Holding someone can help here. I have a fuji that is turning a zinger 18x8 at 7300 rpm. I have a ZDZ 40 that turns a zinger 20x10 at 6300 rpm. Is it possible to say which setup would fly the same plane the fastest? I assume the ZDZ setup would give more vertical?

You can use this
http://personal.osi.hu/fuzesisz/strc_eng/index.htm

to get a relative idea of speed/thrust.

The 20 X 10 @ 7300 RPM wins both for speed & thrust. (vertical)

It also takes nearly 2X the HP.

Thanks sr., at the given specs it looks like the ZDZ will be about 4 mph faster, and 1.5lbs more of thrust. Granted both engines will unload in the air, but don't know to what rpm. Just trying to decide if it's worth an engine swap or not.

How heavy is your airframe & is it steamlined?

How much heavier will the larger engine be? Don't forget the added fuel load for larger, thirstier engine.

Rule of thumb is airframe wieght X 1 1/2 for unlimited vertical.

Airplane is a ESM P 47 which weighs about 16 lbs. the larger cc engine is actually lighter than the Fuji, but I would need to add nose weight for the cg so weight would not change. Not looking to haver just can always use a little more speed and punchiness.

Using ThrustHP to get some approximations; your ZDZ is producing about 2.85 HP at the stated numbers with the 20x10 prop. Airspeed 60mph & 17.4lbs static thrust.

Assuming that the engine produces almost the same HP at a slightly higher RPM for the sake of calculations, putting an 18x12 prop on the ZDZ will increase the airspeed to 78mph.... but you'll drop the thrust down to 13.75lbs.

Switching to an 18x10 prop brings the thrust up to 15.6lbs, airspeed to 68.6 mph & rpm's up to around 7200+.

To get more speed and unlimited verticals you'll need to switch up to a bigger engine or at least one with a higher output.

What are you using for HP/thrust.

A 20 X 10 @7300 RPM is a bit more thaqn 2.86 HP.

You may have mis-read what he posted.

He said; "I have a fuji that is turning a zinger 18x8 at 7300 rpm. I have a ZDZ 40 that turns a zinger 20x10 at 6300 rpm."

His ZDZ only turns the 20x10 at 6300 RPM not 7300 RPM.

His Fuji is producing higher RPM's with the smaller prop, but less thrust, HP and speed than the ZDZ.

Yes I did.

This hasn't been said yet.... ditch the Zingers. Some old school guys still use some big Maple wood props at our field. But all comparisons in plane performance prove them wrong.

There was even a zinger ground tested that yeilded several hundred RPMs more on the ground that produced such a perfomance decrease that the plane crashed on take off. It had just flown well on a beechwood prop, the pilot was warned that the zingers are only used to stir paint by the rest of us.

All the beechwood props and especially the laminated ones are superior to the maple ones.
just my .02

I would try a good beechwood 18x6 on the Fuji and an 20x8 on your ZDZ

I don't think the performance difference is due to the wood they are made from. The difference is the horrible airfoil and quality of the Zinger. I've always thought newer props are made from Beechwood simply because it is a readily available wood that is suitable for the purpose and it is available at a much lower cost. Beechwood does compress easier when bolted to the prop hub. The laminated props solve this issue.

Regardless of the wood difference, kmeyers, you are 100% correct that he should try something other than Zinger.

Talking woodies, not too long ago (summertime) a fellow tried flying his toy with someone's woody, maybe a Biela but might have been a zinger, don't remember. I do remember the tremendous noise the crate made and didn't really go anywhere. It just cranked out the dB's, making every one's ears hurt.

When you want performance out of an engine as TR sez, put on a good quality prop. APC's are the best but they don't work well on most gas engines; hubs are too small. There are a couple of exceptions-- the Syssa and the OS and maybe the Evolution.

The great thing about wood is that you can carve some life into it. Thin the TE and reshape the blade for max performance. It would be a quieter set-up when the prop is right. It takes power to make noise, just the same as it does to make thrust. Which one of these do we want?