Heli blades vs props.

[rdresch]

I need blades for a V22 osprey project,1/10 scale. Heli blades are optimum for heli mode,cheap and easy to obtain. Problem is,when rotating to horizontal,They need alot more pitch. Rotor rpm is 1800 +or - 600mm blades for scale. I could get up to 20 degrees positive in horizontal(plane) mode.
Would this stall the blades? This would be in forward flite with about 50mph airspeed. Prop shaped blades,the real Osprey uses these with 45 degrees reduceing to 0 at the tip, would need to be custom made.A lot more expensive and difficult to replace, a probable necessity. Also I am sure it would require a gear change. This is not a problem but how much? I am looking for a top speed of 100mph. Any ideas? I'd prefer to start with the heli blades but is it futile?
Rudy

[Al M]

That is the downside of tiltrotors. Props are not rotors.

[Sparky Paul]

The primary limit is tip speed, for rotors to props.. the longer the rotor, the faster it gets to a limiting tip speed, rpm wise.
3D foamie motors are turning quite large props at low rpms and generating enoromous thrusts.
For your project it would be better to start with a couple of 400 sized inrunner motors, geared about 6:1 and large.. 12x8 or so props, get a workable system for the hover and forward modes, then find what if anything could do the job with engines.

[rdresch]

I wish it was that simple. This thing will weigh in at 25 lbs. It is powered by a 8 hp wren turbine. With the heli blades I could run as much as 1800 rpm safely. In hover mode with the blades horizontal around 1200 rpm should be enough. In plane mode I would increase to 1700 or so and increase pitch to about 20 degrees. The question is will heliblades still work with that much pitch or will they stall. I have plenty of power, no issue there. Transition will occur at about 40 to 50 mph so that should help. I know that the larger heliblades would be more efficient at hover just not sure about what would happen at 90 degrees to airflow?

[Sparky Paul]

The inflow to the disk will depend on the forward and vertical speed of the plane.
The blades shouldn't be at 90 degrees to the airflow at any time.. They'll be in heicopter/hover mode at zero airspeed, and transitioning to propellor mode slowly as they are reduced in angle to the prop positionwhile the airspeed also slowly increases..
At 90 degrees to the inflow, they will be stalled regardless of the flight mode.

[rdresch]

Sorry I didn't follow.Props horiz in helimode, pods vertical, pitch on blades at hover would be about 6 degrees. As pods rotate to horizontal, and the props are now vertical, should not the pitch of the prop be increased. I say prop but it is really a heliblade. Looking at a prop in front of me it looks to be about 40 degrees of pitch in prop. Less at the tip. If I could put enough pitch into the blades would this work? Please excuse my ignorance, but I really would like to trully understand this.
Rudy

[Sparky Paul]

Pitch angle varies with diameter for any prop.
You will need to know the diameter of your rotors, and chose a pitch.. then compute what that angle (the advance angle) will be out the span of the blade.
Helicopter blades don't vary in pitch the way a propellor does, due to the relatively low speed of the inflow air from above, relative to the inflow air in forward flight.
The rotors on the VS-22 show a large variation in pitch and area out the span, developed by long analysis of the complete flight envelope.
I'll continue to recommend using small electric components to develop your system. Technically you are attempting something at a size that needs a lot of analysis.. in lieu of that, developing a successful system with intermediate stages that advance in complexity and size is the most practical method for an individual.
There are controllable pitch props available for electrics.. used for the Golly-Gee-Whiz effect of inflight reversals, but quite practical for getting your ideas off the ground, inexpensively.

[aerogel]

variable pitch is the way to go if your going to build a osprey and there not that
expensive....There is a 3 blade variable pitch unit out there but I cant find the link....I think it was going for around 40 bucks each...

[rdresch]

Take a look at my gallery. You'll see a picture of the rotorpods . It's already set up for variable pitch. You did give me a idea I can use though. I am going to take my small shogon electric heli stick it out the window of my truck,while my wife drives, and turn the rotor perpendicular to the ground. Then increase pitch,while increasing speed on the truck. It won't be the same as the larger
1/10 scale but it will be a proof of concept. Normal pitch is 7 degrees on this heli I can double it to 14. then drive and see what speed it achieves before losing thrust. I think that's a viable plan.
Sparky the light bulb just went off! Since the rotor blade are rotating the airflow doesn't hit the blades at 90 degrees. It is vector angle determined by
forward speed and fps of the rotating disk. Is that what you were getting at?
Thanks for making me think!
Rudy

[Sparky Paul]

Rudy, you're a lot closer to the situation.. sometimes all it takes is a nudge to get the proper neurons to meet in the head bone..
:)
Paul