Citabria 1970 7GCBC usefull weight

Johan Whiteman

Johan Whiteman

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Joined
Mar 8, 2022
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9
Location
Centurion, South Africa
Hi guys just bought a 1970 7GCBC and came to the conclusion it has no useful load. My empty weight is 1220 lb at last weighing but came out of the factory in 1970 as 1151 lb. No mods done to her according to the logbooks. Will be doing a new weighing this week as the only thing I can think off is that the fuel wasn't all drained and the figures was just copy pasted every time the new mechanic did a weighing? I weigh 198lb and my son 187lb giving us 45 lb (7.5 gal) of useful fuel. This gives us a radius of about 15min from the airfield and less than 30min reserves which is no good.

With the same 150hp engine and airframe how come the post 1994 7GCBC have had an increase in weight to1800 lb yet the empty weight stayed about the same. Surely aluminum gear legs and wingspars could not contribute to this. Any ideas or is it going to be self taught aerobatics aircraft and always only solo as you cannot carry fuel to get anywhere?

So the question is? With the pre and post 94 7GCBC having no big difference in basic weight, engine and design why could I not fly her up to the same weight limit of 1800lb in the normal category? With 2 up and 1/2 tanks she would only weigh 1722 lb. and will make her more usable. The only weight saving could be a lightweight lithium batt but is that legal? How are other owners operating this ac, as pilots must have been midgets in the 70's. Tks
 
I would start by finding the 70 pounds you gained over the years. That seems excessive. As you observe, perhaps the weighing process was in error.

The most cost effective weight reduction step was to yank out obsolete avionics. I haven't used a VOR in decades, so the Nav radio and VOR indicator came out. Also replaced my old mechanical Turn Coord with an electronic AI.

Another good way to save weight is to replace strobes with LED's. The LED power supply is a 5 pound brick, and it is 1970's vacuum tube technology.
 
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Usually Citabria-like aircraft weigh what the factory said, give or take here and there. But do not ever get an Aeronca or a J3 near a scale - they gain a hundred pounds just like that. Then add a metal prop or a starter and battery, and a wing tank . . .

Most think this is blasphemy, so take it with a grain of salt:

It is perfectly legal to take the factory weight and compute the new weight/balance using nothing more complicated than long division. If you do not have a weigh-in stated in your logbook or worse, on a 337, remember that most maintenance documentation can be discarded in a year - and most aircraft have the initial factory weight stored somewhere in OKC on a microfiche or digital equivalent.

As an example - we found a Super Cub with around 380 lbs useful load - a genuine single place aircraft. But the weigh-in was suspect, since the CG was so far forward that no loading would ever be legal. The formula was incorrect. So we assumed the entire process was flawed, noted the errors, re-computed from the original weight shown in the AFM, and converted back to two place with plenty of fuel.

This may not work for those aircraft where some over-zealous mechanic stated a weigh-in on a 337 - those are permanent records. A number of Super Cubs I have seen have that problem. And remember, flying overweight may void your insurance! Paperwork is everything in this game.
 
Johan Whiteman said:
Hi guys just bought a 1970 7GCBC and came to the conclusion it has no useful load. My empty weight is 1220 lb at last weighing but came out of the factory in 1970 as 1151 lb. No mods done to her according to the logbooks. Will be doing a new weighing this week as the only thing I can think off is that the fuel wasn't all drained and the figures was just copy pasted every time the new mechanic did a weighing? I weigh 198lb and my son 187lb giving us 45 lb (7.5 gal) of useful fuel. This gives us a radius of about 15min from the airfield and less than 30min reserves which is no good.

With the same 150hp engine and airframe how come the post 1994 7GCBC have had an increase in weight to1800 lb yet the empty weight stayed about the same. Surely aluminum gear legs and wingspars could not contribute to this. Any ideas or is it going to be self taught aerobatics aircraft and always only solo as you cannot carry fuel to get anywhere?

So the question is? With the pre and post 94 7GCBC having no big difference in basic weight, engine and design why could I not fly her up to the same weight limit of 1800lb in the normal category? With 2 up and 1/2 tanks she would only weigh 1722 lb. and will make her more usable. The only weight saving could be a lightweight lithium batt but is that legal? How are other owners operating this ac, as pilots must have been midgets in the 70's. Tks
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This is why I looked for a Scout. Hard to find affordable Supercubs with any useful load and most Citabrias were in the high 4’s. I cannot overload the Scout even with two 200 lb guys and 135 lbs baggage (extended) and 36 gal fuel
 
Did a very accurate W&B yesterday. Leveled ac according to POH correctly, 8 qts of oil and 1 gal unusable fuel on board. (She has 39gal tanks)
Left wheel 576lb
Right wheel 568lb
Tail wheel 86lb
Total weight 1230lb (1970 factory sheet shows 1158lb and it is still stock standard)
With max weight for the 1970 7GCBC at 1650lb it gives a use full load of 420lb. Basically it is a solo ac? So how is a conversion or checkout achieved not even to mention some aerobatic instruction. Surely American can upgrade it to 1800lb as is done with all the post 94 7GCBC's?
 
Johan Whiteman said:
Did a very accurate W&B yesterday. Leveled ac according to POH correctly, 8 qts of oil and 1 gal unusable fuel on board. (She has 39gal tanks)
Left wheel 576lb
Right wheel 568lb
Tail wheel 86lb
Total weight 1230lb (1970 factory sheet shows 1158lb and it is still stock standard)
With max weight for the 1970 7GCBC at 1650lb it gives a use full load of 420lb. Basically it is a solo ac? So how is a conversion or checkout achieved not even to mention some aerobatic instruction. Surely American can upgrade it to 1800lb as is done with all the post 94 7GCBC's?
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It's a common story in older GA aircraft, the 70's vintage Super Decathlons are similarly limited but so are older Cessna 180's, and a lot of other supposedly four place aircraft, especially as the average human has increased in size. Sorry that that doesn't change your situation.

And welcome to you joining us from South Africa!
 
Fabric planes sometimes gain a little when recovered and gain a lot if repainted over existing covering. 70 pounds would almost have to involve adding something to the panel. I once pulled six pounds of obsolete wire and coax from a bonanza. I'd go through the logs and look for a weight difference on any part that had ever been replaced, battery, tires etc., and look for what has been added or what has been left behind. Then get your check book out and reread Big Eds post because you're going to have save a pound in 70 places.
 
Johan Whiteman said:
Did a very accurate W&B yesterday. Leveled ac according to POH correctly, 8 qts of oil and 1 gal unusable fuel on board. (She has 39gal tanks)
Left wheel 576lb
Right wheel 568lb
Tail wheel 86lb
Total weight 1230lb (1970 factory sheet shows 1158lb and it is still stock standard)
With max weight for the 1970 7GCBC at 1650lb it gives a use full load of 420lb. Basically it is a solo ac? So how is a conversion or checkout achieved not even to mention some aerobatic instruction. Surely American can upgrade it to 1800lb as is done with all the post 94 7GCBC's?
Click to expand...
Johan,
The things I did to lighten up the plane: 1) move the battery to the firewall and replace with a Hawker SBS j-16 (basically an Odyssey 680) saves probably 15-20 lbs with cable removal, box removal, battery replacement), 2) removed the carpet (6lbs)(don't lose your data-plate if it is attached to the carpet!), 3) put in carbon fiber floor from ACA (don't know the exact saving but probably another 5 lbs), 4) LED strobes and removed the whelan power units (5 lbs) 5) lightweight starter (1-2 lbs). Some things that you may consider but I do not know if they are available for the 7GCBC but replacing the gear legs with the new gun drilled aluminum will save something like 25 to 30 lbs.
 
Again, if the aircraft is essentially just like when it left the factory, why would you weigh it? If we told you these aircraft simply always gain a hundred pounds when plaved on modern scales, wouldn't that cause you to be cautious?

I have rarely heard of a good outcome from weighing. Only one - a 1966 7ECA came within six pounds of its factory weight, and that was with a heavy layer of catalyzed auto enamel.

The Decathlon is so close to weight limited when it left the factory - if it tracked what these Scouts are doing a weigh-in could convert it to a 0PCLM.

We had a Helio Courier come to town with a useful load of 230 lbs. That was truly a zero place aircraft.
 
I also forgot. Take out the vacuum pump and put in electrical attitude indicator and related electrical upgrades. Save room in the engine compartment and weight.
 
Ouch! I missed the South Africa angle. You guys need Carbon Cubs, or high gross weight Scouts. At least if you want to carry passengers.
 
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