Increased Max Gross?

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TJTX

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This discussion has shown me how much I really have to learn about so many things for this build. Its amazing how experienced a pilot can be an how little we can still actually know. I pulled out the structural analysis for the Horizon 2 this morning and realized I am probably best off just building and flying to the tested and published data. But, I would still like to learn and better understand my airframe and the factors affecting it. How would you define the "Design Load". Is the limit the the safety factor built in? Is it the ultimate failure point? The Horizon has a published design load of +4G.
 

Dana

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Is the limit the the safety factor built in? Is it the ultimate failure point? The Horizon has a published design load of +4G.
The problem is that not everybody uses the terms correctly.

The limit load factor is the highest you're supposed to achieve in flight. That's the typical +3.8/-1.5 you hear about for normal category aircraft, or +6/-3 for aerobatic aircraft. Those are the legal minimums for standard aircraft, but the manufacturer may design to higher limits.

Then you multiply the limit loads by the safety factor (1.5 or more) to get the design (or ultimate) load factor. The aircraft must not break anywhere up to the ultimate load, but it may experience permanent deformation (it can bend and stay bent). At the limit load or below, the aircraft must not experience any permanent deformation.

The manufacturer should only be talking about the limit loads. Forget about exploring the safety factor, it's there to cover uncertainties (mistakes) in design and manufacture.
 

Daleandee

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The FAA is not going to check up on you if you fly an experimental over gross, but if you have an accident, you bet the insurance company will look at it, and has a good reason not to pay if you were outside of the envelope.
Marc gave an excellent answer to this but my approach was to tell the insurance company up front, in very clear language, what I had done as far as using an engine that was not a favorite of the kit supplier (I'm being kind folks) and about my gross weight increase.

After a couple of days they came back with an offer and the notes I had sent them about the changes were part of that offer. They thanked me for my honesty and provided liability & hull coverage on my plane at a very reasonable cost with the notes I sent printed on my policy.
 

blane.c

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Marc gave an excellent answer to this but my approach was to tell the insurance company up front, in very clear language, what I had done as far as using an engine that was not a favorite of the kit supplier (I'm being kind folks) and about my gross weight increase.

After a couple of days they came back with an offer and the notes I had sent them about the changes were part of that offer. They thanked me for my honesty and provided liability & hull coverage on my plane at a very reasonable cost with the notes I sent printed on my policy.
My wife is in risk management, it is a mixed bag and depends on circumstances. Lets say you have a daughter, which do you reward most, her boyfriend comes to you and tells you his plans for your daughter ... or ... her boyfriend comes to you and tells you what he has done to your daughter?
 

bmcj

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Do you ask for an engineer, or do you ask for a gypsy woman with the tarot cards?
Since you asked, an engineer can only give you the odds that the next chamber is loaded, but a tarot reader might be able to give you an exact answer. 😂
 

bmcj

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My build has a listed max gross of 1050 I believe, I wouldn't think taking that up to 1150 would be that detrimental?
If you make that change, it has no impact on your performance as long as you don’t load that extra weight.

Remember too that it matters where you put that weight. Extra weight added to the wings is carried by the wings and adds very little stress to the airframe, but still impacts your performance numbers. Also, if for example that extra weight goes somewhere like the cargo/luggage box, it may only be a ten percent increase to the total aircraft weight, but a 200-300% increase beyond the allowable load for the compartment floor. Collapse the cargo floor and you risk interfering with control linkages.
 

Map

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This discussion has shown me how much I really have to learn about so many things for this build. Its amazing how experienced a pilot can be an how little we can still actually know. I pulled out the structural analysis for the Horizon 2 this morning and realized I am probably best off just building and flying to the tested and published data. But, I would still like to learn and better understand my airframe and the factors affecting it. How would you define the "Design Load". Is the limit the the safety factor built in? Is it the ultimate failure point? The Horizon has a published design load of +4G.
Check out my video on "Loads"
 

Vigilant1

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Marc gave an excellent answer to this but my approach was to tell the insurance company up front, in very clear language, what I had done as far as using an engine that was not a favorite of the kit supplier (I'm being kind folks) and about my gross weight increase.

After a couple of days they came back with an offer and the notes I had sent them about the changes were part of that offer. They thanked me for my honesty and provided liability & hull coverage on my plane at a very reasonable cost with the notes I sent printed on my policy.
Good move, Dale. I'm glad it worked out.
I can't figure out why folks would fail to be open with an insurance company in cases like this. Surely it is obvious that the investigators and sharpy lawyers of the insurance company will find a way to wriggle out of paying a claim if you give them an invitation to do that. Why pay premiums for a policy that won't pay off when you need it?
 

BJC

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How would you define the "Design Load".
It is easier to communicate in the standard terms of limit load and ultimate load, and their correlating safety factor.

An aluminum airplane whose structure is designed for a limit load of, for example, +6 g with a SF of 1.5, is also designed for an ultimate load of +9.


BJC
 

edwisch

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If you pencil in a higher gross weight, there are other factors, like, all kinds of performance. And if you pencil in a new aft c.g. limit, you're applying for a Darwin award.
 

Toobuilder

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One thing I will offer a slightly more "educated" opinion on is that 2.5G is definitely not enough of a factor. Unless my old un-calibrated G-meter is way off, I see 2G all the time just driving around straight and level in an old 172...

Don't a bunch of Long Eze drivers live with that limitation every day? I thought that there was a significant G load revision after some structural analysis of customer built airplanes.
 

Marc Zeitlin

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Don't a bunch of Long Eze drivers live with that limitation every day? I thought that there was a significant G load revision after some structural analysis of customer built airplanes.
Varieze's, not Long-EZ's. After a wing attach fitting failure (non-fatal) and multiple instances of wing attach fitting corrosion (I've got a set sitting in my hangar that would scare the crap our of you) on Variezes that live near the coast, the Rutan Aircraft Factory issued a positive 2.5G limit on ALL Variezes, pending an eventual "fix" development for replacing wing attach fittings. RAF never came out with a recommendation for replacing the fittings, so the 2.5G limitation still exists for all VE's, not that most VE drivers pay any attention to it. See:

and:

for more info on the subject.

A few folks that work on canards have been able to come up with processes for VE wing attach fitting replacement, but it's a large job, so if you're paying someone to do it, it's not economical on a plane that's worth between $15K - $25K.
 

Pops

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It is easier to communicate in the standard terms of limit load and ultimate load, and their correlating safety factor.

An aluminum airplane whose structure is designed for a limit load of, for example, +6 g with a SF of 1.5, is also designed for an ultimate load of +9.


BJC
My JMR has a ultimate load of +10.1
 
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mcrae0104

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Good stuff from @Dana. @TJTX, since you're talking about a Horizon, remember that when dealing with wood, it doesn't follow the "bending without breaking" thing quite the same way that metals do because it's not a ductile material.

Aluminum has an "elastic region" where it goes back to its original shape after the load is removed--the upper limit of this region corresponds with the limit load (yield strength). Beyond that, there's a "plastic region" where it deforms further even though little (or no) additional load is applied. The plastic region goes right up to fracture, but it reaches its ultimate strength just before it breaks. Generally speaking, the ultimate strength will be about 1.5x the yield strength (hence the 1.5 you see between limit and ultimate loads). You can learn more about this by reading up on stress-strain curves like the generic one below.

For wood, ANC-18 will list a "modulus of rupture" or Fbu (ultimate allowable stress), which corresponds with the ultimate load when the wood breaks. Then it's up to you to "back out" a factor of safety get back down to a limit load. The stress-strain curve for wood will be different from the one shown below, and also depends on the direction (with respect to the grain) it's loaded and the difference between tension and compression needs to be considered.

1625344434751.png
 

TJTX

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Thats something I did not even think about @mcrae0104 . My plans came with a structural analysis. I don't fully understand what most of the formulas are discussing, but I do know they've been looked at and calculated by Fisher. I will use their numbers and try and find weight savings where I can while building. I believe my engine choice will save a few pounds. Also I'm considering Oratex covering which, from what I've read, is lighter than the Stewart System? Plus keeping the interior simple should help. And at roughly 500 lbs useful load, I'm realizing it's not too far off anything comparable and in my price range.
 

Lendo

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Marc, did you ay any time discuss this the original designer/Company and ascertain the effect on SF and G factors. I'm sure there are things like Stall Speed etc. you can safely test for, but strength wise, perhaps not. I'm wondering where that's accounted for in the overall scheme of things. Perhaps the weight is negligible overall?
George
 

rv7charlie

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We obviously don't know each other, so I don't know if this will apply to your specific situation. But for 'average' US builders, the quickest path to improving payload is for the builder/pilot to avoid fast food, etc. Just about any of us could stand to lose 10-15 lbs, and some of us could just about double available payload by putting *themselves* on a weight reduction program. Virtually free weight savings, and reduced medical bills, as well. :)

Charlie
 
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