[erich weaver]

I left my manual at the hangar - could someone tell me what values to use for fuel and baggage when calculating the most aft and most forward weight and balance values? Not sure if these are fixed/assumed values or if I am supposed to vary them.

thanks

erich

 

[dhammer]

Most aft and Forward

erich,

I would think you add up to a tank's or compartments capacity whatever will drive it most forward or aft. For instance in an RV-8, I would guess that full forward baggage, fuel, and no aft passenger or bags will get it worse case forward.

Aft passenger, full aft bags only, and no fuel would go the other way. You need to show calculations that take you up to but not over most aft and forward CG with either full or empty tanks. In other words, you need to know how to load it so fuel burn will not take you out of the CG range in flight.

Does that cover what you're asking?

Don

 

[Build9A]

will this help

Here's a link to Vans website with all the basic info on weight and balance for each model.

http://www.vansaircraft.com/public/downloads.htm

 

[erich weaver]

For my -7A, it seems reasonable to assume the maximum allowable baggage (100 lbs) for the most aft condition, but Im not so sure that using zero fuel as a minimum value is reasonable. By playing with the values, its clear that fuel actually has very little effect on CG, but I would still like to hear a definitive answer on the appropriate minimum fuel value so I can have it right for my inspection. The Vans website posted above doesnt seem to have info on calculaion of most forward and most aft cg.

thanks

erich

 

[Kyle Boatright]

For my -7A, it seems reasonable to assume the maximum allowable baggage (100 lbs) for the most aft condition, but Im no so sure that using zero fuel as a minimum value is reasonable. By playing with the values, its clear that fuel actually has very little effect on CG, but I would still like to hear a definitive answer on the appropriate minimum fuel value so I can have it right for my inspection. The Vans website posted above doesnt seem to have info on calculaion of most forward and most aft cg.

thanks

erich

I don't know about RV's that use metal props, heavy engines, or C/S props, but in my light RV-6 with a wooden prop, I generally launch on longer trips with the CG about .6 in front of the aft limit. Four hours of fuel later (~32 gallons), the airplane is at the aft limit. Often, I'll have a passenger hold a small bag in their lap on landing, just to move the CG a little bit farther forward and reduce the pitch sensitivity of the airplane.

 

[Build9A]

The Vans website posted above doesnt seem to have info on calculaion of most forward and most aft cg.

thanks

erich

The website shows the design CG range, which is the most aft and forward CG limits. The individual calculations comes from the weights you have measured for your individual airplane. But maybe I'm not understanding your question.

 

[John Clark]

Weight, Balance, and Limits

For my -7A, it seems reasonable to assume the maximum allowable baggage (100 lbs) for the most aft condition, but Im no so sure that using zero fuel as a minimum value is reasonable. By playing with the values, its clear that fuel actually has very little effect on CG, but I would still like to hear a definitive answer on the appropriate minimum fuel value so I can have it right for my inspection. The Vans website posted above doesnt seem to have info on calculaion of most forward and most aft cg.

thanks

erich

I've read your post a couple of times and am still not sure that I understand the question. If the question is "how do you calculate the CG limits" there is no calculation required, they are in the quoted web page and the manual. Unless you want to be a test pilot (really!) go with Van's numbers. Remember that the "max allowable weight" in the baggage area is structural only you may or may not be able to use the full weight with the airplane loaded.

John Clark
RV8 N18U "Sunshine"
KSBA

 

[Ron Lee]

fuel

Use VFR reserves for the lowest amount. My opinion.

 

[sportpilot]

empty weight CG

Seems to me you would start with your emptye weight CG. For most forward CG on a side b y side add pilot, and full fuel with no passenger or baggage. For most aft CG again assuming a side by side, add the pilot, passenger, minimum fuel (6 gallons?? or what ever, I dont think your interested in a zero fuel weight ) and maximum baggage ending up at maximum gross weight. Then you would look to see if these calcs are within the envelope for your plane. Keep in mind you can not exceed the maximum baggage allowance or the maximum gross weight. Its hard to say without running some numbers how muxh weight to put in the seats. You might find that a 300# each pilot and passenger with a small amount of baggage will give the most aft or maybe a 200# pilot with 120# passenger and maximum baggage. Use a sperad sheet and you can play with the numbers till they add up right.

 

[az_gila]

Spreadsheet and loading scenarios...

Erich... you don't say what model RV you are talking about.

The easiest way is to use one of the available spreadsheets and just enter in multiple loading scenarios. I have them available for some models if you need one...

We just weighed a local RV-9A with a Sensenich prop and a low comp. O-360, and his worse case loading (CG at forward limit) was a minimum pilot weight of 175 lbs. and full fuel. As fuel is used, the CG travels slightly rearward, but not much - just under a 1/4 inch for 5 gallons remaining fuel.

In this particular case, a lighter pilot (125 lbs) would be OK with a 15 lb load in the baggage area. All other loading cases up to gross weight were OK as long as the minimum pilot weight was kept.

Just enter your specific numbers into the spreadsheet and work out all of your applicable loading scenarios...

gil A

 

[David-aviator]

I left my manual at the hangar - could someone tell me what values to use for fuel and baggage when calculating the most aft and most forward weight and balance values? Not sure if these are fixed/assumed values or if I am supposed to vary them.

thanks

erich

Erich,
The question can not be answered without knowing what your empty weight and cg are and what model airplane you have. With that information, anyone can plug the numbers into a spread sheet and tell you what the limits are.

 

[erich weaver]

Seems to be a lot of confusion over my question which I thought was fairly straight forward, but I'll try again, with more info.

For the record, I have a -7a. I also have a weight and balance spread sheet, have completed my empty weight cg caculation, and have played with the numbers to see the effect of changing the various variables.

While I have run the numbers for various scenarios using MY weight, it is my understanding that for most forward and most aft CG calculations, one should document the calculation using the FAA "standard" pilot/copilot weights of 170 lbs. Therefore, for most forward CG, I have used full fuel, 170 lb pilot, no passenger, and no baggage. This puts me well within the accepted forward CG limits. If I change the pilot weight to my weight, I am still well within the limit. There is really nothing else to do to make my CG more forward, short of reducing the pilot weight further.

For the aft CG condition, it gets more interesting, as it is possible to exceed the aft limit with numerous variations of pilot/copilot weight and baggage. For example, using 170 lbs for both pilot and passenger and max. baggage (100 lbs) I must have 7 gallons or more of fuel on board to stay within the acccepted aft CG limit. Heavier pilot/copilot exacerbates the conditon.

Im confident I have a handle on this. The only issue for me is that there are an infinite variety of ways to each the aft CG limit in my case, but I need to document the most aft weight and CG condition for my inspection. If I can fix my minimum fuel value, then that just leaves me with the baggage to vary until I determine the max amount without exceeding the aft CG. So, once again, is there an accepted minimum fuel value I should use?

Hope this is more clear.

erich

 

[vlittle]

Seems to be a lot of confusion over my question which I thought was fairly straight forward, but I'll try again, with more info.

For the record, I have a -7a. I also have a weight and balance spread sheet, have completed my empty weight cg caculation, and have played with the numbers to see the effect of changing the various variables.

While I have run the numbers for various scenarios using MY weight, it is my understanding that for most forward and most aft CG calculations, one should document the calculation using the FAA "standard" pilot/copilot weights of 170 lbs. Therefore, for most forward CG, I have used full fuel, 170 lb pilot, no passenger, and no baggage. This puts me well within the accepted forward CG limits. If I change the pilot weight to my weight, I am still well within the limit. There is really nothing else to do to make my CG more forward, short of reducing the pilot weight further.

For the aft CG condition, it gets more interesting, as it is possible to exceed the aft limit with numerous variations of pilot/copilot weight and baggage. For example, using 170 lbs for both pilot and passenger and max. baggage (100 lbs) I must have 7 gallons or more of fuel on board to stay within the acccepted aft CG limit. Heavier pilot/copilot exacerbates the conditon.

Im confident I have a handle on this. The only issue for me is that there are an infinite variety of ways to each the aft CG limit in my case, but I need to document the most aft weight and CG condition for my inspection. If I can fix my minimum fuel value, then that just leaves me with the baggage to vary until I determine the max amount without exceeding the aft CG. So, once again, is there an accepted minimum fuel value I should use?

Hope this is more clear.

erich

What I did was develop a loading configuration (no bags, full fuel, max oil) and calculate the pilot weight that was necessary to be at forward CG limit.

This weight (in my case about 90 lbs) becomes the minimum pilot+pax weight for safe flight. It also indicates that forward cg will never be a practical problem... and that's the point of the calculation.

Vern

 

[az_gila]

You set the standards...

Seems to be a lot of confusion over my question which I thought was fairly straight forward, but I'll try again, with more info.

For the record, I have a -7a. I also have a weight and balance spread sheet, have completed my empty weight cg caculation, and have played with the numbers to see the effect of changing the various variables.

While I have run the numbers for various scenarios using MY weight, it is my understanding that for most forward and most aft CG calculations, one should document the calculation using the FAA "standard" pilot/copilot weights of 170 lbs. Therefore, for most forward CG, I have used full fuel, 170 lb pilot, no passenger, and no baggage. This puts me well within the accepted forward CG limits. If I change the pilot weight to my weight, I am still well within the limit. There is really nothing else to do to make my CG more forward, short of reducing the pilot weight further.

For the aft CG condition, it gets more interesting, as it is possible to exceed the aft limit with numerous variations of pilot/copilot weight and baggage. For example, using 170 lbs for both pilot and passenger and max. baggage (100 lbs) I must have 7 gallons or more of fuel on board to stay within the acccepted aft CG limit. Heavier pilot/copilot exacerbates the conditon.

Im confident I have a handle on this. The only issue for me is that there are an infinite variety of ways to each the aft CG limit in my case, but I need to document the most aft weight and CG condition for my inspection. If I can fix my minimum fuel value, then that just leaves me with the baggage to vary until I determine the max amount without exceeding the aft CG. So, once again, is there an accepted minimum fuel value I should use?

Hope this is more clear.

erich

Erich.... you are defining the limit, they can be tighter/tougher than the FAA requirements.

I would use full tanks and no baggage to determine a minimum pilot weight (use what it comes out to, not the FAA non-exisent pilot weight......)

In this case, you would know that a take-off with the defined minimum pilot weight and no baggage would be safe. As fuel burns off, the CG would only get safer...

Then put the minimum weight pilot in with no passenger, 1 gallon of fuel, and max. load in the baggage area. If this is within the aft CG limit, then you have determined two quite applicable "corner points" for you loading charts.

Most other scenarios up to gross weight are probably OK, but still need to be checked.

RV-8 guys have more scenarios with multiple baggage areas...

gil A

PS my concern would be the dimension Van publishes for the pilot arm dimension. Lighter pilots would move the seat back forward, and this would compensate for the lighter weight and make things safer...

Someone needs to put a pilot in at the next weighing they do as an extra....

 

[David-aviator]

.....So, once again, is there an accepted minimum fuel value I should use?

Hope this is more clear.

erich

Set minimum fuel in accordance with FAR 91.151. That will make an inspector very happy. For an RV with a Lycoming, 7 gallons would meet the requirement conservatively.

 

[erich weaver]

Set minimum fuel in accordance with FAR 91.151. That will make an inspector very happy. For an RV with a Lycoming, 7 gallons would meet the requirement conservatively.

AHA! An Answer! I knew it was out there somewhere!

Vern and Gil: There is no minimum weight pilot that will put me at the forward CG limit. With full fuel, pilot + passenger weight of zero, and no baggage, I am still within CG limits. More succinctly, there is no condition in which the the forward CG limit can be exceeded. Hence my focus on the aft CG condition

thanks all

erich

 

[az_gila]

Takeoff

Set minimum fuel in accordance with FAR 91.151. That will make an inspector very happy. For an RV with a Lycoming, 7 gallons would meet the requirement conservatively.

David... so a takeoff with 7.5 gallons of fuel would be OK?

That's well below my personal limitations.... Again, I say use full tanks for the calculations, and any take-off with less would be safe and within limits...

In the case I referred to, this (a 7.5 gallon takeoff) would give a minimum pilot weight of 150 lbs.... BUT if the tanks had any more than 7.5 gallons in them, the fwd. CG limit would be exceeded, unless that pilot gained instant weight....

I say go for the most conservative (i.e., safest) calculation... which is probably full fuel, minimum pilot weight and no baggage for the forward CG limit - but needs to be verified for your particular weights.

gil A

 

[az_gila]

Aft limits...

AHA! An Answer! I knew it was out there somewhere!

Vern and Gil: There is no minimum weight pilot that will put me at the forward CG limit. With full fuel, pilot + passenger weight of zero, and no baggage, I am still within CG limits. More succinctly, there is no condition in which the the forward CG limit can be exceeded. Hence my focus on the aft CG condition

thanks all

erich

Erich... sorry, I was concentrating on the fwd. limit.....

Again, for safety, I would be conservative and use a zero (or the unusable level) weight for fuel when calculating the rear CG limit.

While 7 gallons may be the FAA definition of reserves, you don't want a scenario to occur that would put you in a aft CG out-of-limit situation if you happen to start using those reserves. This could make a high stress situation (low fuel) very dangerous (aft CG exceeded).

Set your standards with zero fuel, and then you will be safe in all situations...

gil A

 

[ksouthar]

I use two spreadsheets to calculate both take off and landing CG conditions. With an RV9A with a Catto propeller, I am relatively nose-light. There is no practical loading that causes a forward CG condition. By limiting baggage to 75 lbs, there is also no practical loading that would result in an aft CG condition.

keith
RV9A
N355RV

 

[erich weaver]

Gil: Point well taken

Erich

 

[vlittle]

I use two spreadsheets to calculate both take off and landing CG conditions. With an RV9A with a Catto propeller, I am relatively nose-light. There is no practical loading that causes a forward CG condition. By limiting baggage to 75 lbs, there is also no practical loading that would result in an aft CG condition.

keith
RV9A
N355RV

My 9A is the same. If it's under 1750 lbs, with 100 lbs or less bags, it will be in the envelope... Unless I lose about 150 lbs. I don't think the other RV's are like this, though.