Exceeding maximum gross weight
Evolution Vs Over Gross
Don’t confuse evolutionary weight increases with operating outside of an aircraft’s published weight. The S-76 is a good example. Each evolutionary growth in weight was a planned, designed and certified as a growth version of previous models. The gross weight increases were accommodated for with structural beef ups and an increase in operating rotor speed to provide the required lift. Similarly, the MH-60K, a growth version of the Basic Blackhawk, operates at increased gross weight form the basic model. It this instance the dynamic components of the MH-60K are identified and tracked separately. The MH-60 component lives are significantly reduced as a result of this higher gross weight envelope.
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I think others on this thread have commented adequately on the possible power limits of flying over gross. The problems develop more insidiously if the power is adequate for near normal operations over maximum gross weight.
The USAF flew it's H-53 fleet over gross in the late 80's and 90's for a variety of operational reasons after the fleet transitioned from the rescue to the special operations mission. Unfortunately for us we did it backwards from the S-76 fleet. We did it, and then told the certification authorities what we had done. They came up with an inspection regime and then we'd go off and do it again. Not real smart on our part, I'll admit, but we never lost an aircraft to over gross operations.
Real problems happen when you operate off the charts. Working with extropolated charts worked fairly well for us for engine power and hover performance, but we were somewhat surprised after the engineering got done that we had also been operating out of permissable cg limits. The aircraft did crack where the engineers thought it would. It also cracked bent and wore out in places they didn't expect.
If lives don't require you to fly over gross, I highly recommend you don't do it, because lives are at risk when you do.
The USAF flew it's H-53 fleet over gross in the late 80's and 90's for a variety of operational reasons after the fleet transitioned from the rescue to the special operations mission. Unfortunately for us we did it backwards from the S-76 fleet. We did it, and then told the certification authorities what we had done. They came up with an inspection regime and then we'd go off and do it again. Not real smart on our part, I'll admit, but we never lost an aircraft to over gross operations.
Real problems happen when you operate off the charts. Working with extropolated charts worked fairly well for us for engine power and hover performance, but we were somewhat surprised after the engineering got done that we had also been operating out of permissable cg limits. The aircraft did crack where the engineers thought it would. It also cracked bent and wore out in places they didn't expect.
If lives don't require you to fly over gross, I highly recommend you don't do it, because lives are at risk when you do.
I just wonder how they work out the max weight? For example if you fly 50lbs overweight in say an R44, however are flying in a straight line are you not puting less strain on the various components than if you are at max weight and doing lots of banks and turns. So I wonder how they come up with the figure. I doubt if an R44 flew continual figures of 8 at 60 degrees that they would ever reach 2200 on the appropriate components. It tends to suggest that somewhere someone is puting their finger in the air and using the laws of average, perhaps thats why many pilots do fly overweight, thinking they can get away with it
As soon as you turn an aircraft you increase the load on it's lifting surfaces. The rotor system would read this as increased weight that it has to counteract. In level flight it is 1G so the rotor is supporting the actual weight.
A thirty degree level turn produces a loading of 1.17G. An aircraft weighing 5000lbs now weighs 5850lbs.
A sixty degree level turn produces a loading of 2G, it is now 10,000lbs.
An R44 would manage the first but unless you are flying a powerful multi-engined helicopter at about 70knots you would be pushed to achieve the second.
A thirty degree level turn produces a loading of 1.17G. An aircraft weighing 5000lbs now weighs 5850lbs.
A sixty degree level turn produces a loading of 2G, it is now 10,000lbs.
An R44 would manage the first but unless you are flying a powerful multi-engined helicopter at about 70knots you would be pushed to achieve the second.
So......flying 60 degree or even 30 degree turns makes the helicopter technically overweight for the duration of the turn but thats ok as you are within the max weight at take off. It therefore must be correct that flying slightly overweight in a straight line puts less strain on the heli than flying within weight through terrain that requires lots of banks/turns. So I'm still wondering how they work out the max weight with such variable forces?
Usage Spectrum
In the US, the military and the contractor cooperatively develop a usage spectrum for each aircraft. This spectrum is developed about a design gross weight, not the aircraft's actual gross weight. I believe the Blackhawk design weight is approximately 16800 lbs and the CH-53E was approximately 48,000 lbs. This developed usage spectrum includes operating scenarios about this weight, including time above it. A percentage of total flight operating time is assigned to each element of the spectrum. As an example:
5% - level cruise at best range
0.5% - Cruise at Vh
1% - 30° bank at best range cruise
These very detailed lists are then used to compute component lives for the aircraft. There are many instances where operational requirements change and the list has to be revisited and component lives are recalculated. The previously mentioned MH-60K is one example where the time spent at higher gross weights required a recalculation of the components lives for that specific model. I hope this helps. Maybe John Dixon can weigh in with more specifics on the Hawk.
5% - level cruise at best range
0.5% - Cruise at Vh
1% - 30° bank at best range cruise
These very detailed lists are then used to compute component lives for the aircraft. There are many instances where operational requirements change and the list has to be revisited and component lives are recalculated. The previously mentioned MH-60K is one example where the time spent at higher gross weights required a recalculation of the components lives for that specific model. I hope this helps. Maybe John Dixon can weigh in with more specifics on the Hawk.
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I'd assume that G loading is part of the design process, I wish I could say what it was, but I don't have the data. But I'm sure the ship has to meet some figure like "safe for all loads below 3G's" or something similar.
I know that's how things go in the airplane world. Again, I don't have the inclination to look up the numbers now, but I'm aware of some air planes which have different categories based on their GW. Example, if you load the ship to 3000lbs, it's a Utility ship, which says it's certified for 5G's of stress. However, if you choose to use 3500lbs as a GW, you're limited to Standard category which may only be 3G loads (bank, maneuvers, etc.)
Anyways, the point I'm trying to make is if you could guarantee the ship would never see more than, say, 1.2G's, without any turbulence, under maximum maneuvering speed, then you would cause no damage beyond increased wear.
Of course, heli's don't always list "max maneuvering speed," you can't ever guarantee you won't exceed 1.2G's, or encounter any turbulence, and the ships were designed with these G loadings more as a transient than a continuous load.
Really though, as others have said, this is all moot. If you fly it over gross, and are caught doing so, the blame for future or current failures will most likely lie on you from the eyes of the victims, employers, and insurers.
I know that's how things go in the airplane world. Again, I don't have the inclination to look up the numbers now, but I'm aware of some air planes which have different categories based on their GW. Example, if you load the ship to 3000lbs, it's a Utility ship, which says it's certified for 5G's of stress. However, if you choose to use 3500lbs as a GW, you're limited to Standard category which may only be 3G loads (bank, maneuvers, etc.)
Anyways, the point I'm trying to make is if you could guarantee the ship would never see more than, say, 1.2G's, without any turbulence, under maximum maneuvering speed, then you would cause no damage beyond increased wear.
Of course, heli's don't always list "max maneuvering speed," you can't ever guarantee you won't exceed 1.2G's, or encounter any turbulence, and the ships were designed with these G loadings more as a transient than a continuous load.
Really though, as others have said, this is all moot. If you fly it over gross, and are caught doing so, the blame for future or current failures will most likely lie on you from the eyes of the victims, employers, and insurers.
Simply stated, maximum gross weight is used to determine component strength and service-life, and rarely has anything to do how much a helicopter can lift.
Unlike fixed-wing aircraft, it’s virtually impossible to design a rotary-wing aircraft using “fail-safe” principles, especially when it comes to dynamic components. For example, try designing a fail-safe pitch change rod. Therefore, helicopters use the design philosophy of “safe-life” components. Safe-life uses the methodology of designing components in such a manner to prevent fatigue failure while in-service. The 2 fundamental elements to safe-life are strength and service-life (time). Generally speaking margins are applied to both elements, however if either element is exceeded, the ultimate result is potential catastrophic failure--maybe not while you’re flying the helicopter, but possibly for the crew after you.
Unlike fixed-wing aircraft, it’s virtually impossible to design a rotary-wing aircraft using “fail-safe” principles, especially when it comes to dynamic components. For example, try designing a fail-safe pitch change rod. Therefore, helicopters use the design philosophy of “safe-life” components. Safe-life uses the methodology of designing components in such a manner to prevent fatigue failure while in-service. The 2 fundamental elements to safe-life are strength and service-life (time). Generally speaking margins are applied to both elements, however if either element is exceeded, the ultimate result is potential catastrophic failure--maybe not while you’re flying the helicopter, but possibly for the crew after you.
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Therefore, helicopters use the design philosophy of “safe-life” components.
. You can still overload the aircraft and then fly it gently and not have any ill effects, in my experience.
You seem to be very experienced as a test pilot.
I have seen an owner/operator cry seeing the bill for the prematurely overhauled transmission.
His credo was:"She's an L3, she'll lift it..."
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You seem to be very experienced as a test pilot.
it's because I'm happy with that statement.
I have seen an owner/operator cry seeing the bill for the prematurely overhauled transmission.
Chopjock,
did you just forget to switch on the irony button or are you just pulling everyones leg?
Could you really be dumb enough to publicly state that you constantly violate rules and regs?
Re-read Jack Carson's post #6.
did you just forget to switch on the irony button or are you just pulling everyones leg?
Could you really be dumb enough to publicly state that you constantly violate rules and regs?
Re-read Jack Carson's post #6.
Avoid imitations
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No But I have owned an Enstrom for over 17 years and put about 1500 hours on her. In the summer there is not enough power to take off much over weight. However when it's cold the power available allows more performance and taking off over weight can be done easier. I absolutely keep her within the power limitations though. When I add a smile it's because I'm happy with that statement.
For example, how do your insurance company, the manufacturer, your maintenance company and the CAA feel about it?
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Could you really be dumb enough to publicly state that you constantly violate rules and regs?
how do your insurance company, the manufacturer, your maintenance company and the CAA feel about it?
The Manufacturer don't want to know unless they are consulted.
The maintenance co. would only be informed if I exceeded Engine limitations etc.
The CAA do not need to be informed unless there is an accident. If I ever broke the ANO I would not ask the CAA how they feel about it.
Does everyone on here weigh their pax before flight?
Is anyone here 100% positive they have never ever taken off over weight?
Gents,
I really wouldn't bother wasting your time with chopjock.
I suspect that he's just a troll. The majority of his comments and opinions on this site seem to be inflammatory in one way or another. I suspect that he just says these things in order to illicit a reaction. Classic troll behaviour.
B73
I really wouldn't bother wasting your time with chopjock.
I suspect that he's just a troll. The majority of his comments and opinions on this site seem to be inflammatory in one way or another. I suspect that he just says these things in order to illicit a reaction. Classic troll behaviour.
B73
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CJ
The problem with exceeding max weight is that there is no way of knowing what, if any effects there will be on the aircraft. Enstrom use many common parts across the range with different maximum gross weight limits. Some of these parts are lifed the same across the range, others are lifed differently or have different inspection schedules. Clearly Enstrom set these parameters for a reason. Going over limit is unlikely to cause any problem in the short term but is russian roulette in the long term because you cannot predict what will fail or when - if anything. The chances of failure are probably slim but you cannot know the full risks.
Do yourself a favour. Buy some scales, if theres any doubt, weigh the pax, calculate your fuel and endurance. If the sums dont add up, dont do it unless someones life depends on it.
Do I weigh them? - Yes if it looks even close.
Edit: check out the life of the main rotor hub plates on a 280 and a 480 - same part, drastically different life.
The problem with exceeding max weight is that there is no way of knowing what, if any effects there will be on the aircraft. Enstrom use many common parts across the range with different maximum gross weight limits. Some of these parts are lifed the same across the range, others are lifed differently or have different inspection schedules. Clearly Enstrom set these parameters for a reason. Going over limit is unlikely to cause any problem in the short term but is russian roulette in the long term because you cannot predict what will fail or when - if anything. The chances of failure are probably slim but you cannot know the full risks.
Do yourself a favour. Buy some scales, if theres any doubt, weigh the pax, calculate your fuel and endurance. If the sums dont add up, dont do it unless someones life depends on it.
Do I weigh them? - Yes if it looks even close.
Edit: check out the life of the main rotor hub plates on a 280 and a 480 - same part, drastically different life.
Last edited by Gaseous; 10th Feb 2010 at 18:11.
Avoid imitations
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Chopjock, You say you don't violate rules and regulations. However, if what you have posted is correct and you are for real (which I do doubt), by operating it overweight you invalidate the C of A of your aircraft and therefore also your insurance. You also compromise your maintenance company, especially the bloke who last signed the aircraft off as serviceable. Believe me, they take that sort of thing extremely seriously.
If you do have an accident, your insurance company will probably deny liability and it would be left to you as an individual, or your estate, to pay damages. I for one don't relish the thought of a wife or kids losing their house over something totally avoidable.
If you do have an accident, your insurance company will probably deny liability and it would be left to you as an individual, or your estate, to pay damages. I for one don't relish the thought of a wife or kids losing their house over something totally avoidable.
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What's the difference between these following examples:
1) Lift at MGTOW and climb out at max performance OAT 15 deg.C and obtain 1600 fpm rate of climb, then cruise at MCP and achieve 85 kts straight and level.
2) Lift at 150 Lbs over MGTOW and climb out at max performance OAT 15 deg.C and obtain only 1000 fpm rate of climb, then cruise at MCP and achieve only 80 kts.straight and level.
3) Lift at 150 Lbs less than MGTOW and climb out at max performance OAT 15 deg.C and obtain 2,000 fpm rate of climb, then cruise at MCP and achieve 90 kts straight and level.
As far as the engine and airframe are concerned, the strain on the rotor head is the same, is it not?
1) Lift at MGTOW and climb out at max performance OAT 15 deg.C and obtain 1600 fpm rate of climb, then cruise at MCP and achieve 85 kts straight and level.
2) Lift at 150 Lbs over MGTOW and climb out at max performance OAT 15 deg.C and obtain only 1000 fpm rate of climb, then cruise at MCP and achieve only 80 kts.straight and level.
3) Lift at 150 Lbs less than MGTOW and climb out at max performance OAT 15 deg.C and obtain 2,000 fpm rate of climb, then cruise at MCP and achieve 90 kts straight and level.
As far as the engine and airframe are concerned, the strain on the rotor head is the same, is it not?
Last edited by chopjock; 10th Feb 2010 at 20:35. Reason: added another example
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Chopjock quote
"What's the difference between these following examples:
1) Lift at MGTOW and climb out at max performance OAT 15 deg.C and obtain 1600 fpm rate of climb, then cruise at MCP and achieve 85 kts straight and level.
2) Lift at 150 Lbs over MGTOW and climb out at max performance OAT 15 deg.C and obtain only 1000 fpm rate of climb, then cruise at MCP and achieve only 80 kts.straight and level.
3) Lift at 150 Lbs less than MGTOW and climb out at max performance OAT 15 deg.C and obtain 2,000 fpm rate of climb, then cruise at MCP and achieve 90 kts straight and level.
As far as the engine and airframe are concerned, the strain on the rotor head is the same, is it not?"
The strain may well be the same, I cant see it standing up in court though.
Surely by that argument "I am not speeding officer because I was driving up hill and therefore I have to use the brakes less if I need to stop !"
"What's the difference between these following examples:
1) Lift at MGTOW and climb out at max performance OAT 15 deg.C and obtain 1600 fpm rate of climb, then cruise at MCP and achieve 85 kts straight and level.
2) Lift at 150 Lbs over MGTOW and climb out at max performance OAT 15 deg.C and obtain only 1000 fpm rate of climb, then cruise at MCP and achieve only 80 kts.straight and level.
3) Lift at 150 Lbs less than MGTOW and climb out at max performance OAT 15 deg.C and obtain 2,000 fpm rate of climb, then cruise at MCP and achieve 90 kts straight and level.
As far as the engine and airframe are concerned, the strain on the rotor head is the same, is it not?"
The strain may well be the same, I cant see it standing up in court though.
Surely by that argument "I am not speeding officer because I was driving up hill and therefore I have to use the brakes less if I need to stop !"