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Build Light; Go Fast

StuBob

Well Known Member
Perusing this site while the primer dries, I find many admonishments to "build light." Was it Art Chard who said to "add lightness?" Sounds good to me. But where does this lightness come from? Since I'm just getting started, I have plenty of opportunity to add it everywhere from the rudder forward.

A related but separate issue is speed. I have a Bonanza. I REALLY want my RV to be a Bonanza killer. But some things remove lightness while adding speed.

So......

1)What are some concrete examples of how you've "built light" or seen it done? I can think of a handful: Minimize priming. Minimize interior/soundproofing. Maybe minimize avionics, but they don't weigh what they used to. I suspect a G3X weighs less than steam gauges with a vacuum pump and plumbing. Light prop (composite or wood). Parallel-valve engine. Polish, don't paint. Lightweight battery.

2)What are some concrete examples of how you've gotten a fast airplane, or known of others to get one? Maybe: More horsepower -- angle-valve 360, Rocket, etc. Constant speed prop. Build light!

But angle valve motors and constant speed props add more weight than you'll ever save by minimizing the interior.

So, tell me your experience with building light and flying fast!
 
I think my biggest mistake in this area was painting! The bottom of the wings, HS, and control surfaces should have had the very minimal paint. Just enough for corrosion protection. Full color saturation is not needed. No one ever looks at the bottom of the plane except me!
 
Did it!

Hey Stuart,

Search my posts. I spent a lot of time thinking about how to keep it light and fast. I posted most of my ideas in one spot. I ended up with a 975 lb RV8A that cruised 205mph at 10,500 on 160hp.

Lance
 
Before you get all crazy - I would really love to see what the difference is in speed between a "fully loaded" RV, versus one, as you call it is "kept light".

If you're only getting a few knots faster by keeping it light, is it really worth it? Even 5 knots faster... does it really matter? I'd rather have all the "creature comforts" and be 5 knots slower
 
Building light is a mindset more than a technique. Yes, your examples are valid, but building light should be on your mind with every decision you make. Build the airplane for the mission, but make it as light as you can to meet that requirement. It makes no sense to minimize avionics if you intend to fly hard core IMC; on the other hand, don't do like the builder of my Rocket and run 14 AWG wire out to power the nav lights. Minimize flex hose wherever possible, and when needed, run the shortest hose you can. Sure that little sender manifold Vans provides is convenient, but does it make sense to run 5+ feet of firesleved hose back and forth across the firewall when a 6 inch hose, an adel clamp and a little extra wire would serve the exact same purpose? Similarily, do you really need a length of firesleved hose to feed the MP guage? No. Not at all. How about 3 axis trim? Slightly nice to have but is it worth the added weight? I didn't think so on my Rocket and now I'm building a new aileron and rudder after removing the servo's, tabs and wiring.

Power adders like going with an angle valve engine will improve the power to weight ratio of an identical airplane, but go overboard and a lighter, lower powered example will match or beat yours. Added power is a tough way to build all out speed with RV's because they really start hitting the wall. More power generally gives you better climb, but not a whole lot of speed. If you want speed, then pay attention to fairing alignment, rigging, and probably most important, cooling drag.

But now is the time to be thinking about light and speed - it's very tough to change things once the airplane is flying.
 
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"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.
 
Building light is a mindset more than a technique. Yes, your examples are valid, but building light should be on your mind with every decision you make. Build the airplane for the mission, but make it as light as you can to meet that requirement. It makes no sense to minimize avionics if you intend to fly hard core IMC; on the other hand, don't do like the builder of my Rocket and run 14 AWG wire out to power the nav lights. Minimize flex hose wherever possible, and when needed, run the shortest hose you can. Sure that little sender manifold Vans provides is convenient, but does it make sense to run 5+ feet of firesleved hose back and forth across the firewall when a 6 inch hose, an adel clamp and a little extra wire would serve the exact same purpose? Similarily, do you really need a length of firesleved hose to feed the MP guage? No. Not at all. How about 3 axis trim? Slightly nice to have but is it worth the added weight? I didn't think so on my Rocket and now I'm building a new aileron and rudder after removing the servo's, tabs and wiring.

Power adders like going with an angle valve engine will improve the power to weight ratio of an identical airplane, but go overboard and a lighter, lower powered example will match or beat yours. Added power is a tough way to build all out speed with RV's because they really start hitting the wall. More power generally gives you better climb, but not a whole lot of speed. If you want speed, then pay attention to fairing alignment, rigging, and probably most important, cooling drag.

But now is the time to be thinking about light and speed - it's very tough to change things once the airplane is flying.
This is as true as it gets! If it is your goal then EVERYTHING you build, assemble, install should be examined to determine what is absolutely necessary and what can go. Decisions on every system will affect the weight.

Here are just a few examples that I dealt with when trying to keep it light. Some were realized in the construction of components, some were decisions on what systems to install and how they would be installed:

Decisions:
  1. Install a 180 HP IO-340 instead of 180 HP IO-360
  2. Install Catto fixed pitch prop instead of constant speed prop
  3. Install all electronic glass panel with no round gauges
  4. Did not install passenger side brake pedals
  5. Installed standard Van's baffle kit instead of plenum
  6. Used Van's supplied plastic brake lines instead of stainless steel lines I had originally planned installing
  7. Install wiring for lights in wings, tail, etc. without conduit. Wires are just run through ribs and bulkheads using snap bushings and secured with lace.
  8. Install new LiPo4 battery (recent decision that saved 12 lbs)

Construction:
  1. Any bracket or flat plate surface that had area to do so, I drilled out lightening holes. Saved only ounces on any given individual component but as a whole saved a lb or two overall. Examples of this include the plates used to mount EFIS magnetometers. I weighed these plates before and after the lightening holes during construction. each of the two plates lost 2 ounces after drilling out the lightening holes.
  2. used lace to tie electrical wiring instead of zip ties. Again minuscule individual savings but does add up with everything else. Plus there is the added benefit of not dealing with those sharp edges that slice your hand open if you are careless with trimming the zip ties.

Most likely other items I am forgetting at the moment but everything adds up if you are serious about weight savings. It really is a mind set more than anything else.
 
It saves about a pound and it's so easy....

Replace the AN365 nuts with MS21042.

And less than a pound and not as easy, round every corner.

Dave
 
A pound here, a pound there. I think before I go crazy with all the little variations, I'll get naked in front of the mirror and ask myself if I can trim a few pounds here and there. ;)
 
here are some engine related notes I copied from here and elsewhere on the net. sorry but I don't know who wrote this.

"Here are some thoughts on using the 0-320 in the Panther. The E2D dyna focal is listed at 268 lbs. This weight is from days gone by before light wt. starters and alternators, taper fin cylinders, and magnesium sumps all of which can be installed to bring the weight down from 268 to the 240-245lb range. The sky tec starter is @ 6 1/4 lbs. I'm not sure about the B&C 8.5 amp alternator but I think it weighs about 1/2 of a 20-40 amp up on the front. The starter ring gear can be modified by shaving off the V belt drive pulley and drilling lightning holes in it. I just did one and it went from 6 3/8 to 5 lbs, or Sky dynamics has a magnesium one that weighs less. Changing out mags to P-mags and using auto plugs instead of standard ($30) aviation plugs will reduce another 6-7lbs. The magnesium sump is 7 lbs lighter than the standard sump.

On my last project I built a set of intake tubes out of aluminum and saved 2 1/4 lbs. If I remember correctly the taper fin cylinders are 2 lbs each lighter so save another 8 lbs. there. One more area is the oil screen vs. the oil filter adapter and oil filter. I would elect to use the standard oil screen and housing which is @ 1-1/5 lbs.

Another big area is using carbon fiber plenums instead of standard engine baffling. Take off at least 5-6 lbs and the plenums do a great job at cooling.
The bottom line is simple. The 0-320 can be made a lot lighter than original--it just boils down to how much money you are willing to spend to get rid of each pound of weight. Any of the above mods mentioned do not take away from the safety or longevity of the 0-320. I hope this info helps when you need to decide on your Panther engine. Larry Vetterman.

Narrow Deck 0320 fitted with tapered intake tube sump. I am told this sump and engine combination can save about 18 lbs over a wide deck regular sump. You should verify this. Bart at Aerosport Power in Kamloops BC stockpiles these kinds of parts for Super Cub enthusiasts.
If you want a really light weight sump, see if Cubcrafters will sell you theirs. It is reported to save 10 pounds over the normal cast sump. Not sure what it saves over the tapered intake tube sump.

A B&C alternator driven off of the accessory drive will save you some weight and no need for a drive belt. The output is limited, but no problem if you dont have a lot of avionics. I have one on my Bucker."
 
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. Parasite drag is the enemy. Getting antennas inside the airframe, fairing any lumps and bumps, minimizing cooling drag, close fitting panels and cowling, fairings etc, that's what will buy you kts. That and optimizing your engine/prop combination and minimizing cooling drag.

Saving 10 lbs will likely have no impact on top speed whatsoever. But it will benefit other things like payload, climb performance etc.
 
In many of these discussions about building light, people forget about the aircrew being part of the aircraft.

I dropped over 20 lbs and my wife did the same. Totally different flying plane now. My approach was to build what I wanted, how I wanted with weight in mind, then reduce our weight as much as possible. That also has additional positive impacts to our quality of life.
 
Light

"Simplicate and add Lightness" William Stout, Ford Motor Company, involved in the predecessor to the Ford Trimotor.
For a traveling airplane, weight will affect speed. Time to climb is affected by weight and the lighter airplane will get to altitude quicker, spend more time at cruise and beat the heavier airplane.
This is even more important if you are able to take advantage of an exceptionally strong tailwind.
 
I define "light and fast" as a good, economical cruise speed, say 170 knots or so. Most of the key elements have already been listed:

- Get the rigging right. Don't forget to look at the HS angle of attack as both of my RVs started out with nose down cruise trim. I added a .040" shim under the forward HS spar on my RV-8A to get the elevators in good cruise trail position. I added a .063" shim in my RV-10 but the spacing between the forward and aft spar is closer.

- Get the rigging right. One aileron in trail and the other up? Something is wrong. Don't forget to get first get the flaps right.

- Get the rigging right. Are you adding a rudder trim tab to compensate for gear leg fairing and/or wheel pants not aligned?

- Cooling drag. If you are adding stuff like NACA scoops and vents you are adding drag. First look to the cooling load to see what can be done. Here is example of the lighter weight parallel valve engines being able to perform better than the fire breathers (you just live with ~2000 fpm climb instead of something more). I use a plenum on my RV-10 and believe it helps a lot on reducing cooling drag.

- While a nice light fixed pitch prop will help in weight, it will be a major drawback for efficient cruise. No matter how you slice it a CS prop will have a lower RPM cruise and this will reduce pumping losses. You can make this up by adding fuel, but then you violate the primary objective. This also eliminates the tradeoff with a high pitch cruise prop being a dog for takeoff and climb.

As previously stated, unless you are adding a lot of weight a few pounds for insulation and such is way down the list of things that will slow you down. Make the airframe work right and match the engine/prop to the mission and 90% of your objective is achieved.

Carl
 
This is a case where Michael and I agree. Prior planning on the project with the goals written down is essential. If you want to build it light, I'm pretty sure there are a 1000 places where you can save some weight. Yes, fluidlines are one of those areas. Just like wiring, engines props, inverted oil systems :eek:, avionics, etc.

Get real data in the planning stage, then stick to the plan. Creature comforts add weight.
Tom
 
Real Comp

My RV7 weighed in at 1133. Another 7 at our airport weighed in at 1040. Almost 100lbs difference. Most of this was in the panel, interior and paint. We had the same engine built by the same guy, the only difference. I had a WW200 and he had a Hartzell Blended airfoil. Throw in about 40lbs pilots difference and we were at about 130lbs apart.

In flight at the same power settings, I would pull away quite easily.

As has been noted, every effort to save weight in the basic build might yield 4 or 5 pounds at the most. Where the weight is saved is in the panel, interior and paint.

The real benefit of light is a better climb rate. You won't really see more speed. Where I think you gain the most speed is building CLEAN. Make sure everything fits and your glass work is as perfect as possible. Clean will help speed more than weight.
 
HP

You read lots of post that say if I had to do it over again I would have went with the 180 instead of the 160 hp does make a difference,
Bob
 
A pound here, a pound there. I think before I go crazy with all the little variations, I'll get naked in front of the mirror and ask myself if I can trim a few pounds here and there. ;)

This x1000. I've lost track of the number of cyclists who like to point out how light their carbon fibre bikes are when I ride up on a heavier aluminum one with disc brakes. They get awfully quiet when I ask if that lightness is needed to offset the spare tire they carry around their midsection.

My -6 was 997# when I bought it, and after some panel upgrades, removal of vacuum system, and addition of classic aero interior, it's only up to 999#. Not the fastest, but I haven't spent *lots* of time on drag reduction... Yet.
 
5kts for leather and comfort is worth it, i've flown bare bones airplanes and fully loaded ones, fully loaded is the way to go
 
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.
 
"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.
 
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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).
 
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).
 
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. :)
 
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.
 
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.
 
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.
 
With respect to cost, there is a big difference between a "basic" arplane and a "light" airplane. Van made many choices in the RV design which were cost driven. Off the shelf materials that may be heavier than required but met cost targets, for example. Off the top of my head I would not be suprised if you could shave 50 pounds off a typical RV airframe if Van ignored cost and instead designed to the absolute limit of performance. You would see machined hinge fittings instead of steel heim joints, tapered longerons, machined structure instead of bolted/riveted assemblies, exotic hardware, etc...

But going after that 50 or so pounds would drive the cost of the kit right through the roof. Make no mistake about it, "light" is expensive.

But when you are building light, we have the luxury of time. We can take the extra hours it takes to select the right materials, cut lightening holes, radius the edges to the minimum, and do all the other labor intensive things that define craftsmanship.
 
The discussion to build light should in many cases be done at the kitchen table. Looking at our population, losing a few pounds individually :) can reap as much or more benefit than just shaving a few ounces here and there on the aircraft structure.

Cheers Hans
 
The discussion to build light should in many cases be done at the kitchen table. Looking at our population, losing a few pounds individually :) can reap as much or more benefit than just shaving a few ounces here and there on the aircraft structure.

Cheers Hans

+1!

HomerSimpson15.gif
 
Build light to save money is more the reality than go fast.

A light weight airplane costs less to build and operate over the years.

If you want to go fast, increase HP.

Look what happened to the BF109 many years ago, it went from something like 631 HP to 1455 HP.

Forget light weigh, go fast. Hang a bigger engine to go fast. :)
 
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. Parasite drag is the enemy. Getting antennas inside the airframe, fairing any lumps and bumps, minimizing cooling drag, close fitting panels and cowling, fairings etc, that's what will buy you kts. That and optimizing your engine/prop combination and minimizing cooling drag.

Saving 10 lbs will likely have no impact on top speed whatsoever. But it will benefit other things like payload, climb performance etc.

If your speed you are trying to increase is around a closed coarse, like Reno, then weight can be a big effect as you are in >1g flight most of the time. Every lb is magnified by the g's you pull in the turn bumping up induced drag. Straight and level weight not big driver in speed.

For long straight cruise I would say building light increase speed (actually decreases travel time) because to stay below TOGW you may need to off load fuel making you have to maybe add a fuel stop and therefore slowing your overall average speed. I built light to allow for a cross country baggage load and full fuel and stay within my established TOGW. As an aerospace engineer and aircraft designer, I consider TOGW as a boundary and not a guideline.
 
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If you want to go fast, increase HP.

Look what happened to the BF109 many years ago, it went from something like 631 HP to 1455 HP.

Forget light weigh, go fast. Hang a bigger engine to go fast. :)

Power required goes up as the cube of speed. To get 5% more speed you need 15% more power; 10% more speed is 33% more power. Going from 180 to 200hp will only net you about 3.5% more speed.

You're much better off focusing on drag reduction to get speed, than adding power.


My take on "build light" in general: Of course, you never want to have useless weight. And all other things being equal, lighter is better. But there are limits. If your efforts to make the airplane light wind up making it unsuitable for your desired mission, you've defeated the purpose. Spending a few extra pounds and dollars on a comfortable interior and additional avionics is probably worth it if you travel a lot with your airplane. Saving half a pound with an hour's work may well be worth it; saving that half a pound if it takes 40 hours' work, maybe not so much. Some weight savings might not be so obvious, either--get your fuel burn down running LOP and/or cutting drag, and a flight that may have taken 18 gallons of fuel might only take 15 or 16. That's a 10+lb weight savings right there.
 
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