Plane different speed next day

[Steve Bakac]

G/Day
      I’m trying to work out what made my plane level lap speeds different over two days
  I’m running a badass 3515  Igor system and his 12/5 3 blade prop 6s 2700 .Now here’s thing  , it flew fantastic  all day Saturday without  touching any settings, but come Sunday morning the plane went quicker in level flight and harder to keep up, with out touching anything from Saturday  .the only thing that changed was that sunday was over cast with a little drizzle of rain here and there through out the day. Compared to sunny Saturday.  Could the thicker air be the coarse?
Cheers steve
   ( downunder)

[Craig Beswick]

Go back to the 25VF on pipe Steve. Haha.

Craig
BrisVegas

[Steve Bakac]

I still have them in the draw Craig lol was a great setup

[katana]

With denser, cooler & wetter air, physics says drag would increase therefore circulation speed should be slower - opposite to what you report, so back to the theories 

[Ken Culbertson]

With denser, cooler & wetter air, physics says drag would increase therefore circulation speed should be slower - opposite to what you report, so back to the theories 

Ah, but the prop would have more bite therefore circulation speed should be faster.  Another of life's mysteries.  Maybe your watch was running slow...?  Speed guys deal with this all of the time, maybe one of them knows.

Ken

[Dan McEntee]

  Having lap times would be a great help. As stated, cooler temps would mean more dense air and more bit from the prop, and then faster lap times. It just may have seemed a lot faster to you if you have never seen this change before. I suggest that you not change anything until another sunny day comes along, and see if the resulting flight is like "normal". If it's significantly warmer, be ready for the lap times to be slower. If it's cooler again and the lap times are still quicker, try a slightly smaller prop or one with slightly less pitch and see how it performs.
  Type at you later,
   Dan McEntee

[Paul Walker]

I use almost exactly that system. Only difference is battery, and likely some of the settings.

I find that the system is very stable on lap times. Last year I flew my Nats plane 3 times (yes, 3 flights) prior to driving across our country to fly in our Nationals. I was forced to use it, and it flew only 0.01 sec/lap different than home.  It also handled the various weather conditions with only microscopic differences.

Saying that, I find the biggest difference to be on the fist flight of the day. It tends to fly a little faster on the first flight, then settles back to its normal speed.

[Ken Culbertson]

I cannot speak for Igor's timer, but I can duplicate what you are experiencing by messing with the accelerometer on a Fiorotti. It would have had nothing to do with the weather but moving it between the sessions could.  Sensitivity could affect upwind boost if the wind was different.

I checked with our local Igor users and they say the same thing that Paul said.  At best  maybe .2 difference.

Ken 

[Steve Bakac]

Thank you all for the responses , I’ll try it again soon to see what happens
   Cheers

[Doug Moisuk]

I am curious to see the resolution of the problem.

[pat king]

Internal combustion engines are very much affected by atmospheric conditions. Typically, the smaller the displacement the more noticeable are the effects of changes in power output. I completely dropped a cylinder on a 454 V8 towing a 19' travel trailer. The only thing noticeable was the dead miss at idle, even through the Rockies.

[Igor Burger]

Saturday without  touching any settings, but come Sunday morning the plane went quicker in level flight and harder to keep up, with out touching anything from Saturday

It is normal. It is quicker in cold air and slower in hot. It is good to keep track of conditions and optimal setting for certain prop and model. I have Android application for Target throttle setting. It is described here:

https://www.facebook.com/363984487112995/photos/a.364101993767911/650808675097240/

Other applications for C/L are here:

http://maxbee.net/download/Altimeter.apk
http://maxbee.net/download/AirDensity.apk
http://maxbee.net/download/Timer.apk

Descriptions:

http://maxbee.net/download/Altimeter.pdf
http://maxbee.net/download/AirDensity.pdf
http://maxbee.net/download/Timer.pdf

However problem is solvable by simple table on paper 

[Igor Burger]

With denser, cooler & wetter air, physics says drag would increase therefore circulation speed should be slower - opposite to what you report, so back to the theories 

Yes, it changes density (but be carefull, humid air has lower density than dry) and plus altitude. Theoretically, dense air will make higher drag, but dense air will make lift of prop airfoil higher by the same magnitude, so it should compesate each other. But it does not, dense air will also make more lift on wing, therefore it will fly at lower AoA and there are several such changes, including change of Re number. Result is that "it depends". Simply it is necessary to measure influence of conditions and keep track for specific model and prop.

[John Carrodus]

Steve
From one ANZAC to another....maybe look at the fuel used and consumption rate overnight! Yours  Only saying.....

[Craig Beswick]

Steve,
this all tells me you need to pull those pipes out of the drawer. LOL.

Craig