Silent J

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Hello all, I'm on a senior design team in college and our UAV design calls for a rpop of 18" with variable pitch. We already have a solid design of our own, but I was curious if anyone knew of a company that manufactured them. It would save us a lot of time in the machine shop... Thanks for any info.

Silent J

William Robison

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Check this site:

http://www.supercoolprops.eftel.com/

Bill.

Silent J

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After reading what I posted, I realized that it could be a little unclear. We're looking for propellors with adjustable pitch. Preferably be rotating the blade along its longitudinal axis, not just different pitches at different sections of its length.

Silent J

William Robison

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SJ:

There have been ground adjustable props advertised in recent years, using a metal hub and wooden blades. Haven't seen them for a while, but Zinger (Zingali Brothers) may havw what you want.

Bill.

MajorTomski

Silent J

Why are you folks looking for a factor of ten increase in complexity and an increase in weight for minimal improvements in performance? May I suggest you optimize a standard simple inexpensive fixed pitch prop for your design cruise speeds and suffer the almost imperceptible degradation in performance on the take off roll and climb?

Been there loooong ago!

Johng

My Feedback: (4)

While I share the questions of majortomski, I would suggest you might look up postings by a username MEC. He had a long thread about building a turboprop powered aerobat with it's own speed governor and integrated variable pitch prop.

Silent J

My Feedback: (2)

Thanks for all of the constructive comments. Now, to explain the reason we need variable pitch: This certain UAV needs to have the capability to hover. And for that we designed a tilting-wing-with-shrouded-propellers. Doring hover mode, the props will be generating their thrust straight down. With 4 of these props--one on each corner essentially--the variable pitch of the props will provide pitch and roll stability by varying the thrust on the corresponding corners. It's quite an undertaking, I know, but we've got 10 of us mechanical engineers along with some strong background in computer design/control to get this done. I would be more than happy to share more info if you would like to hear more.

Silent J

MajorTomski

Oh now you tell us! A quad tandem tilt rotor, why didn't you say so?

You don't want variable pitch propellers you want R/C helicopter rotor heads.

First the VP props are hard to come by and they probably don't come in Right and Left handers. Rotor heads can easily be reconfigured to left and right and symmetrical rotor blades can be screwed on either way.

If you will look at both the old X-19 and X-24 you will see that both birds used counter rotators to simplify the torque problems.

Then I would highly recommend brushless electric motors for power. Again much simpler that trying to get four cranky engines running or geared to work in-opposite directions. With NiMH batteries or a ground power source you can be flying at the flip of a switch.

HTH
Tom

MajorTomski

Or on second thought

Forget the complexity of a variable pitch prop altogether. These folks make ground adjustable pitch L & R handed props up to four blades and 15 inch diam.

http://aircraft-world.com/varioprop.asp?id=45

Drive these with electric motor and your rpm determines thrust much simpler mechanics and control laws. This could almost be done with all off the shelf RC equipment, motors, speed controllers gyros and stabilizing autopilots.

Think aboudit

Silent J

My Feedback: (2)

Thanks for the good info! However, electric motors are not an option. Our endurance requirements and the weight of batteries don't match up very well... What we have decided, by studies in geartrains and our overpowered design, is to use a large heli engine (.91 w/ 3hp)--which has the best power-to-weight ratio we could find--that we are going to house in the middle and drive the propellors with a simple geartrain. We've essentially got 3 hp to lift 10 lbs and with respectable losses in efficiency throughout, we still end up with 15+ lbs of thrust. So, all of the design process so far looks promising. However, we are banking on the OS engine putting out its spec power and that our calculations for prop thrust/efficiencies/power requirements are accurate, which they should be.

Silent J

MajorTomski

Silent J it sounds like a fun project!


Given this data I'm back to suggesting rc helicopter rotor heads simply due to availability, cost and the ability to set them up for reverse rotation

Try here
http://www.towerhobbies.com/listings/cat-cat-e.html


The may I strongly suggest one of these:

https://www.fmadirect.com/site/fma.htm?body=Store

This helicopter autopilot gives you an enormous head start by making the machine artificially stable to begin with.


HTHTom

MajorTomski

Silent J

Check your PMs for more data.

BMatthews

First off I would suggest that there is nothing simple about a drive train to run four helicopter rotor heads through a tilt system. The fertile ground you're working in for creating shaft harmonics and flex and other problems will be something. But good luck.

Secondly you should probably mock up the gear train and engine and do some testing. I think you'll find the power abvailable at the rotor heads has gone down by quite a bit. It's nothing for a drive train to suck away 20 or 30 % of an engines power. You could easily find that your available power is closer to 2 HP or even less after all the drive train losses. Not only is there bearing friction but the large number of right angle transfers will probably chew up a lot of available power. Near as I can tell you'll have at least 4 and possibly 6 of them. And I doubt if you can make open gears last long so that means enclosed boxes and oil supplies. Further viscous losses, not to mention all the seals required.

Your team is biting off a big chunk of complex problems with this project. At least with the advent of easily available gyro modules and the ability to onboard compute using the new microcontrollers you can stabilize the craft. But I think you'll find the drive train problems will compensate for these easy fixes....

And for ducted rotors used in this way I'd take a page from the Boeing Osprey and use constant pitch blades rather than constant angle as most helicopters do it.

At least tell me you've designed in enough wing area and other factors so the craft can glide if the engine quits.

Far from trying to disuade you from this I applaud such a project and wish you and your team all the best luck.

One thing I have no doubt about at all is that all the members of the team will learn a LOT during this project. Both in what works and what doesn't.

toy264

you might get some ideas from this:

http://www.rctoys.com/draganflyer3.php

DanPeoples

Formula for maximum duration and power-to-wieght:

1. Lithium Batteries
2. Brushless or geared brushless motors


Now I want to build a UAV!

davej78

Did a bit of research when considering building a scale Boeing Osprey tilt wing, came up with using heli tail rotor assemblies from a 60 type machine along with 30 size main rotor, using a modified boom assembly figured on rotating boom to get tilt action, Lack of funds prevented further progress but thought the idea may be of some use to you.

robint777

Hello there, I am brand new to flying helicopters and I was hoping
you
could help me with an explanation in laymen terms about rotor blades.

I understand that a single blade design is usually a compromise of
flying
abilities.

However I am unsure of which part of a blade is typically providing
what
type of lift ability/flying ability?

I am interested in understanding a type of blade that most closely
resembles
an actual rotor from a full size manned helicopter.

Can you explain the tip versus middle versus inner flying surface of
such a
blade to me?

Thanks

Robin