Changes in props. Why?

For the past 4 seasons I have been flying the same three planes in OTS,PAMPA and Classic. They are: an El Diablo with a Fox .35 had been running a 10X6 MAS; a profile with an LA .46 and a Top Flite (old style) 11X6; and a VECO Smoothie with a DS.40 swinging an APC 10X6. For some strange reason this summer the El Diablo prefers a MAS 9.5X6, The Profile prefers an 11X5 old style Top Flite, and the Smoothie prefers a 10X6 EW Rev Up! I have changed the nitro content from 6 to 7% but nothing else. IMHOP there should be no need for any changes! Any Thoughts or explanations? The weather has recently become hotter, more humid,and much more windy except for yesterday. Any ideas appreciated!

LAST EDITED ON Aug-14-03 AT 03:30 PM (CDT)
 
I'm kinda in the same boat, I've been flying a Cardinal profile with a LA46 on a 11x6 for three years and love it 2-4-2-4, but lap times were a little fast when I went to shorter lines. So I tried a 11X5, a little higher rpm, slower lap time, same 2-4-2!
I think trim is constant and if you never try anything different you'll never see any improvement. I also think the Rev-ups are a little more efficient prop then a Master Airscrew or the old paddle blade Top Flight, giving the engine a little better performance.

Are the planes getting heavier? Not joking, moisture as well as oil soak can make a difference.

The planes are probably getting heavier and the engine performance is changing. As the engines wear-in the continue to improve until they reach the "peak" performance at eaxctly the right clearances and then begin to deteriorate. Nothing in the system is really constant.

Boeing found on the 747 as it ages it gains thousands of pounds of weight, significant drag increases, and engine effeciency losses. I suspect that we see a micro scale version of this effect as we pile up the hours on our models.

There is also the weather effect. This seems to be a strange summer in many places. Has it been warmer or cooler than average? More or less humid? This summer has been hotter and more humid than normal in Tucson (whatever "normal" is) so probably has some effect. Fortunately for me, my flying skills are so poor that I wouldn't be able to notice.
Steve

Just a couple of WAG's,
You say the weather has gotten hotter and more humid. Both cause the engine power to drop. You need to decrease the prop load to keep the engine happier. More nitro helps get some of that back, but I'm not sure if you have increased it by enough to be noticeable.

Also I wasn't sure whether you mean the change has just happened (because of the weather), or it just seems like you are losing power. I don't know how much you are flying, but at some point the engine stops getting better and begins to go downhill.

Other possibilities include glow plugs which may need replacement. I find that as a plug ages, it gets effectively "colder" (the element begins to look "frosty"). Then I typically lean the mixture out to keep the "fires" burning. This works up to a point where the engine itself begins to overheat and sag. Usually dropping the prop load might compensate a bit.

I'd think the oil and maybe even the higher temp could also part of it, as a painted airplane after several season will gain some weight. But more then likely a better prop for engine...Did these same setups work better before or were they discovered after a couple of seasons?

There is nothing wrong with your models or motors. It's reality that's changing. Most people have become painfully aware of this in recent times. Can't think how you missed it.

Hi All, Many thanks for your thoughts and opinions on my reality check! I have become plug lazy lately since they never seem to wear out any more! Of the models noted only one is painted the rest are Mono Coated. I think that the weather rather than much else has caused the changes however the plugs may be as old as 3 seasons! At any rate we'll see what happens with new plugs.