Friday, January 8, 2010
The cooked foam episode
It's cold here in the garage. Resin likes about a week to cure in the cold and we don't have a week for each layer. Between us we have three 500w work lights so we fired them up and kept them around near the foam. We carefully monitored them to make sure they weren't too hot for the foam and got away with it for a day or so.
Next time you're building a DDWFTTW vehicle propeller in your cold garage and using quartz work lights, here's a little tip -- turns out that the last 5 minutes of the bulbs life, right before it burns out, it produces MUCH more heat than normal. We had a light that had been in the same place for hours and hours with not a problem (all the way back to the day before) and all a sudden we noticed that there was a blister on the foam and then 'poof' the bulb went dark.
After this episode, we went to Lowes and bought a propane salamander heater to bring the garage up to temp without risking the foam. We were able to sand out the blister and fill the void, but it could have been a lot worse.
Next time you're building a DDWFTTW vehicle propeller in your cold garage and using quartz work lights, here's a little tip -- turns out that the last 5 minutes of the bulbs life, right before it burns out, it produces MUCH more heat than normal. We had a light that had been in the same place for hours and hours with not a problem (all the way back to the day before) and all a sudden we noticed that there was a blister on the foam and then 'poof' the bulb went dark.
After this episode, we went to Lowes and bought a propane salamander heater to bring the garage up to temp without risking the foam. We were able to sand out the blister and fill the void, but it could have been a lot worse.
Getting rid of what's no longer needed
Each foam section had 'legs' in the back that were the reference steps for the twist fixtures. Once the top layer of glass was holding the prop in shape, we flipped the blades over and with Rick's custom foam 'scissors' we hot wired off these legs and then sanded them smooth.
When we glued the foam sections onto the spar, the resin leaked out and ran down each seam on the back of the prop. This gave us a hard 'line' at each seam that didn't want to sand easily.
After a few different attempts, we finally found that a small sanding drum on a dremel tool could be used to lower the level of each seam below the desired surface. We'll then fill these seams and sand them level.
When we glued the foam sections onto the spar, the resin leaked out and ran down each seam on the back of the prop. This gave us a hard 'line' at each seam that didn't want to sand easily.
After a few different attempts, we finally found that a small sanding drum on a dremel tool could be used to lower the level of each seam below the desired surface. We'll then fill these seams and sand them level.
Home from the Holidays
After a couple weeks of only sporadic effort, the new year has brought the team back together again. School break for the SJSU students still has a week or two left in it (we have a team meeting coming up after they return on the 14th), but Rick and I have resumed work on the propeller in Rick's garage.
After putting one layer of glass on the front side of each prop blade to create some structure, we removed the twist fixtures from the table and built a couple of clamps sets. These grab the spars and allow us to rotate both blades for sanding and the remainder of the glassing.
After putting one layer of glass on the front side of each prop blade to create some structure, we removed the twist fixtures from the table and built a couple of clamps sets. These grab the spars and allow us to rotate both blades for sanding and the remainder of the glassing.
Monday, December 21, 2009
The first of many
We've now started the rather long and rather laborious process of adding layer after layer of glass to each side of the propeller blades. We're going one layer at 0degrees and then one at 30d and one at 60d.
Here's the first layer of the first side of the first blade. While there will be no more 'shaping' on this blade, there will be a fair bit of trimming and sanding between layers.
Here's the first layer of the first side of the first blade. While there will be no more 'shaping' on this blade, there will be a fair bit of trimming and sanding between layers.
No, it won't make the Honda Insight go DDWFTTW
With both blades of the prop bonded to the spar, we had our first chance to see the general look of the entire prop assembly.
One half is filled, shaped and sanded while the other is rough.
One half is filled, shaped and sanded while the other is rough.
Tuesday, December 15, 2009
Rick got the tapered aluminum spar extension (formerly a ski pole) glued into the carbon spar bushing and the final sections bonded. A bit of filling and sanding and we're ready for glass.
We learned today that for some reason, the glass fabric that we've had on order for a week or so was not shipped. A bit of a delay that we weren't expecting.
We learned today that for some reason, the glass fabric that we've had on order for a week or so was not shipped. A bit of a delay that we weren't expecting.
Sunday, December 13, 2009
Just another Silicon Valley garage project
For the next phase (assembly and layup of the prop) we've had to move venues. With what we've got going at work right now, we don't have the space in the lab to leave the assembly fixures up for a week or so straight. We moved to Rick's garage for a bit.
Here are the first 5 segments evened up and glued. As you can see, the carbon spar ends at this juncture and there is a tapered aluminum spar which goes inside the carbon and continues on out through the smaller sections.
The holes you see along the top of the airfoil are where we poured the resin to saturate the spar/foam interface. The binder clip hold the trailing edge nice and even while the resin cures.
Here are the first 5 segments evened up and glued. As you can see, the carbon spar ends at this juncture and there is a tapered aluminum spar which goes inside the carbon and continues on out through the smaller sections.
The holes you see along the top of the airfoil are where we poured the resin to saturate the spar/foam interface. The binder clip hold the trailing edge nice and even while the resin cures.
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