View Full Version : help to put engine (honda cbr 250 rr) in Osprey 1 hovercraft

OSPREY - n/a
14-Apr-08, 06:47 PM
<font size="4"><font color="darkred">Updated data[/COLOR][/COLOR]

I neead some help

I have one 'osprey 1'hovercrafts with 6 Truflo blades , Aluminium <font color="darkred">pulley 56 tooth [/COLOR]8mm HTD type. I bought one engine Honda CBR 250 rr 45hp 20.000prm ,weight 50kg to put in the hovercraft .

I will use belt. I can’t remove the transmission of the engine and I consider to put one shaft on transmission shaft ( extend) and then put one <font color="darkred">Nylon Pulley 32 tooth [/COLOR]52mm wide 8mm HTD section

index.php?t=getfile&id=1305&private=0(http://www.avdw32.dsl.pipex.com/htd_nylon_pulley.htm (www.avdw32.dsl.pipex.com/htd_nylon_pulley.htm) ,) .

1. It is ok to run with the 5th gear in transmission ?

2. maybe the extent is too long ( 30cm ) and maybe put a help surbase ?


3. have anyone put this engine on hovercraft ?

this is the engine (honda cbr 250 rr)


thanks for your answers !!!

OSPREY - n/a
14-Apr-08, 06:54 PM


OSPREY - n/a
15-Apr-08, 05:42 PM
1. It is ok to run with the 5th gear in transmission and the two pulleyies or the fun run too slow ?

2. maybe the extent is too long ( 30cm ) and maybe put a help surbase ?

hoverchaps - n/a
15-Apr-08, 06:51 PM
Here goes.

What size fan? Is craft intergrated or do you have a lift motor?.

The out put speed of the sprocket will be around 5800rpm in 6th.so you will need to know how fast you want the fan to go. If you used 1st gear I believe to be best the torque is much higher so the engineering will have to be good.

Dont try and make a single unit let the motor float a bit and connect the drive pulley to the motor with some kind of flexible coupling .

I hope this helps, others wont agree but i have built 3 craft using bike motors and this has been best.

Good luck


Paul Fitz - n/a
16-Apr-08, 12:48 AM
Hello Emmanouil, As this is an Osprey 1, I assume the fan diameter is 930mm.

As far as I know the Honda CBR 250RR Primary ratio is 2.966:1 and the 5th gear Ratio is 1.153:1. Your belt ratio will be 96:30 (3.2:1)

This will give an overall ratio of 2.966 x 1.153 x 3.2 = 10.943:1 ratio.

So at 20,000 rpm the fan will turn at 1827 rpm. This is a suitable "cruising" speed for the Truflo trufoil fan, but at that speed the 6 blade fan will only absorb about 30-33 hp when set to about 45 degrees of pitch.

I think your figures for this engine are incorrect at 46Hp @ 20,000rpm

Perhaps somebody can correct me if these figures are for a late model etc.

I think the correct figures are 40ps @ 14,500rpm or

45PS at 15,000rpm for the CBR250RR(L+N)

If you intend to use the craft for cruising, I would suggest that you adjust the gearing to give about 2600 Fan rpm at maximum engine power (i.e. 5.77:1 overall ratio)

which should allow the engine to turn over at about 11000 rpm for cruising with a fan speed of about 1900rpm

You might consider using 9 blades at about 35 degrees. This arrangement would give much better lift especially at part throttle.

With regard to the drive: you show quite a long shaft. This would need to be supported with a minimum of 1 bearing and use a flexible coupling to absorb vibration and misalignment. A strong U-Bolt or similar would need to be fitted around the shaft (but not touching) at the coupling end, to contain the shaft and prevent it from causing serious damage should the coupling fail.

OSPREY - n/a
16-Apr-08, 03:12 PM
The fan diameter is 910mm. yes the engine is 45hp at 20.000rpm It is a special model from honda. look and here http://www.mobile.de (www.mobile.de) there are 2 motorbikes honda cbr250 rr for sale and you can see the description !! I test engine before i put out from the motorbike and the engine goes 20.000rpm !

tell me please what must be the fan speed for the Race ?

(engine ratio is 2.966:1 and the 5th gear Ratio is 1.153:1 ) that rates are for my engine(45hp) ?

How many blades is better ?

Paul Fitz - n/a
16-Apr-08, 07:12 PM
I have read both adverts. Both sold by same company, the German importer of this model. He says in both the overview (Uberblick) and the bike data (Fahrzeugdaten) "...... und Drehzahlen bis 20000 UPM" which means "engine speed up to 20000 rpm" but this is the maximum engine speed and not the speed where maximum power is developed.

I think you need to do some more research to confirm this.

I still think that the speeds I have given you are the best option if maximum power output is at about 15,000 rpm.

For racing 6 blades would be better and you will want to put the maximum power available through the fan (about 41-42 PS after gearbox losses)This you can do with the 5.77:1 o/a ratio. the fan pitched to about 44 deg. and 2600 rpm fan speed. If you reduce pitch to 36-40 degrees the fan will run up to approx 2900 rpm but absorb similar power. I would not recommend Truflo trufoil fans above this speed as they have very flexible blades and small root to the blade. They are not as strong or as stiff as Multi-Wing, Hascon Wing or Wingfan.

If you can confirm that maximum power is developed at 20,000 rpm,

PM me and I shall check the figures again.

Nauti Buoy - n/a
17-Apr-08, 03:20 PM
I think you're going to find that engine in that craft is a horrible mismatch.

Its a very short craft, with an engine that weight it'll be dragging its tail.....my dad at flying fish is currently re-engining(?) an Osprey 1 with one of the B&S 31bhp angines and even that is really too heavy.

I'd think very carefully before putting in all that work for something i think will be a disappointment.

sixpackpert - n/a
17-Apr-08, 06:20 PM
with one of the B&S 31bhp angines and even that is really too heavy.

Russ in '4-stroke is too heavy' shocker http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

OSPREY - n/a
19-Apr-08, 07:02 PM

bryan - n/a
21-Apr-08, 07:01 PM
Hi in the past i used a Yamaha fzr 250 about 45hp.This little motor used to rev at 18,000.I kept the gear box and used 5 gear.The clutch was left on for easy start stop.These little motors are great but i found that they didn,t last long because of the constant high rev,s.I would have to say that the engine noise may be an issue.By the picture i can see the fan frame!!!.Maybe a different frame is needed so that the engine is independent to the frame by use of a centreflex coupling.This will also bring the motor forward and help the balance.Nice little craft good luck.