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RV-14 rudder on RV-7 VS?

mburch

Well Known Member
Patron
My rudder didn't manage to make the cross-country move, so I need to build a new one for my RV-7 project.

Previously I had the RV-9 style rudder with "floating stiffeners" that were not secured at the trailing edge except for a blob of RTV. The new style of rudder construction, introduced with the RV-10 I believe, has the rudder stiffeners riveted together at the trailing edge and joined at the leading edge with a "shear clip", basically turning them into built-up ribs. All else being equal, this seems like a better design, so I'd prefer to build this style of rudder for my 7 if it's possible.

The RV-14 uses this style of rudder construction, and - judging from this builder's photo of the plans - all the parts used in the RV-14 rudder have R-6xx and R-9xx part numbers. So that leads me to believe I could build an RV-14 rudder and it should just bolt on to my RV-7 vertical stab.

Anybody have any better knowledge of why this wouldn't work?

thanks,
- Matt
 
Matt, I have two, count 'em, two RV-7/9 rudders, one has flown. If you're somewhere near Boise, let's talk. I prefer the original 8 rudder on the 7s so these are left overs from kits I've bought 2nd hand.

John Siebold
 
Thanks John - I was actually looking forward to building a new rudder in order to incorporate a few personal touches, but I'll keep it in mind.
 
I did build a second rudder when I got a ding on each side of my rudder due to wind. At the time I tried to tie the stiffners together and it was going to be my own making but it was not easy so I settled for the original.

Now that I have built a 14, I really like how they tie together and if you can use the same stiffners of a 14, I believe it would make it much easier and better.
 
My rudder didn't manage to make the cross-country move, so I need to build a new one for my RV-7 project.
thanks, - Matt
You are over thinking it. I built two RV-7 the very first early small one and the larger one. RV-7 rudder is fine in my opinion. Talk to Van's.
 
Thanks for sharing your opinion. Still hoping someone can answer the question - are the RV-14 and RV-9 (and thus RV-7) rudders the same or different?
 
Thanks for sharing your opinion. Still hoping someone can answer the question - are the RV-14 and RV-9 (and thus RV-7) rudders the same or different?
Call Van's Aircraft Monday is my advice/suggestion. My opinion is you might not get an answer for one or more reasons..... like no one has tried it or it will not fit.... You will be the trail blazer (call Van's).

I assume you are concerned about rudder cracking at the most aft stiffener rivet? Not familiar with RV-9/-10/14 rudders with floating stiffeners or shear clips..... Sounds complicated. I can tell you on the RV-4/6 and early RV-7 rudders, the trick is to extend the stiffener flange common to rudder skin as far back as possible and rivet as far back so you can, while still being able to dimple and buck/squeeze rivet. It will never crack and no blob needed. You have to trim the upstanding angle flange to clear the opposite side of the rudder skin. Early builders left the stiffeners a full inch or more short of TE, to make riveting easier.... The skin would flex around the most aft rivet and crack. I had 900 hours on my RV-4 before I sold her, no blobs, no cracks, and I flew aerobatics, rough fields and raced it.

The "new and improved" RV-10 or RV-14 rudder may have issues yet to be discovered over time.... Cheers
 
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One "Ask Vans" data point on the -14 rudder

Matt,

I saw the same connections as you did between RV-9/10/14 rudder parts and was wondering the same thing. So when I was at the Vans factory in late June, I asked Sterling Langrell if they had thought of retrofitting the -14 rudder to the -7 and -9.

While he didn't (and couldn't, for obvious reasons) say it's ok, he also hinted that it should work. That's obviously not enough to base a decision on but it would be interesting to press Vans on the subject.

Based on other VAF threads and careful reading of several RV-7 accident reports that involve overspeed and tail separation, I don't believe Vans has the flutter margin they think they do in the larger -9 rudder - although I'm happy to be proven wrong with evidence to the contrary. Only Van's knows why the -10/14 rudder structure changed, but it does seem to be a stiffer design and I'd definitely like to know more about using it on a -7.

My $0.02...

Dave
 
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Matt,


Based on other VAF threads and careful reading of several RV-7 accident reports that involve overspeed and tail separation, I don't believe Vans has the flutter margin they think they do in the larger -9 rudder - although I'm happy to be proven wrong with evidence to the contrary. Only Van's knows why the -10/14 rudder structure changed, but it does seem to be a stiffer design and I'd definitely like to know more about using it on a -7.

My $0.02...

Dave

To my knowledge, there has never been an in-flight failure of a tail component on an RV that was being flown within the designed flight envelope. The 14 rudder design may be different because the airplane is physically larger or the construction could be simplified.
 
To my knowledge, there has never been an in-flight failure of a tail component on an RV that was being flown within the designed flight envelope. The 14 rudder design may be different because the airplane is physically larger or the construction could be simplified.
+1. Facts will set you free. Over 10,500 RV's flown over +40 years with a handful of in-flight break-ups going back to the RV-3 (wing issue), mostly attributed to exceeding Vne and G limits (a lot), loss of control and/or construction issues. Two or three RV-3 wing failures were built by the same "pro" builder. Van of course changed the design, but the original if built properly was acceptable.

I looked at all the RV-7 breakups (where parts came down in different places). There were about 5 accidents. 4 were not structural, clearly loss of control and one bird strike. One case was undetermined in my opinion, but no definitive fault of structure was found. The balanced rudder, elevators, ailerons are not flutter prone flown within limits with good margins.

This may be common knowledge but Van changed the original early RV-7 small rudder to a larger rudder used today for spin recovery. Apparently with small rudder it took too many turns to come out of spin.
 
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I fly a -7A with the 9 rudder. My first attempt developed tiny cracks from several of the forward and aft rivets of the stiffeners. So, I re-skinned the rudder prior to painting over 5 years ago. So far, no cracks, but I made sure to more closely follow the building instructions, especially pertaining to rolling the leading edge.

Like some, I really liked the 8 rudder and had actually acquired a completed unit. But, after inspecting the 9 rudder on the plane, still in nearly perfect condition with over 500 hrs. of flight on it, I thought, "Why bother. If it ain't broke, don't fix it." So I sold the 8 rudder.
 
Answering my own question a couple years later: Yes, an RV-14 rudder fits fine on an RV-7.

20220919_rudder21.jpg


No surprise since all the changes from the RV-7/9 rudder are internal, and the important dimensions are identical. Rod end bearings lined up perfectly and even my previous fiberglass tip fairing fits. The only real surprise was in getting my first experience with the "just shake the box" style of modern kit - definitely a more refined experience than I've become accustomed to.

If I had it to do over again I might have built an RV-8 rudder instead (building wedge-style trailing edges is frustrating to me) but for now I'm happy enough with the outcome.
 
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Thanks Matt!!

Excellent, I would not have imagined they were fitted the same. Great work!! Thanks for posting a cold hard fact. That 14 internal design sure looks stiffer.

Matt, did you do any other comparisons - like weight?
 
Matt, did you do any other comparisons - like weight?

I have some pictures on my build log from which experienced RV-7 rudder-builders will get a sense of the structural differences. Overall the changes are pretty simple:

1. A few lightweight aluminum gussets and extra pop rivets turn the formerly free-floating stiffeners into a set of proper ribs, which I have to imagine improves the stiffness of the assembled unit. Probably less chance of the skins cracking at the stiffener ends too.

2. The bottom rib is the same shape, but is split into two halves that are later riveted together. I puzzled over this change until I figured out that it's required due to the different order of assembly for this rudder.

3. Instead of a separate counterbalance skin, the counterbalance arm is incorporated into the big left/right skins. The actual counterbalance rib and top rib are identical, as is the lead weight.

4. The bent flange on the leading edge of the "inside" rolled skin is gone. I guess they decided extra stiffening wasn't needed.

As for weight, I have to imagine they are almost identical, with perhaps a few extra grams for the added parts. Then again, the trailing edge wedge has lightening holes drilled in it, which my old one did not, so perhaps the difference is not as much as I'd have thought.
 
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Matt, how thick are the RV-14 rudder skins?

For comparison, the -9/-7 rudder has 0.016" skins. The -8 rudder has 0.020" skins.
 
Just wondering does anyone have any info/thoughts for someone needing/wanting to change out a - 7 rudder and vertical stab, seeing as how the 14 rudder fits the -7 vertical stab, does/is the RV14 vertical stab interchangeable as well ? So is the RV14 Vertical Stabilizer and Rudder able to be fit to an RV7 ? Any info appreciated.
 
Just wondering does anyone have any info/thoughts for someone needing/wanting to change out a - 7 rudder and vertical stab, seeing as how the 14 rudder fits the -7 vertical stab, does/is the RV14 vertical stab interchangeable as well ? So is the RV14 Vertical Stabilizer and Rudder able to be fit to an RV7 ? Any info appreciated.

Given that the RV-14 vertical stabilizer appears to have the same basic design as the one of the RV-7, I probably would just build another RV-7 VS to avoid any possibility of unpleasant fit issues when you go to bolt it on... i.e. there doesn't seem to be any significant structural difference between the two like there is with the rudder, so the stock assembly is probably the way to go.
 
Given that the RV-14 vertical stabilizer appears to have the same basic design as the one of the RV-7,……

That’s very interesting and encouraging to hear that the 7/9….and 14 rudder are dimensionally identical. Along with that, I’m assuming the vertical stabilizers are also dimensionally the same?

With this information in mind, it has me thinking about my -14 build. For various reasons/benefits that may be arguable, I’ve always preferred the -8 rudder over the 7/9 design. On top of that, I just think it looks better.

For fitment purposes, is there any reason an -8 rudder wouldn’t work on a -14? From what you’ve proven, it’ll definitely bolt up, but I’m also thinking about the fiberglass.

If an -8 rudder is used on a -7, I know the -8 rudder and vertical stabilizer fiberglass parts are used instead of the -7 fiberglass parts. So, if the -14 vertical stabilizer is dimensionally the same as the -7, the -8 fiberglass parts should work as well. Thoughts?
 
That’s very interesting and encouraging to hear that the 7/9….and 14 rudder are dimensionally identical. Along with that, I’m assuming the vertical stabilizers are also dimensionally the same?

With this information in mind, it has me thinking about my -14 build. For various reasons/benefits that may be arguable, I’ve always preferred the -8 rudder over the 7/9 design. On top of that, I just think it looks better.

For fitment purposes, is there any reason an -8 rudder wouldn’t work on a -14? From what you’ve proven, it’ll definitely bolt up, but I’m also thinking about the fiberglass.

If an -8 rudder is used on a -7, I know the -8 rudder and vertical stabilizer fiberglass parts are used instead of the -7 fiberglass parts. So, if the -14 vertical stabilizer is dimensionally the same as the -7, the -8 fiberglass parts should work as well. Thoughts?

So you want to put a smaller than factory designed rudder and VS, onto a plane larger and heavier than the 8 VS/rudder was ever fitted to. Revisit the reasons why the 7 got a larger rudder & VS than the 6 ... twice.
 
So you want to put a smaller than factory designed rudder and VS, onto a plane larger and heavier than the 8 VS/rudder was ever fitted to. Revisit the reasons why the 7 got a larger rudder & VS than the 6 ... twice.

Yes and no. Yes, the smaller-8 rudder, but not a smaller VS.

Matt has proven, the 7/9 and 14 rudder are dimensionally exactly the same, but with the 14 rudder showing to be a stronger design (internally).

Many people, including myself, have opted to use an -8 rudder on their -7. As I mentioned above, the pros and cons of doing this has be argued on both sides of the aisle.

Without having taken any measurements myself yet, I’m only assuming that due to the fact that the 7/9 and 14 rudders are the exact same size, the vertical stabilizers are also exactly the same size. So if all the dimensions are identical, and the -8 rudder has been used successfully many many times on the 7, why wouldn’t it work on the 14?

I understand and appreciate your thought process and you questioning mine, but as I mentioned above, if this transplant has been done successfully on the 7 many times, and the dimensions are exactly the same, why couldn’t the same thing be done on the 14? For better or worse, I just prefer the -8 rudder over the 7/9 and if it’ll work I’m definitely considering it.
 
Yes and no. Yes, the smaller-8 rudder, but not a smaller VS.

Matt has proven, the 7/9 and 14 rudder are dimensionally exactly the same, but with the 14 rudder showing to be a stronger design (internally).

Many people, including myself, have opted to use an -8 rudder on their -7. As I mentioned above, the pros and cons of doing this has be argued on both sides of the aisle.

The 7 has been tested (including spin testing)with both the 8 and the 9 style rudder. The RV-14 has never been tested with anything other than the RV-14 rudder.
That alone might be worth pondering for a bit since there are some pretty major differences between an RV-7 and an RV-14 (overall wing span, wing airfoil, etc.).
 
The 7 has been tested (including spin testing)with both the 8 and the 9 style rudder. The RV-14 has never been tested with anything other than the RV-14 rudder.
That alone might be worth pondering for a bit since there are some pretty major differences between an RV-7 and an RV-14 (overall wing span, wing airfoil, etc.).

Understood. If there were any differences in size between the 7/9 and 14 rudders, I wouldn’t even be considering it, and as you said, there may be other factors to consider as well. However, if there’s no other negatives other than what’s been shown in -7 testing, than the -8 rudder may be a viable option.
 
I've got some skin damage on my 9A rudder from high winds without a gust lock installed, and I've been waiting to replace it until I had a paint shop lined up which is needed for some touchup with other work that I want to do. Now I'm thinking the -14 rudder should go on my 9A simply for the easier build...
 
I've got some skin damage on my 9A rudder from high winds without a gust lock installed, and I've been waiting to replace it until I had a paint shop lined up which is needed for some touchup with other work that I want to do. Now I'm thinking the -14 rudder should go on my 9A simply for the easier build...

Hey Greg, if you’re not in a huge hurry, I’m sure we can work out a deal if I decide to go with the -8 rudder. You can order an -8 rudder kit for me and I’ll give you my -14 rudder that I’m getting with my kit. I love it when a plan comes together. 😎
 
The 7 has been tested (including spin testing)with both the 8 and the 9 style rudder. The RV-14 has never been tested with anything other than the RV-14 rudder.
That alone might be worth pondering for a bit since there are some pretty major differences between an RV-7 and an RV-14 (overall wing span, wing airfoil, etc.).

Exactly the point I was trying to make. Thanks.
 
Understood. If there were any differences in size between the 7/9 and 14 rudders, I wouldn’t even be considering it, and as you said, there may be other factors to consider as well. However, if there’s no other negatives other than what’s been shown in -7 testing, than the -8 rudder may be a viable option.

I have a Prius, an Explorer and a lifted 4x4 Dodge Ram. I have used the big off-road tires from my truck on my SUV. I have also used small passenger tires from my Prius on my SUV. Therefore it stands to reason that I should be able to use the Prius tires on my 4x4 Ram.

There is a huge (and identical) logic flaw in both these statements. Please, casual reader, ignore the flaw at your own peril. This is a perfect example of internet opinions, lacking any semblance of common logic, can be extremely dangerous.

Will an -8 rudder work on a -14? Maybe. Will Prius tires work on the Ram? Maybe. Are there unexplored risks to both? YES!!
 
It’s putting a little bit of a smile on my face.

I have a Prius, an Explorer and a lifted 4x4 Dodge Ram. I have used the big off-road tires from my truck on my SUV. I have also used small passenger tires from my Prius on my SUV. Therefore it stands to reason that I should be able to use the Prius tires on my 4x4 Ram.

There is a huge (and identical) logic flaw in both these statements. Please, casual reader, ignore the flaw at your own peril. This is a perfect example of internet opinions, lacking any semblance of common logic, can be extremely dangerous.

Will an -8 rudder work on a -14? Maybe. Will Prius tires work on the Ram? Maybe. Are there unexplored risks to both? YES!!

I understand and can appreciate your attempt to compare and contrast the use of different equipment in applications it wasn’t intended for. I’m fully aware of and would never attempt to or even consider applying any changes that obviously shouldn’t be done. As an example, I certainly wouldn’t even consider putting an F-18 engine in an RV-3….but daydreaming about putting a 540 in an RV-14 or even putting a turbocharger on it may very well put a little bit of a smile on my face.

The fact of the matter is that the 14 has a 7/9 VS and rudder….(with a few minor structural differences)….but for argument’s sake, they’re the same. So with those facts in mind, I don’t think my question or hypothesis that the 8 rudder can be used successfully on the 14 is completely outlandish. So, back to my basic question; if the 7/9 VS and rudder are being used on the 14 and the 8 rudder works perfectly on the 7/9, why wouldn’t it work on the 14? Would the airplane fall out of the sky? Would it be totally uncontrollable? Would it have such limited cross-wind authority that it couldn’t be landed in anything greater than a 10kt cross-wind? Would it not be capable of coming out of a spin? I certainly don’t know the answers to these questions, however, because there’s such minor differences in the size of the 7/9 and 8 rudders, I highly doubt any if those things would happen.

I’d be happy to hear comments from an aeronautical engineer after they’d taken the measurements from the different rudders and applied all know facts and point to and lay out a compelling argument….for or against. Sometimes it just takes one person to do something that’s a little bit different, and before you know it, it becomes commonplace.

Once again, I’m certainly no aeronautical engineer and I’m only daydreaming about the possibility of doing something that’s not outlandish, but something that’s just a little bit different and outside of the box….and it’s putting a little bit of a smile on my face. :)
 
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———-SNIP———

The fact of the matter is that the 14 has a 7/9 VS and rudder….(with a few minor structural differences)….but for argument’s sake, they’re the same. So with those facts in min, I don’t think my question and hypothesis that the 8 rudder can be used successfully on the 14 is completely outlandish. So, back to my basic question….if the 7/9 VS and rudder are being used on the 14 and the 8 rudder works perfectly on the 7/9, why wouldn’t it work on the 14? Would the airplane fall out of the sky? Would it be totally uncontrollable? Would it have such limited cross-wind authority that it couldn’t be landed in anything greater than a 10kt cross-wind? Would it not be capable of coming out of a spin? I certainly don’t know the answers to these questions, however, because there’s such minor differences in the size of the 7/9 and 8 rudders, I highly doubt any if those things would happen. ———SNIP——

The flaw in this logic is the -8 rudder is significantly different than the 7/9/14 rudders. Plus, the -8 rudder has not been used on the -9 as far as I know.

The fact that the -8 rudder has been used on the -7 has nothing to do with wether it will work on the -14. They are two completely different airframes as Scott has pointed out.

I’m all for experimenting but one should have the correct assumptions before proceeding.
 
I understand and can appreciate your attempt to compare and contrast the use of different equipment in applications it wasn’t intended for. I’m fully aware of and would never attempt to or even consider applying any changes that obviously shouldn’t be done. As an example, I certainly wouldn’t even consider putting an F-18 engine in an RV-3….but daydreaming about putting a 540 in an RV-14 or even putting a turbocharger on it may very well put a little bit of a smile on my face.

The fact of the matter is that the 14 has a 7/9 VS and rudder….(with a few minor structural differences)….but for argument’s sake, they’re the same. So with those facts in mind, I don’t think my question or hypothesis that the 8 rudder can be used successfully on the 14 is completely outlandish. So, back to my basic question; if the 7/9 VS and rudder are being used on the 14 and the 8 rudder works perfectly on the 7/9, why wouldn’t it work on the 14? Would the airplane fall out of the sky? Would it be totally uncontrollable? Would it have such limited cross-wind authority that it couldn’t be landed in anything greater than a 10kt cross-wind? Would it not be capable of coming out of a spin? I certainly don’t know the answers to these questions, however, because there’s such minor differences in the size of the 7/9 and 8 rudders, I highly doubt any if those things would happen.

I’d be happy to hear comments from an aeronautical engineer after they’d taken the measurements from the different rudders and applied all know facts and point to and lay out a compelling argument….for or against. Sometimes it just takes one person to do something that’s a little bit different, and before you know it, it becomes commonplace.

Once again, I’m certainly no aeronautical engineer and I’m only daydreaming about the possibility of doing something that’s not outlandish, but something that’s just a little bit different and outside of the box….and it’s putting a little bit of a smile on my face. :)

You seem to be under the impression that the RV-8 rudder and the RV-14 rudder are the same size just because they could be interchangeable on a specific vertical stabilizer.

They have the same hinge point positions but they are far from being the same overall area. That would be the number one issue with your logical reasoning. If you installed one on an RV 14 you would be flying with a quite a bit smaller Rudder by overall area then it was designed to use.
 
The flaw in this logic is the -8 rudder is significantly different than the 7/9/14 rudders. Plus, the -8 rudder has not been used on the -9 as far as I know.

The fact that the -8 rudder has been used on the -7 has nothing to do with wether it will work on the -14. They are two completely different airframes as Scott has pointed out.

I’m all for experimenting but one should have the correct assumptions before proceeding.

Can you point out the “significant” differences in the two rudders? If there were significant differences, how would they even be remotely interchangeable? Vertical stabilizers and rudders have been mixed and matched successfully on 4, 6, 7, and 8’s many times. If for example the 14 used the 10 VS and rudder then this whole conversation would probably be a moot point….but it doesn’t. Some compelling arguments with facts would be interesting to hear.
 
You seem to be under the impression that the RV-8 rudder and the RV-14 rudder are the same size just because they could be interchangeable on a specific vertical stabilizer.

They have the same hinge point positions but they are far from being the same overall area. That would be the number one issue with your logical reasoning. If you installed one on an RV 14 you would be flying with a quite a bit smaller Rudder by overall area then it was designed to use.

On the contrary….I know the two rudders are a different size, but my point is that I don’t think the size differences are enough to make a difference and has been proven many times to work perfectly in conjunction with a 7/9 VS. If for example the 14 used the 10 VS and rudder than we wouldn’t even be having this conversation…..but it doesn’t, it uses a 7/9 VS and rudder. I really enjoy these point/counter point conversations….it really gets the old wheels moving. :)
 
On the contrary….I know the two rudders are a different size, but my point is that I don’t think the size differences are enough to make a difference and has been proven many times to work perfectly in conjunction with a 7/9 VS. If for example the 14 used the 10 VS and rudder than we wouldn’t even be having this conversation…..but it doesn’t, it uses a 7/9 VS and rudder. I really enjoy these point/counter point conversations….it really gets the old wheels moving. :)

It is still bigger in area than the RV-8 rudder. Isn’t that what you originally were suggesting to use?

I will be very blunt….
Assuming the RV-14 would be fine with a smaller rudder just because the RV-7 is approved with two different rudders is foolish thinking.
None of the people that have been involved in designing and testing testing both of the airplanes would ever fit hunk that without some cautious flight testing.
 
It is still bigger in area than the RV-8 rudder. Isn’t that what you originally were suggesting to use?

I will be very blunt….
Assuming the RV-14 would be fine with a smaller rudder just because the RV-7 is approved with two different rudders is foolish thinking.
None of the people that have been involved in designing and testing testing both of the airplanes would ever fit hunk that without some cautious flight testing.

All I’m doing is connecting the physical dots and asking questions. What I see is a 7/9 that safely shares their VS and rudder with the 14. I also see the 7 (and probably the 9) that can be safely operated with the 8 rudder. With those known facts in mind, I’m merely asking a few logistical questions:

Is the design of the 14 such that it operates safely with the 7/9 VS and rudder?…yes.
Can the 7 (and probably the 9) operate safely with an 8 rudder?….yes.
Are the safety margins and tolerances for safe flight so close that the relatively small difference in size between the 8 and 7/9 rudder such that if used on a 14 would introduces catastrophic flight characteristics?….I doubt it, but I don’t know…but I sure hope not.
Will Vans ever officially test the 8 rudder on the 14?….probably not.
Will I do it?….time will tell.

What I’d like to hear is what potential problems could or would occur and what stage of flight are they more likely occur.

Would it be lack of authority during takeoff and/or landing in a strong crosswinds?
Would it be during cruse flight?
Would it be during spin recovery?

Once again, I’m only connecting the physical dots that I see and asking questions. I would hope that someone could point to more specifics and present a more convincing argument other than “it shouldn’t be done” or “just because it works on one airframe doesn’t mean it’ll work on another”.

Even if the questions can’t be answered with certainty, this has been fun debate.
 
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