Microlighters

I have always read that one cannot use a comb prop on a VW engine, but I would like to know what the reason is if anyone has an explination ?

You can use a composite prop, but not direct drive. The torque reversals on a VW are too severe, and composite props tend to break at the root.

The crank doesn't rotate at the same speed the whole time - as one piston is approaching TDC compression, it slows down, and once it passes TDC, it speeds up again. All engines have this to a greater or lesser extent, but it is worst on small 4 strokes (I doubt you will ever see a direct drive BMW conversion - and most of the sucessful ones use a clutch to disconnect prop drive at low RPM).

4 cylinder 4 strokes are better, but not great. Many composite prop manufacturers will not approve their props to run on a Jab 2200 for this very reason (but they will allow it on a Jab 3300).

The strength of the crank is also an issue - rigid props absorb less of the torque pulses and result in higher stress on the crank. Wood is actually remarkably flexible, and absorbs the toque pulses quite nicely.

Thanks Justin

now next question is what type of prop works best on a type 1 direct drive if you were looking to hit cruise/static more or less middle 50/50 would you suggest a single blade biggish prop like the P prop or a 3 bladed prop?

oh sorry aircraft is high wing medium drag ( similar to BB ) empty weight aprox 240kg

Go Vert wrote:Thanks Justin

now next question is what type of prop works best on a type 1 direct drive if you were looking to hit cruise/static more or less middle 50/50 would you suggest a single blade biggish prop like the P prop or a 3 bladed prop?

Speak to Pieter de Necker (P-Prop) - he will give you the best advice. I have never seen anything but wood and wood/composite 2 blade props direct drive. Length is tricky. Probably around 64". Pitch depends on engine capacity...

Go Vert, the Revmaster series can use composite props Ivo, and Warp-drive because of the 4340 chromolly cranck and the big no 4 main bearing at the prop-hub end. However from personal experience with said engine a P-prop works best , believe me. The Revmaster 2332cc uses a 64x38 prop with a nice wide cord to the blades This works VERY well in the Bushbaby.
Regards
Jean Crous

JeanTree wrote:Go Vert, the Revmaster series can use composite props Ivo, and Warp-drive because of the 4340 chromolly cranck and the big no 4 main bearing at the prop-hub end...

Yup - the Revmaster engine can handle the prop, but if you tell Ivo that you want a prop for a VW (or even a Jab 2200), he will refuse to sell one to you... Haven't spoken to any of the other composite prop manufacturers, but Ivo said that their prop will break.

VW engines = 2 blade wood prop. Anything else = TROUBLE !

Boet wrote:VW engines = 2 blade wood prop. Anything else = TROUBLE !

Wat nou Boet? Ek dog jy sou die stuk tussen die '=' tekens uit los?

Ja VW engines,BUT......to the uninformed, a Revmaster is NOT a VW engine , ONLY the cranck-case is and this is re-machined to such an extent that it no longer can qualify as a VW case The cranck is 4340 chromolly (harder than a Lycoming cranck) conrods are also H-beam 4340 chromolly, cylinder heads are much different on comparison to the aftermarket VW ones, and so my friends the list goes on "ad nauseum"
Revmaster can take wood/composite/metal props....even an oil -controlled constant speed prop

Wat weeg hulle deesdae, fully installed?

JeanTree wrote: Ja VW engines,BUT......to the uninformed, a Revmaster is NOT a VW engine , ONLY the cranck-case is and this is re-machined to such an extent that it no longer can qualify as a VW case The cranck is 4340 chromolly (harder than a Lycoming cranck) conrods are also H-beam 4340 chromolly, cylinder heads are much different on comparison to the aftermarket VW ones, and so my friends the list goes on "ad nauseum"
Revmaster can take wood/composite/metal props....even an oil -controlled constant speed prop

Ja nee dis n dorner se nice machintjie maar is nou F>cken duur vir my poject, ek sal die revmaster wannabe moet laat werk

KFA wrote:Wat weeg hulle deesdae, fully installed?

Toe ek en Jean anderdag gepraat het hy my gese maar het nou vergeet maar vasie baaie

Hi KFA en vriende, sonder exhaust maar verder met alles weeg die Revmaster 78Kg, oil cooler , carb- and- all ek se

JeanTree wrote:Revmaster can take wood/composite/metal props....even an oil -controlled constant speed prop

Revmaster had lots of problems with that CSU metal prop setup and canned it completely. If its direct drive stick to a wooden prop.