Blue on Top Posted January 24, 2022 Report Posted January 24, 2022 9 hours ago, PT20J said: My 1978 M20J and 1994 M20J both had the same prop and engine. The only differences I note are the 1994 has the sculpted wingtips and the one piece belly panel. From the POH charts: Common conditions: 20 deg C, sea level, 2740 lbs, 15 deg flaps, paved, level, dry runway, full power before brake release, landing gear extended until obstacle cleared, cowl flaps open. 1994: Lift off speed 59 KIAS, ground roll 1480'; 50' speed 76 KIAS, 50' distance 2200' 1978: Lift off speed 63 KIAS, ground roll 965'; 50' speed 71 KIAS, 50' distance 1831' Skip @PT20J Skip: Great data. The 1978 data looks good for a "normal" takeoff. There is a second chart in the manual before the "normal" chart that is "maximum performance". Lift off is 62 KIAS and 66 KIAS at 50'. The associated distances are slightly less, too. The 1994 data for lift off speed looks to be in error (but that is what is in the POH). With a stall speed of 57 KIAS, the lift off speed speed would need to be a minimum of 63 KIAS (62 KIAS for rounding errors on the maximum performance data). My somewhat educated guess is that the lift off speeds in the 1994 POH are in error by 10 knots, meaning the example lift off speed should be 69 KIAS. This makes all the other numbers line up. The stall speed at the higher GW in 1994 would have also increased the associated lift off and 50' speeds. The 1996 chart above is also for a "normal" takeoff ... which is up to the OEM to define those conditions. It looks like Mooney went a little more conservative in the later years. It would be interesting to see if there is a "maximum performance" takeoff chart in the 1994/1996 POH which should bring this back to an apples-to-apples comparison. Quote
PT20J Posted January 24, 2022 Report Posted January 24, 2022 1 hour ago, Blue on Top said: @PT20J Skip: Great data. The 1978 data looks good for a "normal" takeoff. There is a second chart in the manual before the "normal" chart that is "maximum performance". Lift off is 62 KIAS and 66 KIAS at 50'. The associated distances are slightly less, too. The 1994 data for lift off speed looks to be in error (but that is what is in the POH). With a stall speed of 57 KIAS, the lift off speed speed would need to be a minimum of 63 KIAS (62 KIAS for rounding errors on the maximum performance data). My somewhat educated guess is that the lift off speeds in the 1994 POH are in error by 10 knots, meaning the example lift off speed should be 69 KIAS. This makes all the other numbers line up. The stall speed at the higher GW in 1994 would have also increased the associated lift off and 50' speeds. The 1996 chart above is also for a "normal" takeoff ... which is up to the OEM to define those conditions. It looks like Mooney went a little more conservative in the later years. It would be interesting to see if there is a "maximum performance" takeoff chart in the 1994/1996 POH which should bring this back to an apples-to-apples comparison. Then 1994 POH didn't have a chart for maximum performance so that's why I used the 1978 normal takeoff chart to keep the comparisons as equal as possible. Here are the charts from the POHs for the two airplanes: 1 Quote
PT20J Posted January 24, 2022 Report Posted January 24, 2022 12 hours ago, Blue on Top said: 4) As for wing tip treatments, squared off tips are actually fairly effective as it causes cleaner vortex separations from the wing. Additional span is ALWAYS good. My apologies to @PT20J (I love you, man), but ANY span outboard of the aileron (Mooney geometry) will increase the aileron control forces and their effectiveness. With the additional span (though minor) will cause less wingtip loss ... especially locally at the aileron itself. Never a problem with pointing out an error -- that's how I learn things. . And thanks for all the time you spend here explaining stuff -- you're a great resource. I'm not clear how moving the ailerons inboard from the tips (or adding additional wing area outboard of the ailerons) would increase control forces and effectiveness. Can you provide more detail about the nature of "wingtip loss" and it's effect on the aileron? Thanks!! Skip 2 Quote
Blue on Top Posted January 24, 2022 Report Posted January 24, 2022 51 minutes ago, PT20J said: I'm not clear how moving the ailerons inboard from the tips (or adding additional wing area outboard of the ailerons) would increase control forces and effectiveness. Can you provide more detail about the nature of "wingtip loss" and it's effect on the aileron? -Skip The aileron itself is a little wing with "localized" pressures and flows. Adding any surface on the outboard end of the aileron will give the surface an "endplate" effect. That surface doesn't need to be (in this case) vertical; horizontal works, too. In essence what the added surface is doing is providing a pressure to fight against. In the Mooney case, it helps that the aileron hinge line is a little forward swept, the airflow is less likely to travel off the end of the wings ... but makes the inboard end a little worse ... especially when the flap is deployed. I'll try an example, so bear with me Let's look at the outboard end of the left wing at the aileron hinge line on the lower (pressure side) surface. If we roll right (left aileron down), the local pressure will increase on the lower side of the hinge line. The airflow, instead of working harder to continue down around the deflected aileron, will take the easier path and travel out the hinge line. A more effective surface equates to higher forces. 1 Quote
Blue on Top Posted January 24, 2022 Report Posted January 24, 2022 1 hour ago, PT20J said: Then 1994 POH didn't have a chart for maximum performance so that's why I used the 1978 normal takeoff chart to keep the comparisons as equal as possible. Here are the charts from the POHs for the two airplanes: Interesting. Not sure why they did that. The lift off speeds should definitely be higher. 1 Quote
carusoam Posted January 25, 2022 Report Posted January 25, 2022 Around ‘94 Mooney was busy Launching the Ovation… The O’s POH has two type of T/Os on the record… Normal and Soft field… Later O POH’s the soft field details are missing…. PP fuzzy memories only… -a- 1 Quote
Hank Posted January 25, 2022 Report Posted January 25, 2022 16 hours ago, Blue on Top said: Interesting. Not sure why they did that. The lift off speeds should definitely be higher. Why would the liftoff speed increase? Aircraft weight is the same. Sure, later Js have higher gross, but he's comparing against the same 2740 weight on both planes. 1 Quote
Blue on Top Posted January 26, 2022 Report Posted January 26, 2022 16 hours ago, Hank said: Why would the liftoff speed increase? Aircraft weight is the same. Sure, later Js have higher gross, but he's comparing against the same 2740 weight on both planes. Great question! I've talked to a couple people from that time at Mooney, and they don't know. I am not giving up. Did the 1994 Js have a glass panel (i.e. Garmin or King)? Quote
PT20J Posted January 26, 2022 Report Posted January 26, 2022 10 hours ago, Blue on Top said: Did the 1994 Js have a glass panel (i.e. Garmin or King)? No, steam gauges. When I bought mine the previous owner had installed an Aspen PFD. I never noticed any difference in response time between the PFD airspeed and the original airspeed indicator. I did a pitot leak test and they were within a couple of knots of each other at 150. Skip 1 Quote
carusoam Posted January 27, 2022 Report Posted January 27, 2022 ‘94 O1… standard airspeed indicator… (King package) Possibly the same device used for the M20J built at the same time… POH Stall speeds listed in tenths of KIAS… Ability to read and interpret the analog instrument… +/- 2kias (?) -a- 1 Quote
A64Pilot Posted January 27, 2022 Report Posted January 27, 2022 On 1/25/2022 at 6:51 AM, Hank said: Why would the liftoff speed increase? Aircraft weight is the same. Sure, later Js have higher gross, but he's comparing against the same 2740 weight on both planes. I know when I flew the S2R-H80 for Certification I was allowed to pull it off as soon as possible and horse it to 50’ which as it has a 54’ wing span is barely still in ground effect. Now however IAW an AC that I don’t have the number to, you do a normal takeoff and climb that you can continue, they way I did it I got to 50’ but couldn’t continue as I didn’t have enough speed to climb out of ground effect. The new way IAW the AC is more realistic, but isn’t maximum effort, but is more conservative, and therefore safer. Just doent give the sales guy good numbers To get a idea of the differences, look at the takeoff distance at max gross weight Air Tractor advertises for their AT-502, then look and see what the number is in their POH, they show the differences in the two different methods rather well for a very heavily loaded aircraft. I don’t have those numbers on me. OK AT’s sales literature claims 1,140’ https://airtractor.com/aircraft/at-502b/ One of you guys better with searching find the POH for the AT-502B, my Googlefu sucks or I would, but I know it’s going to be a big difference Quote
Blue on Top Posted January 27, 2022 Report Posted January 27, 2022 30 minutes ago, carusoam said: ‘94 O1… standard airspeed indicator… (King package) Possibly the same device used for the M20J built at the same time… POH Stall speeds listed in tenths of KIAS… Ability to read and interpret the analog instrument… +/- 2kias (?) -a- Seriously? Stall speeds to the 0.1 knots! I wouldn't believe that . That's in the range of 0.006 psi. WOW!!! Test data is flown multiple times, data is plotted, and certification data curves have to be conservative ... even back then. I'm not done looking into this one! Quote
Blue on Top Posted January 28, 2022 Report Posted January 28, 2022 @carusoam Looks like they did it to 1/2 a knot. That's still tight. Do these values of KIAS and KCAS agree with the appropriate correction curves, earlier in the section? (Note: NOT questioning you) Quote
carusoam Posted January 30, 2022 Report Posted January 30, 2022 (edited) On 1/28/2022 at 1:12 AM, Blue on Top said: @carusoam Looks like they did it to 1/2 a knot. That's still tight. Do these values of KIAS and KCAS agree with the appropriate correction curves, earlier in the section? (Note: NOT questioning you) Airspeed calibration curve in the landing configuration…. We go from 0.5kias accuracy to slide your finger down the paper graph accuracy… I’m not a big fan of paper graphs, since I have seen how easy it is to get accurate data from them using excel and an iPhone… There is an interesting difference between power off and power on…. About a knot or two…. With full flaps down… See if I interpreted that correctly… Best regards, -a- Edited January 30, 2022 by carusoam 1 Quote
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