Cobalt wrote:
complete BS imposed by somebody who “needed to do something”
That is all of it, a smart move would be a time limit suggestion for ground runs: min one for cold days windy days and a max one for warm nil wind days !
My (no longer have it) 180hp Dr400 would readily hit high oil temp and high CHT on very high temperature days, and required step climbs or careful management.
I’m sure it’s related to poor pilot attention to instruments on these hot days.
Someone cleverer than me will probably be able to calculate the coefficient of cooling loss per ‘C of increased OAT.
I have seen several PIC miss-manage engines in club/rented A/C (nothing serious but just stuff I hope I will never do/miss)
The hotter the day the narrower the margins.
The club should enstill better performance from their pilots but that’s no guarantee.
Grounding the A/C is, however unreasonable it seems.
CHT will scale with OAT, more or less, on the ground and in the air.
However, in the context of the max CHT recommendations (say, 450F for Lyco, 500F absolute max) a +35C departure is not a problem, with any “normal” engine installation. Especially in France where +35C is common in the summer. We even had a week of it here in the UK 
There probably are a few GA planes with these engines which will overheat eventually if you thrash them on the ground, fully leaned… I know I really struggled to achieve a decent oil temp on the engine runs done during the CV19 crisis – here.
The +35C leading to cylinder cracks is utter bollox and anybody coming out with that should not be in GA because they don’t have even a basic grip on how things work
In my flight manual there is mentioned “In summer,2’ engine heating maximum (lycoming)”.Is’nt it there the problem in aeroclubs where pilots stay a too long time on the ground before taking off ?For good (tower instructions) or bad reasons .Also if you make circuits,the height is +- 1000 ‘,and the t° with 2,5°,that’s not a lot when the oat si 35° on the ground.And last argument,if it is 35° on ground,the pilot may suffer from the hot temperature.
That are my thoughts
It’s only 34 degrees C here today (really, might warm up a little more later) so lots of Lycomings flying
Where do people come up with this stuff? Smaller Lycomings rarely crack cylinders no matter what you do to them, it’s one of the attractions of my O-320. Obviously running high CHTs is not a good idea regardless but I can’t imagine the Robin cowling is a big problem in that regard. Southern France is not always a cool place in summer.
We had a slight problem (not a real problem, but more of a “heads up”) with the club’s Army Cub (PA19, 90 HP Continental). The problem is not temperature, but related oil pressure. Running too hot is seldom a problem here in Norway, but every now and then the temperature reaches 30 and above during summer time. The problem is oil pressure being too low. It turns out the Continental requires a different, higher viscosity, oil when outside temp go above 25 C (I think it was). Exactly how that helps, except keeping the oil pressure needle within limits, is not clear to me though. The same amount of oil is flowing through the system.
Oil viscosity is a factor in maintaining oil film thickness in plain bearing hydrodynamic lubrication. For that reason, in warmer climates you’d typically use W100 versus W80 in a C90.
Sorry I have to intervene, I do this for a living.
Cobalt wrote:
For water cooled engines, the water (and hence radiator) is typically at around 80 degrees, so the difference between 30 and 40 degrees OAT is a change of delta-T from 50 to 40 degrees, a 20% reduction in cooling capacity.Coolant temperature in a water-cooled engine is not an input data, but a consequence of the kW to be removed.
For an air cooled engine at 180 degrees (quite hot on the ground – around 350 F) , that delta-T reduces from 150 to 140 degrees, less than 10% reductionThis is real, and the only thing the metal can do is become hotter to reject the kW to the hotter ambient. It the ambient gets 10°C hotter, the metal will have to become a fair bit more than 10°C hotter to make up for it. Because air is such a poor heat-carrier, and a cylinder-head such a poor heat-exchanger, the extra degrees needed are more than few.
This is in a nutshell why air-cooled engines have all but disappeared.
Back on topic:
The main issue I have had on hot days this summer in our PA28-161 is long climbs. When you get to FL70 and OAT is still 15°C (a good 1000ft higher DA), if you enrich the crappy 250fpm climb gets crappier, if you stick to constant EGT you redline the oil temp.
But for low altitude VFR bimble at 35°C, my biggest issues were containing the volume of sweat off my body and keeping my brain hydrated and functioning…
This is the same topic as in the ‘shock cooling’ thread, only in reverse. It was established there, already, that the airflow over the cylinder fins only accounts for about 10% of cooling, but that can of course make a lot of difference.
The engine manufacturers temp curves are, in my opinion, very enthusiastic. Aluminum gets increasingly weaker from about 420°F upwards, so the consensus is to not exceed 400°F for a longer period in time. 380°F is even better. 35° C is 95°F. In any configuration, this is about 1/4 of the CHT, so any temperature outside air does of course cool the cylinders, if there is any airflow in the first place.
Tell the mechanic hello from me, I went through all of this. Many Bonanza owners went through it. The real issue is the baffling of the engine, and the pressure differential between the upper and the lower side of the engine in that particular plane. If the baffles are worn out or if there are holes, the pressure differential between upper and lower side just isn’t strong enough to create a cooling airflow. Your club’s Robin will have cracked cylinders in the future. Get the baffling done, and the OAT issue is over.
Your club’s Robin will have cracked cylinders in the future
Is this serious, or a joke?
