Pondering weight...

cjensen · Post by **cjensen** » Tue Dec 19, 2006 9:14 pm

I thought I posted this question here too, but I may have hit preview, and didn't submit before I left...

Anyway, I was thinking about how much thought we put in to building a light airplane. Let me preface this by saying that this doesn't have anything to do with an engine choice, interior material, loaded panels, paint, or anything. I just wonder how a 1200 pound airplane with a 150 pound pilot will fly compared to an 1100 pound airplane with a 250 pound pilot. What about when they are both flown at their listed gross weights?

I was thinking about this because everybody says that the light RV's fly better than the heavier ones. That's probably true for one pilot at a given weight flying two different airplanes, one heavier than the other, but how many of us fly two RV's regularly solo?

Interesting to me, how 'bout you?

captain_john · Post by **captain_john** » Tue Dec 19, 2006 9:22 pm

Chad, I saw this posted over "there" but didn't understand it then, so I didn't answer.

I guess I don't understand the question here either, but here I will ask you more about what you mean by this.

To me, an airplane at gross is an airplane at gross... regardless of how it gets there, be it due to avionics, engine, people or fuel.

They DO say that light RV's are better than FAT ones.

I know that the Citabria likes it light too! You especially feel it on the taxiway!

Sooooo...

What was the initial quesation again?

CJ

cjensen · Post by **cjensen** » Tue Dec 19, 2006 9:28 pm

I'm not even really sure myself. I guess that's why I'm pondering it.

It may very well be a rhetorical question. Seems the answer is in the question...

I guess I really have no way to answer the question since two pilot's view of how an airplane flies is subjective. I can't weigh two weights and fly two airplanes with 100 pound difference in empty weight, so it may not be answerable.

This makes sense in my head, trust me...

captain_john · Post by **captain_john** » Tue Dec 19, 2006 9:36 pm

Well, I know we both have flown big airplanes both alone and at gross!

The Cherokee Six certainly behaves differently with a full load than without!

Rate of climb, taxi turns, flare, yada yada yada...

The difference lies in CG and this is one reason why I chose the -7. Consistent CG placement regardless of souls aboard. Damn dog in the baggage compartment will throw it all off, though!

CJ

Wicked Stick · Post by **Wicked Stick** » Tue Dec 19, 2006 10:06 pm

LOL, especially when Wyatt will want to jump up front and start knawing on the co-pilot stick as it's moving

captain_john · Post by **captain_john** » Tue Dec 19, 2006 10:11 pm

HA!

He is working towards his Private Pilot Certificate!

CJ

Dan A · Post by **Dan A** » Tue Dec 19, 2006 10:18 pm

Okay, as I understand the question. a 1200 lb. plane with a 150 lb pilot vs. a 1100 lb plane with a 250 lb pilot.
My RV8 at gross is 1800lbs and all RV8's are grossed at 1800 lbs. This means that if my plane weights 1200 lb empty,I can have a pay load of 600 lbs. If my plane weights 1100 lb empty, then I have a payload of 700 lb. Gross weight is gross weight reguardless of how you slice it! Since the given weight is the same in both cases then your aircraft will fly the same. Where you set as a pilot is near enough over the CG you probably wouldn't be able to notice the difference!

Dan

Wicked Stick · Post by **Wicked Stick** » Tue Dec 19, 2006 10:23 pm

Chad,

I'd have to say that it wasn't a concern (weight) when I first started working on the tail feathers. But after flying the RV-4 for some 125 hours now, and getting to realize how less weight helps it to perform better in climb and take-off distance, I've started to keep an eye on what I do/put inside my RV-8.

I'm not going to go nuts trying to reduce the weight by drilling holes everywhere, but I do try to save weight were I can by going with a non-counter weighted engine, Grove Aluminum gear legs, and probably a composit prop.

There are a few heavy objects that I consider "creature comforts" and while not necessary, it's simply what I want in my airplane. (autopilot w/servos, heated seats, slightly thicker canopy from Todds.)

That's the beauty of this kit building venture we have all undertaken, is that we can build-em exactly the way we dream about it.

Wicked Stick · Post by **Wicked Stick** » Tue Dec 19, 2006 10:30 pm

Dan A wrote:Okay, as I understand the question. a 1200 lb. plane with a 150 lb pilot vs. a 1100 lb plane with a 250 lb pilot.
My RV8 at gross is 1800lbs and all RV8's are grossed at 1800 lbs. This means that if my plane weights 1200 lb empty,I can have a pay load of 600 lbs. If my plane weights 1100 lb empty, then I have a payload of 700 lb. Gross weight is gross weight reguardless of how you slice it! Since the given weight is the same in both cases then your aircraft will fly the same. Where you sit as a pilot is near enough over the CG you probably wouldn't be able to notice the difference!
Dan

Dan,
That is probably true if all things are equal in side by sides, but in a tandem setup, I think the weight difference of 100 lbs in pilot weights will make a bigger difference in how the amount of stick force is needed in pitch control. So I beleive it WILL effect its characteristics for tandems.

If I had to choose between 2 airplanes on the ramp with all things being equal except empty weight, I'd always choose the lighter one to fly.
10 lbs probably isn't much to worry about, but 100 lbs will be a big difference in my opinion.

papakeith · Post by **papakeith** » Tue Dec 19, 2006 11:05 pm

well I'm just screwed then aren't I

JohnR · Post by **JohnR** » Tue Dec 19, 2006 11:13 pm

With my wife going along on trips I need to keep it light. Ooooh, that didn't sound quite like what I meant to say. She is a light weight but likes to take lots of stuff is what I mean. Therefore, I'll build it as light as I can in areas. I'm still going to add the stuff I want though, so it will weigh what it weighs. I've been loosing a few pounds so if I can continue down that road that will help also.

I'm sure glad Karla doesn't read this board!

l & d lewis · Post by **l & d lewis** » Wed Dec 20, 2006 12:09 am

I look at the question a little different. An airplane at gross weight is an airplane at gross weight. The only performance variable is the center of gravity. I'm building mine light and powerful because I want a hot rod, day/night VFR, and typically won't fly at gross or super long distances. That's why I chose the -8 I agree with John that when its time to travel and take Deb with me, the lower the airplane's weight the more ESSENTIALS she can take, so we both win...... Larry

1:1_Scale · Post by **1:1_Scale** » Wed Dec 20, 2006 12:35 am

I think, like others have mentioned, gross weight is gross weight for practical purposes. However, if you could find some way to distribute the weight differently, an airplane that has it's weight evenly distributed throughout the airframe won't feel as nimble as a plane that has the majority of it's weight closer to the CG. For example, a heavier wing will require more effort to get it to start and stop rolling than a lighter wing.

svanarts · Post by **svanarts** » Wed Dec 20, 2006 1:35 am

Lightness is performance in an airplane. Lighter planes burn less fuel, use less runway, and carry more goods. I built a light RV-4. The RV-7 will probably be a porker. I'm going to build light where I can but I want the creature comforts this time. I'm not concerned at all about the weight this time. No matter how your plane stacks up against another RV weight-wise, it will still be better than anything your spam can buddies fly.

JohnR · Post by **JohnR** » Wed Dec 20, 2006 4:09 am

l & d lewis wrote:I agree with John that when its time to travel and take Deb with me, the lower the airplane's weight the more ESSENTIALS she can take, so we both win...... Larry

Yeah, that's what I was trying ot say!

Post by **Spike** » Wed Dec 20, 2006 10:24 am

JohnR wrote: I'm sure glad Karla doesn't read this board!

Yeah, but she reads her email.

As for the weight thing, its amazing to me the extent that we go in our analysis of stuff. The lighter the TO weight, the better it performs in climb, economy, etc., That seems to be a given. To me, personally, anything after that is just diatribe. How much is plane vs pilot, is irrelavent it seems, TO weight is what matters.

Im with Scott, Im building a porker. At gross weight the RV will perform either better than or equal too any other aircraft Im likely able to acquire. Most likely it will be the former. Dont know if Ill get to do this again, so, this baby is getting the red carpet treatment. Ive been playing with panel ideas lately .... yup .. Ill be happy if this thing is under 1100 lbs

JohnR · Post by **JohnR** » Wed Dec 20, 2006 9:14 pm

Spike wrote:
JohnR wrote: I'm sure glad Karla doesn't read this board!
Yeah, but she reads her email.

You wouldn't! Actually, I'm sure she would think it was funny.

1:1_Scale · Post by **1:1_Scale** » Wed Dec 20, 2006 11:27 pm

JohnR wrote:
Spike wrote:
JohnR wrote: I'm sure glad Karla doesn't read this board!
Yeah, but she reads her email.

You wouldn't! Actually, I'm sure she would think it was funny.

Nice move with the reverse psychology