Sonex use Jabiru and AeroVee (VW engine) in their planes and think they make AeroVee. I thought this was interesting
Ian McPhee On 3 December 2010 09:07, Sonex Aircraft, LLC <[email protected]>wrote: > > > Hello again Sonex eGroups- > > There has been a great deal of data comparisons lately and we would like to > comment on the important points that impact individual aircraft > performance, > the collection, interpretation and reporting process of the data used for > those comparisons, and the very specific numbers digital instruments > provide. > > The obvious assumption we must make is that the airplanes being compared > are > built as accurately to the plans as possible. It does no good to compare an > airframe that is 720 pounds empty, out of rig, and has no fairings to an > airplane that is 650 pounds empty, well rigged, and fully faired. Draggy > airplanes will not only be slower, the engine will not turn up to the > proper > RPM and it will run warmer than it should. Builders who call us for help > with their high CHTs are often surprised when the first question we ask is > whether or not all of their fairings are installed. They are equally > surprised when installing the fairings brings their CHTs down. We must also > assume identical props are installed (which is why we recommend and use > Sensenich propellers), proper engine maintenance has been performed, > similar > compression ratios (for the AeroVee) or horsepower output (for the Jabiru > 2200) between the comparison aircraft, and the pilot has accurately > collected and recorded the data. As you can see, the odds are stacked > against any two pilots of any two aircraft achieving an apples-to-apples > comparison. > > Airspeed Comparison > A book could be written about the different airspeeds (Ground, Indicated, > Calibrated, and True), but the only air speed that matters when comparing > one aircraft to another is True Airspeed (TAS). True airspeed can only be > determined if you have calibrated your airspeed indicator to account for > errors in the instrument and the pitot/static system. This generally > requires hours of flying very precise 2 or 3-way courses with a GPS, > measuring your ground speed and comparing the results to your indicated > Airspeed. And that is VERY simplified description of the process. Again, > this is a topic that a book could be written about and it is way beyond the > scope of this posting. Suffice it to say most pilots do not carefully > calibrate their airspeed indicator, or make any attempt at calibration at > all. Indicated airspeed from one airplane to another is no basis for > comparison, and ground speed should NEVER be used as a basis for comparison > unless both airplanes are flying side-by-side, drag race style. > > Many of today's digital instruments display True Airspeed. This leads > pilots > to believe they are being provided accurate information. It is digital, it > MUST be accurate, right? Wrong! This information is only correct if the > instrument and pitot/static systems have no error, if the barometric > pressure has been properly set, and if the instrument's outside air > temperature probe is also accurate. A cumulative error of only 5% results > in > your TAS being displayed as 161.5 mph instead of 170 mph. > > Empty Weights > Bathroom scales are never a good idea. Period. Digital scales are only > accurate if they have been calibrated. Remember, digital does not guarantee > accurate. And scales from the local EAA chapter or FBO should not be > assumed > accurate just because they came from EAA Chapter and "everyone" has used > them. Maybe every airplane that has been weighed with them is much heavier, > or lighter, than the owner knows. Establishing an accurate empty weight is > critical to determining weight and balance; not only for the FAA when they > license your airplane, but also for that hot day you decide to take your > buddy to Leadville, CO for lunch. The ensuing take-off, after enjoying a > large meal, topping off the fuel, and tossing your cameras and jackets in > the luggage area, is the wrong time to find your weight and balance is > inaccurate by 10%. > > Fuel Burn and EGTs > Many things impact fuel burn. A draggy airplane will burn more fuel for a > given speed than a clean airplane. An airplane burning 100LL will use LESS > fuel than one burning car gas with ethanol. Less energy in the > ethanol-laced > car gas equals less power, which means more gas is needed to go a given > speed or distance. We recommend all flight testing be done with 100LL as > this eliminates questionable fuel as the source of poor performance. We > recommend autogas with ethanol be avoided entirely. The fuel level gauge > and > flow sensor must be calibrated to provide accurate information. And how is > each pilot reporting fuel burn? Average for an entire flight? Indicated at > a > particular moment? At what altitude? On a cold winter day, with all that > dense air, fuel burn may be way up, but so is TAS. Again you can see how > difficult it is for any two pilots to compare any two aircraft. We > recommend > all flight testing be done with 100LL as this eliminates questionable auto > gas as the source of poor performance. > > Leaning is critical to optimizing fuel burn for a given throttle setting. > An > AeroCarb or AeroInjector provides the pilot the ability to lean for best > power at minimal fuel burn. The engine still requires ³x² amount of fuel to > produce ³x² amount of power, but by leaning properly you can avoid burning > 1.2 times ³x² fuel to go the same speed. When you level out at altitude, > optimizing fuel burn happens in simple, repeated steps: > 1. Set the desired RPM. > 2. Lean until the RPM peaks. The fuel burn will drop, often dramatically. > 3. Reduce the throttle again to the desired RPM (remember, the RPM just > rose > while you leaned the mixture). Fuel burn goes down further. > 4. Now, at the again reduce throttle setting, you may have the opportunity > to lean yet again. > > It is not difficult, time consuming, nor terribly scientific in practice, > but leaning can mean the difference between burning 7 GPH or 5.2 GPH. > > When you learned to fly in a Cessna 150 you may have been taught to lean > until the engine ran rough, and then richen a "turn and a half". You had no > EGT gauge, no fuel flow meter. If you were lucky the instructor took the > time to explain why you were doing it. If not, you just did it because you > told to. Either way, the engine didn¹t melt. Most of us have an EGT gauge > these days, so we use that as a reference, but that's all it is. It is not > an indicator that parts are about to melt in your engine. Most days ³Metal > Illness² can be leaned over 1400 degrees. Some days I can't get her above > 1300 degrees. And if you try to lean at a low RPM, the engine will quit > from > fuel starvation at a very low EGT. > > For more on EGTs, we refer you to Mike Busch's outstanding article. "EGT > Myths Debunked" in the October 2010 issue of Sport Aviation magazine. > > Engine Temperatures > This one causes everyone the most angst. First, some basics: > 1. New engines will be hot. Even in January. Even in Wisconsin. Limit > ground > running, get in the air, climb shallow and fast until the engine breaks in. > 2. Aircooled engines will never cool on the ground. We get an amazing > number > of people trying to fix high CHTs on an airplane that has never left the > ground. > 3. The green arc is the green arc, whether it is the high end or the low > end > of the temperature gauge. Green is good. > > We already touched on EGTs, above. "Metal Illness", with her Jabiru 3300, > routinely flies above 1400 degrees at altitude and 2850 RPM. It has done so > happily for nearly 500 hours. Generally, if the EGTs are high but the > engine > runs well and CHTs and oil temperature are good, I'm happy. But pilots must > make this decision for themselves; exceed the engine manufacturer's > published limits, or not? Keep in mind a published maximum EGT of 1375F > does > not mean the engine will melt down at 1380F. And the indicated temperature > is just that, indicated. Probe location, probe condition, reliable wiring > and instrument accuracy all play a part in delivering an accurate EGT > indication. Use this temperature as a reference, not an absolute number. > > Proper CHTs are very important to the life of your engine. As mentioned > above, expect high temperatures on the ground and during your first few > flights as the engine breaks in. If the CHT spikes above the green on your > first flight, level out. If the temperatures do not decrease, throttle > back, > land, and investigate. If you have persistently high CHTs, during or after > the break-in period, then something is wrong. The fix may be as simple as > installing your gear leg fairings and wheel pants. All that drag makes the > engine work very hard and reduces your speed - both increase your engine's > heat. Maybe your cowl openings are not correct. Give us a call, or better > yet, send us an email with photos of your airplane and your cowling > installation. > > Oil Temperature and Pressure > Oil is the lifeblood of your engine; it lubricates and cools. Unfortunately > oil pressure senders routinely provide false highs or lows. Make sure yours > is properly wired - often adding a dedicated ground wire will correct a > faulty reading. You can also check your gauge's accuracy easily by > temporarily installing a quality mechanical gauge. Low oil pressure must > not > be ignored! > > Low oil pressure together with high oil temperature is an indication the > oil > is mostly sitting in the sump and not being pumped through the engine. This > is cause for immediate concern. Land and investigate. The fix may be as > simple as adding more oil. Or, ironically, in the case of the Jabiru > engines, you may have added too much oil. The Jabiru engine does not like > to > be up to the full mark and oil temps will rise quickly if you have too much > oil. Go figure. > > Perhaps the most import thing is to get to know your engine. A sudden or > gradual change in your engine's EGT, CHT, Oil temperature or oil pressure > are indications something may be up. Park the plane and investigate. Use > common sense and deliberate troubleshooting techniques. > > All of this is to say numbers are only as good as the collection, > interpretation, and reporting process. Don't get hung up on the fact you > can > only true out at 163 mph. Don't fret because your CHTs are 30 degrees more > than Bob's on the other side of the country. Be reasonable with your > expectations. CHTs will never all match. EGTs will never all match. An > airplane with only 10 flight hours has not been flown and documented enough > to provide ANY comparative data at all. We are flying hand-built, > recreational aircraft for fun, not competing for a government contract or > pink slips. None of us have the equipment to measure our performance to the > knot or the degree, despite what your $8,000 glass panel is telling you. > > As always, please feel free to contact Betty, John, Jeremy, Kerry, Mark, > Heather Z, Jason, Stephanie, or Heather W at the numbers or e-mails below > with any questions or Comments. > > Blue Skies, > > Kerry Fores > > Sonex Aircraft LLC > PO Box 2521 > Oshkosh, WI 54903-2521 > Tech Line: (920) 230-TECH (8324) > Mon, Wed. and Fri. 10 AM to 12 AM and 2PM to 4PM CT > > Orders and General Info: > Ph.920-231-8297 > Fax (920) 426-8333 > http://www.sonexaircraft.com > > Please use the following e-mail addresses to Contact Sonex Aircraft: > Sales Info: [email protected] <sales%40sonexaircraft.com> > Orders: [email protected] <orders%40sonexaircraft.com> > Accounting: [email protected] <accounting%40sonexaircraft.com> > Tech Support: [email protected] <tech%40sonexaircraft.com> > > __________ > Sonex Aircraft, LLC Technical Support Disclaimer: Any tech support provided > in this e-mail is supplied for your consideration/evaluation only. Only > airframes built strictly to the plans have been thoroughly engineered and > tested by Sonex Aircraft LLC. Any deviations from the Sonex, Waiex, or > Xenos > plans are accomplished at the builder's own risk. > > This email message and all attachments may contain legally privileged and > confidential information intended solely for the use of the addressee. If > you are not the intended recipient, stop reading this message and delete it > from your system. 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