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What does a H Rocket or F1 do here? (Re: Vertical Stabilizer Strength)

BillL

BillL

Well Known Member
We have had three (or more) VS separations and it seems to fail at the forward spar and then the rear spar gets peeled off. The structure above the red line is stiffened by the .032" skin, and below it is doubled up with the adapted to the fuse horns and HS spar connection. But it is "least strong" along that red line. The 702 spar is .032 material.

Does the Rocket make any modifications in this area?

Lets not get into why all this happens, or any speculation. Just stick to the technical question and it will be over quickly.
Screen%252520Shot%2525202016-01-10%252520at%2525207.40.38%252520AM.png
 
Depending on the builder, there may be no additional reinforcement, or up to a 1/8" thick doubler that attaches the HS to the VS spar. Or variations in between.

Depending on the builder, the top deck (F415, if I recall) may be thickened and/or extended further forward.

Depending on the builder, there may be additional, or larger, attach bolts used.

Depending on the builder, the longerons may be upsized to 1" x 1" x 1/8" material. (Why Van's doesn't make this simple change is beyond me.)

There can be many other tweaks back there. And as many opinions on how to do them as there are bellybuttons among this group.

Please note: I'm not an aero. engineer, nor did I stay at a Holiday Inn Express last night. Just a Rocket builder. Others may have additional info.

YMMV! Use at your own risk!
 
vfrazier said:
Depending on the builder, there may be no additional reinforcement, or up to a 1/8" thick doubler that attaches the HS to the VS spar. Or variations in between.

Depending on the builder, the top deck (F415, if I recall) may be thickened and/or extended further forward.

Depending on the builder, there may be additional, or larger, attach bolts used.

Depending on the builder, the longerons may be upsized to 1" x 1" x 1/8" material. (Why Van's doesn't make this simple change is beyond me.)

There can be many other tweaks back there. And as many opinions on how to do them as there are bellybuttons among this group.

Please note: I'm not an aero. engineer, nor did I stay at a Holiday Inn Express last night. Just a Rocket builder. Others may have additional info.

YMMV! Use at your own risk!
Click to expand...

Thanks Vince, I appreciate the sharing - definitely would investigate any change in depth. The 7 is already a bit tail heavy. I had already heard about making the rear deck plate .050". If I win the powerball a dynamic test will be commissioned to get the the bottom of this. Just entertainment and puzzle pieces for now. It seems the 1/8" connector to the HS does extend up above the red line on the drawing.
 
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Analysis

Seems like I recall that years ago an analysis was done on the tail and determined that the area needed to be reinforced. Maybe it was the Evo engineering folks in the Czech, not sure. Never saw the report, only hearsay. I think I stumbled across the info here on VAF.

Bill, if you run across any drawings or sketches, please share if it's permissible. I'm aways interested in this discussion.
Cj


BillL said:
Thanks Vince, I appreciate the sharing - definitely would investigate any change in depth. The 7 is already a bit tail heavy. I had already heard about making the rear deck plate .050". If I win the powerball a dynamic test will be commissioned to get the the bottom of this. Just entertainment and puzzle pieces for now. It seems the 1/8" connector to the HS does extend up above the red line on the drawing.
Click to expand...
 
Here is the VS structure on my Rocket, you can see the doubler on the forward spar. This was built as per the plans (well, the conduit wasn't in the plans).

VFin%20structure%20(800x528).jpg
 
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SMO said:
Here is the VS structure on my Rocket, you can see the doubler on the forward spar. This was built as per the plans (well, the conduit wasn't in the plans).

VFin%20structure%20(800x528).jpg
Click to expand...

That is a great idea....to bad I didn't see this six years ago......I would have mod mine.
 
SMO said:
Here is the VS structure on my Rocket, you can see the doubler on the forward spar. This was built as per the plans (well, the conduit wasn't in the plans).
Click to expand...

Thanks, Mark, does it have the taller, thicker doubler on the aft side too? Does your paperwork with the thickness of each?
 
Yes, it has a taller double on the other side of the forward spar, extends up to the middle rib. If you look closely you can see the rivets attaching it. I don't have the documented thickness of these doublers but I believe they were .090.
 
what are the specifics of the 3 failures? These airplanes can pick up speed easily and exceed their envelope. If the airplane was way above Vne and the fin came off during an abrupt maneuver there is no need to rush out and beef it up. If the wings folded way above 9g would we all go out and beef up the wing spars? The flight limitations exist for a reason. I do know of one of the accidents, the Canadian one, and the airplane was going too fast and was over stressed or the fin fluttered. The damage looks like flutter, but it could have fluttered after an over stress and the failed surface did not have any flutter margin following the failure. There is just no way to know and at the end of the day it doesn't really matter. The envelope was exceeded and it failed. Are the other 2 failures similar in nature?

Remember the Vtailed bonanza - the vtail was fine - the issue was that it was too easy for inexperienced IFR pilots to overspeed. They called it the fork-tailed Dr killer.
 
sblack said:
what are the specifics of the 3 failures? These airplanes can pick up speed easily and exceed their envelope. If the airplane was way above Vne and the fin came off during an abrupt maneuver there is no need to rush out and beef it up. If the wings folded way above 9g would we all go out and beef up the wing spars? The flight limitations exist for a reason. I do know of one of the accidents, the Canadian one, and the airplane was going too fast and was over stressed or the fin fluttered. The damage looks like flutter, but it could have fluttered after an over stress and the failed surface did not have any flutter margin following the failure. There is just no way to know and at the end of the day it doesn't really matter. The envelope was exceeded and it failed. Are the other 2 failures similar in nature?

Remember the Vtailed bonanza - the vtail was fine - the issue was that it was too easy for inexperienced IFR pilots to overspeed. They called it the fork-tailed Dr killer.
Click to expand...

Two of these have been hashed out here as far as it was allowed. You should search and find/read them for all the nuance. Look up the accident reports and read every page and study each picture and graph. That is all for this forum.

I just wanted to know that the Rocket world is doing as they are RV based (even if a lot of parts are different) and exceed the speeds indicated in the accidents, thus the comment to focus on the question in the OP for a factual technical discussion.
 
sent you a PM

HI Bill,

I just sent you a PM on this subject, but just to note, On the RV-8, the attachment bracket that attaches the forward fin spar to the horizontal stab spar (F-681) is 0.063 thick. (ref RV-8 plans). The fin spar is 0.032 thick, but it has the flanges on it. So it turns out that the attachment bracket has 86% of the bending strength of the fin spar.
conclusions and speculations are in the PM
 
scsmith said:
HI Bill,

I just sent you a PM on this subject, but just to note, On the RV-8, the attachment bracket that attaches the forward fin spar to the horizontal stab spar (F-681) is 0.063 thick. (ref RV-8 plans). The fin spar is 0.032 thick, but it has the flanges on it. So it turns out that the attachment bracket has 86% of the bending strength of the fin spar.
conclusions and speculations are in the PM
Click to expand...

Thanks, I looked at the reports, and it appears (no good photograph of this area) that these two failed the .032 at the upper three rivets that attach that .063 lap plate, not in the plate itself. Regardless, dual doublers like the photo above with 2x .090 extending up a foot, is substantially stronger and stiffer. I have not heard the early Harmon Rockets did this, but did use the smaller 6/8 rudder, and don't have the speed of the Evo.
 
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Dual doublers

Thinking out loud, wouldn't dual sandwitch doublers hinder inspection of the spar especially that third row?


BillL said:
Thanks, I looked at the reports, and it appears (no good photograph of this area) that these two failed the .032 at the upper three rivets that attach that .063 lap plate, not in the plate itself. Regardless, dual doublers like the photo above with 2x .090 extending up a foot, is substantially stronger and stiffer. I have not heard the early Harmon Rockets did this, but did use the smaller 6/8 rudder, and don't have the speed of the Evo.
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REAL answer: it depends!

There is more to this answer than I can explain here, but keep in mind that the Czech engineer that helped design the F1 was looking hard at FAR 23 Cert numbers when he made changes to the design. The standard doubler on the F1 fin fwd spar is .125 2024T3. The attach plate on the h stab fwd spar is also .125 2024T3. The h stab has 2 1"X1" 6061T6 angles centered on the front spar, and a 1"x1" 6061T6 angle in the fuselage as an attach point. All empennage spars are .040 2024T3.

The Evo design added a second .125 2024T3 doubler to the fin fwd spar, and some H Stab spar 'additions'.

There are many more changes to the empennage in the Evo design - yes, it was designed for a 240KTAS Vne, but with more margin than the Sport wing version (same Vne). I own that margin - it is not for public consumption.

The Evo RG version I am working on now has yet more changes to this area, including a 4130 attach bracket where the fwd spar of the fin attaches to the H Stab fwd spar. The aft fuselage is also reinforced. Formed skin stiffeners are added to both the fin and the H Stab....and so on.

What many do not consider in their thinking is gust loads. Run the speed up a bit, and the stress of gust loads begin to force changes - in both structure and attach points.

Some of you have suggested a more robust fin fwd spar attach bracket - adding a stiffer attach bracket to any design might not help unless you also look at the parts the bracket is attached to, and the fasteners that are used in that area. Think 'system' when making changes such as this.

Personally, I have never seen an idea that is so good that I can't copy it - DanH comes to mind there. On the opposite side of that coin, there has also never been a situation so bad that I could not make it worse! In any case, you all are welcome to use any ideas I have to 'help' with your aircraft - they are, after all, experimental. Note: you must disclose any design changes to your DAR at the initial inspection.

260KTAS is not friendly territory. Your machine had better be up to the task at that speed, as one bump can cause things to go awry very quickly. I can show you the leftover parts if you want a small example; I am very lucky to be here to type this.

Carry on!
Mark
 
I do recall reading the report on one of the Rockets. There were numerous comstruction errors. It's hard to believe but the forward vertical spar was NEVER bolted to the horizontal spar. There were other vertical or horizontal mounting bolts missing as well. Not just missing bolts. There were no holes drilled for the bolts.
If you push an airframe to or above redline then you are truly a test pilot and need to treat every flight as a test flight. At least provide a parachute for your passenger so he/ she will stand a chance when things go badly.
 
Forward Spar?

R. Daniels said:
I do recall reading the report on one of the Rockets. There were numerous comstruction errors. It's hard to believe but the forward vertical spar was NEVER bolted to the horizontal spar. There were other vertical or horizontal mounting bolts missing as well. Not just missing bolts. There were no holes drilled for the bolts.
If you push an airframe to or above redline then you are truly a test pilot and need to treat every flight as a test flight. At least provide a parachute for your passenger so he/ she will stand a chance when things go badly.
Click to expand...

If you're referring the the accident that I'm thinking of, I don't think it was the forward spar that was left unbolted. The builder neglected to install the angle the attaches the rear VS spar to the top of the rear deck/upper longerons. Then the family sued the aircraft designer claiming that the plans didn't make it obvious enough that the angle was a critical component and couldn't be omitted. Unbelievable! :mad:

Skylor


***EDIT*** I just reread the accident report and realized that the builder left out the rear upper attach bracket as I stated above AND did not drill for the forwar spar attachment fasteners either. This is far more egregious than I previously realized. The fact that this aircraft was able to accumulate any time at all before failure seems amazing.
 
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Thanks Mark!

Thanks for the information. I guess the 4 digit parts are the added EVO parts?

Also, is the HS-009 also 1/8" 2024 T3? It looked thicker on some DocThrock's website pictures.

BTW: I won't be making these mods for matching the F1 speed. I was curious what was reinforced to reflect what might be weak on the standard.

That rocket accident report was just as poor as the plane construction. It makes me think all the fasteners in the HS/VS fairing might have a structural purpose:eek: (JOKE)
 
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