Enough power?

G'day,
I was just wondering if 180 HP was enought for the -7?,..or wdoes it really need a 200 hp???

Thanks
JJ

180HP is PLENTY. Think of a Cherokee 180. It has a gross wieght of 2400 pounds. -7's are something like 1600 at gross. 180 HP is enough for the Cherokee, and will REALLY perform on the RV.

200HP is great too, but it does add a little wieght. Van's just ran a test against two rotary powered RV-8's (see other threads on this story/issue), and the 180 horse -8 was actually faster than the 200 horse -8 for some reason.

Go figure. 180 is fine.

200HP is great too, but it does add a little wieght. Van's just ran a test against two rotary powered RV-8's (see other threads on this story/issue), and the 180 horse -8 was actually faster than the 200 horse -8 for some reason.

Go figure. 180 is fine.[/QUOTE]

Different props, for one thing.

That the 200 HP is a little bit heavier than the 180 may be just what you need in an RV-7. If you study the database of RV weight and balance on Dan Checkoway's website, you will see that most -7s are too tail heavy to carry full bagage without exceeding the aft limit. Dan's -7 is one of a few that are just right...and he has a 200 HP IO-360 with a CS prop. That combination may be nose heavy in a -8, but not necessairly so in a -7.

In a -7, you want *no* extra weight behind the center of the fuel tanks, and you need some extra up front.

Dave Cole
RV-7 Wings

Dave, that is my strategy exactly!

I have seen those W&B scenarios and am seriously considering the IO-390.

CJ

IO-390 -> Anyone running one yet?

Hey CJ!

I am still in your camp on the IO-390 for the -7 but have you asked anyone about the CHT's when pourin' the coals to her? Lycoming evidently didn't have the right people in their booth at OSH because the two people I asked just said, "oh, the temps are no different..." That would be great but I find it a little hard to believe.

Have you done any checking? You're a LOT closer to your Power Plant Purchase than I am...

- Peter

Peter, I am still a ways away... buuuut, I have talked to an -8 driver (Dick Martin) who is using the combination I am looking at quite seriously. That combo is the IO-390 coupled with the Aerocomposites airscrew.

Dick spoke very complimentary about the package and supported everything I had heard around OSH from all the vendors who composed a 390 package.

Being low compression, it does run cool they say.

Fortunatly for us, there should be a few more flying before we lays our monies down and takes our chances.

I just like the fact that it makes a solid 200 (actually 210) horsepower at altitude. It should give a spirited rate of climb through the altitudes.

Have you seen the www.aerocomposites.com prop? It is pricey, but performance is why we build the Van's package. Isn't it?

CJ

BTW, I took these pics of Dick's plane while at OSH.







He took 6th place in the OSH race this year in the sport class. He ran at 221.8 knots. Rumor is that Van said he shouldn't be allowed to run in the RV class because of the engine, so he ran in the sport class with the glass stuff.

Click here for the race results

It is quite a package!

CJ

I find that 180hp is just fine. I can push it to VNE at altittude. 200hp would push it there a lot quicker at lower altittudes. Lot of extra money for very little return.

Norman

Indicated or true or groundspeed?

Norman CYYJ said:

I find that 180hp is just fine. I can push it to VNE at altittude. 200hp would push it there a lot quicker at lower altittudes. Lot of extra money for very little return.

Click to expand...

Huh?! You're saying your RV hits Vne, and we're talking INDICATED airspeed, in level flight, at altitude no less? Specifics, please...model RV, etc.

My RV-7 has a Vne of 230mph. The fastest TRUE airspeed I was able to get out of my 200hp equipped RV-7 was about 217 mph at a density altitude of 8000'. In level flight I can't true out at Vne, let alone indicate Vne.

Maybe Tracy Saylor or Dave Anders or somebody like that can hit Vne, but what's your secret Norman?

)_( Dan
RV-7 N714D
http://www.rvproject.com

No mine is faster

No mine is faster, oh yea, mine is faster and bigger


Look HP is great. However if speed is your goal, reducing drag is the way to go. Speed without fuel burn. There are many things you can do to reduce drag.

From Van's data (which is very accurate)
180 HP RV-7 can do 210mph (true top speed, sea level)
200 HP RV-7 can do 217mph (true top speed, sea level)

So 20 hp is good for 7 miles per hour.

If you use a plenum and Sam James style cowl alone you will pick up 7 mph. You can mod a vans stock cowl and baffles to achieve the same effect as Sam's cowl/plenum kit, however you need to read up on the aerodynamics. Sam's kit is pretty good, so if you copy it you will achieve similar results.

Recommend Kent Paser's book, Economy with speed.

Obviously 200 hp with a cowl/plenum will go faster than a 180hp.

I agree with Dan, if you are not turbo charged you will not exceed Vne if you can't exceed it at Sea Level. However Vne goes down (indicated airspeed wise) with altitude. I'll explain but trust me Vne, the red line on your airspeed gage is good for SEA LEVEL only. Still with out a turbo you will not exceed Vne or flutter margins in level flight for a stock RV. Decending out of 15,000 or 10,000 feet, watch it and don't fly red line because you will have negative flutter margin.

Cheers George

IT is Too big

Captain_John said:

He took 6th place in the OSH race this year in the sport class. He ran at 221.8 knots. Rumor is that Van said he shouldn't be allowed to run in the RV class because of the engine, so he ran in the sport class with the glass stuff. CJ

Click to expand...

He can't run in the Oshkosh RV class because his engine is larger than 360 cu in. IO-390 ?

That is all, his engine is punched out. At least he is honest. He did run in the Sport Class (unlimited up to 1000 cu in) not the RV or Formula FX classes that have max 360cu in limit. There are no tech inspections, so no one would know. Other races use a HP rating for the classes. There is a lot of cheating there. Those little O-200's an O-235's can put out 150-160 hp, but they run in the 125hp class. I guess cubic inches is the best way to go.

Tracy Salyor has an O-360 180HP and is very fast. After making all the drag reduction mods he finally went with a small increase in compression. It made very little difference. Dan will tell you his IO-360 (200hp) engine throttled back and leaned burns less gas at the same side by side speed to other RV's with (I)O-360/320's, but at high power I am sure he will burn more. That 7 mph with HP is not free.

Cheers George

Personally, I am not looking to firewall the sucker and cruise for days on end at Vne plus, say... 5.

Nor am I looking to win any races.

I just want a spirited climb and short take off rolls. I know that comes in the standard package. I want the "plus" package.

Any additional speed would just be fun to use at certain times.

The other reason yours truly finds appeal is for the same reasons Dan likes his 200 hosses in his IO-360. Throttling back at a lower RPM SHOULD prove actually lower fuel consumption at the same speed of an IO-360 at 180 or 200 hp.

Now, I DO REALIZE this falls into the "Gee Whiz" category, because it is unlikely that the fuel savings (if any) won't offset the greater cost of the engine.

It is to me, the reason we fly in the experimental category.

CJ

The 390 might not be more fuel effiencent that the 360. It's more a matter of compression ratio than the avialable HP. I think that the 390 has a lower comp. ratio than the 200hp 360. Now if you built a 390 with 9.5:1 compression you'd probably put out closer to 225hp and get better fuel ecomomy at lower power settings . I don't know yet, but I'm thinking a high compression IO-360 would be the way to go if you want a good combo of power an efficiency. I guess we need a few more 390's in the air before we find out more about them.

Captain_John said:

snipped

I just want a spirited climb and short take off rolls. I know that comes in the standard package. I want the "plus" package.

Click to expand...

The way I look at it, is that more horsepower can be added insurance at high density altitudes. Last month, just down the road at the airport next door, we had a single engine Beech that lost all climbing ability, thanks to an apparent sudden wind direction change, somewhere in the takeoff process. After an intial climb halfway down the runway, it continued to loose altitude until a stall & cartwheel. Airport altitude is 4602' msl.

Living under the airport pattern, I see those "gutless" little Cessnas and Pipers all day long, in what seems like a near struggle to get the fan up front to keep pulling the fuselage & wings along with it. It always looks like one of those huff... puff ....."I think I can, I think I can" scenarios!

And then come along the RV's, Rocket's/F1's, Lancairs & GlasAirs who seem to do three to one in climbing ability compared to those "barely enough engine" Pipers & Cessnas. And of course, the difference is all a function horsepower & weight. Instead of a fan seemingly struggling to pull along it's weight, it's as though these experimentals want to whisk past the propeller!

But regardless, at higher altitude airports, having higher horsepower available, the threat of density altitude problems is diminished. To me, it's one of the best reasons possible for the "bigger" engine.

L.Adamson

and I quote,

"I've never flown an airplane with to much horse power."

I wish I could remember who said that.

I doubt many of you have flown a fully loaded 65hp T-Craft on a 96 degree day out of a 2,000 foot grass strip with trees at either end. Trust me, even a 160 hp RV will seem like a rocket ship. That?s why I?m not worried about the little 140 hp O-290-D2 I?m putting in my -9. 1,150 fpm climb at GW sounds outstanding to me!

N941WR said:

"I've never flown an airplane with to much horse power."

I wish I could remember who said that.

I doubt many of you have flown a fully loaded 65hp T-Craft on a 96 degree day out of a 2,000 foot grass strip with trees at either end. Trust me, even a 160 hp RV will seem like a rocket ship. That?s why I?m not worried about the little 140 hp O-290-D2 I?m putting in my -9. 1,150 fpm climb at GW sounds outstanding to me!

Click to expand...

I still agree, never have quite enough power until you have enough thrust to get you out of trouble. (IE go vertical for an extended period of time, IE demiltarized F-16?). So, while an O-290 is "Good Enough" for your flying, a 160 isn't too much.

I hesitate to ask why you bring up a 65hp Taylorcraft up for this discussion unless you want to illistrate... well I don't know what your point was. I'm assumeing the climb rate wasn't good, but you're comparing a 60 year old airplane with a modern homebuilt. And if you meant to say than anything better than that was exceptable, that'd be just absurd.

osxuser said:

I hesitate to ask why you bring up a 65hp Taylorcraft up for this discussion unless you want to illistrate... well I don't know what your point was. I'm assumeing the climb rate wasn't good, but you're comparing a 60 year old airplane with a modern homebuilt. And if you meant to say than anything better than that was exceptable, that'd be just absurd.

Click to expand...

OSXUSER,

Even on the best of days, that old ?41 T-Craft I had couldn?t climb very fast. What I?m pointing out is you get used to what the craft you are flying can do. If your max ROC is only 200 fpm, 750 fpm, 1,500 fpm, or 3,000 fpm you learn how and when to fly with it or you don?t fly at all.

Granted, if I lived in Leadville, CO @ 9,927? I would be looking at a much larger engine than the little O-290.

I guess the question for the tread starter is why do you want more power? Better ROC, faster speed, high altitude operations, what? Once he can answer those questions he is better able to decide what is best for his mission profile. By using the T-Craft example I was simply trying to state that airplanes can be just as useful even w/o rocket ship ROC?s. Note, I didn?t mention anything about fun in that last sentence.

Since the original question on this thread was does the -7 need more than the minimum power, or something like that, Bill's comment is a good one.

NEED more power? Absolutely not. After flying a few hundred hours in the West, over mountains into mountain strips, at high density altitude, etc. in a 230hp Cessna 182, I can assure you than even a 160hp RV-7 is going to be MORE than adequate--it would blow past the Skylane in climb. Will you need to exercise common sense with a lower-power -7 at higher density altitudes? Absolutely. Would more power get you out of a situation you shouldn't have been in in the first place or allow you to fly when you wouldn't otherwise? Perhaps.

I have no problem with people wanting more power in an RV, but I think very few people would ever NEED it.

Just my opinion on the original question in this post.

alpinelakespilot2000 said:

I have no problem with people wanting more power in an RV, but I think very few people would ever NEED it.

Click to expand...

Great response!

Most people, myself included don't NEED it. We just WANT it after years of flying the spammers.

I think it is just our way of saying, this isn't your father's SPAM can!

CJ

TAS at around 15500ft on a hot day. Actually VNE is hard to get to if your heavy. But a slight down hill at WOT at altittude and your thru VNE pretty darn quick. The RV-6 I built after cleaning it up would hit VNE in level flight quite easily. The RV-7 seems slower. I think the extra 20hp would be great if I was running a constant speed prop and not this fixed pitch one, esp. during the climbs. Red line at 2700 rpm is easy to do at any altittude up to about 19000ft then the engine seems to get tired. Max height has been 24000ft in the summer. If you could ever get VNE indicated at altittude you would certainly be way to fast. Still the best bang for the buck is the 180hp engine. But great climb would be nice too, even if gas is getting higher and higher.

Cheers