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How structural are the baggage bulkheads?

Ed_Wischmeyer

Well Known Member
Most of us, I suppose, are tired of unscrewing and re-screwing all those stupid screws on the two piece baggage bulkhead at condition inspection time -- especially if you're old and stiff and the hangar is hot in the middle of the summer. One "solution" is a one piece honeycomb bulkhead that would be stiff enough that only a few screws would be required to hold it in place.

The question, though, is how structural is the existing bulkhead? No surprise, Van's says that it is structural, end of discussion, but my eyeball engineering doesn't get it. Seems to me that with the horizontal creases in the aluminum, those bulkheads wouldn't carry any vertical loads. Similarly, it would seem that those bulkheads would only carry lateral tension loads, not compression loads. And there is the T shaped structure immediately behind the bulkhead...

Yes, we all have opinions on this, but do any structural engineers have observations on the topic? Please, no pontifications on what to do and what not to do.
 
A primary function of bulkheads like those is to carry shear that develops when the fuselage is twisted. Thus they are structurally important for torsional stiffness.
 
The standard Van's Aircraft position is that the baggage bulkhead panel is structural on all models and should be installed, with all fasteners, for flight.
 
So I talked to a knowledgeable friend not on VAF...

He relates an RV that flew, poorly, with the baggage bulkhead removed. And an RV-8 that had obvious torsional inadequacy with a forward fuselage bulkhead removed.

I don't understand either of these phenomena, but I'm looking forward (sort of) to many more sessions of screwing and unscrewing...

One thing that helps access is that the right side control stick is easily removable.
 
The standard Van's Aircraft position is that the baggage bulkhead panel is structural on all models and should be installed, with all fasteners, for flight.

The question I have, Scott - is the corrugated version critical? For those that want to install air conditioning, it would be great to have a flat sheet there so that you dont have as much air be pulled through the tailcone.
 
Think about it this way: how flimsy would a beer can be if you cut the end out of it.

Since the baggage area cover fastens onto a bulkhead which is essentially a circular C channel, I don't understand how this point is relevant. The bulkhead already has a bunch of metal to help it maintain its shape.
 
What effect would having a baggage tube opening (like some other aircraft) have on the panel?

The tube would be for things like pillows and sleeping bags that are light but voluminous..........
 
EZ

1-Cordless screw driver
2- change your Annual CI to March or April when weather is cooler and flying limited.
 
It seems like a one piece honeycomb bulkhead would provide adequate torsional stiffness, similar to the designed panel with horizontal stiffener bends, but those loads are carried through the circular fuselage bulkheads via all those screws. It you want to replace the light weight bent bulkhead panel, you still need all those screws to carry that load that is fractionately shared by each screw. Maybe that’s why they are #8 vs #6. Just my guess - I’m no Steve Smith.
 
The corrugations raise the shear buckling strength compared to the flat panel.

The bulkhead alone, with no panel, carries much less shear since it doesn't fill the open area. It has much less shear resistance than the corrugated panel.

In this case, if you don't understand "shear" in this context, think "twisting," and it's a lot easier and nearly as accurate.

Yes, properly designed, a honeycomb sandwich could be designed to do the same job. The designer would have to replace both the current shear strength and the shear stiffness. Even then, the honeycomb panel would need the same fasteners at the same locations. The weight might or might not be the same. The chances of it being greater are probably the same as the chances of saving weight there.

The panel might be important to flutter resistance. And it would be sad to find that out the hard way.

Dave
 
The question I have, Scott - is the corrugated version critical? For those that want to install air conditioning, it would be great to have a flat sheet there so that you dont have as much air be pulled through the tailcone.

The position is and has been that it is structural. The panel needs to be installed with all screws.

IF I wanted Air Conditioning and needed to seal the bulkhead, I would be looking at some sort of foam to fill the corrugated triangles to block airflow without adding much weight. With AC, one will still need some outflow of air. Not sure AC would work well if there was no exit for the cold air to blow in and hot air to go out.

Been using a power screwdriver / screw-gun since airplane was built back in 1997. I also have NEW screws in stock and replace any that are getting bad each time I remove / reinstall the panels.
 
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Use torx screws

These might help make it easier/faster to remove/replace the screws.

https://www.microfasteners.com/sbxs0806-8-32-x-3-8-button-head-screw-6-lobe-drive-stainless.html

SBXS-02.jpg
 
structural or not structural

The aircraft designer says it is structural, probably won't get any more plus or minus from the aircraft designer.

If you want to replace it with something else - your call.

It's an EXPERIMENTAL cat airplane. Stay away from making it an EXPERIMENT.
 
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I agree that it is a royal pain: The seat support and canopy (on a slider) make access cery difficult. But it is a necessity, and only comes once a year. I leave my top pannel in and only remove the bottom section (6A slider).
 
Since the baggage area cover fastens onto a bulkhead which is essentially a circular C channel, I don't understand how this point is relevant. The bulkhead already has a bunch of metal to help it maintain its shape.

The beer can example is completely relevant. You are being confused by thinking that since the baggage hoop is similar to the other open bulkheads further back in the tail that it is enough by itself.
Conceptually and topologically the RV baggage fuselage including the hoop is the same as an open topped container. If not a beer can, imagine a cardboard box with an open top vs folded closed and taped. Yes, the RV hoop adds some stiffness over and above the fuselage skin without the hoop, that could be likened to the above box with very short flaps that don't meet in the center. Closing the short flaps on that box does not make it very much stronger. It can still be twisted with ease. A closed panel will add a LOT more shear strength. You have been told by multiple engineers plus a report of anecdotal evidence that the panel is structural. If you wish to research this on your own, bone up on math and get some technical books on Statics, Structures and Materials.
 
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I agree that it is a royal pain: The seat support and canopy (on a slider) make access cery difficult. But it is a necessity, and only comes once a year. I leave my top pannel in and only remove the bottom section (6A slider).

Remove the canopy for better access. Two bolts in the rollers, and slide the canopy off the aircraft to the rear. It takes a minute or two and saves a lot of wear and tear on YOU during the inspection.

I have a piece of plywood cut to match the baggage floor and stand/keel on that to remove the baggage compartment bulkhead, flap mechanism covers, etc.
 
The DER says...

One of my friends is a DER for structures and flutter, and has worked on the RV-9A with me. He gave me some good info without any snarky comments...

He estimates that the corrugated pieces behind the baggage area are good for about a 50% increase in shear. While the same effect could be achieved by making the bulkhead itself stouter, that would be heavier. And as we discussed, my motivation for asking the question had to do with reducing the number of fasteners to improve access.

The Torx head screws will solve the occasional problem of a recalcitrant Phillips head, but my main problem is reaching the stupid things. Another friend suggested a flex coupling. We might try removing the canopy next time, but the doesn't seem to be a one man operation.

Thanks for the good ideas.
 
A 12" extension bit in your electric screwdriver would help with reach, although only for extraction... Insertion will still require you to reach in there. I struggle with this too, and have a tip-up. I dont' think removing the canopy is going to help that much, you'll still end up kneeling on the seat cushions and hanging over the baggage cross-beam to get back there. I find the easiest is to remove the seat backs and place a pad on the cross-beam... Then it's comfortable to lay on while reaching for the screws.

I switched to hex-head stainless screws a while ago, but the round-head bolts only have a 2.5mm hex drive... After stripping one I switched back to cadmium-plated phillips-head screws.
 
Yep, power screwdriver is a must. I end up heavily padding the crossbar behind the seats with towels so it's not too uncomfortable to lean against during this part of the annual. Having long arms helps!
 
Pillows!

Remove the canopy, remove the seats and kneel/lay on a bunch of cheap pillows kept in the hangar just for this. The pillows are also helpful when kneeling on the wing (under your knees) and draped over the side when doing something on the panel or floor. With the canopy off, you can reach most of the screws standing on a stool and leaning in over each side.
 
OK; just reinstalled the baggage bin bulkhead today in the RV-6A. Did it all with both feet on the hangar floor. Tools used were a screwdriver with a lightly magnetized tip and a cordless drill with a magnetic bit holder in the chuck. Screws were started by hand or with the screwdriver and run in with the cordless drill.

The canopy had been disconnected at the front, and slid back with a pillow underneath to cushion the fuselage from the canopy lock. As the rear guide came off the track, another pillow was placed under the rear of the canopy. No need to lift the canopy off the airplane. This had been done to install the Supertracks canopy track extension. Next time around, I'll see if it can be done nearly as easily with the canopy in it's new full aft position.

I've been using Phillips CCP2205 P2 Power Bits https://www.boschtools.com/us/en/boschtools-ocs/power-bits-ccp2205-30140-p/ for a few years.They feature a ribbed tip (ACR - https://phillips-screw.com/drive-system/acr-ribbed ) that they claim allows 50% more torque before camout on the fastener. I've had much better luck removing screws without destroying the screw heads using these bits.

Cheers, David
RV-6A KBTF
 
The canopy had been disconnected at the front, and slid back with a pillow underneath to cushion the fuselage from the canopy lock. As the rear guide came off the track, another pillow was placed under the rear of the canopy. No need to lift the canopy off the airplane.

Exactly what I do for a -9A slider. I find these torx button heads are the bees knees: https://www.mcmaster.com/93701A408
 
...

I've been using Phillips CCP2205 P2 Power Bits https://www.boschtools.com/us/en/boschtools-ocs/power-bits-ccp2205-30140-p/ for a few years.They feature a ribbed tip (ACR - https://phillips-screw.com/drive-system/acr-ribbed ) that they claim allows 50% more torque before camout on the fastener. I've had much better luck removing screws without destroying the screw heads using these bits.

Cheers, David
RV-6A KBTF


ACR bits are the only thing I use on airplanes.
 
Remove the canopy, remove the seats and kneel/lay on a bunch of cheap pillows kept in the hangar just for this. The pillows are also helpful when kneeling on the wing (under your knees) and draped over the side when doing something on the panel or floor. With the canopy off, you can reach most of the screws standing on a stool and leaning in over each side.
Unfortunately, three spinal surgeries have limited my flexibility and ability to do normal things, like leaning in. Hopefully Doug's and all the other comments will help folks who don't have physical limitations like mine.
 
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