Does a hole weight less then balsa?

[Paul Taylor]

So I’m looking to loss some more weight. I have seen a few models with cut outs in the side of the fuse behind the wing. Does this really save weight? TIA

[Brett Buck]

So I’m looking to loss some more weight. I have seen a few models with cut outs in the side of the fuse behind the wing. Does this really save weight? TIA

   Depends on what you are covering it with. Tissue/dope, probably no help because it takes much more dope to fill the tissue over the hole than over the wood

      Cutting holes in things can save some weight, but usually weight is a function of over-building, less-than-stellar workmanship, less-than ideal balsa, and *too much paint*. It is very rare that weight is the sole reason that an airplane does not fly well.

     Brett

   

[Dan McEntee]

   

   I think that after the model has been built is the worst time to try and make it like swiss cheese. Especially if the design did not call for holes or cut outs. Lightness has to be engineered and built into the design and then executed with proper wood selection. I have been down this road before like many others. I remember when I got my first accurate O'haus triple beam balance scale to weigh parts for free flight models and for anything else I could fit on the pan. The proof is weighing the structure as it is before hand, and then weighing the cutouts after you you are finished . i remember being shocked at how little came to that first time. If you take all the cut outs from a Nobler size type airplane and put them on a scale it would be very informative about using this practice.
  Type at you later,
  Dan McEntee

[peabody]

Call Bob Hunt: he sells Helium filled lightening holes.

[Paul Taylor]

And here are a couple more photos that show the judicious use of lightening holes in wing ribs on two of my Lost-Foam wings for my twin motor models. The resulting wings were extremely strong, torsionally resistant, and were extremely light.

Later - Bob Hunt

Thanks Bob for the validation and input.
I know it’s all in the design, wood selection and building skills.

I am just amazed that large stunt planes are built so light. One of my favorite movies is your video of Billy and all his planes. 40 size planes weighing 36 oz. And the Geo XL under 60 oz. I’m struggling to keep a Vector under 50 oz. 😩

[Dave_Trible]

Thanks Bob for the validation and input.
I know it’s all in the design, wood selection and building skills.

I am just amazed that large stunt planes are built so light. One of my favorite movies is your video of Billy and all his planes. 40 size planes weighing 36 oz. And the Geo XL under 60 oz. I’m struggling to keep a Vector under 50 oz. 😩

Well Billy uses trained termites.

Dave

[Sean McEntee]

... our models pull about 15 or so G's in a tight corner. Let's round that up to 16 G's. So that means that one ounce becomes a pound in a corner theoretically (perhaps literally...). A single lightening hole does very little to reduce the weight of a model significantly, but a bunch of them can make a difference. The real difference is in what I like to refer to as "light weight consciousness." Looking at every piece of balsa or plywood that goes into your model and asking yourself the following questions can - and will - reduce your model's finished weight. Question 1: Is this part as light as I can make it? Question 2: Is this part strong enough to do the job? Question 3: Is this part stronger than it has to be? Chances are if the part is stronger than it has to be, it is also too heavy.



Later - Bob Hunt

           

      Very interesting; I never thought of it that way.  Thanks again for the perspective.

      I've been building and flying Free Flight quite a bit in the past few years and, ironically, I've been chasing question 2 alot.  I'm finding, for FF purposes anyway, that the relentless pursuit of lightness often results in models that just don't last very long.  Ive had a few HLG wings fold up on launch, so theres an obvious example of structural failure.  More have just succumb to the field environment:  lots of yucca plants and bushes that tear up models that havent been built to withstand it.

[Serge_Krauss]

A good argument can be made for saving weight behind the wing, since that also allows a shorter/lighter nose. However, most don't seem to design around that savings. I know I haven't - yet. In my profile originals, I've missed slightly and had to add the weight back at the aft end to get the c.g. right (Ha!). The big thing for me though is not "holes", but structure to stiffen my profile fuselages. I cut out an appreciable portion of half-inch thick fuselage material between the wing and empennage in order to insert diagonal truss bracing. I then use 1/16" balsa sheeting to close the boxes and meet up diagonally with 1/16" ply doublers on the nose for a smooth fit. A 5/8" (legal) profile fuselage results. The plane is markedly stiffer in torsion. Epoxied fiberglass laminated on the bias adds to that, and the fuselage doesn't twist under aero loads. I've had to add over 1/4 ounce to the tail to get the c.g. right; so my weight savings is not important, but if I'd guessed better on nose length, I could have saved enough weight to be worthwhile. Overall, that particular fuselage and plane ended up over five ounces lighter that the original wrecked model with the same wing, smaller tail, and a solid 1/2" thick fuselage, because I saved weight in the narrower silhouette.

(I've posted pictures of that plane too often)

SK

[phil c]

Paul, there are lots of ways to build light without changing the structure.  Just using lighter, thicker balsa works wonders since you can 1/32-1/16thicker sheets in strategic places.  It's bad that balsa of any sort has gone up a lot.

Any c/l plane needs to be as light as you can build.  When building the fuselage keep in mind- the fuselage gets most of its strength from the height to thickness ratio. Plain flat 1/8in sides generally work out.  Cutting round holes in the sides weakens them.  It would be get the strength back by gluing 1/8-1//4 longerons along the top and bottoms of each side.  Your going to have to replace the weight loss with something else. 2-3 3/32 stringers on the outside of the fuselage stiffens things up.  They can also give the plane a very distinctive look to flat sides and can mimic many different full size planes.

Spring is coming to most of the country is coming soon.  Hurricanes are fewer, tornados are supposed to be getting fewer but unfortunateley stronger in some places.
I'm cold-blooded and tend to sleep in the winter/

Phil C

[Mike Griffin]

   Depends on what you are covering it with. Tissue/dope, probably no help because it takes much more dope to fill the tissue over the hole than over the wood

      Cutting holes in things can save some weight, but usually weight is a function of over-building, less-than-stellar workmanship, less-than ideal balsa, and *too much paint*. It is very rare that weight is the sole reason that an airplane does not fly well.

     Brett
I agree 100%.

Mike
   

[Dennis Toth]

Paul,
I have used lighting holes in profile fuse core and covered with thin sheet balsa and did save a 1/4oz when it was complete vs. the solid plank. For the built-up fuse one thing that Phil mentioned, and others have at times suggested is using thinner wood. Example if you have 1/8" 4 lb/ft^2 and replace with 1/16" 8 lb/ft^2 it is a push. However, the 8 lb wood is stronger than the 4 lb wood so you could get some savings going with say 6 -7 lb wood. However, as Bob said you need to have structure to support the thinner wood (note the horizontal bracing in Bob's fuse photo).

If you have a kit you could replace wood but the other option is to sand selective areas to shave off some weight. A belt sander with fine grit belt can make quite work of it. The other big area to save weight is in the nose. Here is where lighting holes can work. Some have used increasing size holes in the starting at the back of the firewall former. Another way to reduce the motor mount weight is to taper them from the back of firewall back down to a 1/16" at the end.

Another big area to save weight in the nose is the engine/muffler/ tank and wheels. This is one area of concentrated weight. If you reduce weight in the nose and have to add tail weight to correct the balance it will be much less that what was removed from the nose because of the long moment the tail has. Problem is some engines need specific types of mufflers to work so compromise is needed.

Last area is as Brett said PAINT!! Filler and primer can add tons of weight. Type of paint also has a big impact. Many rattle cans have acrylic lacquer as the base and it is heavy. You need to go really thin with this type of paint also for epoxy's and top clear coat.

Best,        DennisT