Heavy engines rule!

captain_john · Post by **captain_john** » Wed May 11, 2005 9:38 pm

Hey All, I was just running some scenarios on Dan's site and seeing what the deal is for W&B on the -7, it seems that they are SO DAM tail heavy that putting a 200 hp and CS prop is the key to reasonable baggage compartment loading.

Check it out and tell me what you think about this?

http://www.rvproject.com/wab/

Chad, I see Jack put his data in there too!

I am thinking 200hp and WhirlWind airscrew.

CJ

cjensen · Post by **cjensen** » Wed May 11, 2005 10:46 pm

Yep, saw that a couple of days ago. He must have just sent that to Dan, cuz it wasn't there a few weeks ago.

I think he is having his -7 painted this week. I'll get a pic of it after it's done, and post it for him. Should be a head turner...of course, all of them are!!

captain_john · Post by **captain_john** » Thu May 12, 2005 5:50 am

I can't wait to see what the paint job looks like!

Well, as Dan put it somewhere, the -7's lre better with a heavy powerplant. I tend to see his logic. The CG is rear and the HS doesn't "fly" well at low speeds.

Being a taildragger, the forward CG will help the tail heavy plane during the flare in keeping the touchdown and rollout going in the right direction.

I have noticed that in his videos, he prefers wheelie landings. These are hard to do in the Citabria. The Citabria likes 3-pointers.

He also says that this plane in his opinion, is a better taildragger than trike. He also says (and Spike, you will be pleased to hear this) the -9 is a better trike than a taildragger!

Interesting! I can't wait to find out for myself!

CJ

Post by **Spike** » Thu May 12, 2005 8:08 am

Captain_John wrote: Well, as Dan put it somewhere, the -7's lre better with a heavy powerplant. I tend to see his logic. The CG is rear and the HS doesn't "fly" well at low speeds.

Hmmm, I wonder what Van's would say in response to that? I have a guess....

He also says that this plane in his opinion, is a better taildragger than trike. He also says (and Spike, you will be pleased to hear this) the -9 is a better trike than a taildragger!

Actually and quite honestly, I am neither pleased nor saddened to hear it. Its just yet one more opininion on the subject, and IMHO, unless there is a fairly sizable amount of time in type (including both variants), the opinion isn't worth much to me. I'm quite happy with my decision and thats all I need

On the other hand, you tail dragger types seem to have more heartburn concerning the location of the 3rd wheel than we -A types

-- John

cjensen · Post by **cjensen** » Thu May 12, 2005 9:22 am

Whoooaaaa...them sound like fightin' words.

Just kidding! I think there is too much debate on the topic. Some prefer one over the other and have their reasons. I'm a nostalgic person, and that emotion made me decide on the taildragger, regardless of what people and the insurance company say. I want one, I want one, I want one, therefore, I shall have one. I love both types, though. They're all airplanes, and I love them all!!

The steak dinner at OSH should be interesting!!

Post by **Spike** » Thu May 12, 2005 11:00 am

Nope, no fighting words, I assure you

I am just relaying that to me there are boat loads of opinions out there and that I think you have to look carefully as to why you put credence in one vs another.

-- John

cjensen · Post by **cjensen** » Thu May 12, 2005 11:41 am

I know, I know...

I agree with you. I'm a joker...comes naturally.

captain_john · Post by **captain_john** » Thu May 12, 2005 1:00 pm

Well, I value Dan's opinion.

I think he is quite knowledgeable and one thing I have noticed is, you tend to learn stuff along the way when you build one of these things.

I am glad that I am building what I am building too.

CJ

Post by **Spike** » Thu May 12, 2005 1:07 pm

Captain_John wrote:Well, I value Dan's opinion.

Hmm, I might have worded it a bit strongly CJ. I was not attempting to say that Dan's opinion is not a valid one, which, in effect, looks to be exactly what I wrote. What I am saying though is that I dont value that opinion any more than I do any other opinion by a builder or pilot. That is in essence why it "doesn't mean much" to me, simply because it doesnt stand out from any other opinion offered by anyone else. Hmm, hope that makes sense. I am not trying to say that Mr. Checkoway is not intelligent, etc.

-- John

cjensen · Post by **cjensen** » Thu May 12, 2005 1:31 pm

Makes sense to me.

captain_john · Post by **captain_john** » Thu May 12, 2005 7:28 pm

K, that is cool...

Run some W&B's and arrive at your own conclusion.

I agree with Dan... wholeheartedly!

CJ

Post by **Spike** » Thu May 12, 2005 7:50 pm

Hmm, I dont think that I follow you CJ. What types of conclusions am I to come to? I agree that in some loading models it would be easy to exceed the rearward limits of the CG range in the RV-7. I dont think that is necessarily an argument for a bigger engine though. To me that is more of an argument for planning your intended mission and intended passenger size and building accordingly. I would rather move the battery, ELT, etc, than buy a bigger engine because of W&B.

I am also not sure I follow the idea that the tail flies "better" with a forward CG.

Help?

Maybe a

would help

-- John

spikescopilot · Post by **spikescopilot** » Thu May 12, 2005 8:01 pm

HEY!!!!

No religous arguments allowed in here.

Take that crap to the restaurant at Osh.

(Spike is just getting testy cuz he hasn't built in a couple of weeks -- we'se be house shopping

)

captain_john · Post by **captain_john** » Thu May 12, 2005 8:11 pm

Well, ummmmmmm...

I think it is a good reason for a bigger engine!

In my experience, there is no replacement for displacement and I think that this airplane (-7) lends itself well to the heavier powerplant. Moving the accessories will have a marginal effect, but when dealing with the entire powerplant...

Here is what Dan said:

I've heard the RV-9 actually makes a relatively poor taildragger. Because the wing is so efficient, I hear it floats like crazy in the flare unless you nail your airspeed. Any benefit of the -9 being able to "land shorter" than the other models (i.e. -7) goes out the window unless you nail that airspeed.

And the touchdown speed is going to be so low in a 3-point attitude that while the wings are still generating gobs of lift, the effectiveness of the tail, particularly the rudder, will diminish proportionately. Contrast that to a -7 or -8, where you're theoretically able to touch down 3-point at a higher speed -- and the tail is still effective. Landing a -9 taildragger in a crosswind sounds to me to be hairier, more prone, than any landing in a short wing model.

Let's say you choose to wheel land your -9 all the time. Ok, so you regain your tail effectiveness, but you still need to get that sucker slowed up to lower the tail. Lower it too soon, and that big efficient wing will have you flying again. And what we're left with is this -- you need to be going SLOWER (than a -7 or -8) in your -9 when you lower the tail. That makes you even more prone to side gusts.

I'm a tailwheel snob, but even I think an RV-9A makes more sense than an RV-9. If you're building a taildragger, go for the -7 or -8, which settle into the flare easier, and are much more capable performance-wise on the other end of the spectrum. Just my 2 cents.

If it's the efficiency/economy of the -9 that appeals to you, I agree that makes good sense. I just think the -9 taildragger might not be an ideal combination of characteristics.

Just my 2 cents, theoretical at that. Flame on if you disagree. I'm open to being corrected here.

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

It is included in this discussion:

http://www.vansairforce.com/community/s ... ge=5&pp=10

What am I missing?

CJ

mustang · Post by **mustang** » Fri May 13, 2005 12:43 am

John,

The same characteristics are true for any RV. I was flying my friends "4" today and my first landing was downwind about 8 knots and I had the airspeed nailed at 70mph over the fence, Well! It took about 800 feet to stop that puppy. I only had a swath cut about 10 to 12 feet wide in the tall grass and my wingtips were threshing grass seed too. (This was a one-way strip) All RVs need to be nailed on the approach speed to make anything like Van's figures. I bounced pretty far on my first touchdown! To my chagrin, I noticed my flight instructor watching this performance sitting in a Chipmunk on the sidelines???? The worst audience I could have. Wot the Heck is he doing here??? He politely did not mention either of the landings.

The point of this is, that the stuff you mentioned about the "9", is true for all RV taildraggers. For myself, the hardest part of RV flying is slowing the dang thing down for landing. Even with flaps out, the RV feels more like a 767 as far as getting down and slowing down. It just won't do both at the same time.

Coming into our home field this afternoon, I flew across the field at 600 feet (we have a low circuit height) at 185 mph, throttled back to idle over the center of the runway, turned downwind, joining the circuit, and by the time I turned final, I finally had full flaps out and 80 mph on the ASI. I never did have to add thrust until roundout. These planes are slippery, and you really need to get your mind away ahead of the bird for a short, successful landing.

Out in the practice area today, I did a little glide test. I was curious to see how much altitude loss would occur while doing a 360 degree turn. I throttled back as far as it would go, trimmed to a glide speed of 80 mph, and commenced a gentle turn for 360 degrees. I lost 500 feet is all. I thought that was impressive. I had a passenger on board which probably helped a bit, but only 12 gallons of fuel.

It's all interesting, but when you look out at that stubby little wing out there your mind screams, "It's not big enough!"

Cheers, Pete

jim_geo · Post by **jim_geo** » Fri May 13, 2005 12:56 am

Perhaps, now I'm just thinking out loud here, perhaps a mod could be done where a lighter engine say an 0-320 were to be moved a few inches forward. Wouldn't that otherwise solve the problem if there is a problem? Like I said just thinking out loud.

captain_john · Post by **captain_john** » Fri May 13, 2005 6:00 am

Patti, I just noticed your post after I posted mine!

I wasn't planning on starting another little wheel thread with this post!

I am looking forward to OSH like you wouldn't believe!

Pete, I can't wait to try all this on my own!

Jim, I wouldn't really call it a problem. The way I see it, the larger engine is what I want anyway. It looks like the -7 is really made by Van to satisfy guys like me.

I know that Van likes lean, VFR planes, but many builders put all kinds of stuff in them and want the higher HP's. The result was a CG shift to the rear. I am OK with that!

My speculation, entirely.

CJ

spikescopilot · Post by **spikescopilot** » Fri May 13, 2005 7:43 am

Captain_John wrote:Patti, I just noticed your post after I posted mine!

John will be gone this weekend .. the board is MINE ALL MIIIIIIIIIIIIIIIIIIIIIIIINNNNNNNNNNEEEEEEEEEEEEEEEEEEEEEEEEEE!!

Guest · Post by **Guest** » Fri May 13, 2005 4:22 pm

I just spoke to Van's the other day concerning CG problems when using an 320. He said that the -7/7A was designed to work well with any engine in the recommended range. It wasn't designed to work best with any one engine. When using a 320 they supply a longer engine mount. You may have a limited cargo capacity in certain loading situations. I can certainly deal with that. He also mentioned that their -7 is equipped with a 0-320/ FP and flys very well.

Their advise: Build your airplane to your own needs, not the needs of others. They will never fly your airplane. In the end, it all comes down to personal preference. If you are happy with it then that's all that matters.

Bryon
-7 wings

cjensen · Post by **cjensen** » Fri May 13, 2005 4:24 pm

Very well put Byron!