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7 tail on a 6?

gwav8or

Member
Was talking to an RV8OR the other day and they mentioned the possibility of putting the tail of a 7 on a 6. Is this even possible?
 
The standard upgrade is to replace the fin and rudder with that from an 8, not a 7.

Several been done.
 
Considerations ...

The standard upgrade is to replace the fin and rudder with that from an 8, not a 7.

Several been done.

Installed the -8 VS/Rudder on my RV-6A during build. It's one line-item to get all the components, making it easy to order. Adds surface on the VS and rudder. It's 0.020 skin on the rudder. And, it is all factory pre-punched, facilitating assembly. The TE is rolled, not the 'wedge' and it's still possible to get 'curvature' in the TE by rivet sequencing and techniques. (Ask how I know?)

It weighs more than the 'classic' VS/rudder (-6/6A), can't tell you wt or surface area differences but it is more of both. Consideration; if you build a 'light' plane the CG effect may be a factor. My standard FP Sensenich prop, light-wt SkyTec starter, FWF Odessey battery and PlanePower alternator vs a CS prop are factors.

My CG is mid-range to aft CG in almost every load configuration, never in forward range. Keep in mind the potential impact on exceeding aft-CG limits. I'm happy with all the flight characteristics but have no experience with a Classic VS equipped config. I do W&B for all flights and monitor 'weight creep' (junk in the baggage area). Not paranoid or worried but would be aware of it. [Empty 1064 Lbs CG 71.0]

Did NOT offset the VS, straight down the center line. Standard lead weight (per plans) in the rudder, not 'balanced' otherwise.
 
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7 (9) rudder VS 8 rudder

I don?t know if there?s any difference in the 7 or 8 VS, but the rudder is definitely different. I?m building a -7 but I?m incorporating an 8 rudder. So, if the 7 and 8 VS are the same then I?m sure you could choose which rudder you prefer.

The 7 rudder (which is actually a 9 rudder) is larger and will supposedly give you more authority and better spin recovery. The early 7?s came with the 8 rudder but at some point Vans decided that the 9 rudder was more forgiving. How much it really matters in normal everyday flight is above my pay grade, but I haven?t heard of anyone that?s replaced their 8 rudder for a 9 rudder.

I personally like the looks of the slightly smaller 8 rudder and the skins are definitely thicker. Hopefully they?ll be a few people chime in that?s replaced their 9 rudder with the 8 rudder and give a pirep on any differences they?ve experienced in the flight characteristics between the two. Once again, I?m in the building phase, so I can?t give any firsthand experiences yet.

Mark
 
I went down this road. Because of weight (cg), for a -6 you can put an early -7/current -8 tail on it, but not a late -7/current -9 tail on it. Clear as mud? :D
 
I appreciate all the replies. I honestly expected some snarky comments like I normally get in another (Certified Aircraft) forum. So I really do appreciate the replies.

I?m thinking of buying (1-2 years out) an already built 6 and was wondering about the feasibility of replacing the tail with a larger rudder from a 7. Looks like replacing with an 8 rudder is more feasible. Is it possible/feasible on an already flying 6?
 
I appreciate all the replies. I honestly expected some snarky comments like I normally get in another (Certified Aircraft) forum. So I really do appreciate the replies.

I?m thinking of buying (1-2 years out) an already built 6 and was wondering about the feasibility of replacing the tail with a larger rudder from a 7. Looks like replacing with an 8 rudder is more feasible. Is it possible/feasible on an already flying 6?

Yes, but look carefully, it might be exactly the same. Check skin thickness. .016" or .020".
 
I appreciate all the replies. I honestly expected some snarky comments like I normally get in another (Certified Aircraft) forum. So I really do appreciate the replies.

I?m thinking of buying (1-2 years out) an already built 6 and was wondering about the feasibility of replacing the tail with a larger rudder from a 7. Looks like replacing with an 8 rudder is more feasible. Is it possible/feasible on an already flying 6?

I replaced the original VS and rudder on my RV-6 after owning it for a few years. Very straight forward, no complications in installation at all. I didn't even need to modify the empennage fairing (that may have been lucky though).

Cheers,
Bob
 
I have a -7 tail on my -6A. There were no huge differences in the installation. Had to rework the intersection fairing though.
 
Having flown my original rudder -6 for about 10 years now, i'd ask why you'd bother changing the rudder if you didn't have to...
 
My friend just bought an rv6 with a -7 tail on it. We are removing the 200hp, io-360, contant speed prop combo and returning it to the seller. We are building an 0-360 a1d narrow deck engine and prince prop setup for the plane. Can someone with a -7 tail post the w&b numbers for their plane? Hopefully i can get one with a constant speed prop and one with a fixed pitch for comparison. I am trying to work out the position on the battery, elt, etc as we go. My rv6 has a stock .020” metal tail, 0320, whirlwind c/s prop, glass panel, autopilot, flightline interior and 9 lbs dive weight on the alternator. It weighs 1105lbs with a cg index of 71.9”. It is still tail heavy with a pax or bags. I sure don’t need any more weight in the tail.

Left 516
Rgt 511
Tw 78

Total 1105 at 71.9”

I really appreciate the responses.
 
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I just weighed my 6A yesterday. I have an RV-7 tail, wide-deck O-360, Heavy prestolite starter, Catto Prop, flightline Carpet, Classic aero seats. Battery is PC680 mounted on the firewall. ELT is under the baggage floor.

Empty weight is 1068, CG is 72.4"

I will probably add a steel crushplate to help with the CG a bit, that should get the CG to about 71.6". I don't have much baggage allowance at the moment. That Catto prop is just so light...

My friend just bought an rv6 with a -7 tail on it. We are removing the 200hp, io-360, contant speed prop combo and returning it to the seller. We are building an 0-360 a1d narrow deck engine and prince prop setup for the plane. Can someone with a -7 tail post the w&b numbers for their plane? Hopefully i can get one with a constant speed prop and one with a fixed pitch for comparison. I am trying to work out the position on the battery, elt, etc as we go. My rv6 has a stock .020” metal tail, 0320, whirlwind c/s prop, glass panel, autopilot, flightline interior and 9 lbs dive weight on the alternator. It weighs 1105lbs with a cg index of 71.9”. It is still tail heavy with a pax or bags. I sure don’t need any more weight in the tail.

Left 516
Rgt 511
Tw 78

Total 1105 at 71.9”

I really appreciate the responses.
 
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Having flown my original rudder -6 for about 10 years now, i'd ask why you'd bother changing the rudder if you didn't have to...

I agree. The only time it's an issue is slow in a crosswnd.

So up the approach speed and decrease flaps as well as leaving the throttle in a bit.....
 
We have been looking at buying a 6 or 7 already built and flying as well. It is fairly easy to tell if it has the larger rudder, but is there a way to tell if the skin is .02not .016? Did later 6 kits ship with thicker skin but smaller tail? Or are all smaller tails .016?TIA
 
Personally, and I may be prejudiced, but I think the 6/6A with the standard empennage is the best looking RV design out there. As stated above, compensate for x-wind approaches and the size of the VS/rudder is a non issue.
 
Thin

We have been looking at buying a 6 or 7 already built and flying as well. It is fairly easy to tell if it has the larger rudder, but is there a way to tell if the skin is .02not .016? Did later 6 kits ship with thicker skin but smaller tail? Or are all smaller tails .016?TIA

I do not know of a simple test to tell.
Obviously the .016 is thinner....if you could see/feel a sample of both before touching or feeling a rudder you might be able to tell. The main thing to look for on the rudder in a pre-purchase is cracks at the rivets. If they are caused from VS spar misalignment, the cracks would be worse down low and get better higher.
Cracks are not deal killers...just different repairs. Although the misaligned VS issue can lead to more repairs than just re-skinning. Plus may be indicitive of the quality of construction.

Originally the -6's came with the small rudder and .-16 skins.
When Van's found the large rudder from the new-9 worked better on the -7 they also sent larger VS and rudders to the -6 builders....so some later -6 kits have the -7 larger rudders. This is what I think, I may be wrong but close.
FYI--all the rudders work well if built and installed correctly.
 
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Cracks in .016 skins are caused by improper construction technique. Period.
The “big engine” theory was the first “guess” back in the day, but there are way too many of us flying with 180HP and no cracks. If prop wash “beating against the tail” or “vibration” was the cause, it would just be a matter of time before all .016 tails had cracks, regardless of engine size. Cracks typically develop in the first few hundred hours or less and it doesn’t matter what the engine is.
A search on this topic will reveal many discussions, all leading to stress induced by improper construction.

It is very easy to look for this. Lay a straight edge on the control surface. It should lay flat all the way from the spar to the trailing edge radius. If it doesn’t, it wasn’t built right.
This is true for .016 and .020 skins. .020 are just more tolerant of build error.
 
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Jon, while I'm sure I don't have your level of experience, I have a hard time accepting putting a sharp period on your statement and blaming it all on builder error. I'm currently looking at a very well built -6 that easily passes the 'straightedge test', but has multiple cracks in the trailing edge of an elevator, the trailing edge of the rudder, and significantly, multiple cracks around the *leading edge end* of the skin stiffeners. This with <500 hrs on the airframe.

When I look around the rest of the airframe (and most other aluminum a/c structures) I see ribs and other secondary structural elements carried all the way to the primary element (spar, etc), and tied to the web and/or lapped onto the mating structure's flange, with a rivet through all three pieces. Another difference between the control surfaces and the stabilizers, wings, etc is that the two sides are *not* tied to each other by a rib, but can move independently because of the 'untied' skin stiffeners. That combo seems to allow the skin to flex a lot more (relative to other structure's action) around the end rivets of each stiffener. Additionally, there's that longstanding recommendation from Van's to use proseal or other sealant to tie the two sides of the control surface together at the stiffener pairs.

I'd love to have a structures guy weigh in.

Charlie
 
That?s fair Charlie.
There may be, and probably are, more than one factor involved.
If the stiffeners where not tied together with RTV (per the instructions of that period, if the holes where de-burred too aggressively leaving a sharp edge, etc....
I shouldn?t be so emphatic about the induced stress issue. Over the years, the bulk of the Vans ?brain trust? has settled on that being the most probable cause.

I have one small crack that developed mid span on one rudder stiffener. It showed itself within the first 10 hours. 800 hours with no other cracks. I assume I did not properly dress the hole. It isn?t in the typical place where I have seen cracks. The 6 you are looking at has cracks ? in all the right places. ?
 
There may be, and probably are, more than one factor involved.

I agree.

There are many factors that can have an influence on control surface skin cracking. A strong indicator of this is that there are a lot of RV's with a good amount of accumulated flight time that have not had cracks. This is a strong indicator that it is more than just the design not being what it should be. It is true that the control surface design could be more robust. This was done with the RV-10 and 14 but at a rather substantial penalty of additional weight.

Some common causes -

Undesirable level of engine/prop induced airframe vibration

Leading edges that wren't fully formed/rolled to the level they should have been (this puts an excessive preload on the skin just aft of the spar causing cracking to occur at the fwd most rivet)

Trailing edges not fully formed causing a preload in the skin that induces cracking at the aft most rivet.

Lack of the recommended sealant to connect the upper and lower stiffener each other.

Poor prep technique (deburring and/or dimpling... either excessive or inadequate) on the skin rivet holes (those aft holes are a bugger because of the close proximity of the other half of the skin).

I am sure there are others but I am not thinking of them right now.

Add a small influence of a couple or three of these together and you can have a significant enough influence to cause a crack.
 
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With all the unfinished 6 s out there , is there anyone in the Great Lakes area that has one of the 5000 unfinished tail kits laying around? I understand Van sold over 8000 of them and I'm thinking of installing the heavier skin rudder, due to a couple cracks and doing the spar reinforcement on a new HS without losing much down time !
It would be like winning the lottery if there was on one in Canada with a 020 rudder 😀
 
Just another point of reference...........

RV-6, N168TX has been flying since May of 1993 with .016" skins. The original plans did not call for RTV or anything elsa to ty the stiffeners together. This was a later revision. The trailing edges were formed properly and there have been no cracks.
 
Another possible cause for cracks relative to builder error is the inexperience of the first time builder working on the first major kit in the airplane. No experience gained yet and if an error is to be made it could happen in the confined area of the trailing edge of the elevator. You may not fully appreciate the necessity of properly cleaning surfaces before putting that dollop of RTV in there to tie the adjacent stiffeners together. I believe there are more .016 skins flying without cracks, than with.
 
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