There are some pretty specific "rules" that govern speed from a resulting change in power. Basically, to achieve approximately 25% increase in top speed you will have to double the power. To achieve approximately 40% increase in top speed, manipulating power alone, you will have to triple the power. If your top speed is 160 mph on 85 hp, then you'd need a 255 hp engine to gain an additional 64 mph (40%) of top speed. 40% of 160 mph is a 64 mph yielding 224 mph. Take that back to 73% power for cruise, you might run at 200 mph. But a 255 hp engine is going to add a hell of a lot of weight. A turbine engine might do that for you....properly done. Fuel economy will go out the window though...
On Sat, Jun 20, 2015 at 9:16 AM, Mark Langford via KRnet < krnet at list.krnet.org> wrote: > Chris Prata wrote: > > >>My goal is to have a hot cross country KR1 that can cruise > 200 which I know will require substantial power at the upper end of> the > normal power ranges we see.<< > > Kent Paser's "Speed with Economy" is the book Larry is trying to think of. > And indeed, a very low-drag plane is the way to get there, and a KR-1 done > right is certainly in that territory. Roy Marsh won a race at 197MPH in > his turbocharged VW KR2S prototype, but I'm not sure if that race was a > circuit or one-way with a tailwind. Also, his plane uses a NACA airfoil > thinner than the RAF48. > > I assume you mean 200 MPH, and I assume by "cruise", you mean would do > 200MPH wide open at 7500'. It's probably doable with 85 hp, but I sure > wouldn't want to do it with a turbo. I don't know of many guys running > them on VWs, but those that do don't seem to do it for long. of the 42 KRs > listed at http://www.krnet.org/kr-info.html , only two have turbos, and I > know Orma had a lot of problems with his. They're great for bragging > rights, but not if you want to FLY a lot, rather than maintain a lot. I'm > sure we'll hear from the few turbo drivers that are out there, but the are > certainly a minority. VWs are being pushed hard enough as it is, without > compounding things with a turbo. > > Short of going Continental or Lycoming, I think the Corvair is the key to > flying reliably without a lot of maintenance headaches. Despite early > problems with crankshafts, Dan Weseman's new 4340 crank and front bearing > have now done what GPASC and Revmaster did with the VWs...practically > eliminate broken cranks, I believe. Crankshafts are the only problem I > ever had with the Corvair...everything else worked perfectly. > > Yes, they weigh 80 pounds more than the VW, but you'll spend a lot more > time flying and less time rebuilding the engine! They don't burn any more > fuel than a VW when throttled back (except for the slight drag penalty of > the extra weight), and the extra power is far safer from a climbout > standpoint...getting you up to altitude in a hurry if something does happen > on takeoff. A Corvair is actually narrower than a VW engine and only > slightly longer, and a standard KR "Revmaster" cowling will fit it. > > I'm with Larry on speed, but also economy. Whey you realize it costs 30% > more fuel to run wide open than at cruise, you'll likely back off to cruise > and get there slower anyway, at least I do! > > Another thing about the Corvair is the cooling. The things are absolutely > covered with fins. There are all kinds of passages for air flow through > the heads. Take a look at VW heads and there's practically no daylight in > there at all...a fraction of the fin area that a Corvair has. There's a > real difference in the ability to cool the heads and oil between the VW > and Corvair, which I suspect is the major reason why valve jobs are routine > on VWs, and rarely needed on Corvairs. > > Speaking of valves, the hydraulic valves on the Corvair are set with a > feeler gauge on the bench at assembly, and the valve cover never comes off > again until you rebuild the thing. Not true of the non-hydraulic VW > valves, which require periodic adjustment. > > A KR1 with a Corvair would be a rocket, similar to what Richard Shirley > has with his Jabiru 3300 powered KR1 (although his is almost certainly the > slickest KR1 ever built). I think he can do 240 mph or so, but due to > overheating issues, he can't do that for long. > > If it were me, it would be a Corvair, and I intend to back that up with my > next plane. I already have one of Weseman's crankshafts in hand, and just > about everything else needed to build my next one... > > Mark Langford > ML at N56ML.com > http://www.n56ml.com > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
