Build Light; Go Fast

[LettersFromFlyoverCountry]

Originally Posted by RV7Guy

My RV7 weighed in at 1133. Another 7 at our airport weighed in at 1040.

Interested. Mine came in at 1118. And that's with fixed pitch and not much in the panel.

[vlittle]

I deliberately added a heavier battery, heavy duty brakes, larger tires, a sliding canopy and half inverted oil. The heavy battery helps my CG, the tires/brakes help in general, the sliding canopy was a personal preference and the half inverted was for aerobatics. I can gain all of this weight back by swapping the battery with an EarthX, but I would have to manage the CG shift. The EarthX would save me 23 lbs, which is how much weight I need to lose around the middle.

[GLPalinkas]

Originally Posted by brad walton

"Build light" philosophy also has more to do with handling and feel of the aircraft in flight. How it flys rather how much faster. The joy of an RV is its nimbleness.

+1 ... My -6 came in at 1034 lbs. She is lighter than most -6's I see. Not the lightest but I can really tell the difference in handling when she is fully loaded or when flying other "well equipped and appointed" RV-6's.

Had a motivational sign on my bulletin board over my workbench that read "Build Light, Fly Fast".

On a side note, I did manage to average 205+ mph in a SARL race year before last and I had no idea how to race (Racer Bob A egged me on).
My first and only race. May do it again if I'm near another SARL race.

[Toobuilder]

Originally Posted by sblack

In fact weight doesn't affect top speed that much. Weight affects induced drag, and induced drag at high speed is really not a factor...

Depends on a persons definition of "that much"... My Rocket loses about 3 knots in cruise when fully loaded for a weekend getaway. I'm right about 199 loaded, 202+ when solo.

Another thing that I see often is building braketry and other custom "stuff". If you are building a simple shelf for your GPS antenna for example, dont grab that leftover 1x1x.125 bulb angle - make a nice light sheetmetal piece out of some .025 (and cut some big holes in it). Most of the time I see these things they look more like battery trays (and could easily support one).

[rightrudder]

Or put the GPS antennas on the glare shield and dispense with the tray altogether.

[Toobuilder]

Exactly my solution. That's why I'm familiar with the hefty construction of these things - I have two in my scrap pile (where they belong).

[David-aviator]

Perhaps a better title for this thread could be Build Light; Save $$ rather than Go Fast.

A light weight airplane costs less to build and costs less to fly. Everything that adds weight adds to the cost to build.

Weight has to be accounted for in flight, i.e.; more weight requires increased AOA resulting in more drag and fuel burned for a given TAS compared to same aircraft at less weight.

It's a simple matter of aviation physics.

[sblack]

Originally Posted by David-aviator

Perhaps a better title for this thread could be Build Light; Save $$ rather than Go Fast.

A light weight airplane costs less to build and costs less to fly. Everything that adds weight adds to the cost to build.

Weight has to be accounted for in flight, i.e.; more weight requires increased AOA resulting in more drag and fuel burned for a given TAS compared to same aircraft at less weight.

It's a simple matter of aviation physics.

But as I wrote above, you need quite a difference in weight to make a significant difference in speed. The guy with the rocket lost 4 kts with a passenger, so what- 200 lbs? So 20 lbs would be 1/4 kt. Big deal. Induced drag is a tiny part of the overall drag at high speed. But going from the old style wheel pants to the pressure recovery type can buy 3-5 kts.

[Toobuilder]

As long as people are thinking about weight with every change they make, the airplane has a fighting chance. People should build the airplane they want- if they decide for example that they really need leather, sound deadener and air conditioning after an honest assessment, then lets hope they do their very best to pick the lightest method that will deliver those requirements.

Van already cut some corners on the design to accomodate novice builders as well as keeping costs down. There is nothing wrong with this and I'm sure Van did a cost/benefit analysis with every choice, but as a result, these airplanes are not the lightest they can be right out of the gate. Don't compound that problem by taking the easy way out and "overbuilding" just because you have some leftover material laying around. Weight is forever.

[sblack]

Originally Posted by sblack

But as I wrote above, you need quite a difference in weight to make a significant difference in speed. The guy with the rocket lost 4 kts with a passenger, so what- 200 lbs? So 20 lbs would be 1/4 kt. Big deal. Induced drag is a tiny part of the overall drag at high speed. But going from the old style wheel pants to the pressure recovery type can buy 3-5 kts.

But to be clear, I am still building my airplane as light and as simple as I can. Even if it doesn't affect top speed significantly there are many other advantages to having a light airplane. Less cost, less time to build, better payload,better handling, better climb and field performance.