Chris C and netters Whether it be a cold day in Colorado, or a hot one in Arizona or Florida we all battle the effects of negative changes in density altitude, or simply lost performance due to the expanding air providing less lift, thrust, and engine horsepower. Most seem to get caught up in the engine power part of these effects and if it were just that to overcome life would be alot easier. According to the Cessna pilot handbooks of operation for the common 152, 172 variety, the normally aspirated avaition engines seem to lose roughly about 1% of horsepower per 1,000 feet of increase in altitude. This just reflects the effect that the altitude has on the engine alone, NOT the effect on the rest of the airplane. You have to then look at the charts for calculating the INCREASE in takeoff and landing distance to get an idea of the reduced lift and thrust amounts. In short, if given the same airframe to work with, KR2 or KR2S, one must consider not just turbocharging the engine, but also possibly needing to adjust the prop, if adjustable or select a different one if high altitude flying is the main focus. A greater pitch may be required for the 10,000 foot run to prevent it from being extended excessively, especially on a warmer day. Think about starting out at 10,000 feet MSL, and then it is really warm, so the density altitude increases by 1,500 feet. Now your little bird has to be able to takeoff at the equivalent MSL altitude of 11,500 feet! You may literally be getting very close to the service ceiling of the airplane! Typical turbos will only normalize up to about 8,000 feet. So in order for your plane to takeoff and climb out safely, since you are bound to have greater issues with rising landscape than we do in Florida, you may need a Corvair 6 cyl, and a climb prop, or adjustable prop to make your plane safe enough to have the required margin for safety, if say you have a power loss, or fuel contamination, and are only getting partial power. At 10,000 you will need to have 10% more engine horsepower to just be equal in power to that same engine at sea level. Now somehow you also have to come up with a way to get back the lost 10% of thrust at the prop, because even though you are applying the torque to the prop, it is trying to make thrust in more expanded air. Since you can't sweep the wings or extend and retract them, (nice idea though) you also have to increase the standard plane's performance so that you will end up with 10% more lift at sea level to be equal to a standard airplane at your altitude. This means even more from the prop/engine combo. Since most here say that solo minimum HP seems to be about 60, and recommended passenger HP is around 80-100 to be safe, a high altitude person would need between say 20-30% more power and the prop capable of using that power to make up for the lost lift. That means an engine prop combination of around 100-120HP. One final consideration often overlooked is the fact that since the lift is reduced, it is quite possible that the gross weight allowance will have to be significantly lower at these altitudes in order for the airplane to get off the ground without a 747 type takeoff roll. It is known that your true airspeed will be higher even though indicated speed will be the same, so bare in mind that the landing roll will be effected also.
Your test period will be very valuable to learning your plane inorder to be safe, and will very likely result in alot of "tweeking"... 3.6 hours of test flying so far... Colin & Bev Rainey KR2(td) N96TA Sanford, FL crain...@cfl.rr.com http://kr-builder.org/Colin/index.html
