Weight and Balance

See bottom of page for Jungmeister (Bu133) weight and balance info

Cowl Length

People from all over the world have kindly measured the distance from the front cabane attach bolt to the trailing edge of the prop and sent me the measurements:

So what length should a Jungmann cowling be? Pretty much whatever you like! There is clearly at least 6 inches difference between the Spanish and Czech cowls.  Joe's cowl is very close indeed to the original C104 and offers excellent accessibility.

Center of gravity.
This is a very important issue, and the subject of much debate.  To be safe, the aircraft must be loaded in accordance with the charts and data in the pilot's operating handbook. The empty center of gravity is used only for comparison and to calculate the loaded CG.

There are those who say the empty CG is of no interest at all. The only thing that matters is that when the aircraft is in flight it is balanced in such a way that it will recover quickly and reliably from a stall/spin, and that it can attain an attitude on landing that allows the main wheel and the tail wheel to touch the ground at the same time.

This is quite true. It only when fully equipped for flight (including a pilot and passenger) that any of this matters.

On the other hand, can we really say that the empty CG is not important? No, I don't think so. In the case of the Jungmann, the manufacturer specifies a pilot weight and a passenger weight. (90 Kg). There is, therefore, a particular range of empty CGs which will result in a safe flight condition when a pilot of that weight is at the controls.

The information on this page is intended to give you some idea of the range of empty CGs that are likely to result in a safe flying aircraft when flown by a pilot of about 90 Kg. You will only know for sure after you make some test flights with maximum, and with minimum fuel.

So we have to start somewhere and for me, that somewhere is the universal praise received for the flying qualities of Woody Menear's various restorations and also for Brian Karli's aircraft which closely follows some of Woody's practices. To get the best flying aircraft possible, Brian and Woody suggest, strive for as low an empty weight as possible and a CG at about 18 to 19 inches (45.7 to 48.3 cm) aft of the datum. Here are some other figures, again emailed by people from all over he place:

Please bear in mind that the accuracy of these measurements is completely unknown!

The LOM332
Another of those aviation compromises! If you use the "standard" Joe Krybus engine mount and cowl, the quality of which is quite incredible, you will have an a/c which very closely resembles an Aero C104. It will provide excellent access to the accessories mounted on the back of the engine and will be beautifully engineered. The aircraft will be a little less well damped in yaw than an aircraft with a shorter cowl. You will want to guard against a forward CG.

If you attempt to use a standard Spanish cowl, you have a real job on your hands! The only way to make it fit is to make a hole in the firewall and move some of the firewall tubing to make room for the fuel injection pump.  You will most likely end up with an aft CG. Joe tells me that Talmadge Scott needed to buy a significantly heavier prop. to compensate. An aft CG can be a very dangerous thing in an aerobatic aircraft!

I tried to be somewhere in between these two options. My cowling is just a little longer than a Spanish cowl and shorter than a Czech cowl. I like the way it looks and does not require a hole in the firewall, ballast or a heavy prop. Access to the accessories is not ideal, but it works.

Karl Pfister from Canada has sent a copy of his superb weight and balance calculator for the Jungmann. This Excel spreadsheet allows you to enter actual data for your aircraft and produces tables and graphs of the weight and balance. - Thank you Karl. Click on the following link to download the calculator.

Weight and Balance Calculator

Karl also pointed out that the empty CG is not that good a guide to the performance of the aircraft. It is the CG with the aircraft ready for flight that really counts.

From Brian Karli:

From Alan Abell:

Measuring as you ask from the cabane strut bolt to the leading edge of the prop on my aircraft (O-320/ Sensenich 74DM metal prop - 3.5” thick hub - with Woody Menear mount) is exactly 41 inches.   My mount is the same as the one Woody used on his personal ultra-light 0-320 powered Jungmann and also in the first configuration of the ex Dawson Ransom aircraft that Dick Martin now owns.  I do know that although very beefy, the early mounts were intended for the lighter O-320s but Woody and many other people also used them for O-360 installations. His later mounts “were shorter” but he didn’t specify how much.

The E.W. of my Jungmann before I started the weight reduction campaign was 1033 and the C.G. was at 17.5” with, I am told, 10 lbs of lead at the tail post.  There is one ingot back there but I can’t confirm the weight until I remove it.  In order to get a “SWAG” for reference, before I pulled the gear off I did get the aircraft more or less level and used a fairly accurate bathroom scale to weigh the tail.  It was 92 lbs!  Remember though that by that time I had taken something over 20 lbs off the aircraft forward of the CG. 

In a couple of conversations with Woody he advised me that a Jungmann with a C.G. at 18 ½“ aft of LE of center section is ideal and 19” is acceptable.  With the aircraft in level position, the tail weight should be 65 to 68 lbs. Over 70 lbs. is unacceptable.  This year at Santa Paula I took an informal survey of tail weights.  Earl Hickman (the knowledgeable gentleman that he is) was most helpful.  His red C-104, which he says should be identical to my Spanish 1000 series, has a tail weight of 74 lbs.  His others were plus or minus a pound or two but a couple of other aircraft present like Dan Miller’s, were much heavier.  I asked Mike Meloche and although he didn’t produce his weight and balance as Earl had, he indicated that around 75 lbs. tail weight seemed about right. 

Over all about 75 lbs. tail weight for a “standard” Jungmann does seem about right.  Woody’s 68 lbs. would be about 8% of his 850 lb. aircraft and I doubt if many others would come in at much less than 940 empty.  I do know that with my C.G. at 17.5 empty I always seemed to run out of nose up trim although I had no trouble landing the airplane three-point.  The stall was very benign and from what I’ve read of other aircraft, it seemed a little slow to enter spin rotation although it could have been just low-time-in-type pilot technique.  If I applied the 8% theory to my 1033 E.W. then the tail should have been 82 lbs. but the weight and balance shows its 70 lbs. so maybe that’s not such a good measure. 

A couple of weeks ago at the Brodhead MAAC fly-in I had the opportunity to fly Darrin Banfield’s stock right-out-of-the-Spanish-crate Jungmann with the 125 Tigre but no starter and a large amount of steel bolted to the skeg.  Interesting comparison and I wish I could fly them back to back.  You may want to talk to Chris Woodward about it.  He did fly his dad’s airplane in and I understand, wrung out the stock airplane acrobatically.  From my brief experience I was much impressed with the stock airplane and with how torquey that slow- turning Tigre is.  The performance is proportionally less than with the Lycoming power but with much less “storm und drum”.  It was of course, much slower than mine but otherwise a real delight to fly.  If anything the airplane seemed more responsive in roll, about the same in pitch but tended to “hunt” in yaw a little.  I suspect that the roll difference may be due in part to the greater speed stiffening up the control forces a little in my Jungmann although it could be more lack of lube!  It could also be the lesser gyro effect of the slower turning prop.  Even though Darrin said that his Jungmann probably needed a little more weight in the tail I thought it three-pointed just fine.  I’m supposed to be in touch with him soon so I’ll try to get some specifics on his weights and C.G.

 
(These tables are not easy to format in html so their appearance is not exact)

Jungmeister information

Two Bucker owners have been kind enough to share their weight and balance information. One in Metric units, the other in American.

Please note that the Datum on the Jungmeister is different to that on the Jungmann. The Jungmeister uses the leading edge of the LOWER wings, the Jungmann the TOP wings.