When do you cruise faster? Summer/Winter?

[201er]

I'm getting a bit mixed up on this one because not only are there factors like temperature, but also pressure, humidity, and density altitude. What have you noted your actual summer/winter speed spread to be and under what conditions? In theory, should you be flying faster (at same altitude) in summer or winter? How does it play out in practice?

[PilotDerek]

A recent passenger asked me the same question. I did/do not have the answer. I am curious as well. 

[M016576]

Quote: 201er

I'm getting a bit mixed up on this one because not only are there factors like temperature, but also pressure, humidity, and density altitude. What have you noted your actual summer/winter speed spread to be and under what conditions? In theory, should you be flying faster (at same altitude) in summer or winter? How does it play out in practice?

[m20exec]

http://www.google.com/url?sa=t&rct=j&q=digital.library.okstate.edu%2Foas%2Foas_pdf%2Fv45%2Fp193_197.pdf&source=web&cd=1&ved=0CEUQFjAA&url=http%3A%2F%2Fdigital.library.okstate.edu%2Foas%2Foas_pdf%2Fv45%2Fp193_197.pdf&ei=3UIeUJAEqKLaBbO9gfgH&usg=AFQjCNFwVkT96MPYatG11zcheDmh4vUP_g

http://www.google.com/url?sa=t&rct=j&q=temperature%20and%20humidity%20factors%20relating%20to%20aircraft%20performance&source=web&cd=4&ved=0CFAQFjAD&url=http%3A%2F%2Fwww.pilotfriend.com%2Ftraining%2Fflight_training%2Faft_perf.htm&ei=90AeUNnQJ8Gs2gXo34HIAw&usg=AFQjCNGHqL94xMhnS8sJfEl-kpQ6jk14DA

[Jeff_S]

I've always noticed TAS to be noticeably higher in the cooler months for the reasons cited. Funny enough, this came up in conversation with a friend who had put his plane into the shop for a makeover in March, and didn't get it back until July. He was complaining that something they did seemed to have robbed him of speed. But the fact was simply that he had last flown it in much cooler temps and was simply remembering the March speeds as a comparison, which were higher because of the cooler temps.

[201er]

The contradictions I see are that although in the winter you have more pressure for engine operations, lower DA also means lower TAS. My hypothesis would be that you cruise faster in the summer at lower altitudes because you are effectively cruising at a higher DA. So at 4,000ft you may be cruising as fast as you would be at 6,000ft on a standard day, but in the winter you'd have to go all the way to 8,000ft to get that same kind of TAS. However, once you get above the altitude at which MP suffices to produce your desired % power, TAS starts to go down. So crusing at mid-altitudes in NA you are robbed of air and start slowing down. So 6,000ft+ you go slower than at same altitude in winter. How's that? Can someone verify in theory/reality?

[garytex]

Every plane I've ever owned (C-170, Grumman Cheetah, and M-20F)was faster both indicated and true in winter, low or high.

[WardHolbrook]

All airplanes know is density altitude. They don't know what month it is. What you're seeing is the effect that subtle changes in temperature, altitude and humidity have on aircraft performance. Airplanes like cold, dry air. There is more cold, dry air around in winter than in summer.

*Edited for clarity.

[jetdriven]

perhaps its easier to get the airplane up on the step in winter? 

[WardHolbrook]

Quote: jetdriven

perhaps its easier to get the airplane up on the step in winter? 

[sleepingsquirrel]

My M20B manual has Summer/Winter INDICATED airspeeds listed for different power settings and different INDICATED altitudes. The listed TRUE airspeed is one number. Perhaps the effect of humidity on pressure altitude is what makes the difference in Winter speed vs Summer speed.  DA has no seperate factor associated with humidity on the wiz wheel. Rightly or wrongly I was taught that humid air has less mass per fixed volume so it does effect DA as well as temperature does. I believe this effect is taken into account when pressure altitude is put in. I've never in my limited experience been exposed to a graph that explains HP vs humidity.  I suspect humidity displaces O2 in that volume of air sucked into the engine reducing the amount of fuel that can be combusted. I suspect TO distance increases are affected more than landing distance increases in high humidity conditions for a given DA calculation.

My manual does describe climbing to 200 feet above crusing altitude to trim the nose downward to cruise altitude ,"note: as the nose drops the aircraft will lose the extra 200 feet and thus will accelerate more rapidly to cruise speed.". This sounds like getting on the step.

Anyway this made me get my old manual out and review some of the important "jet like" performance touted in the Mark 21 Owner's Manual.