"NJK blew a jug today"
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Hi India Four Two
Read the issue with interest and it also reminded me of differences between descent profiles I would say are common practice in the UK and those I briefly observed in Canada.
I visited Black Diamond a few times prior to the proper start of Spring flying 2 and 3 seasons ago but amongst other things did manage to fly your K21 and a Scout. I will wait to get shot down in flames but would say that most clubs here adopt a higher speed descent once 'out of the danger zone' described by the Lasham research. Whilst your (lack of) failure history appears great I am curious as to how long your average 2000' tow takes from wheels off to back on. I realise that your density altitude is a big factor but with fuel prices in general over here, there is a lot of pressure to keep the operation as efficient as possible and interested in how time wise the low speed and flap descent works out.
Diverging off topic a little but look forward to hearing form you.
Read the issue with interest and it also reminded me of differences between descent profiles I would say are common practice in the UK and those I briefly observed in Canada.
I visited Black Diamond a few times prior to the proper start of Spring flying 2 and 3 seasons ago but amongst other things did manage to fly your K21 and a Scout. I will wait to get shot down in flames but would say that most clubs here adopt a higher speed descent once 'out of the danger zone' described by the Lasham research. Whilst your (lack of) failure history appears great I am curious as to how long your average 2000' tow takes from wheels off to back on. I realise that your density altitude is a big factor but with fuel prices in general over here, there is a lot of pressure to keep the operation as efficient as possible and interested in how time wise the low speed and flap descent works out.
Diverging off topic a little but look forward to hearing form you.
About 1700 hours. Interestingly, the cylinder that failed was a replacement for a previous cylinder failure, a few years ago.
Airflow through a cowl is not always front to rear or symmetrical, throughout the flight cycle.
An engine running on the ground could well have the air coming out the front of the cowl, whilst when the throttle is closed in flight it will generally flow through front to back due to the slipstream.
Thread Starter
Yesterday, I talked to the pilot who had the cylinder failure. He was at about 500' at the end of the crosswind leg, when he heard "a big bang" and the rpm dropped to 2100. He was towing a heavy two-seater (a DG-1000), but he had enough power to manage to get to a safe location, before waving-off the glider.
A and C,
The cylinder box is labelled "Superior Air Parts" and "Millenium Cylinders"
Mechta, that makes sense.
PW Cooper,
A non-flying day today (Thursday) due to rain and low cloud, gave me a chance to look at the times for all our Scout tows this year (April to now). Our field elevation is 3700'. The density altitudes in April would have been not much more than 4000'. but on a typical soaring day from May onwards, with temperatures around 25° C, the density altitudes would be around 6000' and from the end of June onwards, we've had some very hot days (30° -35° C) with density altitudes of about 7000'.
We've done 454 tows this year ( 24 x 1000', 364 x 2000', 31 x 3000' and 35 x 4000'). I calculated the average tow time (normalized to 2000') for each tow-pilot shift in the log book. The normalization factors I used were 0.75, 1.0, 1.75 and 2.2 - our Scout definitely struggles during the upper part of a two-seater 4000' tow - the density altitude at release often exceeds 10,000'!
The minimum time was 7 minutes, the median time was 11 minutes, the average time was 12 minutes, and the maximum time was 20 minutes (on the hottest day so far).
Out of interest, I calculated average tow-times by pilot. Thirteen pilots have towed with the Scout this year. The minimum time is 10 minutes, the average time is 12 minutes and the maximum time is 14 minutes. Note that all these times are engine-start to engine-stop times, not wheels up to wheels down.
I think these are quite respectable results, considering the altitude we operate at and it is gratifying to see that the times achieved by our pilots are all consistently close to each other.
We haven't done enough tows with our 182 to get reliable statistics, because we are all still coming to terms with optimizing the tow performance. As one of our members, who is checking out pilots who haven't flown a CS prop before, said: "In the Scout, you fly the tailwheel, in the 182, you fly the engine!"
One more thing to consider is that our fuel is considerably cheaper than at Lasham! We pay about 74p per litre for 100 LL.
For comparison, 91 octane Mogas is about 54p per litre in Calgary.
A and C,
The cylinder box is labelled "Superior Air Parts" and "Millenium Cylinders"
the fact that the same cylinder failed is not too surprising. This is likely to be the one which sees the most stress-causing conditions in operation.
PW Cooper,
A non-flying day today (Thursday) due to rain and low cloud, gave me a chance to look at the times for all our Scout tows this year (April to now). Our field elevation is 3700'. The density altitudes in April would have been not much more than 4000'. but on a typical soaring day from May onwards, with temperatures around 25° C, the density altitudes would be around 6000' and from the end of June onwards, we've had some very hot days (30° -35° C) with density altitudes of about 7000'.
We've done 454 tows this year ( 24 x 1000', 364 x 2000', 31 x 3000' and 35 x 4000'). I calculated the average tow time (normalized to 2000') for each tow-pilot shift in the log book. The normalization factors I used were 0.75, 1.0, 1.75 and 2.2 - our Scout definitely struggles during the upper part of a two-seater 4000' tow - the density altitude at release often exceeds 10,000'!
The minimum time was 7 minutes, the median time was 11 minutes, the average time was 12 minutes, and the maximum time was 20 minutes (on the hottest day so far).
Out of interest, I calculated average tow-times by pilot. Thirteen pilots have towed with the Scout this year. The minimum time is 10 minutes, the average time is 12 minutes and the maximum time is 14 minutes. Note that all these times are engine-start to engine-stop times, not wheels up to wheels down.
I think these are quite respectable results, considering the altitude we operate at and it is gratifying to see that the times achieved by our pilots are all consistently close to each other.
We haven't done enough tows with our 182 to get reliable statistics, because we are all still coming to terms with optimizing the tow performance. As one of our members, who is checking out pilots who haven't flown a CS prop before, said: "In the Scout, you fly the tailwheel, in the 182, you fly the engine!"
One more thing to consider is that our fuel is considerably cheaper than at Lasham! We pay about 74p per litre for 100 LL.
For comparison, 91 octane Mogas is about 54p per litre in Calgary.
Last edited by India Four Two; 16th Jul 2015 at 21:46. Reason: Added 182 comment
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Sorry India Four Two missed the ground adjustable cooling flap.
It would help if it could be modified so pilot adjustable in the air.
Then it could be closed at top of climb, when the throttle is closed slowly.
It might be a good exercise to move the cyl head temp probe around to actually see which is the hottest one and leave it there and leaning for max power might be a bad thing as reduces detonation margins and gives higher cyl head temps.
On 360s if operating at 65% power or less it generally OK to lean to rough and go rich just to stop it. But above 65% full rich is needed also operating at max EGT or on the rich side operating between Peak and up to 125F down of peak at full power is a danger area for engine damage at high power, best not to do it and keep it a bit richer for cooling.
I try to be a little clearer wrote it in a bit of a rush.
Carbed engines have poor mixture distribution across cylinders and trying to lean for max power above 65% of rated power can place some cylinders in the detonation danger zone.
Peek power is produced when EGT is 125F down on max temperature on the rich side of peek (does not matter what the actual temp is as at peek, as this can depend on egt probe location).
I think you will find Lycoming do not recommend leaning if the engine is above 65% power unless at high density altitude which automaticaly limits the output.
On injected engines mixture can better balanced and with each injector matched to it's cylinder (GAMA injectors) closer control of mixture control can be done with out cooking a cylinder. Also it is possible to run on the lean of peek EGT temps, 50f down at least and still have a smooth engine, but only at 65% power or less.
I think maybe leaning for max power on take off may have pushed your Nu 4 cylinder into the danger zone and the high cylinder temp and fast thermal cycling has caused the problem.
The 360 is always on the edge of failure, unless handled with care and as Lycoming state,
their engine is perfect it's bad operating procedures that break it not the design mistakes!!
It would help if it could be modified so pilot adjustable in the air.
Then it could be closed at top of climb, when the throttle is closed slowly.
It might be a good exercise to move the cyl head temp probe around to actually see which is the hottest one and leave it there and leaning for max power might be a bad thing as reduces detonation margins and gives higher cyl head temps.
On 360s if operating at 65% power or less it generally OK to lean to rough and go rich just to stop it. But above 65% full rich is needed also operating at max EGT or on the rich side operating between Peak and up to 125F down of peak at full power is a danger area for engine damage at high power, best not to do it and keep it a bit richer for cooling.
I try to be a little clearer wrote it in a bit of a rush.
Carbed engines have poor mixture distribution across cylinders and trying to lean for max power above 65% of rated power can place some cylinders in the detonation danger zone.
Peek power is produced when EGT is 125F down on max temperature on the rich side of peek (does not matter what the actual temp is as at peek, as this can depend on egt probe location).
I think you will find Lycoming do not recommend leaning if the engine is above 65% power unless at high density altitude which automaticaly limits the output.
On injected engines mixture can better balanced and with each injector matched to it's cylinder (GAMA injectors) closer control of mixture control can be done with out cooking a cylinder. Also it is possible to run on the lean of peek EGT temps, 50f down at least and still have a smooth engine, but only at 65% power or less.
I think maybe leaning for max power on take off may have pushed your Nu 4 cylinder into the danger zone and the high cylinder temp and fast thermal cycling has caused the problem.
The 360 is always on the edge of failure, unless handled with care and as Lycoming state,
their engine is perfect it's bad operating procedures that break it not the design mistakes!!
Last edited by horizon flyer; 17th Jul 2015 at 14:48.
Thread Starter
hf,
No problem. I've often thought an adjustable flap would be nice, but that would require an STC and significant expense.
Re the CHT, I'm going to find out which cylinder the probe is attached to. Given that the left rear ( no. 4?) has failed twice, maybe the probe should be attached to that one
Could you clarify your sentence about mixture control?
No problem. I've often thought an adjustable flap would be nice, but that would require an STC and significant expense.
Re the CHT, I'm going to find out which cylinder the probe is attached to. Given that the left rear ( no. 4?) has failed twice, maybe the probe should be attached to that one
Could you clarify your sentence about mixture control?
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Assuming the aerotow release procedure is still the same these days i.e after waving off the glider or the glider releases early, the tug descends down and to the right while the glider goes up and left.
Our procedure many years ago during the release was to reduce to 2000rpm and increase the break away turn to 60 degrees of bank, once the ROD started increasing then control it with back pressure on the stick increasing the "g" loading and the ROD, this would produce around a 2500 fpm ROD while keeping the engine warm with the CHT in the green all the time, then at a suitable altitude usually around 500ft stop the turn heading directly for the airfield for a low circuit slowly reducing power as required.
Lookout was maintained and good out of the overhead cockpit windows on the Cub during the steep descending turn, and of course tow times were quick because the descent from the average tow altitude 2500ft to landing was around 2 minutes.
Our procedure many years ago during the release was to reduce to 2000rpm and increase the break away turn to 60 degrees of bank, once the ROD started increasing then control it with back pressure on the stick increasing the "g" loading and the ROD, this would produce around a 2500 fpm ROD while keeping the engine warm with the CHT in the green all the time, then at a suitable altitude usually around 500ft stop the turn heading directly for the airfield for a low circuit slowly reducing power as required.
Lookout was maintained and good out of the overhead cockpit windows on the Cub during the steep descending turn, and of course tow times were quick because the descent from the average tow altitude 2500ft to landing was around 2 minutes.
