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Empty W&B CG Range

Jvon811

Well Known Member
A friend/neighbor is getting close to first flight with his RV-8. Doing the W&B and lining up a DAR.

The empty W&B came out to 1118lbs and 77.4". IO-360, Hartzell C/S prop, nothing crazy.

The DAR says that it's too far forward (Van's published range is 78.7"-86.82" inches aft of datum) and is saying that weight needs to be added to the tail to bring it into range before he'll sign off on it.

Isn't that the CG range is for a loaded, ready to fly airplane, not the empty? For example, by this thread here, many of the posters are forward of the CG limits according to this particular DAR and he wouldn't sign them off.

Even on the EAA's website, in the "Building Articles" section, the example aircraft (an RV-8 fortunately) is forward of the limit when empty. Scroll about 3/4 of the way down this page.

My neighbor is going to call into Van's on Monday for the official word.
 
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CG only means anything for stated conditions. Here creating a table of examples is the best way to demonstrate the CG and total weight will be in spec. Examples include:
- Solo, full fuel and empty
- Pilot and passenger, with baggage, full fuel and empty
- Pilot and passenger, with baggage at gross.

I keep this table in my POH so if ever ramped checked and ask “where is your W&B for this flight” I can just point to the examples.

Carl
 
You are correct. The allowable CG range is for the purpose of flight not what the empty CG is. I suggest that your friend do a couple of sample scenarios showing the worst case load situation at each end of the CG range. Example… Do one for a very light weight pilot and full fuel tanks, and another with a lot of baggage and heavy passenger in the rear at maximum gross weight. These will show where the CG position will be for flight at the opposite extremes of possible load conditions.
I can’t help but wonder about the thoughts this DAR has, and whether he has an understanding of what adding ballast weight at the extreme aft end of the tail can do regarding other performance factors. Changing the CG is not the only influence it would have. I’m not saying it would for sure have a negative impact, but it could.
 
Thanks for the quick replies. 3/3 (so far) for verifying our thought process...

I'm not a DAR nor am I that acclimated with their manuals for signing airplanes off (yet), but it was related to me that this DAR was describing two types of CG ranges for certification (empty and loaded) and Van's published CG ranges "Takes that into consideration" so therefore the empty CG must be in their published range...

I'm still scratching my head on where he's getting that info from...
 
I'm still scratching my head on where he's getting that info from...

I have no idea because it’s not from anything published by us.

With as many RVs as get certified each year I would be surprised if this was this DAR’s first, so I hope he hasn’t been forcing people to ballast their airplanes for an empty CG adjustment to land within the range.
 
One thing more: the aircraft should always be within cg in flight. With my -10 that means checking the cg anticipated at landing, as it can move past the limits as you burn gas.
 
Wow, how can DAR make that kind of mistake?

Here is a W&B for my RV-8. Note that the BEW is 1108.2 pounds with a CG of 78.08". And that is forward of the forward limit of 78.70", and as others have said, this perfectly OK.

i-wdbD9g7-L.jpg


This may help with the DAR. Below is page 14-4 from the Van's RV-8/8A Construction Manual. Note that in their W&B sample calculations, the Empty Weight CG of 76.26" is well forward of the forward limit. Have your friend show the DAR the pages of Van's sample W&B calculations from the Construction Manual (Samples 1 through 5). Of course, your friend will have some W&B examples for his particular airplane.

i-hxDWzCf-L.jpg
 
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The airplane will never be flown empty, so the empty CG numbers are meaningless for flight. They serve only as the baseline from which you derive the flight condition. The crew, fuel and bags are the "ballast" that brings the aircraft into the correct CG range.

Time to find a new DAR. If he cant get this right, I'd question every other decision he's made in the inspection. How is he even qualified to be a DAR?
 
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How can a DAR have such fundamental misunderstanding of something so basic? That would be like a DPE not understanding how stalls work...
 
I sure hope the OP reports back on this one.

Since he is saying, what his friend is saying, that the DAR said....I like to think it's some kind of miscommunication. I sure hope so anyway. Otherwise, things are even more broken with the DAR system than I had thought.

You guys that have built your own airplanes (good on you!) have a clear understanding of W&B but I'm often surprised at the level of ignorance on this subject with the general pilot population. There doesn't seem to be much critical thinking. Plug a bunch of numbers into an app and except the results (whatever they may be) seems to be the prevailing mindset these days.

Again, I hope it's a simple misunderstanding.
 
The airplane will never be flown empty, so the empty CG numbers are meaningless for flight. They serve only as the baseline from which you derive the flight condition. The crew, fuel and bags are the "ballast" that brings the aircraft into the correct CG range.

+1, best reply here…
 
I will report back when I do learn more information.

It is not my intent to smear a DAR or start anything on the internet. I'm not even sure of this person's name. My neighbor has gone several email rounds back and forth with this person and they still insist the Empty CG must fall within the published limits. So when my neighbor came to me asking if I thought this could be correct, I said no. It was always my understanding that the Empty CG Arm wasn't subject to Van's published CG Range.

But then again, I'm not a DAR so I could have been wrong. It's happened only once before, and don't tell my wife...
 
There are so many light aircraft that can't possibly fall within the "flight" CG limits without crew that it boggles the mind to think this guy is sticking to this. Gliders, canards, any pusher... ****, even my L-39 jet is so far out of flight limits without the meat servos aboard.

This is basic Airman Certificate knowledge stuff. How is this guy a DAR?
 
Years ago , I went thru same situation with inspection by FSDO, HAD TO ADD
40lbs to tail of my RV 4 for him to approve! AS SOON AS I GOT A/W CERTIFICATE
and he left, it immediately came out before flight on advice of my IA !
 
Part 91.9 requires you have the weight and balance information on board the aircraft which includes the weight and moment AND the approved envelope of the aircraft. It also is prohibited to operate without complying with the operating limitations.

The DAR may be technically correct that an empty plane would be operating outside the limitations…..if it were a drone…..but it isn’t.

Out of curiosity, what is the minimum weight that the pilot must be with empty fuel tanks to be in the envelope?

Perhaps that limitation could be listed on the weight and balance page of the POH to satisfy the DAR. If it does, then everyone is happy.

Of course that probably means your 2 year old may not get to solo even when he throws a tantrum.
 
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DAR vs FAA

A neighbor used the FAA and I was there to help. It went great, was free and he even did the Repairmans Certificate at the same time. On Wednesday the FAA is going to do my single seater just finished. (Very simple pop rivet airframe). Not that DARS are not ok to do this but what’s the apprehension with using the FAA? The last 5 years of interactions have been great. For W&B he asked me to show him 3 scenarios. One as far aft as reasonable one as far forward as reasonable and conditions that showed one in the middle. His program letter he sent me for the passenger warning had a note “not needed for single crew operation”. Seems very reasonable and emails and calls was very helpful.
 
A neighbor used the FAA and I was there to help. It went great, was free and he even did the Repairmans Certificate at the same time. On Wednesday the FAA is going to do my single seater just finished. (Very simple pop rivet airframe). Not that DARS are not ok to do this but what’s the apprehension with using the FAA? The last 5 years of interactions have been great. For W&B he asked me to show him 3 scenarios. One as far aft as reasonable one as far forward as reasonable and conditions that showed one in the middle. His program letter he sent me for the passenger warning had a note “not needed for single crew operation”. Seems very reasonable and emails and calls was very helpful.

Absolutely no problem at all having the FAA do the certification.

The major difference is that DARs are more experienced and typically perform a pretty detailed inspection. The FAA is primarily interested in compliance with the 51% rule.

For example, out of 1,083 certifications, I have found only 3 where I didn't find discrepancies of one kind or another. If you have a discrepancy would you rather find it in the hangar or in the air?
 
Not that DARS are not ok to do this but what’s the apprehension with using the FAA? .

1. Some but not all FAA inspectors have a reputation of being more interested in paperwork than actually inspecting the airplane.
2. More common, the FSDO claims they are overworked, can’t spare anyone.

True story: in early 2011 I called my fsdo, tried to set an inspection appointment 6 months out for my 10. They said, ‘Call back when you’re within 2 months.’ Four months later I called again, they said, ‘We’re too busy. Hire a DAR’. They gave me a few names. Hired one, he was very reasonable and helpful. One year later, my hangar-neighbor finished his 10. He called the FSDO, they ssid ‘Hire a DAR’. He replied that he wasn’t able to find one. He was put on hold, then the FSDO came back on, said, ‘We can’t find anyone either. We’ll send someone out.’ Who shows up? My former DAR, who is now a new FSDO employee. Exactly the same inspection, except now he can also sign off the limited repairmain application, plus, of course, it was free.
 
Absolutely no problem at all having the FAA do the certification.SNIP....

Good luck with that. My local FSDO did my first two builds but for the third they made it clear to me that I had to use a DAR, as in they no longer did it.

Carl
 
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