The B52 thread got me thinking to ask this here. I have two airplanes. Both are significantly modified from how they left the factory. The old Mooney has numerous speed mods to reduce drag, especially cooling drag, and the "new" one has an STC where they pulled the TSIO360 off of it and hung a TSIO520 on it.

Took the new one up to 10,000ft and stalled it clean and dirty and it broke right at the bottom of the green and white arcs exactly as expected. The POH supplement had a section with a couple power settings and performance, but no reference to best glide. It's a heavier plane than it was when it left the factory, with an extra 200lbs on the nose and a 300lb max gross increase. Using the original POH as a reference, where should I be looking for changes in the numbers for best glide, Vx, Vy, et cetera, relative to the detailed tables and charts for the original lighter configuration?

Thanks. Fuel burn is about double in the new plane for a realistic 60-70kt increase in cruise speed (down low it's not as pronounced, but the ability to quickly get into the flight levels with the turbo makes a big difference). She's down right now getting a new engine monitor installed so I've been running conservatively rich until I have more data. My real world experience after a couple hundred hours is that my trips take 2/3 the time in the new plane with a 20-30% increase in fuel consumed. Instead of 155kts TAS, I'm doing 220, but negative head and crosswind components have a lower effect on time; I'm climbing at 140kts (26-30gph) at 1300-1600fpm instead of 105 (14-16gph) at 800-1000fpm. I don't get routed around Class B airspace and get direct more often at the altitudes where I cruise and I feel a lot better taking trips breathing O2. The controls feel heavier, but I think that's related to the heavy forward CG and the rigging is not right; ailerons are reflexed up and that needs to be corrected -- that might work for a 727 with gobs of thrust, but I suspect the camber is taking HP for lift that should be going towards thrust.

A few questions for you.

1 - is the max gross weight the same as previously?
2 - is the acceptable CG range the same?
3 - does the changed engine significantly change the profile at the nose (i.e. is drag essentially the same for all aspects, or changed)?

If the answer to all of the above are "no" then your numbers shouldn't change noticeably.  The extra thrust would allow you to climb at a somewhat steeper angle, but the overall aerodynamics of the airframe would be pretty much the same as before, so you'd just have a higher climb rate due to the extra power.  With the glide, the only thing that matters is that the overall drag profile is the same, and that the weight of the aircraft in operation is within the range for which the original speeds were calculated.  Center of Gravity range changes would likely require so much recalculation that I expect your allowable limits haven't changed.  If they have, then all bets are off.

For significant drag reductions (e.g. speed mods on the other aircraft), your climb and glide speeds would likely increase somewhat, but you'd almost certainly need a bunch of engineers to do a lot of expensive testing/calculating to determine exactly how much.  Note that this includes such things as fairings, etc., but does not include any changes to the airfoil, which will change literally everything used to calculate those performance numbers.

*disclaimer - I am not an aeronautical engineer, and did not sleep in a Holiday Inn Express any time within the last year.  Your modifications should have resulted in a Supplemental Type Certificate (STC) which would note any required changes to those reference speeds.

Mike

I'm pretty sure these are just out of rig. I asked some other owners with the same conversion and their ailerons are rigged in-line with the trailing edge of the wing, which is what the maintenance manual specifies and how my other Mooney is rigged. We'll experiment some more with the rigging once I get some good baseline values with the engine monitor.