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  #31  
Old 11-25-2022, 06:03 PM
blaplante blaplante is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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.
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  #32  
Old 12-17-2022, 12:00 AM
meloosifah meloosifah is offline
 
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Originally Posted by Mark33 View Post
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!!
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  #33  
Old 12-17-2022, 10:17 AM
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Mark33 Mark33 is offline
 
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Quote:
Originally Posted by meloosifah View Post
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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Last edited by Mark33 : 12-17-2022 at 11:11 AM.
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  #34  
Old 12-17-2022, 11:13 AM
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mfleming mfleming is online now
 
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Quote:
Originally Posted by Mark33 View Post
———-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.
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  #35  
Old 12-17-2022, 11:30 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Mark33 View Post
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.
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  #36  
Old 12-17-2022, 11:38 AM
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Mark33 Mark33 is offline
 
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Quote:
Originally Posted by mfleming View Post
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.
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  #37  
Old 12-17-2022, 12:01 PM
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Mark33 Mark33 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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.
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RV-7- IO-360, EFII, Whirl Wind C/S, (Built and sold)
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  #38  
Old 12-17-2022, 09:50 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by Mark33 View Post
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.
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Opinions, information, and comments, are my own unless stated otherwise.
You are personally responsible for determining the suitability of any tips,
ideas, etc. obtained from any post I have made in this forum.


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Hubbard, Oregon
Formerly of Van's Aircraft Engineering Prototype Shop
FAA/DAR, EAA Technical Councelor
RV-6A (aka "Junkyard Special ")
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  #39  
Old 12-18-2022, 12:06 AM
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Mark33 Mark33 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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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RV-7- IO-360, EFII, Whirl Wind C/S, (Built and sold)
RV-4- O-320, Catto three blade, P-Mags (Sold)
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RV-7- Sold project
RV-14- Building

Last edited by Mark33 : 12-18-2022 at 09:22 AM.
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