Guides / Design
Getting heat out of an ESC or a payload without adding weight
August 13, 2026
On a small aircraft there is no fan, the air speed changes constantly and every gram of heat sink is a gram not spent on battery. Thermal parts are therefore a weight problem disguised as a temperature problem.
The good news is that most UAV thermal failures are contact problems, and those are cheap to fix.
Start with where the heat is stuck
Heat from an ESC or a processor has to cross four things: the die to its package, the package to your part, the part itself, and the part to the air. In machined hardware, the biggest resistance is almost always the third of those, the interface between the component and the metal.
That makes the first questions practical ones:
- Is the mounting face flat and clean.
- Is the interface material thin, and is it the right one.
- Is there enough clamping force to hold them together.
A perfect fin field bolted to a bowed face performs worse than a plain block bolted to a flat one.
Material
6061-T6 for anything thermal. It conducts heat at roughly 167 W per metre kelvin against about 130 for 7075, it machines cleanly, it anodises evenly and it costs less. There is almost no case for 7075 in a heat sink unless the part is also carrying serious structural load.
Copper conducts roughly twice as well and weighs three times as much. On an aircraft it shows up only as a small spreader directly under a hot component, never as the whole part.
Fin geometry that a machine can actually cut
Fins are thin walls, and thin walls have machining limits. A practical envelope for milled aluminium fins:
| Parameter | Practical range | Note |
|---|---|---|
| Fin thickness | 0.8 to 1.5 mm | Thinner is possible and slower |
| Fin height | up to about 8 times the gap width | Limited by cutter reach and chatter |
| Gap between fins | 1.5 mm and up | The cutter has to fit, plus chip clearance |
| Base thickness | 3 to 5 mm | This is the spreader, do not starve it |
Two design notes that matter more than the exact numbers. In natural convection, taller and fewer beats shorter and many, because the air has to move. In forced convection from propeller wash, closer fins work, as long as they are aligned with the flow rather than across it.
And on a multirotor, propeller downwash is the cooling. Point the fins along it. A beautifully finned surface facing the wrong way is a weight penalty with a nice finish.
Flatness, finish and the interface
- Flatness across the component contact area, roughly 0.02 to 0.05 mm for a small face. On a pocketed part, machine this face last.
- Finish around Ra 1.6 or better. Polishing does not help, the interface material fills the roughness.
- Interface material should be as thin as the flatness allows. Thermal pads are forgiving and much worse thermally than a thin paste or a phase change film. If a design relies on a 1 mm pad to take up a gap, fix the gap.
- Clamping with screws and a stiffener, not with adhesive alone, wherever the part will be serviced.
Anodise blocks heat in one place only
Type II anodise adds a small thermal resistance across the surface. On fins radiating into air, black anodise is broadly neutral to slightly helpful, because it improves radiated heat at the cost of a thin insulating layer.
Under a component it is different. Mask the contact face, or you have put an insulator exactly where the heat has to cross. This is the most common thermal mistake we see on a drawing, and it is one line to fix. The growth and masking detail is in anodising UAV parts.
Cold plates, when air is not enough
On heavier aircraft, high power payloads and hybrid systems, a liquid cold plate starts to make sense. Machined versions are usually a milled channel in a plate with a lid, sealed and pressure tested.
The machining decisions are:
- Channel cross section and path, which sets pressure drop.
- The sealing method, o-ring groove or friction stir welded lid or brazed. The groove rules in sealed UAV enclosures apply.
- Port threads and their sealing type, which should be specified, not left to the shop.
- A pressure test requirement, stated on the drawing with a pressure and a duration.
We machine and assemble plates like this, and we say plainly on the quote which parts of it, such as welding or brazing, are placed with a partner. The capabilities page lists what is in house.
What to send for a quote
The model, the power to dissipate in watts, the maximum ambient temperature and the allowed component temperature. With those four numbers a shop can tell you whether the part is plausible before it is cut, rather than after.
Send it through the RFQ page and the answer comes back within 24 business hours.
Frequently asked questions
Does aluminium alloy choice change thermal performance?
Yes, more than people expect. 6061 conducts heat at roughly 167 W per metre kelvin and 7075 at around 130. For a thermal part that is a real difference, and 6061 is also cheaper and easier to machine.
How flat does a mounting face under a chip need to be?
Flat enough that the thermal interface material is thin and even. Around 0.02 to 0.05 mm across the contact area is a sensible target for a small face, with a finish around Ra 1.6 or better.
Are machined fins better than extruded?
Not thermally, for a simple shape. Extrusion is cheaper at volume for constant cross sections. Machining wins when the part is also structural, when the fin field has to work around other hardware, or at the quantities most UAV programmes actually run.
Need this part quoted?
Send the model and the quantity. Price and lead time come back within 24 business hours.