Right Prop for the Day

I was flying today and thinking I wonder if most stunt flyers fly enough to experience that each day has it's own prop needs. Here in Houston we get lots of different types of weather and prop changes are needed more than in an area that is not like ours.
What I am finding more and more is the need for props that suit the weather. I have props for wind, heat, heat and humidity, cold, cool, etc. I am starting to change prop only, instead of all the experimenting I was doing with pipe length, head clearance, nitro, line length, and so on. When I settled on a set up that was right for most conditions, but not perfect, I began to fine tune my props. On days that lap speeds were right but maneuvers were a little wimpy I try a little more diameter and or pitch. On the days that my runs are a bit punchy it seems a little less pitch or diameter or both help. The draw back to this seems to be it takes a few flights to find the right combination. I am finding more and more that I can pretty much guess it after the first flight. I keep notes and refer to them when I can not remember what to change to. As for the engine and power train it is set to give me a little room to go either way on the needle as well, to help with the prop choice. If you engine set up only allows you to run the needle at one setting then the prop choice is even more important. I have mine set so if I need to lean out(or richen) a few hundred RPMs to get the speed I want it will not ruin the stunt run. I run 3 blade carbon props and 2-3 tenths of pitch can mean a big difference in performance. If is the balance between enough drive to get you through the maneuver but not drive toward the ground in a hurry on the back side. This would translate to a lot of work in wood but should be the same procedure. I have pitched 1,000s of props in wood in a past life event and know first hand what a little change can do. It is more a situation of reading what you plane is doing and assessing what to do to get the kind of flight you are looking for.
Since I fly a lot by myself I am just wondering if I am catching up to all you experts that all ready know this stuff?
Richard Oliver

Matt's set up is pretty much the same as yours (both running pipes) in the way it responds. He has about a half turn of needle "available" to him to "fine tune" the engine, but it doesn't vary much in lap speed. Conditions, however, affect the lap speed. In cool weather (below 70 degrees) the lap speed increases by a couple tenths of a second with the "main" prop, and in hot weather (above 85 or so, and/or high humidity) it slows down to about 5.4 (I know, Doug, that's not slow to you.) The problem, he has found, is that the speed differences can not only affect your timing, but the trim on the plane. The solution for trim is a slight adjustment in leadout position. However, the prop situation appears to be the cure for the varying lap speeds due to weather conditions, and if lap speeds can be maintained, then trim changes are not needed, either.

As Ted has already posted, he changed props because of wind (as did others) but "too hot" or "too cold" can be other reasons to make prop changes. And, you are right. We are only talking a couple of tenths of a second in lap speed differences. It doesn't take much difference in prop pitch to make up the difference. (I remember Billy Werwage once changing props every flight, testing them for varying conditions.)

As you and I both know, if just one judge can be convinced that just one maneuver was worth one more point, it can make a difference in your placing.

Snip from Richard Oliver's original post...

>I have props for wind, heat, heat and
>humidity, cold, cool, etc. I am starting to change prop
>only, instead of all the experimenting I was doing with pipe
>length, head clearance, nitro, line length, and so on.

Very interesting. I remember two years ago at the NATs, someone was going around saying all anyone needed was one prop and a back-up. We could all "get rid our drawers full of Bolly's". Just a little turn of the needle was all that was needed.

I also keep a special prop to scratch my back.

LAST EDITED ON Aug-23-03 AT 10:58 PM (CDT)
 
To a point that is still true. I ran the exact same prop this year as last year at the Nat's. At this years NAT's when the wind blew (30+)I added RPM and when it didn't I richened, simple as that. I did see a need for a prop that might be better in the high winds like we had this year. I have 3 props now and find that all will work by simply adjusting the needle to the proper speed for the day, but one of them works a little better in the wind than the others.My post was in regard to my findings and hopefully to help someone else in their quest to find "the set up". Not everyone runs a RO-Jett. Good to hear your injury is to a point you are up to flying in the team trials.
Richard Oliver

>I was flying today and thinking I wonder if most stunt
>flyers fly enough to experience that each day has it's own
>prop needs. Here in Houston we get lots of different types
>of weather and prop changes are needed more than in an area
>that is not like ours.
>What I am finding more and more is the need for props that
>suit the weather.

Ditto on the weather. We are at the high point of the worst type of weather for power and lift here in Dallas. It has been particularly humid and hot this year. I wore three shirts and two hats a day this weekend playing in the City Championships, it was simply miserable with no discernible wind to cool you down (101 F with about 75% humidity).

I have watched a lot of experimentation compensating for the weather, especially with nitro and pipe. To a certain extent nitro is a good fix for conditions, but agreeing with Richard I would have to say that nothing is as dramatic at the change in prop. Most specifically pitch. More pitch for hot, humid, dead air. Less pitch for wind. More pitch in hot dead air will result in harder corners and more punch. Less pitch at a higher RPM in wind results in less speed up. Nitro can be used much in the same way by using more nitro in the calm, hot, humid air. The motor will certainly be more happy but the airplane may not be as happy as it would be with more pitch.

In a nutshell cool weather props will fly soft and flounder around a lot more in the real hot weather, no matter how much nitro you shoot to them.

Hoping someday to be a good enough pilot to notice this difference and understand enough about props to pick the right one. Right now I am happy if the airplane will get through the pattern without crashing