Airplane Empty & Gross Weights

[mike.smith]

Greetings,

I was chatting with several other homebuilders today, and I was asked what my empty and gross weights are. Obviously I don't know my empty weight yet but I'm hoping to keep my plane at or (hopefully) under 650 lbs, and after setting 1150 as a gross I'll have a full 500 lb useful load.

I have a tail dragger Sonex with an AeroVee. I set my gross at the design load because, well, that's what it was designed for. I'm not an engineer and I wasn't going to start being one on my first aircraft build. I have flown at 1100 lbs on a warm summer day, and it was scary how poor the performance was. Flying at 1150 would just scare the crap out of me. You can set all the numbers you want; you're the builder. But setting 1150, or 1200 or 1250 doesn't mean jack if the airplane can't safely climb, remain airborne, and land properly at those weights. Consider your safety (and that of your passenger!) before you consider upping your loads just to be "legal" on paper.

[Gary]

I haven't actually flown my relatively-new-to-me Sonex yet (the plane and I are still in preparation mode) but here's the data from my POH:

Aircraft: Sonex
Engine: Aerovee/Hummel 2387
Gear setup: taildragger
Avionics: MGL, COMM, Transponder, and little else
Empty weight: 615
Gross weight: 1200
Notes: Painted

[SonexN76ET]

Gary,

I think you should have your plane re-weighed. 615 pounds is impossibly light.

After you have it weighed, you can then know how much you can safely carry.

I personally would flight test it once again incrementally up to gross weight. I am confident that once you get close to 1100 pounds gross you will determine that going any higher is foolish because of increased takeoff distance and low rate of climb.

Also out in California you will be dealing with many landing areas at high density altitudes that will further diminish climb and take off performance.

Please be careful out there!

Jake

[Gary]

Hi Jake,

Your advice is well taken. Re-weighing is definitely on my agenda -- I've been planning on it to verify/discover both my true empty weight and my true CG. I'm actually more keenly concerned about CG, given the forward-fuselage-mounted fuel tank and the CG migration with fuel burn.

You're absolutely correct that 615 pounds is light, but I'm hoping that it's not impossibly light. When I was shopping, I ran into several planes with paperwork empty weights of 610 - 630 pounds, and a table from the old Yahoo group shows figures as low as 558 pounds. Empty weight and CG were high priority items in my shopping.

Various comments and warnings about paperwork gross weight versus prudent practice are also well taken. I figure that the ultimate responsibility is mine in any case and go/no-go decisions must consider everything. My higher-than-normal MGW just gives me a little more legal latitude.

[gammaxy]

You're absolutely correct that 615 pounds is light, but I'm hoping that it's not impossibly light. When I was shopping, I ran into several planes with paperwork empty weights of 610 - 630 pounds, and a table from the old Yahoo group shows figures as low as 558 pounds. Empty weight and CG were high priority items in my shopping.

Hi Gary,

Here's a recent thread where a bunch of builders posted empty weights:
viewtopic.php?f=3&t=1766

My tailwheel Aerovee 2.1 Sonex is polished and weighs 648 lbs. If I removed the Sonex upholstery and sat directly on the sling (8 lbs), replaced my battery with a lighter Lithium Iron one (13 lbs), and used the aluminum cylinders that aren't recommended any more (8 lbs), I'd be at 619 lbs.

My wheel pants/fairings weigh 6 lbs (I suspect some people do the initial W&B without them--I did and added them in afterwards), but I wouldn't want to remove those to save weight since it flies so much better with them. The fiberglass wing and tail tips also weight a non-negligible amount and some weight savings might be possible there (I think some people make sheet metal ones that might weigh a little less, and early Sonex didn't have them). My fire extinguisher is only ~2.5 lbs. My EFIS, RDAC, Com Radio, Transponder, ELT, position/strobe lights, and wiring weigh ~10lbs total.

[SonexN76ET]

Gary,

Regardless of your experience level, please take the Sonex transition flight training. It was the best $850 I ever spent (five flight hours plus ground school. Yes, you can probably fly the plane without it, but if something goes wrong you will have that training and confidence to safely complete the flight. It is a great deal of fun and extremely informative. All in all, a good experience. My brother is a Marine Corps Harrier pilot and I won't let him fly my Sonex unless he takes the transition training.

These planes are great fun, but you need to give them proper respect, just like any flying machine.

Sonex has put out some good information on gross weights and properly weighing your aircraft. Don't be afraid to ask Sonex directly if you have questions.

Jake

[Waiex 49]

Not trying to argue, just offering another data point.

I flew my Waiex without any transition instruction whatsoever. No big deal, it is an easy plane to fly. Easiest tailwheel plane I have ever flown. I read the POH, hopped in, and went flying.

I did, however, have large runways for these first flights. KMHR has 6,000 x 150 and 12,000 x 200 runways. I started out on the big runway. My first flights were also on days with perfect weather and zero wind.

Nothing wrong with transition training, but my personal choice was not to waste my time and money to go all the way to Wisconsin for a few hours of dual.

My only problem with the Waiex was the POS Aero Vee engine, which I have since replaced.

Again, just another guy with an opinion. Nothing wrong with transition training if you want to go that way. We all make our own judgement calls. Your results may vary.