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View Full Version : to shaft or not to shaft - that is the question



tonybroad - n/a
29-Dec-06, 09:50 AM
If, (hypothetically)one were to consider shaft driving a TZR powered F3, what ball park revs and lift fan size are we looking at to get things started rather than re-inventing the wheel



any tips on what not to do would save time also



thanks in advance



Tony

pest619 - n/a
29-Dec-06, 11:26 AM
Hypothetically eh...? Im doing this but im using a smaller duct and more blades than most- 8bladed 500 duct spinning at just below 4000rpm but its for a bag skirt.



The usual approach has been 560mm duct with 5 blades spinning a lot faster.



SO hypothetically would you be making a new hull? If so ours should both be ready about the same time...

andycollins - n/a
29-Dec-06, 11:53 AM
I can't remember exactly what I ran RandomOrbit at but I think the lift fan span at about 3,500-3,750ish. I did the numbers for about 8hp to the front.



As for things to look out for.... You will (hypothetically) have two pulleys on the engine output shaft, one going up for thrust, the other going across for lift with some kind of "outrigger" between the main bearing and the shaft bearing. Make sure that the "outrigger" is beefy anough for the job as the forces pulling on it are quite great. I had a couple of goes before I got it right.



Also, Make sure you've got a good way of changing belts as when you have two, you're much more likely to need to change one and also one is bound to be in the way of the other. Avoid schemes that mean that to change the lift fan belt you have to take the duct guard of or similar.



Having driven the same hull, first as an integrated craft and then with a lift fan, I wouldn't go back. It's great to have the lift air at the front where you need it rather than shoving it in the back and forcing it round to the front. RandomOrbit was always a pretty safe craft, even when integrated, but it never ploughed in after fitting the lift fan, not even once.



If you do go for two fans, I'm sure you'll enjoy it.





Come on in, the water's lovely http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif







Cheers.



Andy.

chrismdaly - n/a
29-Dec-06, 06:58 PM
I tend to agree with Andy's comments.

chrismdaly - n/a
29-Dec-06, 07:01 PM
P.S. Remember to allow for the flex of the craft.

mick - n/a
31-Dec-06, 08:08 AM
Dear Tony and of course the other chaps on the bourd, shaft drive for you ,im shocked nay surprised, all that complicated things running round at great revs, what are you thinking of, i surgest thearepy would be in order .



Happy new year every body for tomorrow, looking forward to racing.

tonybroad - n/a
31-Dec-06, 08:50 AM
Happy New Ears to you Mick



I've tried the back to basics approach Mick - now it's time to send the air the correct way through the thing and see what happens



Tony

Nick Long - n/a
31-Dec-06, 09:44 AM
now it's time to send the air the correct way through the thing and see what happens






Yes, it seems crazy to be pumping the air forwards when you're trying to make the craft go faster.



Happy New Year everyone.



Nick

tonybroad - n/a
31-Dec-06, 10:07 AM
Happy New Year Nick



well if you can't beat 'em - join 'em (well i beat all the TZR shafties except you Nick)



now... will i need one of those fancy anti-plough-in bouncy castles underneath ?? we'll have to see



Tony

slap - n/a
31-Dec-06, 02:44 PM
think we are going to have some close racing again this year coming. happy new year to ya all http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

chrismdaly - n/a
31-Dec-06, 02:52 PM
Happy New Year

Anne Scrimshaw - n/a
4-Jan-07, 03:40 PM
As someone who has raced integrated, shaft drive and twin-engined, I can say that a shaft drive craft is probably the easiest craft to drive. It’s like an integrated, in that when you let go of the throttle you stop, but definitely less ploughy. Although engineering wise a bit of a headache, and probably not much lighter than having a lift engine, so only really worth doing if like you, you don’t have the spare capacity.



I really wouldn't want to go back to racing integrated now, or bag skirts for that matter, but that’s another story.



Also you may like to think about how much lift you have at part throttle – it’s useful to still have some for wind down laps or driving through the paddock.



Happy New Year

Anne