I figure he had to do a bunch of reinforcement work on the airframe - just because you put a big-ass motor on the airplane doesn't mean that Vne automatically goes up.
Not having an aero engineering background, I do wonder what mods have to be done in that case. I'm guessing significant work on the elevator and stabilizer assemblies....
@inigo88 - can you shed a little light on that?
I definitely recommend watching the video series, but from memory everything firewall forward is new. New heavier engine with a much further forward CG, requiring much beefier engine mount. Nose landing gear and landing gear bay assembly completely new (made of machined billet aluminum and carbon fiber). Engine mount firewall attachment fittings and the longerons would have been reinforced all the way back to the empennage, since the engine mount is reacted directly into the longerons which are the fwd-aft fuselage bending members (same design as in your RV-6!). He may have also mentioned some empennage attach upgrades as well.
This is all really good stuff. The only thing I can add is that I have about 3 years of experience flying a King Air 200. Hot starts were never an issue and I don't remember being concerned about hot engine temperature numbers at all. Compared to a TBM700 where I was constantly very concerned about hot temperatures during start, taxi and take off.
This is good insight. If hot starts we’re unlikely, and assuming the power turbine blades are Titanium (they look it in the photos) I wonder if there’s a material science explanation, like the flaws in the Ti CFM56 blades in the southwest fan blade accident, which may have contributed to a premature fatigue failure.
Bingo. I’ve done a considerable amount of research on this and you’ve summarized it the same way I would. Jet fuel is about 12% heavier per gallon, and consumption is significantly higher. The math isn’t in favor of a conversion unless you factor in reliability and fuel availability. Otherwise, burning extra fuel, heavier fuel for a loss compared to a piston airplane of the same performance range. An easy example is the Soloy conversions of Bonanzas, 206s and such. Sure speed is higher, and some other metrics but the Bonanza airframe has limitations too, Va, Vne and fuel burn goes up but the useful load comes down.
Bingo x2! Due to the higher fuel consumption Mike had to convert virtually every structural bay he could in that Legacy into a wet fuel bay. This included the areas between the ribs under the baggage compartment, the D section of the wings, virtually everything he could. This additional weight required additional structural reinforcement.
What’s interesting to think about in addition to the “does the added speed and shorter enroute time make up for all this extra weight and fuel I’m burning?” trade study, is how that added fuel weight affects performance characteristics and safety. He says in the video that his final approach speed is 140 KIAS and his “over the fence speed” is 120 KIAS, which is high for a Legacy.
You can look to the four forces of flight and the lift equation for why this would be the case. Since the airframe lifting surfaces (wing, horizontal stabilizer) are unchanged, and in stead un accelerated flight Thrust = Drag and Lift = Weight, that added weight means you are asking for an equal and opposite addition in wing lift.
The lift equation says:
If L (pounds of lift force) must go up to match the corresponding increase in gross weight, and your wing airfoil shape (lift coefficient CL) and wing area (S) are unchanged, and you’re operating in the same standard atmosphere (air density, Greek letter “rho”), the only thing left to do is fly faster (V). If L must go up, V must go up. This likely raised the stall speed and would have implications to FAR part 23 certification (Lancair Legacy is experimental, but most modern experimentals still strive to comply with the airworthiness standards).
