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HelicopterTurbine Helicopters › Predator/Wren800mm and 850mm blades continued.
11-28-2005 06:11 PM  12 years agoPost 1
Bell Bloke

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UK

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I suppose the best thing is if you have some points or questions Neil please be totally direct with me and I will do my best to answer them. This may be helpful to other people as well. By the way I'm on standard plastic blade grips, but a basic knowledge of mathematics can sometimes be useful.
I however failed all my exams at school.....too busy racing.
Thank god I have access to one of Britains top physicists.....MR CHEESE!!!
It has to be said that the calculations have been done and the chopper has flown, however nothing is ever totally 'a sure bet'. There is always a small risk with any change you make to a proven system.
However the world through the centuries has been full of the, 'can't dos' and the, 'it'll never work' people, and sometimes they've been right.
Then there have been the have a go types, people who are prepared to take a calculated risk and push the boundaries for the greater benefit of there follow man or woman.
The former type of people like routine in their lives, they don't like danger. They would rather play it safe, sitting in their comfort zone and living their lives without incident and without ever making any mistakes. These people are safe dependable, reliable and stable, they make society function at a grass roots level and we need them!
The latter type, however are the ones in history who have given us the wheel, radiography, penicillin, the jet engine and even the helicopter.
I, in my own little way like to think I'm leaning towards this latter section of people. Through my life I have taken some calculated risks, and some less so.
I have had some disappointments but I always get there in the end, and if I say I'm gonna do something, I'll do it.
Past successes have shown me that many people have adopted some of my ideas and have been thrilled with them, in this and other areas.
e.g. In this field alone people are now converting some Century and Hirobo helicopters to Electric and LI-Po. (Another doomed idea)
You can see my latest, in Rotor World, last month and this month. (Hirobo Lama). http://www.rotorworld.co.uk/
And what are we taking about here, all I’m doing in this instance is running slightly heavier, bigger blades...... it's hardly ground braking, I've been doing it on my Lama for over a year now!

Neil, I am genuinely not having a go at you here, your criticism is absolutely fine, the last thing I want is everybody to sit quietly saying nothing for fear of offending.
However, with your engineering background don't you think some disc loading tables and centripetal stress calcs posted here would be a bit helpful, because to be honest it's most awkward for me to disturb Mr. Cheese these days as he's very busy with matters of national security.
So please Neil, why not try and help.
For Free.
I have sent you an olive branch, feel free to send me back the bird!
Fighting, although fun, ain't gonna get us anywhere.

Colin Chapman, Team Lotus.
A great man, a great team, my inspiration.

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11-28-2005 09:43 PM  12 years agoPost 2
Bell Bloke

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Right it maybe a bit premature but here are Mr Cheeses' stress calculations based on the fact that I told him that the standard Predator is routinely flown on 720mm blades with a static weight of 190grams at a heads speed of 1900rpm. Here is what he printed out for me:

SIZE, WEIGHT, RPM, & ROTATIONAL WEIGHT AT GIVEN
RPM IN KGs
(Head load in kg)


720mm 190g 1900rpm 276kg

800mm 220g 1800rpm 319kg

850mm 290g 1375rpm 261kg

850mm 290g 1400rpm 270kg

850mm 290g 1450rpm 290kg

850mm 290g 1500rpm 310kg

850mm 290g 1520rpm 319kg

850mm 290g 1650rpm 375kg

Interesting isn't it!

Notice how it is possible to run the 'oversized, heavy' 850mm 290gram blades to over 1500rpm which still gives a comparable figure to the 800mm 220gram blades at 1800rpm.
If you really want to play safe the BIG 850mm 290gram blades could be run at 1375rpm which would put it in a safer load area than the standard 720s'
I have personally, tested and flown them at 1650 rpm on plastic blade grips, and at that speed the blades weigh a whopping 375kgs each thats 58 stone!!!
Amazing!
I am now running at 1450rpm which is nice.

For casual reference my Century Bell 47 500mm 110g blades run at 1580rpm and at that speed each blade weighs 77kg.
Hope you folks find this useful.
Science not Fiction.

Ps. If you want me to work out any other loadings just post them here and I will pass them onto MR. Cheese.

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11-28-2005 10:23 PM  12 years agoPost 3
Bell Bloke

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Here are some really bad snaps of them taken at my girlfriends house, big eh!
Lovely for floaty autos.

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11-29-2005 12:00 PM  12 years agoPost 4
Bell Bloke

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Yes chopper jockey, you are absolutely right, the blades are measured at the C of G. This is a good average as forces from the C of G to the head are progressively less and forces from the C of G to the tip are more, so all things being equal. The formula is applied to all of the calculations, so all things being relative too. I was wondering what they would fail at, perhaps 3 times there working load? Isn't that what the industry works to?

Greg those blades look mighty hansom 950s' on an 11kg heli. When you run out of fuel you could go slope soaring with it!! Seriously that has the same kind of lift as a glider!
Fantastic that's what I say, I mean why make life difficult for yourself.
How long can you do an engine off sustained hover for?

Oh by the way your head load is:

340kg of load on your head at 1350rpm, I guessed the blade weight at 350grams, you are well in the safety zone.

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11-29-2005 12:27 PM  12 years agoPost 5
Bell Bloke

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UK

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Other figures that may be of use.

On the 290g 850mm blades @ 1380rpm, here are the throttle and pitch points from a Futaba radio setup.

-3

6.5(hover)

+10

Throttle is at
(1) = 0.5%
(2) = 70%
(3) = 80%
(4) = 90%
(5) =100%


Idle up is at
(1) = 60%
(2) = 70%
(3) = 80%
(4) = 90%
(5) = 100%


Turbine peed in hover is 101,000rpm
Turbine temp is 435 degrees.
Gearbox temp is 44 degrees.

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11-29-2005 12:48 PM  12 years agoPost 6
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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Blades

Bellbloke,
I bet you can't workout when it is going to rain!!!!!!!!!!!!!!

Very interesting post, points out to me , that in future I'll be hovering 30 meters away from me!!

Best regards,
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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11-29-2005 01:11 PM  12 years agoPost 7
richie1967_uk

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London UK

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Hi Ross

What were you curves for you 810 Razors? I am all rebuilt and ready to go......

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11-29-2005 02:26 PM  12 years agoPost 8
Bell Bloke

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UK

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Hi Folks.

Richie the 810 razors are:

-3

6.5(hover)

+10

Throttle is at
(1) = 0.5% (65% idle-up)
(2) = 75%
(3) = 85%
(4) = 95%
(5) =100%

Headspeed from memory is 1650 in the hover. Good luck Bud!
By the way you may need to lengthen your boom supports as I picked up a tail vibe at this rpm. If you go under or over the rpm the vibe goes but it is eather too fast or too slow on the head.
It did it with all 3 sets of blades, it's just a resonance in the longer boom, nothing to worry about, you just have to tune it out.

chopper jockey, the limpet probe is on the bottom of the gearbox casing near the drain plug. Temps are a little lower today because of the cold, mine normally runs at 50degrees, maybe I will test it again when it is a little warmer, although I have a feeling that rain is on the way.
Your right WIRLYBIRD, since reading those figures I stand a lot further away from my heli now, it's fairly terrifying to think about the forces involved with these big machines.
The thing that amazed me was the load difference between a 50sized and a 90sized model, a real eye opener.

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11-29-2005 03:57 PM  12 years agoPost 9
richie1967_uk

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I was thinking of getting some longer supports, but will deffinately get some now. I was also thinking of mounting them lower down on the frame....

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11-29-2005 07:33 PM  12 years agoPost 10
Bell Bloke

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Yes, I forgot to say you will have to do that, but just mounting them lower still is not enough to stop this little vibe, supports must be longer too. I no longer have this vibe because I've dropped my headspeed down to 1380rpm which is well outside where it comes in at. It seems to come in at 1450-1500rpm and is out again at 1550rpm (on mine anyway). When I put my long struts on I will post the measurements. All the best, Bell Bloke.

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11-30-2005 11:45 PM  12 years agoPost 11
mr u,pratt

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turbine overheat while doing a chaos

can any one tell me why my turbine overheats while i'm doing a chaos and occasionally inverted backwards funnells

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12-01-2005 12:40 AM  12 years agoPost 12
hdsprockett

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Carson City, Nv

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800 MM Predator

Thought I'd show my Pred w/800 Razors and a 945 boom. I also made some longer braces out of carbon fiber arrow shafts. The Wren should arrive any day and we will see how it spins. All those numbers look good but I'm still keeping it away from solid objects and living things. We do our best to be safe but anything made by man can (and if neglected eventually will) fail. I'm feeling kind of lonely over here with my Predator but I'm plugging along.

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12-01-2005 10:46 AM  12 years agoPost 13
coolice

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Northamptonshire, England

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hdsprockett : Looks good so far. From the pictures it looks like you'll be converting a Carbon Predator, am I right?

If so this will be good to know about if your going for the full WREN conversion as we haven't fitted the turbine module to a Carbon before.

Please keep us informed of how it goes.
.

Ian Contessa
Team Robbe SchluterUK
Midland Helicopters

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12-01-2005 12:55 PM  12 years agoPost 14
Bell Bloke

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Looking good hdsprockett

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12-01-2005 01:57 PM  12 years agoPost 15
Peter Wales

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Orlando Fl

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Hey Ross

Work out the head loading on my Lama

950mm blades giving a 2.3m disk, big blade holders! Each blade weighs 550gms and the head speed is 1050 rpm

Peter Wales
http://scalehelicopters.org

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12-01-2005 03:02 PM  12 years agoPost 16
AirWolfRC

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42½ N, 83½ W

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You will need to provide the CG of the blades from the main shaft before that can be done.

Then the basic formula A = W² R can be applied to find the centrifugal forces. Radius ( R ) to the CG needs to be known.

You can do this yourself with a simple calculator.

F = (RPM)² R Wt / 563312
where ---
F = centrifugal force in pounds
RPM = head speed
R = radius to CG of blade in inches
Wt = blade weight in ounces
563312 = constant to handle all the unit conversions

Wolfgang

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12-01-2005 03:29 PM  12 years agoPost 17
Bell Bloke

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Hi Peter, I make it 373kg of load on your head, per blade. The C of G will make a slight difference to the final figure but to keep all things relative I just take it that the blade C of G is about blade center, and then there are the blade grips which vary in length so I take the measurement from 1/2 the total radius.

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12-01-2005 03:42 PM  12 years agoPost 18
Bell Bloke

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What do you think AirWolfRC, do you concur?
Peter is that your Lama spec?

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12-01-2005 03:46 PM  12 years agoPost 19
AirWolfRC

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42½ N, 83½ W

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If I use 1/4 of the disk diameter, I get 390 Kg

If you want that in metric,

F = (RPM)² R Wt / 892850
where ---
F = centrifugal force in Kg
RPM = head speed
R = radius to CG of blade in Meters
Wt = blade weight in gm
892850 = constant to handle all the unit conversions

Wolfgang

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12-01-2005 04:13 PM  12 years agoPost 20
Bell Bloke

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AirWolfRC, I don't know, garbage in garbage out, I put in a headspeed of 1030rpm not 1050rpm, you are absolutely right it's 390.5KGs, sorry about that Peter.

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HelicopterTurbine Helicopters › Predator/Wren800mm and 850mm blades continued.
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