hey guys,i need to know if 16lb of thrust with a 18/10 at 7900rpm is good,or can i get more.thanks.

What do you have turning it?

More RPM is more thrust.

What type of flying are you doing? Do you need good mid range or more speed?

I have a huskavarna 42cc on a extra300.I am trying to learn more 3d flying.I also tested a 18/8 and got 15.5lb of thrust at 8900 rmp.

Get a hold of Scott he can set you up.
Here is one of his sale pages, http://www.rcuniverse.com/market/item.cfm?itemId=178884 ,
you can contact him through it.

Bigger carb and "better" exhaust usually works on most engines.

What brand of prop are you using? I have tested many props on gas engines and I have found out that in the 18" range you will get more thrust and rpm from an APC brand prop than others. Here is an example of the props tested on a Brillelli 25Gt engine I have.

MAS 16x8 prop: 8200RPM Thrust: 12lbs
MAS 17x6 3 blade: 8000RPM Thrust: 12.3lbs
Dynathrust 18X6 prop: 7800RPM Thrust: 12.4lbs
APC 17x6 prop: 8800RPM Thrust: 14lbs
APC 18x8 prop: 8000RPM Thrust 14.3lbs

The APC props cost a little more, but you will get more RPM and Thrust out of them over other brands.

Thanks

No enough info to work with here, but for 3D you want to go up on the diameter and down on the pitch. Try something like a 20 x 6 for your application and you will have much more static thrust for 3D work. More diameter and less pitch also helps to keep the speed down, which can help a lightweight 3D airplane live longer!

I also agree with the APC prop advice, and that's what I use almost exclusively.

Good luck,
AV8TOR

Thanks for all the info guys,but the bigest thing is, am i maxed out for thrust.Or does any body have better numbers with a 42cc.

Let's see.....

Smaller APC prop.
Bigger carb better exhaust.

If this was a chain saw You should have a working rpm of 10,000 rpm.
If it was a blower then around 8,000.

A 16 x 8 APC prop at 10,000 gives around 19 lbs of thrust.
A 17 x 8 APC prop at 10,000 gives around 25 lbs of thrust

Both of these numbers require less than 5 horsepower.
So you should prop to run in these rpm ranges.

I had a Stihl 088 that ran 13,000 rpm. It had a bored out carb, hollowed out muffler and about .025
milled from the base to raise the compression and raise the port height.

It was very fast.[sm=biggrin.gif]

Ralph,

I believe your numbers but am curious about how you arrived at the thrust numbers.

Bill

The numbers come from ThrustHP.
I know it's a little optimistic but the numbers he gave were close to what ThrustHP gave so it
was comparing apples to apples.

Ralph

I use ThustHP also just to get an idea of what a prop will be pulling at a certain RPM. I also have tested many props using a digital scale attached to a plane and running the engine wide open to see how much thrust is really being produced. You will find ThustHP is 4lbs off from what is really being produced. If you have a prop spinning 10000RPM and ThrustHP is saying you will be getting 19lbs of thrust you will really be getting 15 lbs. of thrust.

I thought you might like to know for sure. Remember to subtract 4lbs from what ThrustHP is saying and you will be in the right area.

Depends on the prop ?
18-6 Mejzlik at 9000 rpm, 25+ on the ThrustHp chart, actual measured thrust at the tailwheel is 17+...
Verified by more than 1 customer with a converted G26

I've heard that a scale attched to the plane wasn't an acurate messurment either.

Might not be the actual thrust, but it tells what the difference is between props...
The chart seems to be closer with larger engines...

HI guys: Can someone post a photo of the inards of a G26. I would like to see what makes them rev so well. Thanks Capt,n