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02-14-2020, 06:20 PM
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Join Date: Dec 2018
Location: Granada Hills
Posts: 820
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Quote:
Originally Posted by airguy
You can burn lower grade fuels with that compression if that's an attraction for you.
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Curious as to if the old 7.0 : 1 compression ratio on the 150HP 0-320 could run on regular 87 octane unleaded pump gas or Mogas. Did it originally run on 80 octane Leaded fuel? The lower compression would seem to be a much lower stressed engine, on all components.
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02-14-2020, 06:32 PM
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Join Date: Jan 2005
Location: Oklahoma City, OK
Posts: 924
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Quote:
Originally Posted by NinerBikes
Curious as to if the old 7.0 : 1 compression ratio on the 150HP 0-320 could run on regular 87 octane unleaded pump gas or Mogas. Did it originally run on 80 octane Leaded fuel? The lower compression would seem to be a much lower stressed engine, on all components.
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We have a 1969 C-172 with the O-320 E2D. It's STC'd to run 87 mogas.
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RV9A under construction--N781DM reserved
Donated
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02-15-2020, 08:47 AM
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Join Date: Jun 2018
Location: Amarillo, TX
Posts: 30
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O-320 E2D Mogas concerns
My 9a has the O-320 E2D rated 80/87 Mogas. The engine runs great on the Mogas until it doesn't. The issue seems to be the vapor pressure of the Mogas and temperatures in the engine compartment. Make special considerations for your fuel system especially at the carb. The crossover design of the exhaust saturates the carb with heat creating good conditions for boiling fuel in the carb bowl especially in the winter when the Mogas is formulated with a higher vapor pressure (lower boiling point). Once boiling, the float goes to the bottom and flooding of the engine occurs. This happened again to me on a warm winter day ealier this winter. The engine quit me at 11,500 msl when I ran the Mogas. The Avgas was turned back on and all was well again. We unloaded the Mogas and put it in my friends Super Cub that has the same engine but different cowl set up. The engine ran fine throughout takeoff, cruise, and landing in the Super Cub.
So, as many others have pointed out, make great consideration of how you will keep the fuel system and carb cool if you are going to use Mogas with this engine.
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02-15-2020, 11:19 AM
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Join Date: Mar 2007
Location: Sonoma County
Posts: 3,821
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Quote:
Originally Posted by Tumper
I didn?t mean to cause a stink on the forum by introducing science/safety into the discussion. However, I wanted anyone who is considering a 360 with 180HP in their RV-9 to fully understand what they are doing. I am assuming all of us that are flying a 180HP RV-9 have been through this thought process and already know all this.
If you are still a little murky on the subject, please search ?Flying High and Fast by Ken Kruger? and spend as much time as is necessary to fully understand where the concerns of 180HP in an RV-9 exist. If you don?t fully understand find a friend to help you.
And?thanks for the great discussion.
It?s a jungle out there, let?s be safe.
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Here...... https://vansaircraft.com/wp-content/...1/hp_limts.pdf
__________________
VAF #897 Warren Moretti
2019 =VAF= Dues PAID
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02-15-2020, 02:54 PM
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Join Date: Feb 2018
Location: Louisville KY
Posts: 95
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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.
__________________
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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02-15-2020, 05:53 PM
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Join Date: Jan 2005
Posts: 959
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Quote:
Originally Posted by Aviaman
@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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Vne is not the only concern. See post #28.
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02-16-2020, 06:22 AM
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Join Date: Feb 2018
Location: Louisville KY
Posts: 95
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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.
__________________
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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02-16-2020, 12:08 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Aviaman
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,
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".
__________________
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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02-16-2020, 03:49 PM
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Join Date: Feb 2018
Location: Louisville KY
Posts: 95
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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.
__________________
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 04:00 PM.
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02-18-2020, 07:53 AM
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Join Date: Feb 2006
Location: South Carolina
Posts: 659
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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.
__________________
"Pilots: Looking down on people since 1903"
(author unknown)
RV-9, N556RM, O-320, Dual PMags, Catto 3 blade.
FLYING since 2018
Mosquito XEL ready for flight
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