Prop advice in general

[PropBuster]

Hi Joe and Jim,

In general, when flying at higher altitude venues, do you change the prop to a different size / pitch?

The reason I'm asking, I fly at 4550' ASL, and soon will be at 5500' ASL, and I'm using a 20x6 Xoar laminated on the OS GT-33 on a 3DHS 72 Extra.

It just seems to be lacking, it was fine in the winter but today was the first warm day I've run it, and it seems soft in vertical, slows down way too fast on uplines. (It is running just slightly rich from winter jetting adjustments, admittedly.) Maybe go to a 19x8?

Is there a rule of thumb for higher altitude props on gassers vs. flying at sea level, for example?

Thanks!!!!!!

 

[flylow3d]

Hi Joe and Jim,

In general, when flying at higher altitude venues, do you change the prop to a different size / pitch?

The reason I'm asking, I fly at 4550' ASL, and soon will be at 5500' ASL, and I'm using a 20x6 Xoar laminated on the OS GT-33 on a 3DHS 72 Extra.

It just seems to be lacking, it was fine in the winter but today was the first warm day I've run it, and it seems soft in vertical, slows down way too fast on uplines. (It is running just slightly rich from winter jetting adjustments, admittedly.) Maybe go to a 19x8?

Is there a rule of thumb for higher altitude props on gassers vs. flying at sea level, for example?

Thanks!!!!!!

I really wish I could be of some help with this question. We travel quite a bit, but I haven't ever flown in a high altitude environment so I have zero experience with prop sizes and such. I'm trying to think of someone I could contact that might know but no names come to mind. If I figure out something, I will be sure to let you know.

Joe

 

[quadracer]

Briansifsof flies at some crazy altitudes I believe, he might chime in to help.

 

[gyro]

Hi Joe and Jim,

In general, when flying at higher altitude venues, do you change the prop to a different size / pitch?

The reason I'm asking, I fly at 4550' ASL, and soon will be at 5500' ASL, and I'm using a 20x6 Xoar laminated on the OS GT-33 on a 3DHS 72 Extra.

It just seems to be lacking, it was fine in the winter but today was the first warm day I've run it, and it seems soft in vertical, slows down way too fast on uplines. (It is running just slightly rich from winter jetting adjustments, admittedly.) Maybe go to a 19x8?

Is there a rule of thumb for higher altitude props on gassers vs. flying at sea level, for example?

Thanks!!!!!!

FWIW, I did have to "prop up" on some electric motors when I was living in Vegas (2800msl). I definitely seem to get better electric performance here in Texas at 800msl or so.

The only problem with doing it on gas, is you really aren't "feeding" the plane the oxygen it needs at higher altitudes. You might even find that propping down to a smaller diameter might make a huge difference. Since your engine is oxygen starved at higher altitudes, by "unloading" the engine a little (like the 19x8 you mention) I suspect you might get better performance.

My opinion isn't based on RC experience, but rather full scale combustion engine performance knowledge..

 

[PropBuster]

Thanks Joe and Gyro! I went home, grabbed some other props, and went back out after posting this. Put the 18x8 break-in prop back on and WOW it's back. That and the head temps went down by 25 degrees. It's at 275 now.

I wasn't thinking about the gas engine's power loss from altitude, just the "thin" air for the prop, but that advice is spot on - the engine isn't making the HP it could at sea level. So while the thinner air is fine for the prop to push against, the engine isn't able to get after it. Makes perfect sense.

So I think my lesson learned is that I can run a bigger prop in the winter when the air is super cold (10F) and dense, since the engine makes more power, and in summer prop down. I forgot how much faster this plane is with the 8 pitch, such a noticeable airspeed increase too.

Time to try a 19x6 because the plane just doesn't want to slow down much for landings with the 18x8, I'm overshooting everything. Even with the throttle trimmed down to "landing" idle, I'm coming down hot and it's a bit nerve wracking.

Thanks again for all the good input !!!!!

 

[gyro]

Thanks Joe and Gyro! I went home, grabbed some other props, and went back out after posting this. Put the 18x8 break-in prop back on and WOW it's back. That and the head temps went down by 25 degrees. It's at 275 now.

I wasn't thinking about the gas engine's power loss from altitude, just the "thin" air for the prop, but that advice is spot on - the engine isn't making the HP it could at sea level. So while the thinner air is fine for the prop to push against, the engine isn't able to get after it. Makes perfect sense.

So I think my lesson learned is that I can run a bigger prop in the winter when the air is super cold (10F) and dense, since the engine makes more power, and in summer prop down. I forgot how much faster this plane is with the 8 pitch, such a noticeable airspeed increase too.

Time to try a 19x6 because the plane just doesn't want to slow down much for landings with the 18x8, I'm overshooting everything. Even with the throttle trimmed down to "landing" idle, I'm coming down hot and it's a bit nerve wracking.

Thanks again for all the good input !!!!!

That's awesome, glad you've made some progress. I had summer and winter props in Vegas due to temps.... Looks like you need them for density altitude!

Good luck!

 

[PropBuster]

Just ordered 19A and 18A Xoar 3d props from Valley View. Figured it might help the low end boost to use a bonafide 3D prop! I'll let you know what happens...stay tuned!