G-SLOT Posted November 8, 2019 Report Share Posted November 8, 2019 Grateful for your thoughts on the speed of an Ovation II that I had the pleasure of flying today. She was retrofitted with a FIKI TKS system and has VGs installed. 310hp upgrade with the Hartzell prop. Flying at 9,500' at 55% power, our TAS was 156kts whereas the POH says it should have been 170kts. I'm wondering whether the TKS system plus the VGs would explain such a disparity between the book figure and our actual true airspeed or whether there might be some other issue to consider, such as rigging, etc. Just in case I have messed up the calculations: - 9,500' pressure altitude (FL95) - OAT: -2 celcius - Fuel flow: 10.2 GPH (LOP) - TAS calculated by averaging ground speeds heading N, S, E and W. - As we were LOP, I calculated power as 55% by multiplying FF (10.2gph) by 14.9 to get actual HP and using 280hp as the denominator for the percentage power (the TAS/pwr tables assume a 280hp engine rather than 310hp). Manifold pressure was set at 20" and RPM at 2,400 but, LOP, I don't believe this makes a difference. - Goes without saying: flaps and gear up, speed brakes retracted! 2 guys up front and only about 25 gallons in the tanks. Smooth and clear air. Quote Link to comment Share on other sites More sharing options...
ilovecornfields Posted November 8, 2019 Report Share Posted November 8, 2019 Does the POH have LOP numbers in it at 10 GPH? Did you try flying ROP? Quote Link to comment Share on other sites More sharing options...
exM20K Posted November 8, 2019 Report Share Posted November 8, 2019 couldn't find an O2 poh online, but that speed looks pretty close to POH numbers for Ovation: Quote Link to comment Share on other sites More sharing options...
ilovecornfields Posted November 8, 2019 Report Share Posted November 8, 2019 I have an Ovation with FIKI and VGs. I haven’t really noticed any decrease in cruise speed with the VGs. TKS definitely costs you a few kts. I usually fly between 8-12k’ and I get somewhere around 155 kts at 55% power, 165 kts at 65% power and 175 kts at 75% power. I almost always cruise between 50-60% power. Plane is fast enough and it’s not worth the increased fuel flow for me to go faster. I don’t cruise LOP unless I’m approaching max range. I did early on and by all indications I was doing it “right” but after pretty much every mechanic told me It was a bad idea I decided to listen. Quote Link to comment Share on other sites More sharing options...
MooneyMitch Posted November 8, 2019 Report Share Posted November 8, 2019 “I don’t cruise LOP unless I’m approaching max range. I did early on and by all indications I was doing it “right” but after pretty much every mechanic told me It was a bad idea I decided to listen. “ Charles Lindbergh knew what he was talking about and proved it! Quote Link to comment Share on other sites More sharing options...
Mark89114 Posted November 8, 2019 Report Share Posted November 8, 2019 I have TKS and 3 bladed prop. Your numbers are similar to mine. My personal opinion is TKS cost 8-9 and 3 bladed prop about 2. I posted similar question years ago and my speeds arent out of line. I run 65% LOP. I dont think the additional fuel burn and cylinder heat is worth the extra 5 knots. Quote Link to comment Share on other sites More sharing options...
ilovecornfields Posted November 8, 2019 Report Share Posted November 8, 2019 20 minutes ago, MooneyMitch said: “I don’t cruise LOP unless I’m approaching max range. I did early on and by all indications I was doing it “right” but after pretty much every mechanic told me It was a bad idea I decided to listen. “ Charles Lindbergh knew what he was talking about and proved it! Did his engine make it to TBO? Quote Link to comment Share on other sites More sharing options...
MooneyMitch Posted November 8, 2019 Report Share Posted November 8, 2019 27 minutes ago, ilovecornfields said: Did his engine make it to TBO? .............and beyond. "Charles Lindbergh visited the South Pacific and taught fighter and bomber pilots how to achieve much greater range through optimal powerplant management—mostly oversquare operations and lean mixtures. For example, the P–38 was considered to have an operational range of just 400 miles, but Lindbergh taught the P–38 pilots how to stretch the range to 950 miles by operating them oversquare and leaning them brutally. Some pilots were reluctant to follow Lindy’s guidance at first, afraid that they’d damage the engines, but ultimately the guidance became standard operating procedure for the aircrews." My IO-550G was operated it's entire life, LOP. No issues. The engine went well beyond TBO and was touted absolutely void of carbon build up internally by overhaul shop. Engine was running quite strong, with little oil consumption at time of OH. I suggest mechanics are giving you incorrect advice. My intentions are to not drift this thread on LOP. It's discussed ad nauseam EVERYWHERE already, and repeatedly too ! Quote Link to comment Share on other sites More sharing options...
ilovecornfields Posted November 8, 2019 Report Share Posted November 8, 2019 I’ll have to search the interwebs to see if the Spirit of St. Luis made it to TBO. Perhaps we can debate the point at the Spirit of San Luis sometime... I don’t want to turn it into a ROP vs LOP debate either. I took the class. Drank the Kool Aid. Signed up for Savvy. Tried it out. I have nothing against people running their engines LOP (or doing touch and goes, or landing with no flaps, etc...). What you do with your own airplane that doesn’t hurt anyone and doesn’t increase my insurance rates is fine with me. People handle uncertainty in different ways and I tend to go with the more conservative approach. I’ve seen the science and made my decision which I retain the right to change in the future. It’s funny how when we get these polarizing topics people try so hard to make others see their way of doing it as the only right way. I think it’s cognitively more difficult to accept that we don’t know the answer and to make a choice anyway. Quote Link to comment Share on other sites More sharing options...
Niko182 Posted November 8, 2019 Report Share Posted November 8, 2019 (edited) 10.2 gallons is 49 percent power. Those numbers look about right. Edited November 8, 2019 by Niko182 1 Quote Link to comment Share on other sites More sharing options...
MooneyMitch Posted November 8, 2019 Report Share Posted November 8, 2019 33 minutes ago, ilovecornfields said: I’ll have to search the interwebs to see if the Spirit of St. Luis made it to TBO. Perhaps we can debate the point at the Spirit of San Luis sometime... I don’t want to turn it into a ROP vs LOP debate either. I took the class. Drank the Kool Aid. Signed up for Savvy. Tried it out. I have nothing against people running their engines LOP (or doing touch and goes, or landing with no flaps, etc...). What you do with your own airplane that doesn’t hurt anyone and doesn’t increase my insurance rates is fine with me. People handle uncertainty in different ways and I tend to go with the more conservative approach. I’ve seen the science and made my decision which I retain the right to change in the future. It’s funny how when we get these polarizing topics people try so hard to make others see their way of doing it as the only right way. I think it’s cognitively more difficult to accept that we don’t know the answer and to make a choice anyway. The Spirit it is! Yes, I should have prefaced my text by saying.............based on my experiences. Happy you are loving your beautiful Mooney Ovation ! 1 Quote Link to comment Share on other sites More sharing options...
GeeBee Posted November 8, 2019 Report Share Posted November 8, 2019 The Wright J-5 in the Spirit of St Louis had a 5:1 compression ratio. You could operate it at 1000 degrees LOP and it would make no difference to its longevity unless you were burning kerosene. Quote Link to comment Share on other sites More sharing options...
Cruiser Posted November 8, 2019 Report Share Posted November 8, 2019 310 HP Scimitar 3 blade prop with TKS Running LOP all the time in cruise. Mostly 5000 to 7000 MSL. Maximum Power 2300 RPM 50°F LOP 12.8 GPH 168 KTAS this should be right around 13 nmpg. 1 Quote Link to comment Share on other sites More sharing options...
MooneyMitch Posted November 9, 2019 Report Share Posted November 9, 2019 If my memory serves me well, for me up higher (8K or above), my stock Black Mac prop (I believe it was called back then), 2500 RPM, 20-30 ish LOP, 12.8 or less = 175K. Does that sound about right, or am I having happy exaggerated dreams ? 280 or 310 HP, does the 550 know the difference at those settings? Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 9, 2019 Report Share Posted November 9, 2019 Something is causing a mis-match in the OP’s data... To get 175kts... at 10k’ (round numbers...) ROP, 15 gph... FT, 2500rpm To get 165kts... at 10k’ LOP, 12.5 gph... FT, 2500rpm If you are flying along only using 10gph 155kts sounds pretty good... The 310hp engine allows for and recommends cruising at 2550 rpm... FF and speeds will be a touch higher... If you want to go faster, push the throttle and Or mixture and or prop in... The higher you fly, the less drag there is caused by things hanging in the wind... PP thoughts only, not an aerodynamicist... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 9, 2019 Report Share Posted November 9, 2019 Tim, When you get a chance... Add some data to your avatar area... it will help us recognize you in future threads... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
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