ianboag Posted April 4, 2011 Share Posted April 4, 2011 I like the idea of getting my J160C off the ground in a bit less runway. The obvious (?) way would be a finer pitch prop. I am OK with the resulting drop in cruise speed. Say going from the standard 60x42 to a 60x40. Not that a J160 will ever be a Zenith 701 or Savannah or any of those football-field planes, It also wouldn't seem off the planet to go to a larger diameter prop - say 64x38 even. 4" on the diameter is 2" on the radius etc, so one would have to jack the nosewheel up a couple of inches which should be reasonably doable. Has anyone been there and done any of this? IB Link to comment Share on other sites More sharing options...
facthunter Posted April 4, 2011 Share Posted April 4, 2011 Ian, what you say is correct. You have outlined the limit on cruise speed. (Engine revs) and the ground clearance with prop dia increase. Bigger prop also brings in inefficiencies due to tip speed which comes in at a lower figure with a wooden prop that with other types. Some people report the original wood prop as being a bit innaccurate in shape and pitch, so perhaps a diffferent brand would help anyway. (There is somebody in Christchurch making wood props). I like to keep a wood prop on the Jab motor for safety reasons. Nev Link to comment Share on other sites More sharing options...
ianboag Posted April 4, 2011 Author Share Posted April 4, 2011 Man in Christchurch is Brent Thompson. Here at Feilding we have good experiences with his product. There's a man with a 3300 in a Zenith who says his BT prop blows the Jab one into the weeds. Ditto with a Pioneer 300 here where the GT prop was taken off his 3300 and replaced by a BT one. I have a 60x40 on order with Brent. There is about a two month lead time. You know you're at the front of the queue when he sends a bill. I'm wondering about a 64x38 instead. The static thrust is quite a strong function of the diameter ..... One has heard the term "plank" used about the Jab prop :-) Just curious if anyone has already done any of this ...... Warp drive even? The Sensenich ground adjustable is a bit more money than I feel like spending. IB Link to comment Share on other sites More sharing options...
facthunter Posted April 4, 2011 Share Posted April 4, 2011 Sensenich make good props but there is an AD on it on the JAB motor only. 42 back to 38 is a big drop. Also pitch figures do not always mean what they seem. There is always slip. A larger dia will translate to more static thrust but so will a wider blade. Both of these will load the engine which is something that Jabiru are concerned about. If you don't reach the stipulated take-off RPM then you engine will not be delivering the power, (as distinct from thrust) that it is capable of and rated to. Nev Link to comment Share on other sites More sharing options...
ianboag Posted April 4, 2011 Author Share Posted April 4, 2011 So - be a dev Nev - what would you do? Yes 42->38 would be a huge drop if one was not increasing the diameter ..... That's why I have a 60x40 on order with Brent. In your money it costs a whole $A700 which is not a lot compared to the cost of a Jab plank or a Sensenich or anything composite .... I'm curious to know if anyone has gone the slightly-more-diameter-less-pitch route or would I be a pioneer? IB Link to comment Share on other sites More sharing options...
facthunter Posted April 4, 2011 Share Posted April 4, 2011 It's your money Ralph. Be nice if you could try one first. So many experiment with props. I suppose you could put them above the bar at home. Well you have put me on the spot SO... I'd go for 2 inches finer and widen the blade a bit and see how you go. My Citabria had a "cruise" prop and was a bit of a Ground hugger on a warm day. A "top" overhaul ( new cylinders) made the difference eventually, by raising the take-off RPM about 150. Nev Link to comment Share on other sites More sharing options...
ianboag Posted April 4, 2011 Author Share Posted April 4, 2011 Ralph? The 2" was where I started here and a Brent Thompson prop. Brent thinks 60x40 is good for Jabs. I am tempted to push this a little further 64x38 (more diam - = more thrust - and less pitch). It will fly I'm sure and if it ends up over the bar so be it :-) Just curious to know if anyone has tried this before on a J160 ...... IB Link to comment Share on other sites More sharing options...
facthunter Posted April 4, 2011 Share Posted April 4, 2011 I know your name is Ian. "It's YOUR money Ralph" was an old saying here in Aus. (Perhaps I am the only one remembering it). There is an old saying also about props. "Keep your prop as long as possible for as long as possible".. I think the dia increase is too much but you can reduce it if you wish, unless there is some reason due to its construction why it can't. I would be guided by your Mr Thompson. I won't hog the thread, though .Good Luck. Nev Link to comment Share on other sites More sharing options...
Vev Posted April 5, 2011 Share Posted April 5, 2011 Hi Ian, For what it's worth, I put a carbon fibre ground adjustable prop on my 160. When I set it up I focussed on the static RPM to ensure I got a min of 2900, which improved the take-off distance and climb. In summer (that is, when we had summer in Melbourne) I had leaned off the pitch to get a few more revs (about 50 rpm more) which was great on hot days too. Whilst you technically lose a little bit of speed you make this up with a few more cruise revs .... in cruise I pay more attention in keeping the CHT and EGT in the right spot which is an outcome of load and of course fuel flow. The only effective in-flight fuel adjustment is the throttle and you need to have enough load on the engine to get the Bing to run on the finer part of the needle and use more of the main jet. Getting the fuel flowing to keep the engine cool is critical in the Jab and you need to be on top of this if you change the prop pitch. If you use a finer pitch prop at the same cruise RPM as before you will run too lean and over heat the top end. Don at Jab says never to be frightened to fly the Jab like a fighter and get stuck into it, keep the revs up and pour the fuel in.... in my experience I agree with his sentiments. Hope this helps? Cheers Vev Link to comment Share on other sites More sharing options...
Modest Pilot Posted April 5, 2011 Share Posted April 5, 2011 Be aware that if you change the factory prop you may have to re jet the carb, it's a bit tricky I'd talk to Don at Jabiru first. You need EGT and CHT's to make sure that you don't go to lean, you will probably need to cruse at higher cruise rpm to keep the EGT's down. Link to comment Share on other sites More sharing options...
ianboag Posted April 5, 2011 Author Share Posted April 5, 2011 Hasn't Don retired? Higher cruise revs are a given of course - one doesn't want to be too slow. Vev tells me with is fined-off-leap-off-the-ground prop he cruises at 105 knots/3150 rpm. Every bit of folklore one reads about the Jab engines says that is good for it. Only drawback I suppose is that it tends to be a bit noisy in the cockpit. Link to comment Share on other sites More sharing options...
Guest Pioneer200 Posted April 5, 2011 Share Posted April 5, 2011 Hi Ian, how are you finding the J 160 compared to your last Jabiru (200?) I fly ZK JRW down here in Ashburton, nice plane to fly, does lack a bit in the getting off the ground quick stakes though, and currently out of air due engine issues!!! We have the Jab 160 and Pioneer 200 ZK PAA both use 2200 engines. I do prefer the toughness of the jab airframe over the pioneer and it makes a great trainer for our group. Might see you down this way with your jab one day. Sorry folks , bit off thread!! Link to comment Share on other sites More sharing options...
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