VW direct drive

[Bushbabie]

There is always much debate around the belt drive. Having owned DWY for the last two years our only concern has been the wear on the belt. Third belt wearing against the lower pulley back plate. What are thoughts on direct drive with the VW engine? If the Revmaster can run with direct drive why cant the VW or can it? DWY has a 2.1 l with fuel injection. I have been chatting to Jean Crous regarding this and am keen to hear some other suggestions and comments. Would the lower prop position and thrust line be an issue? Your thoughts gents....

[HansH2]

Kobus van Staden would be the best person to answer that question. He built the Cubbies.

[Bushbabie]

Locally Sonex and KR2 have used VW with direct drive.
Aerovee manufacture with direct drive.
Kitfox - see this video https://www.youtube.com/watch?v=UmYDXI_Zego
Great Plains sell the direct drive hub adaptors.
A few Zenith Air are fitted with VW direct drive.

[Shumba]

Many years ago when I initially ordered ZU-DVR from Kobus, I discussed the direct-drive issue with him. I believe the problem lies with the sideways thrust on the crankshaft bearings when you bolt a prop directly onto it. Apparently some machining needs to be done on the crankcase to install a thrust bearing, an issue which is sorted by Revmaster and other companies when they adapt these engines for aeronautical use.

Although the cam belt reduction drive on the Cubby and other applications prove to be problematic, the idea is sound since you gain no horsepower but substantially on torque which is so necessary to swing the bigger props for higher thrust to weight ratio. With the direct drive engines you need to pump up the RPM to gain thrust but propellers start loosing efficiency after about 2300 RPM and tip speeds get close to the speed of sound so you need to use smaller diameter props.

Since reduction drives exist and are successful on many applications, I think that a properly engineered system is the way to go. Just a stupid question. Why can't a chain and sprockets not be used. These parts are freely available and relatively affordable and I am sure such a system could be developed since chain drives are used in many applications and proven as very dependable. Wear could also be detected very early and maintenance is low if high quality components are used.

Hope this helps.

[giarc64]

Howzit Tyrone

1. reduction drive and higher thrust line allows to swing a longer prop which is more desirable for a fat aerie like the cubby. Remember only a small section of the prop makes power . now by going direct drive the thrust line is lower and and prop clearance an issue. also with the direct drive you cannot run the same size length prop as with the RD drive. only way to over come this is to raise the engine and this requires new engine mount and a whole bunch of other stuff.

also the local cubby engines are not built to the required spec to run direct drive. the number 4 bearing needs to be a much beefier thrust bearing to handle the huge gyroscopic forces that are created by running direct drive. this is further exasperated by running a longer and heavier prop.

there is a cubby that is using a jabbi direct drive.

it all comes down to pros and cons and your risk level. the cost of putting in a direct drive and all the other bits and pieces is not worth the cost and to be honest there is still some things that can go wrong.

thus its easier to stay with the current setup and monitor and change the belt every 100 hours. if the belt is wearing on the bottom pulley back-plate, your tension is too loose. the belt should not wear on the sides but rather on the teeth.

this can be alleviated by getting new pulleys made. we had the same issue and got new pulleys made and the problem is gone.

Cheers
Craig

[HansH2]

One thing about this section of Avcom is that one gets intelligent replies to ones postings, not like the crap in General and Academy.
There is a newer technology Gates belt on the market, Chris Visagie from Stateside has the info. JP also has gen on it.

[Bushbabie]

Sonerai with a 2.3L Type 1 VW ENGINE. Looks like direct drive. viewtopic.php?f=2&t=156754
But until then can someone advise where to get replacement belt pulleys?

[richardfloyd]

Hi guys

I have just fixed up my falke 1600cc direct drive vw - running perfectly.

I am also in the process of building up a spare 1835cc vw direct drive.

It has taken me a year and lots of time to work out the process, pitfalls, etc.

Anyone who would like the correct contacts, suppliers, etc is welcome to email me on floyd@stratocorp.biz.

I also attach a spreadsheet so you can see the costs involved - I have spent much more than this in school fees. This spreadsheet is a best case - you will not do it cheaper and should put a 20% contingency on it. It also excludes driving around, telephone, etc. When one starts one always thinks its going to be cheaper. But the mechanical lessons learned and ability to maintain and care for the engine is astronomically improved through the process.

Cheers

Richard

[Jean Crous]

To add to this long asleep thread , I run a Revmaster R2300 direct drive in my Bushbaby, which has a much larger frontal area behind the prop than the Cubby, and a wider cockpit. I run a 64x34 P-Prop with a cord width of 133mm. I get a 1100fpm climb at 70-75 mph, with an RPM of 2840
The Cubby is lighter than the Bushbaby, has a smaller frontal area behind the prop and I daresay a higher lift wing. To fit the direct drive engine in the Cubby one would HAVE to make a new engine mount to put the thrustline in the right place, thus raising the engine . Prop clearance will not be an issue with the new taller main gear.
In straight and level the engine turns up to 3050 RPM with an indicated speed of 118mph (I have a certified ASI ) . Cruise I set the RPM to 2550 and get a speed of 93 mph.
The other gain is the weight, the Revmaster weighs 80kg installed, the VW Cubby engine is 110kg, and yes we did weigh it
Regards
Jean.