Jabiru Variable Pitch and C.S. Props

[Guest ROM]

Same old problems, disperse!

 

A certified aircraft, ie. factory built J230 Jab used for training, hire and glider towing must have a prop certified and approved by the aircraft manufacturer.

 

The aircraft manufacturers, understandably in their own self interests, will steer clear of prop manufacturers who have not certified their props with their national authorities.

 

Airmaster props are not certified.

 

Very, very few manufacturers of LSA / Ultralight props have bothered to do any certification as they generally produce small numbers of props in any one configuration and the certification expense is not justified if you don't know how many props of that series you are going to sell.

 

A chicken and egg situation and we, the customers, miss out on better performing aircraft and lower prices because of it.

 

If you are a kit built aircraft owner, different situation.

 

You can use an axe to cut out your own prop if you want to!

 

Your problem but make sure you have the make, type and serial number of the axe in your aircraft build records.

 

 

[glenns]

Interesting I thought that Jabiru had approved the Sensenich and MT props. It certainly reads that way from the Jabiru web site. I also rang and checked and got the response that Sensenich had done lots of testing and it was ok to use it. I did call RAAus to see if it could be used on the certified aircraft and someone was going to ring me back but it did not happen. The conversation I had was that if Jabiuru are saying you can use it then it is ok (LSA). The big question I guess is are they saying you can use it or just saying you can use it :-)

 

 

[Guest brentc]

I understand it and I stand to be corrected that there are no certified or approved propellors other than the timber one. Quote - Rod Stiff just before Christmas. Probably not likely any time soon either as Rod is working on his own Carbon props and he said it was almost impossible to find a company that can supply him with enough for his needs.

 

That being said, a Carbon prop may not be out of the question for LSA, IF Jabiru provide you with a letter approving it.

 

Jabiru may tell you that a MT / Sensenich is 'approved' however this is only for homebuilts, as in they approve the prop for homebuilts because people in the US are using them without issue. If you wait another couple of days when the $AUD reaches parity a new Sensenich prop may become a lot cheaper!

 

 

[Guest ROM]

Beat me by a whisker, Brent!

 

On kit and non certified aircraft, you can use the Sensenich and MT props when and how you want to!

 

Aircraft used for hire and reward, for pilot training and for glider towing must be certified.

 

Certified aircraft cannot be changed in anyway without the specific approval of the certifying authority, which under LSA rules is the manufacturer.

 

Therefore alternative propellers cannot be used on the above certified aircraft without the specific approval of the aircraft manufacturer.

 

And get that approval in writing before you make any assumptions!

 

 

[glenns]

Agreed and understand guys, I wont say who I spoke to at Jabiru (They should have been able to answer correctly) but I pointed out those obvious points and that I was talking about a certified aircraft that was being used for Hire/Fly/Training and Glider towing. I still got a positive response. It was then I went for the confirmation from RAAus to verify but I haven't chased it back up again. I might do that today and see what response I get. Obviously I am expecting to get the negative response but it will be interesting to see.

 

 

[glenns]

Well you were right of course. After talking to RAAus and back with Jabiru I questioned the misleading entry on the website saying that the props were authorised. The response was that they were the only props that were authorised for the Jab Engines but they were not authorised for the Certified/LSA Aircraft. Jabiru are talking with Sensenich as well as designing there own. Interesting thing though is that they have not been looking at the ground adjustable! I pointed out that most people who had brought a J230C Glider Tow option would be looking for this option. Seems it is now at least on the table. For how long remains to be seen. No expected delivery time was given for either of the props but I would presume it would be a while.

 

 

[Guest ROM]

The ground adjustable prop is not a particularly attractive proposition for a mixed operation, Club owned, glider towing LSA.

 

I have never done a pitch change or even seen it done on a ground adjustable prop so some one with a ground adjust prop may be able to correct or enlighten me.

 

Ground adjustable props probably take 20 minutes or half an hour to do the fiddling to change the pitch.

 

I think some types of ground adjust props do not have interconnected blades, ie. each blade has to be set individually which would really slow the process down as great care has to be taken to get each blade within a half a degree angle of pitch to one another or you have problems with vibration and etc.

 

And I see from a comment on this forum that a difference of one degree in the pitch setting of a ground adjust prop can make a large difference to to the performance of the aircraft.

 

A mixed operations Club aircraft like our J230 has to be very versatile.

 

It may be used for training in the morning.

 

By midday a few glider tows may be required.

 

Later somebody may want to bash the circuit or go out for an hour or so cross country.

 

When the A/C gets back there would be another few tows waiting and then a few more training flights.

 

Tomorrow morning it is going for a 3 hour training X country.

 

There is no way that a ground adjustable prop is versatile enough for this sort of use.

 

We might as well stay with the cheaper, very simple fixed pitch prop.

 

An inflight, variable pitch or constant speed prop are by far the best options for our operation.

 

From comments on here and other sources, even that option should be limited to constant speed for glider towing as the tug pilot has to keep his wits about him when towing with a low HP, low inertia aircraft while keeping a real good lookout when there is some other glider and power traffic around.

 

The tuggy just would not have time or the inclination to fiddle with a inflight VP prop so a constant speed prop is the way to go.

 

As I said in a post midway through the first page of this thread, "we still have to find the prop make and type that is fully compatible with the Jab 3300 engine, will be very reliable, perform as advertised, has good back up, has a long TBO, is easily maintained, is easily repaired, and has no long term deleterious effects on the engine or airframe".

 

If the Jab prop is developed we will probably invest in one as soon as they have been proven or if some other manufacturer can come up with a CS prop that Jabiru are prepared to certify for their aircraft.

 

We are actually waiting for a new towing prop [ due today ] for our Jab as there was a complete stuff up by Jabiru on ours and others towing props leading to totally unacceptable towing T/O and climb performance.

 

It was only after we sent our factory supplied fixed pitch towing prop back that the cock up was found and we were acknowledged as being being right in our complaining.

 

So we will see how we go in the next couple of days with our LSA J230 glider towing.

 

If it works out then we will have a very good and versatile mixed operations, club aircraft.

 

Even more so if we can eventually equip it with a suitable constant speed prop.

 

 

[Guest brentc]

There's a mob in the Czech republic building Woodcomp props suitable for Jab engines that are elecrically adjustable in flight, but not constant speed. The 912 version is all carbon I believe and the Jab version is carbon inter-weaved with timber. Perhaps a reg35 engineer could approve this prop?

 

 

[Guest ROM]

Had a look at Woodcomp some time ago.

 

I have also been in touch with another J230 tug owner who is also looking for a versatile adjustable prop.

 

Woodcomp appear to be the only LSA prop manufacturer that I have found so far who has bothered to get certification on their props from various national aviation authorities.

 

Their blades are used as options in a number of other manufactures prop hubs such as Airmaster.

 

Where did you get the info that they were OK for Jab engines as I can't find any reference to Jab engines on their home site which would be the authoritative source rather than any of their agent's sites.

 

Woodcomp have not been approved by Jabiru and I cannot find any mention in Woodcomp's home site of Jabiru engines.

 

Rotax, BMW, subaru and etc, yes, but not Jabiru.

 

The American agent's site mentions Jabiru in their "suitable for" section.

 

Again I need to be enlightened; I am not at all sure that a reg35 engineer has any jurisdiction over RAA aircraft as the certifying authority and the organisation held responsible for the parameters that the aircraft can operate under is the manufacturer and not CASA or any of our aviation authorities so if the certifying manufacturer says "no" then that is it as far as approval is concerned and no reg35 engineer will alter that.

 

 

[Guest ROM]

A couple of years ago, I came across the Aerotek 2000 propeller web site but subsequently lost the site and forgot it after my old computer tossed in the towel.

 

Aerotek was / is made of the original designers of the Airmaster props which they sold out of but retained the right to do further work on propeller design.

 

I don't know if they are still extant as their website seems to date back to about 2001.

 

They have a list of test results and graphs on their site that lay out the results of constant speed props being fitted to various aircraft including a 6 cyl 3300 Jabiru engine in a Jabiru aircraft.

 

The CS prop on the Jabiru 3300 engine really gives a big boost to the overall performance on their figures.

 

One really interesting item was the big improvement in the climb performance of a fixed pitch prop when a pitch change of 1.6 inches on a 47.5" pitch prop to 45.9 " pitch or a pitch angle change from 17.5 degrees to 16.9 degrees.

 

This very small pitch change led to an increase in climb rate of 27% at 2000 feet and 34% at 4000 feet.

 

At 65 kts, there was a 51% increase in the ROC. or an effect at the propeller equivalent to an increase of 14.8 HP on a T/O weight of 477 kgs.

 

The test figures and data can be found here at ; http://homepages.ihug.co.nz/~aerotek/index.htm

 

The very small changes in propeller pitch for large increases in performance is quite eye opening.

 

It may also explain the odd occasion where I have been told that having a ground adjust prop is of no performance advantage over a fixed pitch prop as the operator of the ground adjust prop probably has not been aware of the performance sensitivity of very small pitch changes at the critical performance points.

 

The original, so called glider towing props supplied to us by Jabiru for our J230 glider tug, appeared to suffer from an almost total lack of any quality control by Jabiru.

 

A normal, non towing T/O run required a T/O distance as long as the standard prop and simply was not capable of doing any sort of reasonable climb rate glider tow.

 

The two original towing props varied in their dimensions from one another by up to 5 mms in the chord and amazingly the chord widths between the two blades on the same prop varied by at least 3 to 5 mms.

 

This on both props!

 

That was the part we could measure.

 

Very small pitch changes and thickness ratios and chord thickness positions we could not measure.

 

As the power output and engine revs can be significantly changed by as little as a one mm change in chord width, to have these sorts of variations on individual blades on the same prop is simply very bad engineering and bad quality control as well as causing significant vibration problems and no doubt strains on the crankshaft as well.

 

Jabiru have since supplied another wood towing prop to us which is better but not brilliant for the T/O and climb but now the cruise has dropped to about 105 kts, again not really acceptable for our purposes.

 

Engine designers put a hell of a lot of effort into their engine design and then incredibly just hang a lump of twisted wood on the front and expect their engines to take on the world.

 

Propellers are one of the most critical design components of an aircraft as they are the item that turns engine power into aircraft performance.

 

A good propeller can turn a moderate performing aircraft into an excellent performer and vice versa.

 

When will aircraft designers and manufacturers ever learn or relearn this lesson?

 

 

[Guest brentc]

I've just had a read of the quoted website above. They have quoted a maximum speed of 126 knots. If the prop is as good as they say, max speed should be near VNE of 140 knots. With my old standard timber prop I could hit 140 so it would need to be a lot better to part with my money. Just my 2 cents worth.

 

 

[Guest aircraft1]

Contact Michael Coates from X-Air he is the AU woodcomp dealer and has info on the Jabiru versions.

 

 

[Guest ROM]

Brentc, I assume you had a 3300 in the small fuse Jab or an SP equivalent.

 

There is one floating around this area that has the 3300 in the SP fuse with a Jab prop but he only gets a max cruise of 115 kts from which I gathered that Aerotek wasn't doing too bad at 126 kts.

 

Aircraft 1; best not mention the above gentleman in my hearing, thankyou.

 

I am also well aware of the different Woodcomp prop versions.

 

 

[Guest brentc]

Interesting figures as there's a few around here that go as quick, if not quicker than J200/400 figures and so they should too with a 6 cylinder up front in such a light airframe. I once had a bit of a race with a 6 cylinder SP here and he blew me away pushing through VNE straight and level very easily! I popped off my spark plug leads trying to compete!