More powerful engine on a 9/A

[Doakes]

I could not find on Van's website just why one could not put say 180/200 hp engine on the RV9.
Besides the answer- because Van did not design it that way, what would be a reason?
The only major difference between the 7 and the 9 is the wing.
Thanks for the reply in advance and Merry Christmas.
Dave

[Snap]

It has to do with wing loading and G loading. You can have two acft of the same weight but one with a bigger engine. If you say, pull up severely, the one that is going faster(bigger engine) will have a huge G/wing loading. This will cause more fatigue and possibly go beyond the structual limits of the acft.

Make sense?

[Spike]

Actually there was a great write up about this very thing in one of the previous RVators with a long detailed explanation including performance graphs, etc. The bottom line that they were getting at was that with a 160HP engine you had a bit of safety margin before over stressing the airframe. One of the things talked about was the large spread between Va and Vne due to the low stall speed of the airplane which forces Va down. With a larger engine it was in their opinion too easy to shrink down that safety margin especially when you take into account things such as gust loading on the aircraft. Seems to me that they were trying to design an aircraft that could handle gusts in the 50fps range or so but that increased performance from a larger engine would take away their safety margins. There may be some wrong info in here so please forgive me. Its been a while since I read the article. I would think you could find a copy of it somewhere. It was very interesting reading. Needless to say it will be 160HP or less on my 9A.

-- John

[Doakes]

Thanks for your replys, I quess there is a limit on how big or fast one can travel.
I will try to find the article and read up on it.
Dave

[captain_john]

I quess there is a limit on how big or fast one can travel.

The limits, as far as I can tell is pushed only by one thing... $ MONEY $ !

After having given it some thought, (I do that from time to time, think) it seems that the higher altitude you desire, the more it costs.

Consider the 3' step stool in your shop. It is about twenty bucks, quite stable and reliable. If you want more altitude, you get the 6' steppy out. That costs around $60 and is just as effective, but weighs more and uses a larger footprint. In order to get higher a more costly and sometimes a different design is called upon. Case in point, extension ladders, scaffoldings and man lifts. Each of these costs slightly more than the next.

If you want more altitude, you could get an ultralight. This limits you to a maximum of several hundred to thousand feet AGL. Weather is also a serious consideration. In order to be more worthy, an enclosed cockpit and heavier wing loading is needed. This comes back to the money thing again.

Conclusions:

Airplanes don't run on fuel, they run on money.

If you want a fast airplane, you build (or buy) one.

There is no replacement for displacement.

These are the laws of altitude as defined by me.

CJ

[Spike]

Yes CJ, you may be onto something. However we must not forget to honor the law of diminishing returns. Remember that each foot higher that you go the more money each additional foot costs. And we must not also forget the surcharge for the rate at which your add those additional feet. The faster that you add those feet the bigger the "power" surcharge that is levied against you.

-- John

[captain_john]

Indeed! Case in point: Proteus

...and to an even greater extent, SS1.

Recently I exchanged emails with Bob Waldmiller who is on the Scaled Composites team and tried to glean a bit of the future from him. No such luck! They are a tight lipped bunch over there in the desert!

CJ

[Jim Martin]

Thanks guys. I too was curious about adding more hp don't know why it will do more than I need and then some.Happy New Year

[mustang]

Yes, I read that article in the RVator recently. Basically, in a nutshell, if you put in more power, the temptation to cruise faster will put the airframe in the jeopardy zone due to unforseen gust loading. The longer wing of the nine has the potential of overstressing the spar somewhat easier than the 4, 6,7, 8, which all have shorter wings. That is why the "9" has no aerobatic rating, lower "G" rating and a lower limit on the Vspeeds.

Airplanes, like boats, are all compromises, and the lower stalling speed (by means of increased span) of the 9 has a penalty that must be paid accordingly.

The latest RVator compilation (21 Years of RVator), is highly recommended reading for newbies to get some sense of history, engineering, and performance information of the RV line. I read it every chance I get. The latest iteration is pretty much up to date with all the most pertinent articles ever written from all the issues and is available for around 30 bucks online. If you don't have it, get it.
Cheers, Pete