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My Rotax 912iS install is coming in a little heavy at a calculated 204lbs, so I decided to compare it to the 3300 installation. Per the plans, "The total engine package weight consisting of the engine (with accessories and exhaust), propeller, cooling system, battery, and charging system shall not exceed 200 lbs." I calculated a very common 3300 installation as follows:

Engine weight: 184 lbs
Sensenich two-blade prop: 8.4 lbs
Old solid spinner: 2.8 lbs
Odyssey PC680: 15.4 lbs

Total: 210.7 lbs

Notes:
The engine weight taken from here https://youtu.be/AWbGCbpDb4k?t=502
The prop weight is from old research, please correct me if it's wrong.
I weighed an old solid spinner myself.

You could lose a good 12 lbs today with the new spinner and a lithium battery, but many older Sonex have flow with the above basic FWF components, including factory planes. How did they get the weight under 200 lbs?? How should accessories like the smoke system, or a nose wheel, be accounted for? I know this topic has come up many times over the years. Is there a consensus opinion on the 200 lbs FWF limit?

My Aerovee Prince prop was just under 4 lbs. The Sensenich prop I borrowed was almost a pound heavier.

My experience may not be consensus. I have an A-model Sonex with a Corvair up front, FWF 220 pounds plus, with 1100 hours and 2400+ landings. I try to keep a sharp eye on things and do a thorough annual every winter (two weeks in a heated hangar) — haven’t observed any signs related to stress between the engine mount and FWF attach points yet.

Thanks Bryan, I couldn't find accurate numbers online for the prop weight.

jaflint wrote:I have an A-model Sonex with a Corvair up front, FWF 220 pounds plus, with 1100 hours and 2400+ landings. I try to keep a sharp eye on things and do a thorough annual every winter (two weeks in a heated hangar) — haven’t observed any signs related to stress between the engine mount and FWF attach points yet.

You sure are getting a good bit of flying done! 8~)

I can verify what you have stated as to finding zero issues with the increased FWF weight as I'm also flying behind a Corvair. I'm low time with over 300 hours & 700 landings (pavement & grass). I don't fly aerobatics but others with Corvair conversions have.

If it helps, there is some FWF weight information included in the Corvair discussion thread from a few years ago:

viewtopic.php?f=9&t=4273&hilit=justification#p32707

When I first did the weight and balance on my Sonex with 3300 and Odyssey 625 (13.2 pounds) it worked out just right. At the time I thought "Phew, that's lucky." I couldn't think of anything else except ballast weights that I could put there to shift the C of G further forward.

Peter

My Waiex has an aft CG. I'm not out of CG unless I have two people, lots of baggage, and no gas. I don't do that. When we went to Oshkosh I had about 5 lbs of stuff I could easily move to the glareshield if we got down to 2 gallons.

Zack wrote:Thanks Bryan, I couldn't find accurate numbers online for the prop weight.

I found my pictures. The Prince was 3.936 lbs before repair and 4.006 lbs after. The Sensenich was 4.7 lbs.

FWIW: Camit 3300s are about 8 lbs heavier than Jabiru 3300s mostly due to more steel in the cylinder barrels. No problems with mine, but I do have a 3 lb diver's lead weight bolted in the tail. Had an EarthEx battery for while and eliminated the lead weight, but battery was showing problems each spring so went back to the Odyssey 680.

David A.

Okay, here are the updated numbers from others in the thread:

Engine weight: 184 lbs
Sensenich two-blade prop: 4.7 lbs
Old solid spinner: 2.8 lbs
Odyssey PC625: 13.2 lbs

Total: 204.7 lbs

For reference, here is my Rotax 912iS install:

Base Engine w/Gearbox: 140.21
Propeller: 19.5
Governor: 2.2
Spinner: 2.2
Exhaust System: 10.36
Fuel Pump Assembly: 3.53
Air Filter: 0.33
Oil Cooler: 1.32
Oil Tank: 3.31
Oil Thermostat: 0.55
ECU: 2.49
Fuse Box: 4.45
Ambient Sensor: 0.132
Wiring Harness: 5.51
Electric Starter: 1
Starter Relay: 0.32
Coolant Radiator: 3.3
Battery: 3.9

Total 204.612

I feel more comfortable with my FWF weight but I'm still a little puzzled by the Sonex guidance. For example, on my B-model plans they say the battery can be installed aft of the firewall for CG purposes but that it should count toward the 200 lbs total engine weight limit? I guess it is to maintain useful load under the 1100 / 1150 max gross weight.