OK, Chemistry lesson time.

Air is primarily Nitrogen (N2, 80%) and Oxygen (O2, 18%). PV=nRT. Where n is the number of molecules in a gas, P is Pressure, V is Volume, T is absolute temperature (in Kelvin) and R is a constant.

For a given volume of gas at a temperature and pressure, the number of molecules in that volume is constant. Whether those molecules are Hydrogen, Oxygen, Nitrogen, water, methane, or any other molecule that is gaseous at that temperature. Number of molecules is constant. In a mixture of gasses, each gas contributes to the pressure a "partial pressure" that relates to how many molecules of that gas are present.

Water at a specific temperature has a specific vapor pressure. That means that as the temperature rises, the vapor pressure will also rise. This is commonly mistakenly believed to be the amount of water the air can hold. Air does not "hold" the water the way a solvent holds a solute. In the atmosphere, we refer to humidity as a percentage. At 100 percent humidity, the partial pressure of the water is at its its maximum. Any less, and the partial pressure of water is less than its theoretical value in a stable system.

Now lets look at the weights of the gasses of concern. Oxygen as a diatomic gas has a molecular weight of 32. Nitrogen has a molecular weight of 28. Water, with one Oxygen Atom and 2 Hydrogen Atoms, has a molecular weight of 18, significantly lighter than Oxygen or Nitrogen.

Now the answer. As the temperature of the atmosphere rises, the number of molecules in a given volume is reduced, thus reducing the density. Further, as water contributes more to the partial pressure of the gas, futher reduces the density. Therefore, the least dense air is the hot, humid air experienced in the summer.

As the temperature drops, the number of molecules in a given volume increases. Further, the number of water molecules is reduced as the partial pressure of water is reduced. Consequently, the colder and drier the air, the denser it becomes.

It is this phenomenon that leads to golf balls travelling further on hot humid days. This is also why airplanes must reduce weight in order to take off on hot humid days, and why helicopters have to correct for "density altitude".

Back to landings. In cold weather, our planes don't stall as easily, but will also slow down faster due to the denser air.

Brad

O.k. Real life time, cold day, plane drop like rock. Warm day, float like feather. Don't know why. Just know is so.

O.K. REAL LIFE time. When your butt is strapped into an aircraft on a short runway with trees at the end you had better pray for a cold day with the wind off the nose. I have 14 years of commercial flying experience in both hot humid Texas summers and cold Iowa winters, and for sheer performance of the aircraft I will take winter every time. Take offs and landings are shorter and climbs are amazingly faster. That is real life.

The 4-star is so forgiving, regardless of the weather conditions, this problem still comes down to technique and experience.
I want to add that while there is more to think about, You will find flying a tail dragger wonderful. It is sort of like the difference between driving a car with a stick shift, and one with an automatic transmisison. You have to think of truly controling the airplane all of the time including on the ground. It also gets you really thinking about the rudder. Easing in and out of the elevator and knowing just how much rudder to hold in and ease out of as well to keep your aircraft going straight.

Just an opinion. But power makes a heck of a difference. Dense air = more thrust but it also= more drag. Grab a glider and see which day does better. In my opinion a warm day makes for better flights, landings and take-offs. May-be that is just me.

John,

I believe that your thinking is correct.

Nose heavy models must fly and land faster, just like over-weight models.

The key words are: "It floated a minute and then nose-dived".

In order to keep the air speed up, the nose has to point down during the whole approach until just before flair.

Floating level for a minute means the plane is trading air speed by lift, and that the tail is working hard to keep a high AOA.
The tail just stalled due to high elevator upwards deflection, and the moment created by the wing lift respect to the CG just took over, pitching the model down.

Do not strecht landings until being close enough to the ground, then just flare with style.

(Edited for spelling correction)

Thermals!!

Thank you for your service. What did, or do, you fly for the AF? I have 9 yrs as an avionics tech "Pointy Head" on F-16's in the USAF.

Maybe that's it. Thermals. I've heard warm air rises!

Yes most gliders fly much better on warm days as that is when thermals are strongest, however slope gliders that get thier lift from wind blowing up a slope work better on cold windy days.

Wow, this topic has gotten way off track. Get your plane balanced properly and go fly it! do not worry about the weather unless you are uncomfortable flying in it (cold, rain, wind etc). The best way to get this down is to do it. It is important to have your aircraft properly trimmed. This is not rocket science, unless everyone wants to take this thread there as well!

AMEN!