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  #41  
Old 02-15-2020, 03:54 PM
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Aviaman Aviaman is offline
 
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Location: Louisville KY
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@pilotjohns I have an O-360, 180 hp, in my RV-9A with a Cato 3 blade fixed pitch prop. Mine gives a WOT TAS in level flight of about 185 mph. That?s way below Vne. Whatever the risk of an O-360 might be, exceeding Vne in level flight isn?t it.
At higher altitudes, available power drops so much that TAS is still limited.

There are some considerable advantages of a 360, such as better rate of climb, shorter takeoff roll, cruise at lower % rated power, etc. I?ve never observed any downside to an O-360 in my RV-9A nor have heard of any from others with an O-360. Of course any plane can exceed Vne- - just push the stick forward.
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Cessna 170B-sold
Zenith 601XL-sold
Vans RV-6 slider-sold
Vans RV-9A slider, flying
O-360, AFS EFIS, True-track autopilot, Garmin GDL-82 ADS-B, Garmin 327 Transponder, Garmin 496

Dues happily paid Jan 3, 2020
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  #42  
Old 02-16-2020, 07:22 AM
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Aviaman Aviaman is offline
 
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At a TAS of 185 at WOT, my IAS is well below Vno, which is 180 = the end of the green arc on my ASI. This is at around 8000?. At that speed and altitude, I?m indicating in the 160s (mph). Vno is an indicated airspeed. So I there is no problem with Vno either, at least not with my plane. Perhaps a constant speed prop makes a difference. Or my engine is underperforming. Maybe at higher altitudes it works out differently, but so far I haven?t seen it. It should be pretty simple: don?t exceed Vno in anything but calm air and don?t exceed Vne anytime. Whatever the risks of a 360, if any, the advantages are considerable: better short field performance, higher rate of climb, cruise at lower % rated power (less stress on engine), higher ceiling.
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John
Cessna 170B-sold
Zenith 601XL-sold
Vans RV-6 slider-sold
Vans RV-9A slider, flying
O-360, AFS EFIS, True-track autopilot, Garmin GDL-82 ADS-B, Garmin 327 Transponder, Garmin 496

Dues happily paid Jan 3, 2020
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  #43  
Old 02-16-2020, 01:08 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Aviaman View Post
At a TAS of 185 at WOT, my IAS is well below Vno, which is 180 = the end of the green arc on my ASI. This is at around 8000?. At that speed and altitude, I?m indicating in the 160s (mph). Vno is an indicated airspeed. So I there is no problem with Vno either, at least not with my plane. Perhaps a constant speed prop makes a difference. Or my engine is underperforming. Maybe at higher altitudes it works out differently, but so far I haven?t seen it. It should be pretty simple: don?t exceed Vno in anything but calm air and don?t exceed Vne anytime. Whatever the risks of a 360, if any, the advantages are considerable: better short field performance, higher rate of climb, cruise at lower % rated power (less stress on engine), higher ceiling.
John,
This post is not made with the intent to pick at you personally, just to reemphasize the reason that the RV-9 has a maximum recommended engine HP of 160, and hopefully get more people like you to gain a proper understanding.

By your own admission, you were unaware that the engineering decision to limit HP to 160 was made primarily based on the Vno, limitation. That is not unusual. There are numerous long term RV-9 owners here in the forums that still mention only Vne when the max HP conversation gets revived.

Point being, that until this point, it sounds like you assumed you were fine as long as you are below Vne. That is not necessarily the case.

You mentioned that as long as you are below Vne, you are always below Vno IAS. This will probably be the case at higher altitudes like the 8000 ft example you gave, but a lot of the time not the case at lower altitudes. Down low, the actual IAS and TAS values start to converge and it is very possible to be operating in straight and level cruise within the yellow arc range (above Vno).

Your point about not operating above Vno in anything but smooth air is a good one, but in reality it is not realistic. Turbulance is not like speed bumps on a road. You can't see it ahead of time. It only takes one single acceleration event to overload the airplane.

The worst turbulence bump I have ever experience in 27 years of flying RV's was when my wife and I were over central TX headed west in our RV-6A, back towards PHX from S&F many years ago.
We had been in glassy smooth air for at least an hour. With zero warning we hit a bump that caused a major positive and then negative high G load event that put both out heads on the canopy (yes our belts were tight... no, the airplane didn't have 5th point crotch straps), and caused momentary loss of control. It immediately went back to glassy smooth for another hour. This whole event was over in less than 5 seconds.

I have always felt that it was probably caused by wake turbulence from a large aircraft that had crossed our path during climb from Dallas/ Fort Worth.

So to come full circle on the discussion.....
The largest recommended engine for the RV-9 was chosen because it is a high performance airplane (though many don't think of it that way since it is more at the bottom of the performance line up in RV models), and if higher HP is used, the typical pilot will probably at times be operating within a regime that is causing a reduction in safety ( this is in large part because a lot of pilots have experience in airplanes that would not come anywhere close to cruising in the yellow range regardless of what altitude they were flying).

In a nut shell.... Yes, if pilots properly control the speed (to do that they need to actually know what the limitations are) of their RV-9, then it doesn't really matter what engine is in it.
The scary thing though, (and these repeated discussions in the forums show it time and again) is that the majority of people (even those that have been flying big engine RV-9's for years and exclaiming things like "it hasn't fallen out of the sky yet"), don't have a full understanding of what the actual design limitations are.

If anything good could come out of these higher HP discussions, it would be that more people get educated on what the limiting factors are that people need to keep in mind, and possibly work to spread the word to others that don't know. Especially when they hear someone telling others that "as long as they keep it under Vne, they will be fine".
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #44  
Old 02-16-2020, 04:49 PM
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Aviaman Aviaman is offline
 
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I tend to get into the weeds in technical discussions. You motivated me to read the Kruger article again.
Let me discuss it as I understand the article.

Here’s what appears on page 1 of the article “Flying High and Fast”.

“No, the real problem is not mechanical. The real danger is exceeding the Never Exceed Speed, noted as Vne.” So far, no mention of Vno, but will come back to that.

Yes, at extreme altitudes TAS will become very high with sufficiently high IAS. The example he gave was with a turbonormalized engine, which is very unlike what we are discussing. A normally aspirated engine dramatically loses power with altitude. Because of this, my 360 does not exceed Vne, or even come close, in level flight at any altitude that I have flown. In any case, my EFIS computes and displays TAS. So IMO, exceeding Vne is not in the cards, (except in a dive.)
Now, maybe my engine underperforms (carbureted, fixed pitch prop) and others can go faster. But my own experience doesn’t support the possibility of exceeding Vne in level flight.

About Vno. That is the upper limit of the green arc (or the lower limit of the yellow arc). It’s generally understood to mean only go above that limit when in smooth air. Is that a guarantee of no high loads from unexpected gusts like what you described ? No. Flying in the yellow arc is a matter of judgement and the assumption of risk. However that limit was defined for the RV-9 Just like it was for any other standard category plane. (I have experienced sudden gusts like you described, so caution is advisable). There is no reason to regard that limit as defined differently from other aircraft. For the RV-9 its 180 mph IAS. One should give due caution to that limit as one would with any other plane.

I suspect this hp limit on RV-9s was motivated by Vans fearing that RV pilots would think RV-6 and 7 performance was to be expected or considered safe in the RV-9. No, that wouldn’t be a good idea. It is not stressed for acrobatics, and has lower load limits.
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John
Cessna 170B-sold
Zenith 601XL-sold
Vans RV-6 slider-sold
Vans RV-9A slider, flying
O-360, AFS EFIS, True-track autopilot, Garmin GDL-82 ADS-B, Garmin 327 Transponder, Garmin 496

Dues happily paid Jan 3, 2020

Last edited by Aviaman : 02-16-2020 at 05:00 PM.
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  #45  
Old 02-18-2020, 08:53 AM
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Robert M Robert M is offline
 
Join Date: Feb 2006
Location: South Carolina
Posts: 659
Default What engine?

I purchased a used O-320 engine with no logs. Completely torn apart, checked out and rebuilt, about $12g?s total. Added dual PMags and Catto 3 blade prop. This plane jumps off the ground at my (sea level) altitude. I flew in the Repucci aircraft back when it had the O-290 - also VERY impressive performance. I am, like a few others? in that I want flying to be fun. The RV-9 can hit Vne really quickly by just pointing the nose down so engine size is really not a factor unless flying from higher elevations. I usually cruise at around 125 - 130 MPH, sipping gas. Bottom line, the choice is your, get what YOU want.
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  #46  
Old 02-18-2020, 10:52 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Aviaman View Post
I tend to get into the weeds in technical discussions. You motivated me to read the Kruger article again.
Let me discuss it as I understand the article.

Here’s what appears on page 1 of the article “Flying High and Fast”.

“No, the real problem is not mechanical. The real danger is exceeding the Never Exceed Speed, noted as Vne.” So far, no mention of Vno, but will come back to that.

Yes, at extreme altitudes TAS will become very high with sufficiently high IAS. The example he gave was with a turbonormalized engine, which is very unlike what we are discussing. A normally aspirated engine dramatically loses power with altitude. Because of this, my 360 does not exceed Vne, or even come close, in level flight at any altitude that I have flown. In any case, my EFIS computes and displays TAS. So IMO, exceeding Vne is not in the cards, (except in a dive.)
Now, maybe my engine underperforms (carbureted, fixed pitch prop) and others can go faster. But my own experience doesn’t support the possibility of exceeding Vne in level flight.

About Vno. That is the upper limit of the green arc (or the lower limit of the yellow arc). It’s generally understood to mean only go above that limit when in smooth air. Is that a guarantee of no high loads from unexpected gusts like what you described ? No. Flying in the yellow arc is a matter of judgement and the assumption of risk. However that limit was defined for the RV-9 Just like it was for any other standard category plane. (I have experienced sudden gusts like you described, so caution is advisable). There is no reason to regard that limit as defined differently from other aircraft. For the RV-9 its 180 mph IAS. One should give due caution to that limit as one would with any other plane.

I suspect this hp limit on RV-9s was motivated by Vans fearing that RV pilots would think RV-6 and 7 performance was to be expected or considered safe in the RV-9. No, that wouldn’t be a good idea. It is not stressed for acrobatics, and has lower load limits.
John,
The article was written as applicable to all RV models so it does apply to the RV-9 as well, but don't confuse that article with being the reason for the 160 HP recommendation for the RV-9.

The RV-9 is a slightly different breed of RV and has a lower max. HP limit than the other models for a different reason. I think I have now thoroughly explained the reason.
As you mentioned, Vno should be obeyed while flying any aircraft, to which I agree, but having been present and participated in the static load testing of the RV-9 wing and other major air-frame components, and having direct knowledge of many of its design details, I can stand behind my explanation of why there is a smaller engine recommendation specifically for the RV-9.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #47  
Old 02-18-2020, 11:22 AM
Vansconvert Vansconvert is offline
 
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Default Vno for a 7a

What is the vno for a 7A? I don't see that published anywhere on the Vans site.
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  #48  
Old 02-18-2020, 11:44 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Vansconvert View Post
What is the vno for a 7A? I don't see that published anywhere on the Vans site.
Vno is the start of the yellow arc range in the following document -

https://www.vansaircraft.com/faq/air...ings-by-model/
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #49  
Old 02-23-2020, 12:30 PM
NinerBikes NinerBikes is offline
 
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Surprised, other than the cost, no one talks about running a turbocharged motor at elevations above 10,000, in a RV-9.

No talk about ever running a Rotax 915 IS rated at 141 HP, and it's not losing HP at those elevations.

True, your climb rates won't be as good at lower elevations, but probably past 8000 feet and above, where the RV-9 wing does so well, it's still making good power, where a normally aspirated engine isn't. And it's pretty much FADEC capable. Fuel injection.

And to add some blasphemy, the engine is not a design from 1951 or 1953 when 320's and 360's first came out? Fresh design with current technology, manufacturing techniques and metallurgy. Car engine design, snowmobile engine design, jet ski design and other gasoline powered toys have not stood still. Any fresh new designs out of Lycoming lately? Just asking, for a friend. Wink.

Thoughts?

Sorry I am so simple minded... but if you want a o-360, why don't you build or buy something designed for it, a RV-6 or RV-7? Making something capable of doing something it was never designed for, is lost on me. Get the right tool for the flying mission.

Last edited by NinerBikes : 02-23-2020 at 12:42 PM.
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  #50  
Old 02-23-2020, 01:04 PM
Kyle Boatright Kyle Boatright is offline
 
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Quote:
Originally Posted by NinerBikes View Post

Thoughts?
Go for it. Keep us posted.
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