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View Full Version : TZR 250, pulley HTD 16 tooth 50mm wide 8mm ,Where can i find ? The ratio is ok ?



OSPREY - n/a
24-May-08, 06:10 PM
hello,

Is anyone known where can i find one pulley HTD 16 tooth 50mm wide 8mm

I want to fit straight onto TZR crankshaft ! http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

thanks

Paul Fitz - n/a
25-May-08, 03:34 PM
To my knowledge, nobody supplies a 16T Pulley as a standard item. A pulley of this size would have to be manufactured as a special.



It would have a PCD of 40.74mm and an outside diameter of 39.36mm. Allowing 6.8mm for the outer ring containing the teeth, this leaves just 32.5mm approx. for the central bore. This is insufficient for a taperlok bush. The pulley would have to be made to fit directly onto the shaft with a keyway and grub screw locking. I doubt if there would be sufficient material for the grub screws.



The biggest problem, would be that too few teeth would be in contact with the belt to transfer 45-50HP reliably. The belt life is likely to be very limited if it works at all.

hovercad - n/a
25-May-08, 06:20 PM
Shame you wanted HTD.

H section avaliable from K&M. Ive got one sitting in my garage.

Time and money went else where so never used.

Let s hope you can find what you want failing that different top pulley.





Craig

OSPREY - n/a
25-May-08, 08:08 PM
Thanks for your help but my top pulley is ready and have <font color="darkred">HTD 56 tooth 8mm pulley .[/COLOR]

My hovercraft is the Osprey 1 6 tuflo blades, fan diameter is 930mm and I will put one <font color="darkred">TZR 250 engine.[/COLOR](I will buy it soon )

I want race setup and I tell to put <font color="darkred">16 tooth HTD[/COLOR] engine pulley

This will give an overall ratio of <font color="darkred">ratio 56/16 = 3.5:1 [/COLOR]

I think this is ok for race ! ???



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Paul Fitz - n/a
25-May-08, 09:01 PM
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This will give an overall ratio of 2.966 x 1.153 x 3.2 = 10.943:1 ratio 56/16 = 3.5:1 I think this is ok for race! ???
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No. Your ratio will be 2.966 x 1.153 x 3.5 = 1:11.969 o/all



i.e. at 14,500 rpm engine speed - Fan speed = 1,211 rpm

at 20,000 rpm engine speed - fan speed = 1,670 rpm



This will not work well at all.



Personally, with a 56 upper pulley I would use a 34 lower giving an overall ratio of 2.966 x 1.153 x 1.647 = 1:5.632



giving at 14500 rpm engine speed - Fan speed = 2574 rpm

20000 rpm engine speed - Fan speed = 3550 (thoeretical)

The fan would absorb the maximum power and stop the fan actually reaching the 3550 rpm. the true maximum revs could be adjusted by pitching the blades.



This of course assumes max power is produced at 14500 rpm,as discussed before.

hovercad - n/a
25-May-08, 10:37 PM
I did a calculation. i may be wrong that the tip speed would be 139m/s This was using 10000 rmp for the TZR.lower pulley connected direct on crank.

Top pulley / bottom pulley = ratio

56/16 = 3.5 = ratio 3.5-1 (ie 16 tooth turns 3.5 times to turn the top pulley once.)

Duct is 930mm (?)

Pi x diamater = Circumference.

3.1415926 (etc etc etc) x 0.930 = 2.92168 meters



10000 / 3.5 = 2857.1428rpm (speed of fan)



2857.1428rpm x 2.92168 meters =8347.6569 (Meters per minuite)



8347.6569 / 60 (Seconds) = 139.1276 meters/second



what have I done wrong with the calc??



Craig



Ps I have not put all the digits that the calc showed.

OSPREY - n/a
26-May-08, 10:11 AM
I did a calculation. i may be wrong that the tip speed would be 139m/s This was using 10000 rmp for the TZR.lower pulley connected direct on crank.

Top pulley / bottom pulley = ratio

56/16 = 3.5 = ratio 3.5-1 (ie 16 tooth turns 3.5 times to turn the top pulley once.)

Duct is 930mm (?)

Pi x diamater = Circumference.

3.1415926 (etc etc etc) x 0.930 = 2.92168 meters



10000 / 3.5 = 2857.1428rpm (speed of fan)



2857.1428rpm x 2.92168 meters =8347.6569 (Meters per minuite)



8347.6569 / 60 (Seconds) = 139.1276 meters/second



what have I done wrong with the calc??



Craig



Ps I have not put all the digits that the calc showed.






My engine is TZR 250 !!

This set up is ok for the OSPREY 1 for Race ?? 56/16 = 3.5 ratio

Paul Fitz - n/a
26-May-08, 02:26 PM
My apology Osprey



When you quoted the gearing for the Honda engine you previously enquired about, I missed the point that you are now using a TZR.



So Brain engaged, and start again :0)



Fan: The Truflo 6 blade fan will absorb approx 46 HP at the following speeds and pitch

45 Deg - 2200 rpm

40 Deg - 2400 rpm

35 Deg - 2600 rpm

30 Deg - 2800 rpm



The blade angle is measured at the tip. Because the fan uses blades without twist they tend to distort more at higher revs. I would not recommend these blades above 2600 rpm. They will twist and reduce the thrust considerably.The blade distortion is also increased with high blade angles.

The blades tend to perform best at lower speeds and angles, but at low angles velocity is lost.



I would therefore suggest the best option for a TZR would be between 35-40 degrees.



10000/2600 = 3.846:1 or 56/15 = 3.733 ---> 2678 fan speed @ 10K engine speed

10000/2400 = 4.166:1 or 56/14 = 4.000 ---> 2500 fan speed @ 10K engine speed



As you can see, with the 56T top pulley the lower pulley will need to be 14T-15T for Practical fan speeds. If you are able to obtain a 16T Pulley



10000/2800 = 3.571:1 or 56/16 = 3.500 ---> 2857 fan speed @ 10K engine speed



Craig-



Tip speed should be calculated on the fan Diameter not the duct.

930 duct with 7.5mm tip clearance = 915mm

Calculated as you show using 2857 fan speed = 136.85 m/sec

Truflow blades can be used up to 168 m/sec as M/wing etc. (They just shouldn't http://hovercraft.org.uk/images/icons/smiley_icons/icon_surprised.gif[ )



HTH

hoverchaps - n/a
26-May-08, 02:53 PM
why dont you use the motor that craft was designed for. the 35 hp brigs goes straight in and will give hours of quiet trouble free running and what you save in fuel will pay most of cost quite soon .

dont re invent the wheel

OSPREY - n/a
26-May-08, 04:47 PM
why dont you use the motor that craft was designed for. the 35 hp brigs goes straight in and will give hours of quiet trouble free running and what you save in fuel will pay most of cost quite soon .

dont re invent the wheel




Because my friend the 35hp Briggs Stratton cost to much (over 1000 euro)and it is 56 kg weight !!

And here in Greece I can find TZR 250 engine very cheap (from 100 euro but need repair ,300-500 and work fine !!)



thanks for your help .

thanks Paul !!

hovercad - n/a
26-May-08, 05:48 PM
Paul thanks for letting me know my maths wasnt as bad as thought.

I did put a get out clause with the fan/duct diameter with a (?)

so covered my self there.lol



Osprey.

In the past H section was adequate up to 50hp if I remember correctly.

It may work out cheaper to rethink and go for H section as K&m have done the TZR adapter for the crank but in H section.



At one point I was going to use a 54 top 16 bottom H section but withh smaller duct.



Its amazing the amount of bits in the garage for things that never get used.





Craig