IO 360 180 HP in a 9A

[grubbat]

Liability

We talk about increasing margins on the airframe and from Vans perspective, they may want to keep their margins wide by not disclosing any additional information besides what has already been shared publicly. I'm sure they don't want the newbie recently converted Cessna/diamond driver to get behind the curve (or envelope) in a -9 and thus give the experimental industry another NTSB entry and the insurance industry another data point.

Nevertheless, it is nice that Scott has the patience of Job to attempt to answer questions from folks who want to know more and don't mind asking questions so others can benefit. While some may question why so many questions, this is the -9 forum and they can always move on.

My question is what additional margin does the -9 get when he limits the gross to 1600lbs and drops 3ft off the wings by going with a smaller wingtips? 4.4g? 5.6g? 6g?

 

[rvbuilder2002]

Yes, Scott has been very patient but he still has not answered the basic question, and neither has anyone at Van's; since the -7 and -9 share many of the same parts what on the -9 is the limiting factor?

Bill,
You seem to be fishing for what you should change to make your airplane equiv. to an RV-7.

The simple answer... everything that is not the same.

The main things common with the two are fuselage/landing gear/engine mount (even that is somewhat different because of a different center section area for the different wings)and vertical tail.
Everything else is totally different.....

 

[RVbySDI]

In addition, the conversation doesn't ever seem to include installing an (I)O-340 in a -9 (A), why is that?

Ummm, well I can answer questions from first hand experience flying a 9(A) with an IO-340. Ask away. However, I am not going to get into the 'more than 160 HP will kill you argument'.

The main things common with the two are fuselage/landing gear/engine mount. . .

Interesting, I thought the landing gear were different between the two models. The 9(A) definitely sits up higher than the 7(A). I always attributed that to a different landing gear design. What can you tell us about this? Is my assumption wrong on this issue? If so, why do the 9(A)'s stand taller than the 7(A)'s?

 

[rvbuilder2002]

Ummm, well I can answer questions from first hand experience flying a 9(A) with an IO-340. Ask away. However, I am not going to get into the 'more than 160 HP will kill you argument'.

Interesting, I thought the landing gear were different between the two models. The 9(A) definitely sits up higher than the 7(A). I always attributed that to a different landing gear design. What can you tell us about this? Is my assumption wrong on this issue? If so, why do the 9(A)'s stand taller than the 7(A)'s?

I was speaking in the context of design.
They are not exactly the same parts, but very similar. The main gear can't be the same, because it is attaching to a different center section.

BTW, no one has ever said that if you build an RV-9 with more than 160 HP it will kill you. What has been stressed (over and over) is that you are reducing your safety margin. If operated with a clear understanding of the multiple issues involved, it can probably be done safely. The problem is, this thread and others like it, demonstrate that there are people who have done so, but they don't really understand what the limitations are.

 

[kamikaze]

The problem is that everyone id discussing HP instead of airspeeds.

The airframe is designed to withstand certain loads, which is in part a factor of airspeed NOT HP.

Using the example Scott gave, about 3.8G's ... the limit is at Vc (maneuvering speed) not X HP.

Van's recommended 160HP because that's what their work tells them can get you close to Vc ... and above Vc in turbulence, you could exceed the G limit.

In the end, it's about speed, not HP. You can put as many HP as you want, so long as you don't exceed the SPEED limits (Vc and others) on the airframe (All other facotrs being equal, such as CG, etc. of course).

But, if you add HP, you augment the chances you'll exceed some important speed limits, and in the end, possibly get you in trouble.

So, as Scott said, it's about margins.

If you're confident you always manage your speeds well, go ahead and put 180 ... ? From the sounds of it, sounds like at least one person can't exceed Vc in level flight with 180HP ... but always remember these are true speeds ...

 

[esco]

Thanks again, Scott, for your time, attention, and civility.

I was out just this weekend, in my FP 320, at 10,500' in clear, apparently smooth air.
I thought of the VN diagram and slowed to cross a ridge far below me.

The unexpected, invisible wave bounced me round a bit; when I glanced the VSI showed I was ascending >1000 FPM.
I'm glad to have been well inside the limits before I hit it.



"Patience of Job" may be an understatement.

 

[rockwoodrv9]

Scott,
I appreciate being able to ask questions here rather than having to call the company. I know for me, my questions do not mean that I want to make the 9A I am building something it wasn't designed to be. There are plenty of planes I could have chosen but I chose the 9A because it did more of the things I wanted.

If putting a O-360 on a 9 will spin the mount off the plane, I would really want to know that. That is why we ask the questions. Answering just that it is not advised only invites a second question. If it is not advised only because I can over speed it, I believe I could control the throttle. If not, I shouldn't be flying at all.

Where I live, density altitude is a real issue. An extra 20 hp may or may not make the difference. It is hard to imagine thinking extra takeoff and climb power is less safe.

There is no group of people that are more opinionated than pilots. We need actual data or facts to be convinced - and that isn't always enough!!

 

[rockwoodrv9]

10,500' is below pattern altitude at many of the airports out here.

Thanks again, Scott, for your time, attention, and civility.

I was out just this weekend, in my FP 320, at 10,500' in clear, apparently smooth air.
I thought of the VN diagram and slowed to cross a ridge far below me.

The unexpected, invisible wave bounced me round a bit; when I glanced the VSI showed I was ascending >1000 FPM.
I'm glad to have been well inside the limits before I hit it.



"Patience of Job" may be an understatement.

 

[RVbySDI]

I was speaking in the context of design.
They are not exactly the same parts, but very similar. The main gear can't be the same, because it is attaching to a different center section.

BTW, no one has ever said that if you build an RV-9 with more than 160 HP it will kill you. What has been stressed (over and over) is that you are reducing your safety margin. If operated with a clear understanding of the multiple issues involved, it can probably be done safely. The problem is, this thread and others like it, demonstrate that there are people who have done so, but they don't really understand what the limitations are.

Thanks for the clarification on the landing gear.

My 'kill you' statement was just a facetious way of describing the discussions of exceeding engineered margins by putting higher HP engines than is recommended. I have indeed read everything I can find for the past 10 years now on this topic, including this one already mentioned:
https://www.vansaircraft.com/pdf/hp_limts.pdf

That includes this very informative figure:

I cannot answer for Bill, but I do recognize the issues associated with increased cruise speed that I am able to achieve with more HP. Having flown for 4.5 years now behind this engine, and along side many friends in their 360 powered 7's, I will say definitively the 9 can assuredly achieve Vc speed in straight and level flight. It is my responsibility as pilot to recognize what flying at or above that speed does to the risk factor of flying this airplane. I do not always keep my cruise speed at 150 mph IAS, but, I also do not fly at 180 mph IAS either. Once I press beyond that 150 mph mark I am extremely cognizant of the margins for my plane. I am very attuned to the air turbulence around me and monitor very closely the environment in which I am flying. Smooth air is where I attempt to fly. When not in smooth air I absolutely will not push too far to the right of that graph. And yes I know how quickly that smooth air can change.

p.s. After reading all of these posts and re-reading the above mentioned article I realized that I should clarify my experiences with specific cruising speeds I fly in my 9. I historically cruise in the 135 - 145 mph IAS speed when traveling cross-county. Having said such though, it is TAS (True Airspeed) I pay the most attention to. In my opinion it is the most crucial speed when at altitude that can cause a pilot the most grief if not monitored appropriately. Because of this most of my posts tend to reference TAS instead of IAS. I originally made such a reference above. With that in mind I feel it important to clarify one point. I have yet to push my airplane with the IO-340 to Vc during any cross-country trip. I have done so however during Phase I testing and other subsequent test flights where I was attempting to determine specific performance parameters for my 9.

LIVE LONG AND PROSPER!