Hang Test (Method of hanging)

[Tim]

G'day Paul, yes you were right - I have changed it to pitch pivot.Given that no other variables change with the machine except the rotors, then it is the rotors changing the trim spring requirements The only thing that can do it is variation in rotor axis and spindle axis alignments caused by "rotor blowback". The amount of variation will determine the amount of misalighment from the pitch pivot, and hence the trim spring requirement.Tim McClure

[asra]

Tim, I see what mean.But I dont understand what "Blow back " is ?Could you please explain. Thanks Sam. [?]

[asra]

Gday paul we have changed blades several times & found that trim can change this has been put down to the rotor disk flying @ different angle due to change in reflex angle as less reflex = flatter flying blades which will lend themselves to flying faster & more reflex will fly with more angle & lend themselves to flying slower

[Tim]

G'day Sam. We have just recently being talking about this somewhere but I couldn't find it. The blow-back angle comes from the advancing blade receiving more lift, causing precessive forces to make the blade rise at the front. To stop the gyro from climbing, slight forward stick is required, resulting in slight misalignment between the rotor spin axis and the rotor head axis. This misalignment is the blow-back angle (the rotor gives the appearance of being blown back slightly from the head axis). Variation of this phenomenon with different blades results in different trim spring tension requirements.Tim McClure

[asra]

Tim I'm trying to get my head around this, so when you say the advancing blade rises at the front (leading edge I gather ), are you talking about the inbord, middle or outbord section, of the blade.Because my understanding of the rotating blades is that the angle of attack decreases the further move away from the blade root, similar to the washout in an aircraft wing.Could you tell me were I can learn more about this.Regards Sam. [?]

[asra]

Yes ! all this is very interesting ... however the Physics of the above rotor head remain that when hung in a haing test , by the teter bolt... the bar the rotor is attached to will be pulled up... thus moveing the stick to the full foward position.... there is no getting arround it .... now a trim spring may pull the head back enough to "Ballance the stick in the middle of its throw" but without a spring there is no way the stick can go to any other positionin a haing test because of the offset of the bolt that holds the rotor berring / teterbolt assembly and the bar pivot bolt are NOT in the same line ... the offset means simplyit will tilt the head ! .... no amount of lead /lag rotor spin or anything like that is going to change the fact that there is an offset in the works .... its not some misterious property of the gyro.... its simply an offset that needs to be adjusted by the trim spring , simple as that ..... the larger the offset the heavier the spring...... and My gyro has a large offset ! heheheheh !.... So Sami....... do your haing test get the machine to haing at the perscribed angle , say 10 degrees nose down.... and adjust the trim spring to move the stick to the midle of its throw.... i.e. half way between the stops of up and down on the stick's position ...... Thats how i seez it .... Its possable i'm dead wrong , but i don't see how ... the physical properties of the device in question is purdy plane the way i see it ! ..... thats my 2 coppers anyway .... if anyone cares !C ya !Bob......" Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

Tim said, Given that no other variables change with the machine except the rotors, then it is the rotors changing the trim spring requirements The only thing that can do it is variation in rotor axis and spindle axis alignments caused by "rotor blowback". The amount of variation will determine the amount of misalighment from the pitch pivot, and hence the trim spring requirement.Tim McClureIt looks like Tim keeps a good eye on the US form.[^]Butch. Trailing edge reflex helps autorotation at the very low rrpm, and also adds quite a bit of stability to a rotor system. The disadvantage is that reflex also adds drag to the rotor system.Always "bloody" compromises!!!!Aussie Paul.[]www.firebirdgyros.com

[asra]

Ahhh Ok I stand Corrected ... thanks paul ! ....sorry Tim !.... C ya !Bob....." Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[Tim]

No worries Bob. I will try to post a "hanging" diagram - might make it a little easier to understand.Download Attachment: [img]icon_paperclip.gif[/img] Rotor head.doc20.94

[asra]

Hi guys,I am finding this particular topic very interesting. I fly helicopters for a living and have "had a go" at a benson type design that I found in the NT..... long story, but it was hidden in a shed on Bohemia Downs and I got it for $800 bucks..... Anyway, the phenominon you guys were refering to as 'blow back' is called flap back here in Oz. Interesting to note, because you guys are flying teetering heads then the 'flapping to equality' of the rotor system usually accounts for the 'dissimetry of lift' caused by the advancing/retreating blades. I just enjoy using big words. Flap back is encountered in every rotor craft that has the ability to flap...... basically everything.I have a question though.... Can the stick position be a result of a larger/smaller lift force acting through the pivot point when you change blades, from what I can see there is a moment arm (as shown in the photo originally) that is a measure of lift. It is then offset by the spring.Could be wrong of course. I am relatively new to Gyros. Having said that I have got myself an EJ22 that I am doing up and will hopefully build one around it.I should say hi to Mark Clifford while I'm here, been a number of years now, but I use to chase your horses and fix your fences working for helimuster many years ago..... the Gyro I was referring to above was the one that Bill Nyman and I went harvies in..... small world.CheersPaul

[mrford61]

G,day Paul,Yes it has been a long time ( and many floodgates!! )Great to see you renewing your interest in gyro,s. I have a fair idea the gyro you mention was the machine used in the filming of Mad Max. Havent been in touch with Bill for ages but think it is still flying. Have just yarded 1600 steers to start drafting but I will try and find a photo I had of it later and post it tonight.All the best.Mark.

[asra]

G'day Mark,Yep, the machine is still flying. I speak to Bill fairly regularly, he has been in Emerald for a few years now. Had his second little tacker so hasn't been doing much flying at all. I hope to bring the gyro up to where I am at the moment to basically model my own machine on it.... possibly.As to the origins of the Gyro, I too was told it was the single seater in the movie from John (can't remember his last name now) the manager of Bohemia at the time when I bought it ... I think Bill did a bit of research on it as well. The data plate is original so shouldn't be too hard to find out for sure. I do know that the one I bought originally had a VW donk in it.Sounds like your busy. You must be slowing for the wet season soon hey? Will chat soon.CheersPaul