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That sucks if you want to use a longer prop.  You would think they would build it to take a very popular standard 70" to 72" prop.  Just another reason why Rotax anoys me.  Like the $600 gear to take care of the SI.  After paying the extorsion prices Rotax charges for their engines you would think that when they discover a screwup on their design they would offer the parts to rotax owners at or near cost instead of continuing to rob them.

Yet still, the Rotax 912 series are the best engine available for a light sport class airplane...

Weight, power and RELIABILITY.

Looking forward to it!

I remembered seeing an article linked from this forum about making bungees, so I looked it up again. They show a tool made from a pair of Vise-grips. This must be similar to the tietite tool. I see now why it's important. The article describes how the cord is stretched to that it narrows during the wrapping process. When tension is released, the cord expands again inside the wire wraps and creates increased friction for a firm connection. Here is the article:

http://avidflyer.wikia.com/wiki/Shock_Cord_Fabrication_and_Replacement

Thanks for the extra information. I think that pretty much covers it. I'll check out the tietite tool.

Luke,

I added to my post above with the wraps I use, but for the MKIV, I think it was 7 or 8.  It is not rocket science though so if you start with 7 and it sags a little when they are new, I would just rewrap them with 8 wraps, divided up equally as I described.  If you are tying the safety wire with standard twist pliers you will really need to be sure to get the wire tight before twisting it.  The tietite tool tightens up the wire wraps as you cinch it down so it really gets the wire wraps tight before bending it over to finish it.  You might want to get one of these tools just for this, they are a bit spendy but not near as much as you save on just one bungee vs ordering them already made up.  You can order them from their web site.

That is why the EarthX is the battery to use, and also why they are more expensive than the others.  They have a buit in charge control system that keeps all cells equally charged continually, and you do not need a special charger to charge them, you just use a newer styler battery charger.

IMO, the Li batteries are still too much of a gamble - don't want an explosion or fire in my bird, and cant afford the charger anyway.

EdMO

I understand that the IVO prop is a lot lighter than the WD.

EdMO

Thanks Randy. That sounds good. I've got safety wire twist pliers. Do you remember how may wraps of the bungees over the truss (top and bottom) you use?

Luke,

I have been making my own for my extended wide gear.  Be sure to buy the aircraft grade bungee material; it uses natural rubber rather than the cheap synthetic rugger in the hardware store bungee material.  the natural rubber works well in cold temps and does not get hard, plus lasts much longer.

I use 1/2" on my Avid+ but on a stock Avid MKIV they used 3/8".  Buying it in bulk lengths from AC Spruce or Wicks is a lot cheaper.  I make a loop on the ends and tie them with stainless safety wire using a safety wire tightener tool (tietite or something like that)  Use double wraps on each tie and do it twice.  They hold great. 

I don't remember the standard # of wraps for the MKIV but I think I used 7 or 8 on my wide gear.  On the Avid+ I use 9 wraps; 8 full wraps and a half wrap on each end.  Make the bungee up to length (I think it is 90" for the wide gear but have someone else confirm it for sure.)  Lay the bungee out and divide it up by the # of wraps using 1/2 of a wrap at each end and mark it with a felt marker.  The marks will be the place you want to cross the gear leg tube as you wrap it.  You will need someone inside the plane to pull the end up and a person under the plane to pull it down, stretch it and hold it while feeding the end up to the guy inside.  1/2" is a pretty good workout to wrap but 3/8 is easy.

Good to hear your friend has had good luck with these. I'm a long way of from buying a battery, but If I go with a starter on my plane, I'll definitely use one of these after hearing this. That's a pretty huge weight savings for a single relatively small item.

Searching through the archives, it sounds like there are different grades of bungee cord. I checked the normal places (copied from the web sites):

Aircraft Spruce:

• 1/4 in
• 3/8 in
• 1/2 in

Aircraft Spruce is a lot less expensive. Is there a reason?

The cords that came with my plane are of unknown age, and they look just like the kind you buy at the hardware store (very stretchy). Aircraft bungees I've seen before seemed much harder to stretch.

Wicks has standard inch sizes, and they go up to 1/2". The old ones I have are about 3/8". I'm going to re-do my seat truss to make it strong enough to handle wide gear (bungee type) in case I decide to go that route down the road. I need to make sure it can fit the number of wraps required.

I know all this stuff has been hashed out pretty good in old threads, but some of the information isn't specific on a few points. One old thread said 7 wraps for standard gear, and 8 wraps for wide gear. Another says 6 wraps for standard gear. Also, they don't say if they mean 7 wraps over the top and 8 wraps under the bottom, or 6 wraps over the top and 7 under the bottom.

I think I also read that the standard gear uses 3/8, and the wide uses 1/2"?

Can anyone shed some more light on this, or verify any of the specifics? I don't need official information of what Avid specified or anything. Just hearing what setup has worked for others, so I can replicate it would be great. Hoping to do some welding in the near future...

Thanks,

Luke D.

A 912 gearbox max weight is a 3-blade 68" warp with nickel leading edge and tapered tips. Any more and the max moi is exceeded.

That sucks if you want to use a longer prop.  You would think they would build it to take a very popular standard 70" to 72" prop.  Just another reason why Rotax anoys me.  Like the $600 gear to take care of the SI.  After paying the extorsion prices Rotax charges for their engines you would think that when they discover a screwup on their design they would offer the parts to rotax owners at or near cost instead of continuing to rob them.

For anyone interested, EarthX batteries is recognizing the experimental aviation market.  They have a section for experimental aviation on their web site and are coming to the Alaska Aviation Trade Show in Anchorage next weekend, 3-4 May in the Fedex hangar for you AK guys!

The are having a 10% show discount and will have a limmitted amount of batteries for sale (10% off and no shipping cost)  I just ordered the ETX 36C (5.9"x3.4"x4.5" and 3.5 lb  to replace my PC680 (15.4 lbs).  I plan to move it to the firewall also to get rid of a couple of pounds of cable.  They aren't cheap at $349 but with the show special it came to $314 and I will just pick it up at the show.

Very nice folks and great to deal with.  Call them today if you want to get one at the show and be sure they have what you want because they are shipping them today for the show.  1-877-810-1842. 

Read the info in their web site.  I think this is the best and safest LI battery available and it is performing well in the temp extremes.  My buddy has been running one on his 0360 Cub for over a year now and says it easily outperforms the PC680 he had on it before.

I'll be there the first four days. 

A 912 gearbox max weight is a 3-blade 68" warp with nickel leading edge and tapered tips. Any more and the max moi is exceeded.

I plan to be there the whole week, but that may change based on client needs.  I'll be in the campground with a house that follows my Black Ram 2500 Longhorn around sometimes.......  Hope to see you there!

Mark

Booked my commercial tickets to Wisconsin yesterday! Pretty excited that I am finally going. Staying for 9 days. Hopefully will get to meet some of you guys.

Taper tip, or square?  The square tips are known to have a pretty high moment, especially if they have the metal leading edge.  I believe that's why the taper tips exist.

That's a Warp Drive 70".  I don't know how it compares to other props, but that's an idea worth looking at.  

J

What prop are you using?  The thumbnail looks like a three blade of some type.  I'm wondering if it has a high moment of inertia, making your situation difficult.

You can't use the clutch with the e gear box. I don't have any other answers for you. I used sleeve retainer on mine when I put it back together and so far no slipping.

I see you figured out where to hook it up. Here are some screenshots of how mine is set. Will give a starting point.

Thanks Paul, I'm thinking I may have set the spans too wide. Also not sure whether to set OP low alarm at 15psi (min OP at startup per Rotax manual) or 22psi (min OP during normal ops). And another question arises regarding max OT. The Rotax manual specifies a normal oil temperature range of 190-230 deg F. For short periods, the temperature may go as high as 285 deg F with synthetic oil. Since I use SportPlus 4, was thinking 120*F for low alarm (min OT for take off) and something between 230 and 285, say 260 or so?

Here are the two pages from my manual that deal with the friction cone and the large gear.   The info is at the bottom of the pages. Jim Chuk