Changing gross weight with the FAA...

[jtpitkin06]

There is more to gross weight limits than simple wing loading g limitations. A wing may be able to withstand 6 g’s at 1050 pounds without failure. However, your simple calculation doesn’t take into account the performance at weights greater than 1050. The power to weight loading may not be sufficient to allow for climb.
Simply put, you could yank on the stick and the wing won’t break. But the airplane is so heavy at 1432 pounds it can’t get above pattern altitude.
Short wings on a light aircraft can produce a speedy ship. But there’s always that pesky piper to pay.
Notice the heavy hauler gains a whopping 100 pounds in gross weight, but it takes six feet more wingspan to do it. The longer wings have a greater wing bending moment so the g limitation is lower. This tells me the Speedwing 1050 weight is near the limit of its performance. If you were to actually load the short wing to 1432 the induced drag may be so high it may not be possible to climb with just 100 hp.

John Pitkin
Greenville, TX

[DBVZ]

If I understand you correctly, it becomes a performance issue rather than a structural issue and may depend on the HP of the engine. Something that could be determined during a 5 hour flight test program as part of a weight change "major alteration"?

[t j]

There seems to be some confusion on where a specific Kitfox's maximum gross weight is documentated. Here's my take on where it can be found.

My operating limitations contain this paragraph:
"...Following satisfactorycompletion of the required number of flight hours in the flight test area,the pilot must certify in the records that the aircraft has been shown to comply with 91.319(b). Compliance with 91.319(b) must be recorded in the aircraft records with the following or a similarly worded statement. "I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso____, Vx____, and Vy____, and the weight_____ , and CG location_____ , at which they were obtained."

Now, being that V speeds and Vso by definition for an aircraft are determined during flight testing at maximum gross weight, there you have your maximum gross weight required to be recorded right there in your aircraft's log book.

[DBVZ]

The following aircraft operating data has been demonstrated during the flight testing: speeds Vso____, Vx____, and Vy____, and the weight_____ , and CG location_____ , at which they were obtained."

Now, being that V speeds and Vso by definition for an aircraft are determined during flight testing at maximum gross weight, there you have your maximum gross weight required to be recorded right there in your aircraft's log book.

You would think so, and perhaps that is what the FAA intends and expects. But the Avid Mk IV I mentioned with 1320 on the data plate shows test flights were done at 1070. All signed off by the DAR with 1320 listed as max gross on the top of the official W/B, even though the most forward, aft, empty CG calculations are all at lower weights. Go figure. BTW, the Operating Limitations I saw for that plane seems to have been signed off with those items blank, for the builder to fill in. DAR not doing his job? Or builder not doing his? Or both?

Also, the Operating Limitations are not in the aircraft log book are they? Need to be carried in the aircraft, and the log books are not.

[MotReklaw]

I am confused, which is not uncommon.

I thought the DAR signed off on the plane before the flight testing so these Phase I testing items aren't even entered into the log book when the DAR signs off.

I probably misread/misunderstood this thread.

[DBVZ]

That is what the question marks are about. I have not been through this myself. If it is normal for the DAR to issue the operating limitations before flight testing starts, and for the owner to fill in the blanks on it, then it makes the process kind of suspect when 1320 shows up as max gross and it looks like the owner tested at 1070. I saw a post that said you could set max gross at 2000 if you wanted but the DAR would likely want to see your justification. When would he see it? I think the original W/B is done before the first flight, to show that the test pilot has looked at the CG and load issues. If the owner did not flight test at the recorded max gross, the V speeds will be wrong for the max gross on that W/B.

Back to the original question, if a change of max gross is a major modification requiring another 5 hours of flight test, here is what I would think that means. First, evaluate if the structure can handle more weight, or rather if a reduction on the G-load factor still gives you enough safety. Then:

1. Fly it at current max gross +50 and record the Vso, Vx, and Vy, and CG location tested at that weight. It would seem like the stall speed would be important to know for a lot of things, including keeping it LSA legal as the weight is increased toward 1320 if that is the intent. I would also want to test climb rate at about 1000 MSL and ceiling standard day, but the FAA form seems not to care about that.

2. Fly it at current max gross +100 and record the Vso, Vx, and Vy, and CG location tested at that weight.

3. Fly it at current max gross +150 and record the Vso, Vx, and Vy, and CG location tested at that weight.

4. Fly it at current max gross +200 and record the Vso, Vx, and Vy, and CG location tested at that weight.

Quit when you get either the max gross you would like, or when you get close to performance you do not like. Climb rate at or near 500 fpm, or ceiling at or near 10,000, or stall at or near 50 mph for example in a kitfox or avid you want to operate LSA. All provided you do not exceed reasonable loading for the aircraft structure. As noted earlier, for a speedwing with +6/-3 that would not be much of a problem since the wing is so short. Am I missing something?

[rogerh12]

If it helps with an example, when I upgraded my zenith 601 HDS 75 hp VW engine to a 100 HP VW engine, I informed the FAA as required by law as it counted as a major change. The FAA just had my A&P inspect the changes during the annual conditional inspection, and sighed off the work.

The FAA issued me a new pink slip, and also gave me the option of increasing the gross weight by 50 lbs on the new pink slip (though I declined as the landing gear was not modified to take the extra load). Of course, this is not exactly the procedure as outline “by the book”, but hey, the FAA can do whatever the want in these matters, yes?

They assigned me a 10 hour fly off (Note: I bought the plane from the original builder)

Hope this helps


Roger

[MotReklaw]

"....That is what the question marks are about. I have not been through this myself. If it is normal for the DAR to issue the operating limitations before flight testing starts, and for the owner to fill in the blanks on it, then it makes the process kind of suspect when 1320 shows up as max gross and it looks like the owner tested at 1070...."

Dwight,

I built two homebuilts. On both of them, the DAR ask me what the Max Gross was. I told him and he wrote it down. I showed him my W&B calculations. Then, during Phase I testing, I entered the following information in my log book concerning the above:

"I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso____, Vx____, and Vy____, and the weight_____ , and CG location_____ , at which they were obtained."

I guess I am not sure what you are talking about so I will bow out of this thread.

Best to you,

Tommy

[DBVZ]

I guess I am not sure what you are talking about so I will bow out of this thread.

Best to you,

Tommy

I think I misunderstood your prior post. Thanks for the information you provided.