G'day folks,
In an attempt to improve my limited knowledge of flat air-cooled aero engines, I have been reading articles and opinion on lean of peak (LOP) ops. I have been talking to others and experimenting ad hoc. * One correspondent, David Brown, Australian rep for Advanced Pilot Seminars (Walter Atkinson, George Braley & John Deakin etc), mentioned a John Deakin article on debunking Vx (speed for best climb angle) and Vy (speed for best climb rate), and forwarded it to me along with other advice - thank you David. *
Some time ago I had seen the Deakin article on debunking Vx and Vy. I think that the article was used in a debate on the pros and cons of 'the turnback' following engine failure after take-off. Probably the debate was in a thread on vansairforce. The Deakin article is here:
http://www.advancedpilot.com/articles.php?action=article&articleid=1842
*
In the article, as an aside, John Deakin mentioned an optimum cruise climb speed for his Bonanza that 'felt right' and which was '?. fairly close to Carson's speed, or Vz...'.
In summary, Advanced Pilot Seminars recommends:
noting an EGT (eg No 1 cyclinder EGT) at a safe point after take-off;
leaning fuel/air mixture to maintain that target EGT during the climb; and notes that the target EGT indicates the optimum mixture for take-off at airfield at higher DAs (>4000ft ?).
In addition, John Deakin prefers to climb at Carson?s speed. I knew of Carson?s speed (optimum range speed, max speed per unit of fuel burned, or 1.316 x the speed for best Lift over Drag, L/D), but I can not remember noticing the term Vz before.
Slowly as I gleaned information, cautiously I have evolved the following procedure for operating our RV-7 (all data observed on the Dynon D100 EFIS and D120 EMS, conversions approximate):
Leave mixture lean after start, during run-up checks, and set full rich for takeoff (sea level).
After take-off, about 500 to 1000 ft AGL, note No1 EGT ? for us about 730C, 1350F.
Climb at 105 - 110KIAS (121 - 127 mph), leaning mixture to maintain target EGT.
After stabilising at cruise altitude, for us usually between 6500 and 9500, I ease (lean) the mixture until I sense the onset of ?slight stumble?, then slowly richen the mixture to cruise at 30litres/hour (8USG/hr), Wide Open Throttle (WOT), 2400RPM, 65ish% power, LOP, 138 to 140KIAS (159 - 161 mph), 155 to 162KTAS (179 - 187 mph).
Then the temps slowly cool, eg, at 6500 press alt, +9C (48F) OAT (DA aprox 7250ft):
Oil - 80psi/90C (194F),
CHT - 144/154/167/155C (291/309/333/311F),
EGT - 712/696/696/705C (1314/1285/1285/1301F).
Leave mixture lean during descent & rejoin, select full rich and prop full fine for the base turn.
Lean mixture after landing.
Shutdown from 1100RPM with mixture, unless checking for RPM rise while leaning at idle.
On hot days, especially the second climb of the day, my oil temp would exceed the red line (118C, 245F) if I did not climb at 120KIAS (138 mph), and once at 130KIAS (150 mph, +45C, +113F OAT, second climb). * Max CHT in the climb so far has been 210C, 410F. * There was a big reduction in climb rate between 120 & 130KIAS climb speed !
Our aircraft, 150 hours since Aug 2011 (again, all flight data as observed on the EFIS, so repeatable for our aircraft, but probably not for any other aircraft):
RV-7 QB, tip-up, VFR, built to plans, basic weight 492kg (1085lb) painted & complete, CofG 1987.4mm (78.24?) aft of datum, eg: light and CofG well forward.
Hartzell BA propeller, HC-C2YR-1BFP/F496-2.
Aerosport experimental (ECI parts) IO-360-M1, parallel valve, 8.5:1 compression, 1x Emag, 1 x Pmag - both mags with jumper fitted ? the A curve, least aggressive, (timed at TDC, so firing between 25 and 30 deg BTDC), auto plugs NGK BR8EIX. AVGAS 100LL, SW (Megitt) 7 row oil cooler.
GPS box indicates static position error varying linearly from about 1 knot slow near the stall to about 4kts slow at cruise - standard Van?s static source rivet, Dynon heated pitot just outboard of the plan position.
Observed stall speeds are close to Van?s website RV-7 numbers (assuming that Van?s stall speeds of*58 mph at 1800b, and 51 mph at 1400b, are for full flap):
816kg,1800lb:
clean - 57KIAS, 66 mph.
half flap - 53KIAS, 61 mph (flap parallel to full down aileron - thanks Mel Asbury)
full flap - 51KIAS, 59 mph.
635kg, 1400lb:
clean - 51KIAS, 59 mph.
half flap: 46KIAS, 53 mph.
full flap: 45KIAS, 52 mph.
One aerodynamic rule of thumb suggests best L/D of about 1.4 x Vs. So for our RV-7 clean stall of 57KIAS, our best L/D, Vy etc, should be 1.4 x 57 = 80KIAS, 92 mph. And our Carson?s speed should be 1.316 x 80 = 105KIAS, 121 mph.
My sawtooth climb & descents, flown during Phase 1 tests, indicated a Vy, and best glide, of 80KIAS. * So the rules of thumb seem correct for our RV-7 - or all my errors cancel each other !
Unless I am in a hurry to climb at Vy, usually I cruise climb at Carson?s speed - 105KIAS, 121mph for me, and, at max weight on one rare standard day, a time of 3min 50sec from brakes at release sea level to 6500ft.
Between 6 and 10000ft, I would have to reduce power considerably to maintain Carson's speed in the cruise. I would have to reduce power still further to maintain best range speed (best L/D or 80KIAS). Because using less than full throttle incurs an efficiency penalty, I expect that I should cruise climb to the full throttle height for Carson's speed, or even higher for best L/D, and thus best range. Until I buy a portable oxygen system to allow me to cruise at WOT above 10000ft (national limit) at the necessary lower power settings, I will not be able to gather perfomance data on the optimum WOT altitude cruise options of Carson's speed, and best range. I guess the WOT altitude for power for Carson's speed would occur at an DA considerably above 10000ft, and for best L/D speed even higher again. So I am weighing my desire for a portable oxygen system against my desire for simplicity and minimum weight.
In the meantime, usually I am content to cruise at WOT and 30 litres/hour at about 155+KTAS between 6 and 10000ft without the extra complexity and weight of an oxy system.
To date I have not noticed any issues with LOP operations. Indeed, my spark plugs seem much cleaner, and I fly further or longer per unit of fuel.
I am interested in:
opinion on cruise climbs at Carson?s speed (& the new to me term Vz?),
opinion on target EGT climbs.
A comparison between climbs at Vy and cruise climbs in regard to time, distance, and fuel used ? not a quick or easy task to gather and analyse such data.
If you do respond to this thread, please define the units which you quote, eg: mph vs knots; and, TAS vs IAS. Data & opinion from operators of other RV models would be welcome.
Disclaimer: I am not involved with Advanced Pilot Seminars. My training and experience has led me to treat with caution any advice which recommends straying from manufacturers' limits, procedures and advice.
Again David Brown, thank you for the information and advice, and your patience and persistence with my scepticism. I hope that I save enough money on fuel to attend an Advanced Pilot Seminar. If I win the lottery, I would attend a seminar in the US, buy GAMI injectors, and visit Oshkosh.
Best regards,
In an attempt to improve my limited knowledge of flat air-cooled aero engines, I have been reading articles and opinion on lean of peak (LOP) ops. I have been talking to others and experimenting ad hoc. * One correspondent, David Brown, Australian rep for Advanced Pilot Seminars (Walter Atkinson, George Braley & John Deakin etc), mentioned a John Deakin article on debunking Vx (speed for best climb angle) and Vy (speed for best climb rate), and forwarded it to me along with other advice - thank you David. *
Some time ago I had seen the Deakin article on debunking Vx and Vy. I think that the article was used in a debate on the pros and cons of 'the turnback' following engine failure after take-off. Probably the debate was in a thread on vansairforce. The Deakin article is here:
http://www.advancedpilot.com/articles.php?action=article&articleid=1842
*
In the article, as an aside, John Deakin mentioned an optimum cruise climb speed for his Bonanza that 'felt right' and which was '?. fairly close to Carson's speed, or Vz...'.
In summary, Advanced Pilot Seminars recommends:
noting an EGT (eg No 1 cyclinder EGT) at a safe point after take-off;
leaning fuel/air mixture to maintain that target EGT during the climb; and notes that the target EGT indicates the optimum mixture for take-off at airfield at higher DAs (>4000ft ?).
In addition, John Deakin prefers to climb at Carson?s speed. I knew of Carson?s speed (optimum range speed, max speed per unit of fuel burned, or 1.316 x the speed for best Lift over Drag, L/D), but I can not remember noticing the term Vz before.
Slowly as I gleaned information, cautiously I have evolved the following procedure for operating our RV-7 (all data observed on the Dynon D100 EFIS and D120 EMS, conversions approximate):
Leave mixture lean after start, during run-up checks, and set full rich for takeoff (sea level).
After take-off, about 500 to 1000 ft AGL, note No1 EGT ? for us about 730C, 1350F.
Climb at 105 - 110KIAS (121 - 127 mph), leaning mixture to maintain target EGT.
After stabilising at cruise altitude, for us usually between 6500 and 9500, I ease (lean) the mixture until I sense the onset of ?slight stumble?, then slowly richen the mixture to cruise at 30litres/hour (8USG/hr), Wide Open Throttle (WOT), 2400RPM, 65ish% power, LOP, 138 to 140KIAS (159 - 161 mph), 155 to 162KTAS (179 - 187 mph).
Then the temps slowly cool, eg, at 6500 press alt, +9C (48F) OAT (DA aprox 7250ft):
Oil - 80psi/90C (194F),
CHT - 144/154/167/155C (291/309/333/311F),
EGT - 712/696/696/705C (1314/1285/1285/1301F).
Leave mixture lean during descent & rejoin, select full rich and prop full fine for the base turn.
Lean mixture after landing.
Shutdown from 1100RPM with mixture, unless checking for RPM rise while leaning at idle.
On hot days, especially the second climb of the day, my oil temp would exceed the red line (118C, 245F) if I did not climb at 120KIAS (138 mph), and once at 130KIAS (150 mph, +45C, +113F OAT, second climb). * Max CHT in the climb so far has been 210C, 410F. * There was a big reduction in climb rate between 120 & 130KIAS climb speed !
Our aircraft, 150 hours since Aug 2011 (again, all flight data as observed on the EFIS, so repeatable for our aircraft, but probably not for any other aircraft):
RV-7 QB, tip-up, VFR, built to plans, basic weight 492kg (1085lb) painted & complete, CofG 1987.4mm (78.24?) aft of datum, eg: light and CofG well forward.
Hartzell BA propeller, HC-C2YR-1BFP/F496-2.
Aerosport experimental (ECI parts) IO-360-M1, parallel valve, 8.5:1 compression, 1x Emag, 1 x Pmag - both mags with jumper fitted ? the A curve, least aggressive, (timed at TDC, so firing between 25 and 30 deg BTDC), auto plugs NGK BR8EIX. AVGAS 100LL, SW (Megitt) 7 row oil cooler.
GPS box indicates static position error varying linearly from about 1 knot slow near the stall to about 4kts slow at cruise - standard Van?s static source rivet, Dynon heated pitot just outboard of the plan position.
Observed stall speeds are close to Van?s website RV-7 numbers (assuming that Van?s stall speeds of*58 mph at 1800b, and 51 mph at 1400b, are for full flap):
816kg,1800lb:
clean - 57KIAS, 66 mph.
half flap - 53KIAS, 61 mph (flap parallel to full down aileron - thanks Mel Asbury)
full flap - 51KIAS, 59 mph.
635kg, 1400lb:
clean - 51KIAS, 59 mph.
half flap: 46KIAS, 53 mph.
full flap: 45KIAS, 52 mph.
One aerodynamic rule of thumb suggests best L/D of about 1.4 x Vs. So for our RV-7 clean stall of 57KIAS, our best L/D, Vy etc, should be 1.4 x 57 = 80KIAS, 92 mph. And our Carson?s speed should be 1.316 x 80 = 105KIAS, 121 mph.
My sawtooth climb & descents, flown during Phase 1 tests, indicated a Vy, and best glide, of 80KIAS. * So the rules of thumb seem correct for our RV-7 - or all my errors cancel each other !
Unless I am in a hurry to climb at Vy, usually I cruise climb at Carson?s speed - 105KIAS, 121mph for me, and, at max weight on one rare standard day, a time of 3min 50sec from brakes at release sea level to 6500ft.
Between 6 and 10000ft, I would have to reduce power considerably to maintain Carson's speed in the cruise. I would have to reduce power still further to maintain best range speed (best L/D or 80KIAS). Because using less than full throttle incurs an efficiency penalty, I expect that I should cruise climb to the full throttle height for Carson's speed, or even higher for best L/D, and thus best range. Until I buy a portable oxygen system to allow me to cruise at WOT above 10000ft (national limit) at the necessary lower power settings, I will not be able to gather perfomance data on the optimum WOT altitude cruise options of Carson's speed, and best range. I guess the WOT altitude for power for Carson's speed would occur at an DA considerably above 10000ft, and for best L/D speed even higher again. So I am weighing my desire for a portable oxygen system against my desire for simplicity and minimum weight.
In the meantime, usually I am content to cruise at WOT and 30 litres/hour at about 155+KTAS between 6 and 10000ft without the extra complexity and weight of an oxy system.
To date I have not noticed any issues with LOP operations. Indeed, my spark plugs seem much cleaner, and I fly further or longer per unit of fuel.
I am interested in:
opinion on cruise climbs at Carson?s speed (& the new to me term Vz?),
opinion on target EGT climbs.
A comparison between climbs at Vy and cruise climbs in regard to time, distance, and fuel used ? not a quick or easy task to gather and analyse such data.
If you do respond to this thread, please define the units which you quote, eg: mph vs knots; and, TAS vs IAS. Data & opinion from operators of other RV models would be welcome.
Disclaimer: I am not involved with Advanced Pilot Seminars. My training and experience has led me to treat with caution any advice which recommends straying from manufacturers' limits, procedures and advice.
Again David Brown, thank you for the information and advice, and your patience and persistence with my scepticism. I hope that I save enough money on fuel to attend an Advanced Pilot Seminar. If I win the lottery, I would attend a seminar in the US, buy GAMI injectors, and visit Oshkosh.
Best regards,
