Ectomorph26

Is there an engine calc program out there for glow and gas engines or perhaps someone can direct me to a place with the formula's for calculationg performance.

I'm looking for mainly a way to calculate thrust for a given RPM horsepower and prop size/pitch as well as efflux velocity.

For example I'm trying to figure out the difference in performance between a 2-stroke .61 engine turning a 2 bladed 12x6 @ approx 12,000rpm

vs

The same engine geared 2:1 turning a 4 bladed prop as well as a way to determine the proper sized 4 bladed prop @ 5,500-6000 rpm.

I've got some gears coming I've ordered and I plan on trying to make a reduction drive for smaller glow engines. Using 3 gears since unless I want the prop to spin backwards it's a necessity mounted between two aluminum plates on a custom engine mount. I'm thinking if the gearbox will hold up and it should since they are steel gears the mount I'm working on should allow for mounting the gearbox to pretty much any 2 or 4 stroke glow engine.

I don't know why this hasn't been done yet. I see reduction drives for large gas engines but nothing for small glow engines. Even then they tend to be high dollar belt driven reduction systems.

This stems from my desire to be able to turn a scale prop on my skyshark Stuka when it's finished. As well would be great for 3D planes as well allowing them to use smaller lighter more cost effecient motors without losing unlimited vertical or hovering performance.

In fact most of them seem to be running engines that in level flight could rip the control surfaces off of them in order to get the thrust necessary to hover and do vertical manuevers.

w8ye

My Feedback: (16)

http://home.wanadoo.nl/pereivers/Goodies.html

http://www.lcrcc.net/thrust_calc.htm

http://www.gobrushless.com/testing/t...calculator.php

On this one CLICK on GOODIES for the calculator

http://www.bmaps.net/

DarZeelon

James,


I use the [link=http://www.mvvs.nl/prop-power-calculator.xls]Reivers PropPower calculator[/link].

It is the most versatile and accurate of them and only the thrust number seems too optimistic.


If you have MS Office software on your PC, you can download it for free; and if you don't, you can always run it on the web site.


As to your idea, it has been tried and everyone always reverted to direct drive props.
Cost and inefficiency have been a deterrent to mass following of that trend.

The only exception that does use geared props, is RCV engines that have an integral gear system and the current 'turboprop' trend... You can't have a prop that spins at 150,000 RPM, can you?

pe reivers

The calculator is not optimistic, but in real life the fuselage has resistance when put in the prop wash. This resistance is not accounted for yet, so the fish scales may give results between 85 and 95% of the calculated value, depending on fuse frontal area to prop disk ratio and drag factor.
So much I want to do, and limited time to do it in.

Pepe J

My Feedback: (2)

OS offered 61 size FSR two strokes with gear reductions back in the early 80's. They can be found for sale occasionally here at RCU, "Z"bay or RC Canada. I believe they had a weight in excess of 30 oz. without a muffler. The RCV would be a better choice IMO as suggested earlier or a four stroke with a specialty muffler is an option, although, what you're planning on doing is what makes this a great hobby.

asmund

don`t those rcv engines have a 2-1 reduction built in them. Maybe their 60 engine is just what you need in your stuka??? or the 91 if the 60 is to small

w8ye

My Feedback: (16)

The RCV "SP" series has the 2:1 reduction