Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
gross weight
- Thread starter ShawnR
- Start date
)
There is a much broader range of engine HP options for the RV-9(A) compared to the other RV models.
The lower gross weight spec is for one built with the 115/118 HP engine in order to assure reasonable climb performance in high density altitude conditions, etc.
The lower gross weight spec is for one built with the 115/118 HP engine in order to assure reasonable climb performance in high density altitude conditions, etc.
The gross weight from Vans is a recommendation, and the actual gross weight is assigned by the builder - you. BUT having said that, you must convince the DAR that you can justify a higher gross weight than Vans recommends, and that will likely prove a little more difficult. It's not just an issue of maintaining C/G and balance, there is also a maximum nosewheel weight that is quite easy to exceed while still in C/G if you go with a higher gross weight.
My DAR gave me +10% just for asking on the gross weight based on the engine/prop I had installed and he said "Anything more than that, and I want to see an engineering analysis." Good enough for me...
My DAR gave me +10% just for asking on the gross weight based on the engine/prop I had installed and he said "Anything more than that, and I want to see an engineering analysis." Good enough for me...
I did pretty much the same as Airguy. I spoke with several other 9 owners and used 1800 as my gross.
I have a FP and Catto prop which are pretty light compared to a CS and metal prop. My empty weight is just under 1100 pounds.
I did my first long trip of 6 hours each way and learned a couple things. We were at about 1735 total as close as I could figure. I did weigh everything so I am pretty sure of the total.
1. My takeoff roll was a few seconds longer than when I fly solo but climbed great. I had to climb through a cloud hole and did a study climb from 1500' to 5500 at over 1500 fpm.
2. The plane was easier to land at the heavier weight. I have no idea on why. We have the Bison bags that fit directly in the seat space so most of the baggage weight was almost at pilot location.
3. With one notch of flaps, it took off and climbed great.
I have an O-320 160HP. I dont think I would want to be heavy in a high DA. I would be cautious of getting too heavy.
I have a FP and Catto prop which are pretty light compared to a CS and metal prop. My empty weight is just under 1100 pounds.
I did my first long trip of 6 hours each way and learned a couple things. We were at about 1735 total as close as I could figure. I did weigh everything so I am pretty sure of the total.
1. My takeoff roll was a few seconds longer than when I fly solo but climbed great. I had to climb through a cloud hole and did a study climb from 1500' to 5500 at over 1500 fpm.
2. The plane was easier to land at the heavier weight. I have no idea on why. We have the Bison bags that fit directly in the seat space so most of the baggage weight was almost at pilot location.
3. With one notch of flaps, it took off and climbed great.
I have an O-320 160HP. I dont think I would want to be heavy in a high DA. I would be cautious of getting too heavy.
PilotjohnS
Well Known Member
Gross weight takeoff
I did a max weight takeoff in my IO320 fixed pitch 9A. After I exited ground effect but before the speed built up, the AoA chirped at me. Did not expect that. But after that, my climb at 100 kts was fine. The plane didnt seem to be affected by the extra weight. Next time I will use a notch of flaps. With the new nose gear, I also got a slightly higher gross weight.
I did a max weight takeoff in my IO320 fixed pitch 9A. After I exited ground effect but before the speed built up, the AoA chirped at me. Did not expect that. But after that, my climb at 100 kts was fine. The plane didnt seem to be affected by the extra weight. Next time I will use a notch of flaps. With the new nose gear, I also got a slightly higher gross weight.
rocketman1988
Well Known Member
I think people may be missing an important point about increasing their gross weight over the recommended value.
The aircraft will fly at those weights BUT there are many other factors (ie engineering analysis) that go into deriving the recommended number. Think about things like how the structure responds to the extra weight at different load factors (like gusts when you are in turbulence). Those load factors can easily spike higher than you think, and that multiplies the load that needs to be carried.
Performance factors also need to be considered.
Overall, a small increase over the recommended value will likely go unnoticed; the large increases, though, are definitely cutting in to the structural and performance margins of the design.
I do recall an example of an RV-10 that listed a gross weight significantly higher than the recommended number. Did it fly? Yes but I would guess the margins were next to nothing...
The aircraft will fly at those weights BUT there are many other factors (ie engineering analysis) that go into deriving the recommended number. Think about things like how the structure responds to the extra weight at different load factors (like gusts when you are in turbulence). Those load factors can easily spike higher than you think, and that multiplies the load that needs to be carried.
Performance factors also need to be considered.
Overall, a small increase over the recommended value will likely go unnoticed; the large increases, though, are definitely cutting in to the structural and performance margins of the design.
I do recall an example of an RV-10 that listed a gross weight significantly higher than the recommended number. Did it fly? Yes but I would guess the margins were next to nothing...
The gross weight margins are there for many factors, probably chief among them being the gust factor and the landing loads. (I can hear Scott McDaniels grinning from way over here).
In flight the wing has to lift the heavier fuselage, creating higher bending moments at the center section joint with the main spar, and gust factors are unforgiving. At landing, the gear has to support all that weight as well, at whatever final vertical velocity you arrive. We all have perfect landing technique, right?
The point here being - it's not about the weight - it's about the accelerations.
And all this assumes you actually keep the load where it should be and the C/G is ok. What about burning off the fuel enroute and the CG shift for landing?
Kolg asked a valid question about my assumptions for the 10% increase, and I suppose he deserves an answer for it - the answer is I did nothing on paper to justify the heavier load. My "extra" weight is all in the extended range outboard tanks that I installed, and the heavier gross weight is for takeoff only. I use the 67 gallon fuel load extensively for long cross country trips, and in flight the gust load is not transferred to a heavier fuselage, since the wings themselves hold the extra weight and must be lifted first by a gust, before transferring any load to the center spar section. Spin recovery will certainly be affected - but the 9A is non-aerobatic in the first place, I don't partake in any aerobatics at all, and that's a risk I choose to accept. The primary load issue I have to keep in mind is ground ops with fuel in the outboards, where the extra weight with a long moment arm puts a lot of negative bending load on the wing spar and center joint trying to transfer that weight to the gear. Therefore I only carry as much fuel in the outboards for takeoff as I intend to burn before my first point of landing - which puts me solidly back in the original design box, landing with no fuel in the outboards and some in the standard inboard tanks.
As noted above I do have to watch my C/G, and there is a maximum nosewheel weight limit of 325 which I can certainly reach out and touch with full fuel, and taxi for takeoff has to be done gingerly keeping the spar in mind. Any landing with fuel still in the outboards is, to me, considered an emergency op and requires a visual spar inspection for bending or stress before further flight - and yes I've had to do that twice in the 1500 hours I've flown the airplane.
To Kolg's larger (intimated but not expressed) question of why I did that - I can only answer "Because I can". This is experimental aviation, we have more freedoms here if we are willing to take certain risks, I reduced those risks in my modified operations and made the decision to accept the rest, and the DAR agreed with my logic.
In flight the wing has to lift the heavier fuselage, creating higher bending moments at the center section joint with the main spar, and gust factors are unforgiving. At landing, the gear has to support all that weight as well, at whatever final vertical velocity you arrive. We all have perfect landing technique, right?
The point here being - it's not about the weight - it's about the accelerations.
And all this assumes you actually keep the load where it should be and the C/G is ok. What about burning off the fuel enroute and the CG shift for landing?
Kolg asked a valid question about my assumptions for the 10% increase, and I suppose he deserves an answer for it - the answer is I did nothing on paper to justify the heavier load. My "extra" weight is all in the extended range outboard tanks that I installed, and the heavier gross weight is for takeoff only. I use the 67 gallon fuel load extensively for long cross country trips, and in flight the gust load is not transferred to a heavier fuselage, since the wings themselves hold the extra weight and must be lifted first by a gust, before transferring any load to the center spar section. Spin recovery will certainly be affected - but the 9A is non-aerobatic in the first place, I don't partake in any aerobatics at all, and that's a risk I choose to accept. The primary load issue I have to keep in mind is ground ops with fuel in the outboards, where the extra weight with a long moment arm puts a lot of negative bending load on the wing spar and center joint trying to transfer that weight to the gear. Therefore I only carry as much fuel in the outboards for takeoff as I intend to burn before my first point of landing - which puts me solidly back in the original design box, landing with no fuel in the outboards and some in the standard inboard tanks.
As noted above I do have to watch my C/G, and there is a maximum nosewheel weight limit of 325 which I can certainly reach out and touch with full fuel, and taxi for takeoff has to be done gingerly keeping the spar in mind. Any landing with fuel still in the outboards is, to me, considered an emergency op and requires a visual spar inspection for bending or stress before further flight - and yes I've had to do that twice in the 1500 hours I've flown the airplane.
To Kolg's larger (intimated but not expressed) question of why I did that - I can only answer "Because I can". This is experimental aviation, we have more freedoms here if we are willing to take certain risks, I reduced those risks in my modified operations and made the decision to accept the rest, and the DAR agreed with my logic.
Last edited:
The new nose gear doesn’t increase the approved, gross weight rating of the airplane. It just changes the allowable weight on the nose wheel as computed in the weight and balance.
A recent, and similarly related thread in the RV-6 forum.
https://vansairforce.net/community/showthread.php?t=222745
https://vansairforce.net/community/showthread.php?t=222745
scottmillhouse
Well Known Member
As another data point with my 9A with a 160hp O-320 and CS prop, I used 1800 for XC with two and camping baggage. No problem with performance and W&B by the numbers but did note the plane upon departure with full fuel at high density altitude at 1800 # would “wallow” a bit like in slow flight. Reduce climb rate and it was fine. Always assumed it was because it was close to aft CG limit.
RV8JD
Well Known Member
Here is something else to consider: At the Van's recommended Max Gross Weight for the RV-3B, RV-4, RV-7/7A, RV-8/8A and RV-14/14A, (and I think the RV-6/6A also) the airplane's Design Load Factor Limits are the the Utility Category Limits (+4.4/-1.75 G).
However, at the Van's recommended Max Gross Weight for the RV-9/9A and RV-10, the airplane's Design Load Factor Limits are the Normal Category Limits (+3.8, -1.5 G).
So increasing the Max Gross Weight slightly above the Van's recommended numbers on the RV-3B, RV-4, RV-7/7A, RV-8/8A and RV-14/14A, and the RV-6/6A, gets you somewhere between the Utility Category Limits (+4.4/-1.75 G) and the Normal Category Load Factor Limits (+3.8, -1.5 G).
But increasing the Max Gross Weight above the Van's recommended numbers on the RV-9/9A and RV-10, gets you less than the Normal Category Load Factor Limits of +3.8, -1.5 G, which is definitely not recommended for normal operations.
Ref: https://www.vansaircraft.com/flying-an-rv/
Having said all that, I would stick with Van's recommended Max Gross Weight numbers, as they have done the design analysis, ground testing, and flight testing to validate their airplanes for all of the different design load conditions (static, dynamic, maneuver, gust, and landing).
However, at the Van's recommended Max Gross Weight for the RV-9/9A and RV-10, the airplane's Design Load Factor Limits are the Normal Category Limits (+3.8, -1.5 G).
So increasing the Max Gross Weight slightly above the Van's recommended numbers on the RV-3B, RV-4, RV-7/7A, RV-8/8A and RV-14/14A, and the RV-6/6A, gets you somewhere between the Utility Category Limits (+4.4/-1.75 G) and the Normal Category Load Factor Limits (+3.8, -1.5 G).
But increasing the Max Gross Weight above the Van's recommended numbers on the RV-9/9A and RV-10, gets you less than the Normal Category Load Factor Limits of +3.8, -1.5 G, which is definitely not recommended for normal operations.
Ref: https://www.vansaircraft.com/flying-an-rv/
"The RV-3B, RV-4, RV-7/7A, RV-8/8A and RV-14/14A have been designed for the operational stress limits of the aerobatic category (+6.0/-3.0 G) at and below their aerobatic gross weights. The operational stress limits for these aircraft between their aerobatic gross weights and their maximum design gross weights are utility category (+4.4/-1.75 G). The RV-9/9A, RV-10 and RV-12 are not designed for aerobatic flight.
The design operational stress limit for the RV-9/9A is utility category (+4.4/-1.75 G) at less than 1600 pound gross weight and is standard category (+3.8/-1.5 G) between 1600 pounds and the aircraft’s design gross weight. The design operational stress limit for the RV-10 is standard category (+3.8/-1.5 G).
No RV should ever be operated above its design gross weight limit."
The design operational stress limit for the RV-9/9A is utility category (+4.4/-1.75 G) at less than 1600 pound gross weight and is standard category (+3.8/-1.5 G) between 1600 pounds and the aircraft’s design gross weight. The design operational stress limit for the RV-10 is standard category (+3.8/-1.5 G).
No RV should ever be operated above its design gross weight limit."
Having said all that, I would stick with Van's recommended Max Gross Weight numbers, as they have done the design analysis, ground testing, and flight testing to validate their airplanes for all of the different design load conditions (static, dynamic, maneuver, gust, and landing).
Last edited:
JonJay
Well Known Member
So, are folks “grossing up” as they intend to fly this way or just because they are the “manufacturer” and can?
This has always bothered me in EA. The kit producer designed the airplane, however, the builder is the “manufacturer”. If you sell the airplane documented as a higher gross weight than the designer, with no modifications or further engineering, you could be liable should there be an accident related to gross weight. Of course, you could be liable regardless as a manufacturer and I don’t live my life that way, but….
RV’s in general, fly quite nicely over weight. This can lead to a false sense of security. The fatal accidents I have seen over the years related to being heavy are things like an overshoot or base turn stall/spin accidents in high density altitude conditions. I have never seen a structural failure accident.
The heavier you are the more margin of safety is lost. We all know this, or do we? If you gross up, and fly that way, you hopefully have a good understand of what this does to your airplanes performance, fly accordingly, and hope you don’t encounter anything unusual during the flight regime. (Higher than calculated DA, severe turbulence, necessary aggressive move while low to the ground, etc….)
You will lose safety margin if you gross up and fly that heavy.
This has always bothered me in EA. The kit producer designed the airplane, however, the builder is the “manufacturer”. If you sell the airplane documented as a higher gross weight than the designer, with no modifications or further engineering, you could be liable should there be an accident related to gross weight. Of course, you could be liable regardless as a manufacturer and I don’t live my life that way, but….
RV’s in general, fly quite nicely over weight. This can lead to a false sense of security. The fatal accidents I have seen over the years related to being heavy are things like an overshoot or base turn stall/spin accidents in high density altitude conditions. I have never seen a structural failure accident.
The heavier you are the more margin of safety is lost. We all know this, or do we? If you gross up, and fly that way, you hopefully have a good understand of what this does to your airplanes performance, fly accordingly, and hope you don’t encounter anything unusual during the flight regime. (Higher than calculated DA, severe turbulence, necessary aggressive move while low to the ground, etc….)
You will lose safety margin if you gross up and fly that heavy.
Last edited:
PilotjohnS
Well Known Member
Never at groos
I never plan to fly over Vans gross weight. My gross weight increase is just for paperwork. My extra gross weight is way less than the 10% everybody is assuming. I added a few pounds just so that a ramp check wouldnt bust the FARs. It is strictly to allow me to take off with full fuel on long cross countries to avoid a mid flight stop for fuel in the hot desert during a long cross country. Better to be a few pounds over on take off than risking a high DA takeoff. JMHO. yMMV
I never plan to fly over Vans gross weight. My gross weight increase is just for paperwork. My extra gross weight is way less than the 10% everybody is assuming. I added a few pounds just so that a ramp check wouldnt bust the FARs. It is strictly to allow me to take off with full fuel on long cross countries to avoid a mid flight stop for fuel in the hot desert during a long cross country. Better to be a few pounds over on take off than risking a high DA takeoff. JMHO. yMMV
Lots of good advice here on the gross weights. Yes, we as builders are the manufacturer and can change it, but it should be changed with caution. These are the experimental aircraft of Paul Poberezny's era where the builder actually knew more than anyone else about their particualr airplane. In our era, and especially with the top tier kit providers such as Vans, there has been REAL engineering analysis AND testing, both of flying articles and by computer simulations and fatigue testing. It's best to adhere to them.
Yes, I hear that some have done testing in their aircraft, but if we are honest with ourselves we have a really young fleet. The half donzen or so times that you really flight test at the higher gross weights really doesn't validate anything, except you got safely back on the ground. Only time will tell if the life of the airframe has been shortened in any appreciable way. Keep in mind we still issue bi-weekly AD's for a certified fleet that probably has trillions of hours on it.
Yes, I am one of those with tip tanks. My mission for the 10 was always Alaska trips, and I know you can fly sometimes for 3+ hours and have to turn around. I've been there. I know I don't want to be in a bad spot due to weather and start making bad decisions based upon fuel. I also know from experience that other aircraft such as Barons, Bonanzas, twin Cessnas, etc, have allowable increases in gross weights when tip tanks are added and have fuel in them. When I am operating with tip tanks I only allow the increased gross weight to include the extra fuel, and I SLOW DOWN drastically in rough air, and slow down anyway in smooth air. No sense being a test pilot! Besides the extra stress from the extra weight, there are other considerations, such as flutter. No way do I want to tickle that one.
Vic
Yes, I hear that some have done testing in their aircraft, but if we are honest with ourselves we have a really young fleet. The half donzen or so times that you really flight test at the higher gross weights really doesn't validate anything, except you got safely back on the ground. Only time will tell if the life of the airframe has been shortened in any appreciable way. Keep in mind we still issue bi-weekly AD's for a certified fleet that probably has trillions of hours on it.
Yes, I am one of those with tip tanks. My mission for the 10 was always Alaska trips, and I know you can fly sometimes for 3+ hours and have to turn around. I've been there. I know I don't want to be in a bad spot due to weather and start making bad decisions based upon fuel. I also know from experience that other aircraft such as Barons, Bonanzas, twin Cessnas, etc, have allowable increases in gross weights when tip tanks are added and have fuel in them. When I am operating with tip tanks I only allow the increased gross weight to include the extra fuel, and I SLOW DOWN drastically in rough air, and slow down anyway in smooth air. No sense being a test pilot! Besides the extra stress from the extra weight, there are other considerations, such as flutter. No way do I want to tickle that one.
Vic
