View Full Version : Future of F3

tonybroad - n/a
9-Jan-08, 11:05 PM
I'm going public on my latest craft and engine set-up

check out the Mods and Sods section of my website (link below)and tell me what you think.


The future of F3 ? let me know - do you like the colour scheme as well - all in the gelcoat you know !

Don83000 - n/a
9-Jan-08, 11:19 PM
check out the Mods and Sods section of my website (link below)and tell me what you think.

http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif Well we would look if we could http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif


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profqwerty - n/a
10-Jan-08, 08:11 AM
Just shows how popular he is http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

tonybroad - n/a
10-Jan-08, 08:28 AM
http://hovercraft.org.uk/images/icons/smiley_icons/icon_redface.gif worked last night when i did it, i must have pushed it over the limit - i'll try and sort it

Don83000 - n/a
10-Jan-08, 09:03 AM
Hi Tony well just got onto your page and read the mods part then the site shut down again saying overload of data but I'm sure you will fix it. I think your idea is brilliant and I hope it works as well as it looks and the colour scheme is awesome. Somebody that thinks out of the box makes a nice change.What bhp are they in stock form and at what rpm.

tonybroad - n/a
10-Jan-08, 09:09 AM
thanks for your comments, the site may have shut down as i was amending it

each engine is just under 30Hp @ 11750 rpm, peak torque 21Nm at (get this) 8500 rpm and they weigh 15kg each with all anciliaries

Quick solution - if you can't get the site up, i've pasted the piece below

Dear Diary

9th January 2008 *Happy New Year - well i hope it's going to be

Well here's the first pics of the new F3 craft for 2008

Instead of a 250 engine I'm fitting two 125cc Rotax Max Kart engines in parallel. If it works it will mean an affordable solution to the ever increasing engine availability problem for F3. Rotax Max's are raced all over the world (UK, Europe, America, Canada, Malaysia) bits are affordable and readily available off-the-shelf, you can even buy them brand new in a box ready to run.

With 40-50 hours between re-builds and good reliability I'm hoping it will change the current opinion on F3 and perhaps get the Europeans thinking again. A couple of my students race them and they have few engine problems all season (with maintenance i should add) and seizures are extremely rare.

They are a really neat self-contained compact unit with balance shafts, water pump, radiator, vacuum fuel pump, ignition, powervalves, loom, electric start all neatly packaged together - engine fitting and removal should be a doddle. The engines were developed for karting and are not screamers, they produce good torque low down which is what the karters want for pulling out of corners

As standard two Rotax Max's will produce more power and torque than a TZR and two of them are only 5kg heavier than the Yam and they have electric start ! It's all making sense at the moment i just hope it all comes together. This year will be a development year for sure so i'm not expecting fireworks straight out of the box but if it can at least equal the performance of the 2007 Yamaha craft i'll be pleased - that's the target for this year anyway.

For kart racing these engines are sealed - perhaps this could create fairness within F3 or would it lead to stifiling development, that's up for debate, another issue is that a single 125 Rotax Max engine in a light hull would be perfect for a Junior class of craft

I'd like opinions on this idea - either way

We all need to consider the future of our formulas - 503's are currently very popular but with Rotax not making the engines any more what's the long term future for the formula or for F1X ?

nickyd - n/a
10-Jan-08, 01:27 PM
Hi Tony,

That looks the puppies!! Is that black and orange????

Really interested to see how it runs. How have you connected the two motors?

Would you ever consider making the hull for anyone else?........


tonybroad - n/a
10-Jan-08, 01:59 PM
Hi Nick

colour scheme is black and signal red

the idea is that the motors will run like twin-engined pro-karts which have an engine either side of the driver with a centrifugal clutch on each driving a common rear axle

so i have the engines mounted independantly from each other and both have centrifugal clutches driving the bottom driveshaft via a small chain at just over 1:1 - the driveshaft runs through a bearing block then drives the regular fan pulley belt setup

i don't normally make hulls for anyone else

nickyd - n/a
10-Jan-08, 02:07 PM
cool cool,

look forward to seeing it at Jakes.

good luck


sixpackpert - n/a
10-Jan-08, 03:14 PM
We all need to consider the future of our formulas - 503's are currently very popular but with Rotax not making the engines any more what's the long term future for the formula or for F1X ?

I agree that we need to look to alternatives. I don't think there is a need to panic about 503 at the moment, engine production ceases this year but parts are available until 2021 and there are an awful lot of engine's out there that can be bought complete or for spares. I should think that environmental issues (bloody tree huggers! http://hovercraft.org.uk/images/icons/smiley_icons/icon_mad.gif )will be a more pressing issue than the supply of engines and spares.

Back to work now! http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

bryan - n/a
10-Jan-08, 06:19 PM
That looks so nice and shiny it was most i could not to drive over and give it a good rub myself......! with new ideas like this i would hope F3 to be safe. Looks like your usual high spec Tony intresting to see to how she flys.Whats the price of a single motor and exhust pipe...!

jon_curtis - n/a
10-Jan-08, 07:27 PM
impressive aint it!

got any pics of the drive train?

tonybroad - n/a
10-Jan-08, 09:07 PM
here's a mock up of the engines and driveshaft, the engine bases have changed since this pic and the negines are closer to the shaft - theres a couple of 14 tooth sprockets welded to the driveshaft and a 12 tooth sprocket on the centrifugal clutch - there'll be a reaction stay from the driveshaft brackets to the engine for adjusting the chain and reacting to the chain tension


as for cost Bryan i've been watching prices on ebay for a few months now and a good sealed engine with not many hours on it with rebuild logbook and everything ready to run goes for around 650 - not cheap but affordable

if you're not bothered about the engine being sealed some unsealed or bare engines go for 300+ - very recent engines or championship winning engines go from 750 - 1000, brand new in a box ready to run about 1300

jon_curtis - n/a
10-Jan-08, 09:52 PM
so what sorta hp does each engine put out? 25 ish? or more?

Mart366 - n/a
10-Jan-08, 09:55 PM
Hi Tony,

looks good :thumb:

quick q, is it simplex or duplex chain your using?

what are your thoughts on methods of lubrication & tensioning of the chain?


tonybroad - n/a
10-Jan-08, 10:11 PM
engines put out just under 30Hp stock

chain will be the same simplex 219 chain as they use to drive th ekart rear axles, it'll be moving at the same speed over the sprockets and pretty much under the same forces

not planning any autolube for the chain just going to clean and boil the chains in grease after each outing

bryan - n/a
11-Jan-08, 07:20 PM
The Honda rs 250 is a twin, both cyliners on the same stroke with a balance crank. I found that if both cylinders were not tunned the same the one cylinder would drag the other down which would make the engine lose hp. Will this be the same even through the slip clutches!!. If you need to set exhust temps with engine rev,s, and water temps i have a digitron you are more than welcome to borrow.

jon_curtis - n/a
12-Jan-08, 03:16 PM
couldnt one overdrive the other? or would the clutches stop this?

tonybroad - n/a
13-Jan-08, 09:17 PM
the only thing we know is running two seperate single engines independantly through centrifugal clutches to a common shaft works fine with pro-karts and other twin engined karts


how the engines fire in relation to each other is an unknown and it will be interesting to see whether they find the same position each time, on the pro kart the engines just seem to sort themselves out - we'll know the answer in a week or two


Arny - n/a
14-Jan-08, 12:24 AM
I have raced prokarts (owned my own rather than hired) and I have raced with Rotax Max 125 karts (I have also raced Ital 100cc in Formula C and TKM 100cc but that is another story).

The twin engine issue is not a problem. Providing you balance the throttles and chain tensions between the two engines they tend to sort themselves out. I don't know how it works but it works. We also swapped engines over every season to balance out any uneven wear but we were going around a circuit in one direction so that should be an issue for hovercraft! http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

The Rotax Max 125 is a super engine. Bullet-proof when raced and easy to work on. Noise levels are good too as they replaced Formula TKM which used TKM 100cc aircooled engines... these Rotax watercooled engines were much quieter and most racers preferred them to the TKM.

We rebuilt after 25 to 50 hrs but that was to get max power/reliabilty for racing. I am sure that 100hrs would be fine for hovercraft or even more if they weren't run at max rpm.

tonybroad - n/a
14-Jan-08, 11:54 AM
thanks for that Arny - the chain tension issue is one thing i havn't considered so thanks for that

i don't know how the engines sort themselves out but one thing i intend to do is monitor the firing of each engine and see if they find the same place each time

the silencers are very long and i've also mounted the exhausts inside the plenum chamber so i'm hoping it will be the quietest F3 out there (and hopefully the quickest)

any tips on keeping the Rotax's running sweet maintenance-wise would be appreciated i.e. how often to clean P Valves things to watch out for with the clutches etc.



Arny - n/a
14-Jan-08, 01:05 PM
Take a look here...

http://www.karting.co.uk/KandK/Tech/RotaxPowerValvePrep.html (www.karting.co.uk/KandK/Tech/RotaxPowerValvePrep.html)

These clutches are very prone to high wear rates if the engine is run for any period of time at very low power so the centrifuge has engaged the engine but it isn't fast enough to stop slippage. On a kart that sometimes happened if speed was lost in a corner so the revs dropped below the fully-engaged level. The clutch would then slip for a while until the revs were up high enough to fully engage. This might not effect operation on a hovercraft but I could see a situation where you are perhaps manoevering at low speed and hence low revs... if the clutch isn't fully engaged it will get VERY hot and wear out the pads very quickly. Only trials will show if that is a problem.

Karters inspect and clean the PV at least after every day operation. I don't suppose it will need that but may be. The PV is critical to getting good performance. Take a look at this site too... I know it is race kart related but all good stuff when running the Max...

http://www.g-rpm.com/Care_and_Feeding_of_the_Rotax_Max_FR125 (http://www.g-rpm.com/Care_and_Feeding_of_the_Rotax_Max_FR125_Rev._12203 .pdf) _Rev._12203.pdf