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Cox Engine of The Month
Phred's Foam adventure
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Phred's Foam adventure
I lost my foam cutting hardware years ago in a Army move. My buddy Jeff Dawson cuts his own cores for all the combat planes he sells. I have helped him a bunch so he will cut just about any wing profile for me.
I want to set my airplane shop up so I can do my own. My original set up was simple but dangerous. A 30" bow of spring tension Ni-chrome wire, connected to the output of a 110 VAC Variac. Worked well but I did not have any safety switches, fuses, or a positive stop on the Variac preventing VAC above 24 ( the starting point of lethal AC voltage).
I have a few items here for a good DC setup at 13.6VDC up to 45 Amp. The original 1997 power supply in the RV is/was old skool transformer iron core heat and humm monster with no real battery management other then constant 13.6Vdc.
I replaced it with a more intelligent 90 Amp version that senses battery bank conditions and adjust from recharge, float, and every 90 day sulfite bust mode.
I ordered a Harbor Freight Router speed control.
I ordered some Iconel and Rene' wire (have Ni-Chrome on hand from Sig)
Fairly simple using the router speed control to adjust the 110 VAC into the Ac to Dc power supply (because it is a dumb supply it will not care) to adjust wire temp. Bows from 20 to 30 inches and small diameter high resistance wire should draw between 3 to 6 amps to get into the 600F range. The PS has 45 Amp max 40 amp continuous spec so it has PLENTY of overhead
A 30" bow is plenty to cut 20-29" wing cores any thickness and width. For the larger wingspans we just use two or more cores.
I cut these last year with Jeff's bow:
I want to set my airplane shop up so I can do my own. My original set up was simple but dangerous. A 30" bow of spring tension Ni-chrome wire, connected to the output of a 110 VAC Variac. Worked well but I did not have any safety switches, fuses, or a positive stop on the Variac preventing VAC above 24 ( the starting point of lethal AC voltage).
I have a few items here for a good DC setup at 13.6VDC up to 45 Amp. The original 1997 power supply in the RV is/was old skool transformer iron core heat and humm monster with no real battery management other then constant 13.6Vdc.
I replaced it with a more intelligent 90 Amp version that senses battery bank conditions and adjust from recharge, float, and every 90 day sulfite bust mode.
I ordered a Harbor Freight Router speed control.
I ordered some Iconel and Rene' wire (have Ni-Chrome on hand from Sig)
Fairly simple using the router speed control to adjust the 110 VAC into the Ac to Dc power supply (because it is a dumb supply it will not care) to adjust wire temp. Bows from 20 to 30 inches and small diameter high resistance wire should draw between 3 to 6 amps to get into the 600F range. The PS has 45 Amp max 40 amp continuous spec so it has PLENTY of overhead
A 30" bow is plenty to cut 20-29" wing cores any thickness and width. For the larger wingspans we just use two or more cores.
I cut these last year with Jeff's bow:
fredvon4- Top Poster
-
Posts : 4001
Join date : 2011-08-26
Age : 68
Location : Lampasas Texas
Re: Phred's Foam adventure
I've built several power supplies, both in DC and in AC. The AC output supplies sometimes have a tendency to develop some harmonics and cause the surface of the foam to be wavy. Here are a couple of pics of my DC heat controller and a 12v power supply converted from a salvaged PC power supply. If I need a long bow, I'll use a Pyramid 13.8v supply to drive the heat controller. I generally use .018 bright stainless steel wire (spring steel) from McMaster-Carr (285' for $10.80).
Re: Phred's Foam adventure
Well done Andrew. Good safe design and very neat engineering of layout and box.
As a Ham Radio operator I have several AC to DC power supplies but all are either store bought or purpose built (by me) to maintain constant current to keep the transmitter finals happy.
I fondly remember building several Heath Kit projects in the 60s with my dad and he stressed to me the importance of "neat" and efficient construction/layout.
As a Ham Radio operator I have several AC to DC power supplies but all are either store bought or purpose built (by me) to maintain constant current to keep the transmitter finals happy.
I fondly remember building several Heath Kit projects in the 60s with my dad and he stressed to me the importance of "neat" and efficient construction/layout.
fredvon4- Top Poster
-
Posts : 4001
Join date : 2011-08-26
Age : 68
Location : Lampasas Texas
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