here:
https://www.sportclass.com/prs/
Formation experience is one of the big keys to success. Safe for solo in a 4-ship, performing all the maneuvers in our Formation Guidelines, is a basic min experience level to start our class Formation Warmup and move right into PRS. That doc and our training reference material are on that same website tab.
WRT aircraft, there are many layers to that aspect of racing. Just a few thoughts, from a guy that races hard, but also wears a safety/leadership hat:
- I would strongly discourage just bolting on HP (turbo, supercharger, N2O, higher compression or more cubes) to an otherwise stock RV, with a Vne of 200 mph (4/6) or 230 (7/8). While you have no doubt read or heard about 260+ to 270+ mph qual speeds in a couple RVs and Rockets, those are not stock aircraft. Mine is a 6, but it was built like a Rocket, and has a 275 mph Vne. It's also been modified extensively since I began racing too. The other fast RVs have all committed extensive time, money and testing to making their aircraft fast.
Our Sport field has been getting faster each year, and the "closer-to-stock" RVs are at the back of the field, running in our very fun Medallion heat. But each year, we all wonder who will get bumped off the bottom as more Legacies and Glasair IIIs show up (we have 9 Rookies this year, including an SX-300, 3 Legacies, 3 Glasairs, a Rocket and an RV-4). So as the field speeds up, the push to go faster, and not get bumped, has led to more forced air induction and more chemistry (N20). We do collude a bit on best practices, and keep an eye on safety (our own and each others') throughout. Reach out to us if you go this route...its important, and we want you and everyone to be safe.
- If you push to fly faster, be methodical about the process, and take airframe strength into consideration. That is a many-faceted issue all its own. The airframe is a system of systems, and one's approach to strength and flutter mitigation must approach it as such. We don't want to simply move the failure points around.
So, say you did take that approach, and are ready for more HP. Good discussion points above about FAI, N2O and Hi Comp. All have their advantages, disadvantages, and challenges (logistics and cockpit management/pilot workload).
- We have 10:1 and 11:1 motors in some of our RVs. None are boosted (TC or SC). Those that opt for boost typically drop compression to 7:1 or less. I owned and raced a Glasair III with a TIO-580 that we ran at 6.5:1 and boosted to 67" MP. The big dogs I was chasing...and couldn't catch...are well over 80", probably approaching 100"+...but they won't tell...and they go through engines sometimes. So how fast do you want to go...and how fat is your wallet?
- Another data point on compression. Mine is 10:1, and when I upgraded from an RSA-5 servo on an updraft sump, to one of Don Rivera's FM300B servos and forward facing cold air induction, the MP increase I saw has led me to no longer push the throttle all the way in on sea level takeoffs, to ensure detonation margin. I run rich on takeoffs too. I'd slightly modify the other poster's comment below about 12.5 to 1 AFR to say that is best case, with good, no great, cooling. I'm closer to 10:1 on takeoff (high heat, low cooling flow), and I'll lean a bit for climb...into the 11s to low 12s, and I climb at fast speeds to keep airflow up. To get to 12.5 to 1 and not get hot requires lots of speed to cool if you're running a buffed out engine. I cruise happily at 23 squared up high, and run LOP (15.5 to 1 AFR), but if I run it up to 27 squared to race, I carefully ease it towards that goal of 12.5 to 1, tho I couldn't quite get there on most race days (pre-nitrous, more on that below).
- We have a supercharged RV-8 and a turbocharged RV-7 racing now. Both have learned a lot along the way, both have replaced cylinders, but both have also had good success and are fast. Boost-versus-compression ratio has been a part of that learning equation. So have cowling mods and AFR monitoring. It can be a high workload, especially coming down the chute in line abreast as you come up to full power, then down at 50' AGL on the pylons as you keep the engine running at its limits while racing others. Great fun, if approached carefully and professionally.
- Nitrous is perhaps the least expensive performance enhancing drug, at least in terms of start-up cost. It is logistically burdensome to use, and has cautions, just like boost and hi compression. We have race teams using a really big HP shot to qualify fast, and then using a much smaller HP shot to race a full 6-8 lap race. Some are chasing RV/Rocket qualifying records, but can't carry enough to run a full race at that hi (really high) HP, nor could they cool the motor at that HP for a full race. Others, myself included, use the same amount of N2O for qualifying and racing. I want that record too, but at a HP/Drag mod combination that can be sustained for an entire race. What I have found is that cooling that higher HP for a full race is a big challenge. We've added water sprayers, and tweaked that all race week last year to try to balance cylinder temps and trying to lean towards best power with N2O (its not quite the same place as normally aspirated, non-nitrous). Its actually a fun science. We've also had some pretty spectacular failures with N2O mods too, so this, perhaps even more-so than FAI or hi compression, is a mod that needs to be studied, planned, and executed carefully.
All the mods can go wrong quickly, so we prepare, modify, test, re-test, and race, with the goal of never having to say, "It looked really, really good...right up the point where it looked really, really bad!"
I hope that gives you some good motivation, and a good feel for the field of play you are considering stepping on to. Its incredible fun, and we take great measures to ensure, and have great pride (the good kind) in, a well prepared pilot and racing machine.
Bring the surgical tube though...the drug is very, very addicting!
Cheers,
Bob