The new 100mm and 90mm Fans by Stumax are in the final stages of development.
Here is a short preview by Stu:
Stumax is currently finalizing the development of two new fans, designated SM100-45 and SM90-45, being 100mm dia and 90mm dia with 45mm hub dia. As there is a demand for a good sounding 90mm fan for a while now, Stu originally tried trimming down an SM110-52 to end up with a 90mm fan unit. However it became quickly apparent that this approach resulted in a too heavy fan unit. At the end Stu designed the SM100 around a SM110-45 motor tube, utilizing the same strator design but with shorter blades to end up with a 100mm fan unit. The goal for the 100mm fan was 5kW using a Neu 15 series motor. Testing shows that the power vs rpm calcs were pretty close, and a 1521-1.5Y on 12S seems to be a good choice, needs a lot of flight testing to confirm, of course. For the SM90-45 it looks like a 1515-2Y will be a good choice on 12S for 3kW, or perhaps a 1515-1.5Y on 8S – again, this needs to be thoroughly tested before these figures are put in stone.
The rotors are 11 bladed, with the blades being individually injection moulded from long glass filled Nylon. the blades are assembled onto front and rear rings which lock them all together. Once the rotor is assembled, it is attached to a shaft adapter which then mounts to a dummy shaft in the lathe, then the front face is machined flat and the bore at the front is machined out to accept the aluminium ring which forms the locating face for the spinner. A lot of work and fiddling, but this ensure the spinner runs 100% true. As assembled, the rotors are close to being perfectly balanced, and I’ve actually run them without further balancing. Production rotors will be dynamically balanced.
Thrust-wise, the SM100-45 is matching the 110mm fans up to 3.8kW then it tails off a bit as expected. On 3.8kW it delivers 6.0kg thrust. The static efficiency is up around 92-94%, which is staggering, really, and the reason it’s performing close to a fan with much more FSA. The SM90-45 is giving just over 10lb static thrust with just under 3kW, which is still pretty good considering it’s a cut down rotor and loses the aerodynamic tricks that have been used at the blade tips.The FSA for the SM100-45 is 6264sqmm and 4771sqmm for the SM90-45.
The SM90 is basically the SM100-45 rotor trimmed down to 90mm, using the same motor tube and a 90mm dia shroud. Also new are the shrouds of both the SM100 and SM90 which are carbon/Rohacell sandwich construction at this point.
Sound-wise, the SM100-45 is quieter than the SM110-52 but the sound isn’t as interesting, simply because the SM110-52 was designed to have certain pleasing harmonics, and the SM100-45 was designed to be super efficient (hence its quietness).
Release date: Well, Stu is not promising a release date but he hopes to have the first batches done within one month. As with all Stumax products the fans will only be released once they are 100% right.
RC-Warbirds will carry the SM100 and SM90 as soon as they are available. Please drop us an email for more info’s and pre-orders.