Sport Class speed potential

[gp70442]

For about 10 years now, Sport class speeds have been stuck at just over 400. Up to now, only 3 teams have posted numbers in that range, one has retired. (please correct me if my history is inaccurate) I'm sure there are several others that are working hard and are knocking on the 400 mph door. With the engine packages and airframes available today, how likely are we to see anything more that incremental speed increases over the next several years? Will a step change in speeds require a new airframe and/or engine package?

I guess #42's misfortunes showed us that a lot of things have to go exactly right in order to achieve 400 and above.

If we consider 450 to be a competitive Unlimited speed, what will it take to get a Sport plane to run that speed?
Are the current engine/airframe packages pretty much at their aerodynamic and HP limits?

Over the years there have been a few new designs that seemed to have potential but none of them ever made it to the ramp. Due to rarity of warbirds and obscene costs of operating Unlimiteds, I see Sport as being where the action is currently and going forward.

Another thread here got me to thinking along these lines.

GP

[Stewartspony]

With the Sport Class race speeds increasing every year and have crossed the 400 mph mark in a few instances, I was wondering if any of the teams have done ground vibration tests to look for the onset of flutter? Most of the Sport Gold racers are racing at speeds 100 mph over the manufacturer’s published Vne. The only design that I am aware of that has had ground vibration flutter test accomplished is the Thunder Mustang. What about the rest?

[TarDevil]

Watching this thread.

[flyboycpa]

Another thing that worries me are the RV's that are running 260-280 mph in the VOS.

[RAD2LTR]

I'm not sure current planes in the Sport class will ever run 450 mph. They are limited in displacement, and sure, turbos can go some distance for making up for the lack of displacement, but when you consider a Merlin is roughly 1000 cubic inches larger than the average sport class engine, you will need insane amounts of boost to make up the difference. If I'm not mistaken, the class is limited to 1000 cubic inches displacement, right there they are at a minimum of 650ci smaller than the smallest displacement unlimited engine. (Yes, short of the Pond Racer, the smallest engine to run in the unlimiteds is the Merlin.)

Sure, the sport planes are likely aerodynamically cleaner, smaller, and lighter, but I think they might need more engine, and more propeller to overcome the drag at 400+. Its sort of like the 500 mph barrier the Unlimiteds have run into. (Dago is the only one to actually run a 500+ mph race, and only once if I'm not mistaken.) Sure you can go faster than the 400 and change for the sport class, and 500 for the unlimiteds in straight level flight, however that all goes out the window when you start pushing Gs in a corner, and with today's race course being mostly a constant turn, things will have to radically change in order for the sport class go be able to carry that speed around a turn. Strega and Voodoo need 3500+ hp to run in the high 490s, that is quite a bit more power than what the current top sport class racers are producing. Sure, a smaller, cleaner plane will require less hp to go the same speed, but even at half that power, its probably close to twice the amount that the current sport class racers are making. (Not sure what the actual numbers for the top sport class planes are, but I'd have to guess its well under 1000hp. )

As others have pointed out, things like flutter and other aerodynamic demons start to rear their heads at speeds above 400 mph, and testing likely will need to be looked into when the class starts getting much faster than it currently is. With the Unlimiteds, NACA experimented with flutter and other similar phenomenon in the '40s, because military lives depended on it. I highly doubt NASA is doing flutter testing on Legacys and RVs because outside racing, they will never reach those speeds.

just my $0.02,
Will

[L.E.D.]

Other things being equal, horsepower required goes as the cube of airspeed. (Twice as fast means eight times as much horsepower.) 400 to 450mph "only" increases the power around 50%. The fast sports are producing about 750-800 hp now so they'd need ~1200hp.

[TarDevil]

It isn't hard at all to get a couple thousand reliable horsepower from modern V8's. Turning it into thrust is still very problematic, but once that threshold is conquered the new stars of RCAR will light the skies.
You don't need to weigh 4500 lbs to go 500.

[gp70442]

The fast sports are producing about 750-800 hp now so they'd need ~1200hp.

A 1000 cu in engine is capable of 1200 hp. Whether that can be achieved with a 6 cyl air cooled engine is doubtful I think. It was mentioned that current top Sport racers are developing near triple their rated power so I was guessing in the range of 900 hp. 1200 is not that far away.

I'm not going to start imagining "pie-in-the-sky" airframes and engine packages but I think sooner or later someone is going to do it. John Sharp did it (with a tricked out existing engine) and was in a class by himself for several years. Hot rodders are building new billet engine blocks and custom cranks at prices that are not out of this world. If someone were to make a new 8 cyl block for a IO-550, suddenly 1200 hp is in sight without increasing frontal area. Feeding, cooling and liquid storage would be other development challenges of course. #42 tried an 8 cyl but it wasn't force fed and I'm assuming there were very good reasons for that or he would have done it. I'm not sure what the rules say about engine packages other than the cu in limit.

Racers are going to race and they will not be content with 410 mph for long because it won't win forever. I believe the Sport class WILL continue to develop.

[GRNDP51]

Not holding my breath, but I really hope Swiss Thunder is the next one to set the sport class gold winning speed standard. Once the engine package starts working, add in the Rapid Travel mods and some of the things that Blue II was experimenting with and that should be a 425+ plane. Only a guess, but Blue II was doing nearly 400 in qualifying and that has a ton of drag Rapid Travel didn’t have. I think the engine they are experimenting with in Swiss Thunder should be good for more hp than Blue II’s was also...

It’s pretty cool that all 3 sport planes to do over 400 are different airframes. I’m curious to see what the 8-cylinder Legend will do if it’s ever raced.

[Samuel]

Once you get up into the unlimited gold speeds, don't you need something that looks like an unlimited racer?