Not to mention the fact that Colin isn't trying to sell you anything....makes a big difference in the information stream.
Scott --- Colin Rainey <[email protected]> wrote: > Netters > This debate about best engines for experimentals, > and whether to turbo, whether to Gear drive/PSRU or > direct drive has been going on for a while now, and > I suspect will probably continue, kind like the > Ford/Chevy debate (Chevy is best, LOL ). I am NOT > going to take sides of whether a builder should > choose auto or aircraft engine, normally aspirated > or turbo, or direct drive or PSRU. All these things > are in the archives, and found in literal volumes in > other writings, both Internet and books like, "Auto > Engines for Experimental Airplanes" by Robert Finch, > just to sight one example. There are many others. > > What all Netters, especially you new members need to > take to heart is that engine selection is VERY > important. Looking at certified aircraft, you will > see that it it the single most important factor when > considering an aircraft's present value, how many > hours on the engine. Of all the expense of owning > an aircraft, once it is completed, the most money > you will spend will be for the engine, and its up > keep/maintenance. Turbo charging is the cats meow > for cheap horsepower, but just ask Orma Robbins > about how this "enhancement" comes with its own > unique set of problems to deal with and overcome. > Also, the article sighted states that turbo charging > generally adds at least 50% more power. This is out > right fiction! The best that I have seen proven by > dyno runs is approximately 40%, and this is with > associated engine modifications, AND the use of an > inter cooler, which is not mentioned in the article > at all. B&M, Vortech, Banks Turbo-charging, and > Paxton all report similar values for their "bolt-on" > systems. I am not saying that a turbo or > supercharger cannot add 50% or more power, but that > rather that bolt on systems do not give that kind of > increase, and do not want builders running out and > buying a turbo for their engine expecting to get a > 50% increase in power and torque by just hacking the > exhaust in order to add the turbo. > > The same rules hold true for direct drive vs PSRU. > There are definite benefits to a PSRU, but to set > one up on a 2.2 to 1 reduction, just to achieve > maximum horsepower from an engine from a dyno run, > and say that is best does not take into account all > phases of flight for the engine, only take off. That > is the only time you will use max power. This > amount of reduction although it makes the max power > available according to the dyno, it does not allow > for a reasonable rpm for cruise. This is because > the prop will be slowed to 2000 to 2100 rpm, which > begins putting it below its cruise efficiency speed. > Just compare certified props that are made to run > in this range of rpms. They produce max thrust at > near redline, and produce best cruise thrust at 75 > to 80% engine power. This puts the prop at around > 2300 to 2400 rpms on a 2750 redline. This puts the > engine in the re drive at 5060 rpms for the 2300, > and 5280 rpms for the 2400 rpms at the prop. Now > your engine is running just like the Rotax family of > engines and can expect the same life, or simply 50 > to 100 hour maintenance intervals with a major a max > of 500 hours out. It also makes the combination > "peaky", where basically you spend literally all > your time at or near peak rpm. > > Robert Finch's book details a lot of engines that > have been successfully used in direct drive > configuration; the Buick V8, the VW family, the > Corvairs, and several others mentioned in his book. > In larger aircraft that have more generous weight > allowances for the engine, the more complicated and > heavier engines have a good appeal. BUT for our > applications, in order to stay in the RECOMMENDED > weight range of engines AND their output, direct > drive offers the best answers, and air cooled the > simplest installation. Above all, it takes research > and study to decide and engine install, and talking > to other actual pilots of those engines. Don't get > sucked into the trap of some fancy numbers > calculations and good advertising on one web page > where one engine is presented as the experimental > airplanes dream engine. There are a lot of > "assumptions" and over generalizations made at the > expense of the builder. No quick answers here. It > takes years to build a KR, take enough time to study > your engine completely BEFORE spending any money. > > > Colin Rainey > [email protected] > EarthLink Revolves Around You. > _______________________________________ > Search the KRnet Archives at > http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to > [email protected] > please see other KRnet info at > http://www.krnet.org/info.html > __________________________________ Yahoo! FareChase: Search multiple travel sites in one click. http://farechase.yahoo.com
