Rotor Blade up sizing ????

[asra]

My machine is an open frame Rotax 582 powerd pusher, see pic.I am currently running Jack Alan 23.5 ft. 8 inch cord blades.They fly realy well, but with the 70 lt tank full of juice it realy struggles to climb. I havent a VSI yet, but feel it is probably climbing at around 200-400 ft p/m at full power. Speaking to another blade manufacturer I was told if I was to increase the blade length I would inturn increase my machines rate of climb, which is what I want, but also enable it to fly faster.He went on to explain that a larger rotor disc will fly at a reduced A of A to produce the same lift therefore reducing the amount of drag produced.This does make sense, but has enyone done the above and found this to be correct. And were their any adverse effects due to over rotoring the machine. Regards Sam. []Image Insert: 75.86

[NiqueNaque]

Sam,Ross Bannerman had the same experience as you have with a large seat tank, in his case 60 lts on a 503 rotax, very marginal in his experience.I suspect it is a square law rule, as lift is proportional to velocity squared, and since weight = lift for you to fly, if you increase your weight by 10%, you have to increase your speed by 21%, because 1.1² = 1.21 or 121%. So, with an engine with a limited power output, say 60 HP, the velocity can´t increase as it is controlled by the avalable power, so the speed has to drop, hence the struggle to get airborne.I´ve got the same blades as you have and have a 4´ hub bar on it.It is out of balance [35 cents at the tip of one blade] and the stick shake is not healthy. For the limited time I did spend in it, about an hour, it held revs very well and cranked up very quickly. The speed of rotation was a good deal less as well, though I´m yet to recalibrate the tacho to come up with the exact reduction in revs.I´ll let you know when I do, maybe after this week end.Cheers,Nick.

[Tim]

Unless you are a very heavy dude Sam there must be something holding your machine back. Can you borrow other blades to try?Tim McClure

[asra]

Nick, I've got a 2 ft hub bar on mine, and am currently considering a 4 ft one as an easy fix.Tim if given the oppertunity I would love to try another type of blades allowing me to try and feel the difference if any first hand.Regards Sam.

[asra]

SamIt may be worth trying a reduced rotor blade pitch, as an experiment.My machine climbs a little better with reduced rotor blade pitch , for only a small increase in rotor RPM. Initial set up 1.75 degrees, reduced to 1.3 degrees.What is your rotor RPM with different loads.Ross B

[asra]

RossI have played around with different pitch settings and found it flys at a happy medium at about 1.5, although it did climb better at fully adjusted pitch blocks.I will play with the prop as at full power it is only acheiving about 6200 rpm, will adjust it this weekend to between 6500 & 6800, should make a difference.At the setting I have it currently she flys in trim at 50 knots hands off, and burns about 15-16 lt per /hour at 5200-5500 rpm.Fining out the prop will probably increase my burn rate but increase my climb.Regards Sam.Image Insert: 31.01

[Scott Hogan]

Hi Sam,A mate of mine has one of the lightest gyros you would find, a Rotax 503. The whole aircraft weighs about 105kgs and he is pretty light as well (about 75kgs). He used to have 22 foot Gerrys´ fabricated rotors and had a rotor disc loading of about 1.04 lbs per square foot. He now has 23 foot McCutcheons and says they are absolutely awesome. Very stable in flight and rotor disc load of 0.95 lbs per square foot.This might give you an idea of where you could go with rotor size.With his 22´ rotors he could take off like a helo with about 25 kts of wind.As far as I´m concerned, it´s hard to be ´over-rotored´, it´s all good.Hoges

[asra]

Thanks ScottyI know the McCutcheons are high inertia blades and they would fly better in adverse weather. They would also hang on during landing.The blades I have are quiet light in comparison, but I am very comfortable flying them. The profile Jack used on them is not the NACA 8H12 but another type of prifile. Regards Sam.

[asra]

Sam,Changing the prop pitch to get 6800 engine rpm will make a significant difference with a Rotax 582. It will get a lot more power at the higher rpm - you should really feel the difference.Four things improve climb: more thrust (power), longer rotor blades, less weight (McCutchen blades are good but they do add a lot of weight to the gyro), and better rotor blades (better lifting blades like the Dragon Wing blades).Ken Rehler, New Braunfels, Texas USA - www.rvk-architects.com/ken/gyro/

[NiqueNaque]

Ken,Good to see you here on the forum.Cheers,Nick.

[asra]

sam is that a super cam pitch adjuster on your ivo prop. i've got one and i have heaps of strife getting all 3 blades the same pitch. i'm only getting 6200rpm at present

[asra]

MattYes it is the IVO quick adjust.I have had no problems with mine, and found it a great thing as I am able to adjust all 3 blades in less than a minute.Regards Sam

[asra]

Sam, You look a bit like Darth Vader there in the pic.Ted

[asra]

Ted Thanks mate, I'll remember that !!!Regards Sam []Image Insert: 54.07

[asra]

I'm with Ken. I set the pitch to give 6800 RPM at full throttle, straight and level. This gives me about 6400 RPM at the max angle of climb. I have heard many theories as to why people set the max RPM lower, but none of them hold water. I invite the people that do set there RPM low to look at the power curve graph for their engine and see what they are missing out on. I have flown 500nm in a day at 6500 RPM and I rarely criuse at less than 6000RPM. Feed them well and they'll do it all day.Daryl Patterson