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  #11  
Old 08-03-2017, 08:43 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by AlanTN View Post
Is there adequate engineering documentation for all the other numbers supplied in the POH?
Yes there is.

You obviously have a different viewpoint regarding this than I do.

If I discovered that a manufacturer (doesn't even have to be aviation related) changed some of their publicly declared technical data in such a way that it indicated a lower level of performance, I wouldn't find it necessary to publicly call them out and say "so which is correct?
It kind of seems obvious... to me anyway.
Why would a company change performance values in a way that downgraded their claimed performance if it wasn't correct?
If your reason for doing so is because you now question whether any of the performance claims are valid, that is your prerogative and there is probably nothing anyone at Van's could say to change that.

The best I can recommend is you ask Van's Aircraft customers.
You will probably find that the major majority of them will say at the very least their airplane meets all of performance specifications and, and many will say they actually exceed them.

Good luck in your research.
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Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 08-03-2017 at 08:56 PM.
  #12  
Old 08-03-2017, 09:36 PM
AlanTN AlanTN is offline
 
Join Date: Apr 2011
Location: Linden, TN
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Quote:
Originally Posted by vic syracuse View Post
Yes, the new IS engine is actually about 25% MORE efficient at cruise power settings. There is even a detent on the throttle quadrant for the best economy position. At power settings less than that, it does become less fuel efficient than the UL engine.

Vic
Vic it was my impression from reading the Rotax webpage that anything less than 97% power on the 912iS was economy mode. Also it looks like the throttle detent is not just one position, but has a finite length of perhaps 2 times the lever length. In normal cruise does that correspond to 5500 and 5000 rpm?

And a technicality: 45 gallons IS 25% less than 60 gallons, but that is not how you calculate fuel economy. Fuel economy is based upon miles PER gallon. So if you used 60 gallons to go 1500 miles that would be 1500/60=25mpg. Likewise if you used 45 gallons to go the same1500 miles that would be 1500/45=33.3mpg. 33.3mpg/25mpg=1.33 which is a 33% increase in fuel economy. That is a big improvement! :-)

Are there actual measurements showing that at any setting the 912iS is LESS efficient than the 912ULS? I have not heard that anywhere else before.
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Last edited by AlanTN : 08-04-2017 at 10:51 AM.
  #13  
Old 08-03-2017, 10:26 PM
rgmwa rgmwa is offline
 
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If the current range values in the POH are overly optimistic for whatever reason, then I assume they will be amended. I don't mind what the values are as long as they are reliable. Knowing Van's they will be probably tend to understate rather than overstate the performance anyway.
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  #14  
Old 08-04-2017, 04:42 AM
Dave12 Dave12 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Yes there is.

You obviously have a different viewpoint regarding this than I do.

If I discovered that a manufacturer (doesn't even have to be aviation related) changed some of their publicly declared technical data in such a way that it indicated a lower level of performance, I wouldn't find it necessary to publicly call them out and say "so which is correct?
It kind of seems obvious... to me anyway.
Why would a company change performance values in a way that downgraded their claimed performance if it wasn't correct?
If your reason for doing so is because you now question whether any of the performance claims are valid, that is your prerogative and there is probably nothing anyone at Van's could say to change that.

The best I can recommend is you ask Van's Aircraft customers.
You will probably find that the major majority of them will say at the very least their airplane meets all of performance specifications and, and many will say they actually exceed them.

Good luck in your research.
Both of the RV's I have built were right on the money according to Van's claims.
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  #15  
Old 08-04-2017, 01:28 PM
AlanTN AlanTN is offline
 
Join Date: Apr 2011
Location: Linden, TN
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Quote:
Originally Posted by rvbuilder2002 View Post
Yes there is.

You obviously have a different viewpoint regarding this than I do.

If I discovered that a manufacturer (doesn't even have to be aviation related) changed some of their publicly declared technical data in such a way that it indicated a lower level of performance, I wouldn't find it necessary to publicly call them out and say "so which is correct?
It kind of seems obvious... to me anyway.
Why would a company change performance values in a way that downgraded their claimed performance if it wasn't correct?
Scott, I think you are misjudging me.

When I first posted this question in another thread during Oshkosh it was because I had a high regard for the integrity of Van's test data. Although I thought the original range numbers might be a little optimistic, there were enough people on this forum that had achieved results that were close enough that I thought the range numbers were reasonably accurate, given the test conditions.

I assumed that the new numbers might have been posted in haste before Oshkosh, without time for them to be thoroughly vetted. I was trying to alert someone to the problem so they could correct the inaccurate range numbers. I expected them to be higher, and I still do!

Parasitic drag at 131mph (5500 rpm) is nearly 28% higher than at 116mph (5000 rpm). It does not seem reasonable, and it is counter to the experiences of many people posting here, that the range at these two different power settings should be less than 1/2% different. The 912ULS is not computer controlled so that can't be the reason in this case.

Another reason I question the new numbers is that the range at 5500 rpm is listed as 630 miles for the 912iS and as 433 for the 912ULS. That represents more than a 45% increase in fuel economy. I don't think that is too likely. I think it is much more likely that he 433 mile range for the 912ULS is too low.

Quote:
Originally Posted by rvbuilder2002 View Post
If your reason for doing so is because you now question whether any of the performance claims are valid, that is your prerogative and there is probably nothing anyone at Van's could say to change that.
If the company website indicates the range numbers in the POH are up to 41% too high, (which I don't believe), and you, also, state that they were not accurate, don't you think for safety reasons it would be prudent to ask if there might have been similar problems in the calculation of weight and balance, climb rate at density altitude, etc?

Quote:
Originally Posted by rvbuilder2002 View Post
The best I can recommend is you ask Van's Aircraft customers.
You will probably find that the major majority of them will say at the very least their airplane meets all of performance specifications and, and many will say they actually exceed them.
Scott, how can you suggest that the majority of customers will say that their airplane meets all performance specifications if you yourself think the range numbers in the POH are 28 to 41% too high? Is that reasonable?

Please ask someone in engineering to carefully review the new range numbers, I am fairly certain there are some problems, and it is to the advantage of Van's to get them corrected as soon as possible.

Regards, Alan Bishop
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  #16  
Old 08-04-2017, 02:44 PM
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RV6_flyer RV6_flyer is offline
 
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Not sure why people are beating up Van's Aircraft for different performance numbers with a different engine on a revised airframe.

Van's designs airframes around engines that are proven power plants. In the past everyone believes the numbers that Van's have published and have had little trouble duplicating them.

Rotax updates their engine and Van's Aircraft modifies their airframe to accommodate it. The performance is different in a good way and people complain.

I believe Van's numbers but until one does some Rotax research, it sounds too good to be true when seeing this large of an improvement.

4-years ago, the General Aviation News reported on the fuel economy improvement of Rotax 911 iS engine being better than predicted. Quoting the article: "26-36% lower consumption"

The above linked article is over 4-years old and supports the improvement numbers that Van's Aircraft published with the revised airframe and new engine combination.

Please stop complaining about Van's Aircraft numbers and start thanking Van's Aircraft for the updated powerplant and airframe.
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  #17  
Old 08-04-2017, 03:04 PM
rgmwa rgmwa is offline
 
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Quote:
Originally Posted by RV6_flyer View Post
Please stop complaining about Van's Aircraft numbers and start thanking Van's Aircraft for the updated powerplant and airframe.
That seems a bit harsh. I don't see anyone here who doesn't think that Van's have done a great job in improving the RV-12. The 912iS is a welcome upgrade to an already great design, and the improved performance numbers bear this out. It seems to me that the discussion is more about clarifying how far the current RV-12 will theoretically fly on a tank of fuel. Most of us with RV-12's will have worked this out already.
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  #18  
Old 08-04-2017, 03:10 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by AlanTN View Post

Regards, Alan Bishop
Alan,
Good luck in your quest to find a suitable airplane for you. It is obvious that the RV-12 is NOT........
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Any opinions expressed in this message are my own and not necessarily those of my employer.

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Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
  #19  
Old 08-04-2017, 04:01 PM
AlanTN AlanTN is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Alan,
Good luck in your quest to find a suitable airplane for you. It is obvious that the RV-12 is NOT........
Scott, I have read many of your posts to this forum over the past several years and thought the vast majority of them were very helpful.

But it is obvious that you must have some kind of mental block here, because it appears you are not reading what I have written with an open mind and thinking about what I am saying.

I have said I am a prospective RV12iS builder. I have said I think the design is brilliant. I think all of the new changes are positive. I really like the move to the fuel injected Rotax. I have said that in the flight out to Oshkosh it appears to be 33% more fuel efficient than the RV-12. What more can I say?

Why can't you look at the obvious inconsistencies in the current numbers and agree that it makes sense to take a closer look at them? It will only help Van's to get the numbers right!
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  #20  
Old 08-04-2017, 04:19 PM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by AlanTN View Post
Scott, I have read many of your posts to this forum over the past several years and thought the vast majority of them were very helpful.

But it is obvious that you must have some kind of mental block here, because it appears you are not reading what I have written with an open mind and thinking about what I am saying.

I have said I am a prospective RV12iS builder. I have said I think the design is brilliant. I think all of the new changes are positive. I really like the move to the fuel injected Rotax. I have said that in the flight out to Oshkosh it appears to be 33% more fuel efficient than the RV-12. What more can I say?

Why can't you look at the obvious inconsistencies in the current numbers and agree that it makes sense to take a closer look at them? It will only help Van's to get the numbers right!
Allen:

It is very clear you are not reading other posts and not doing any research on the Rotax engines.

See this: http://www.vansairforce.com/communit...4&postcount=16

Follow the link in that post to a 4-year old article where someone else reports "consumption averaged 32.6% less (in a range of 26-36% lower consumption) burning an average 3.25 gph." with the new 912 iS engine.

Scott is correct, the RV-12 is not an aircraft for you.

Gary
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KVVS RV-6
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Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.
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