• Homebuilt Airplanes is a vibrant community of pilots, plane builders and industry experts. Our thousands of active members use HBA to trade detailed technical information, discuss best practices, share their builds, plan get-togethers and buy/sell planes & parts. In addition to the community you gain access to, you gain access to over 20 years of curated knowledge by some of the brighest in the industry.

    Access to HBA is subscription based. It is free for 7 days so you can get to know our community!

    Click Here to Become a Member and Access HBA

BLOOP 4 Twin


Captain Turnbuckles
Supporting Member
Jan 3, 2023

There have been lots of posts on Redundancy lately. For the Bloop 4 I have in progress, that is a Moster 185 + Hand Deployed Parachute. For quite some time I was toying with the idea of twin electric motors for simplicity and reliability. It's not going to give me what I desire in mission range just yet. Watching Mike Sandlin's Bluebird fly, I'm strongly thinking about doing dual Atom80s. Think Lazair but as a twin pusher. One motor wouldn't be sufficient for most takeoffs but could get me back to field should I lose an engine. I may also be able to extend the TBO if I can run lower RPMs with the ever so slight increase in thrust.

I know I'd lose some efficiency spinning two props. I'd also add some weight having dual motor mounts, fuel lines, throttle linkages, frame bracing, ect. It would also give me a frame I could change over to Electric someday should I get too many noise complaints or battery tech catches up. I'm also considering this as I'm (175-185) 25-30lbs heavier than Mike Sandlin. So instead of adding weight to the tail or shifting the pilot position from the plans I could add this motor!

I can run models on weight, balance and thrust numbers... what I don't have a clear understanding on is how the turbulence from the propwash coming from each side will change performance. I ponder this as many twins have twin tails. Has anyone here placed two engines on a single engine design? The numbers seem to work out but will two motors change the wake on the rudder and elevator much? Mike Sandlin's Bloop 1 was a twin tail and may have been best suited to the twin Atom80 setup.

BLOOP 4 (without motor) - 168-178lbs
With Moster 185 - 200-210lbs - Thrust 171lbs (2 blade 130cm) 8500rpm
With Dual Atom80 - 214-224lbs - Thrust 242?, 121lbs each (2 blade 130cm) 9650rpm - ideally, with the extra thrust, I'd back down the RPM quite a bit.

On the weight, I feel I have enough wiggle room for added frame supports, motor mounts and what not to double. Vittorazi has a new Cosmos 300, that may also qualify... but it's new, not as well proven as these two motors. I'd like to keep the motors separated as opposed to linked, spinning a single center prop. She'd probably fly a little faster and stall speeds changing of course but hopefully not too much.

Bloop 1.jpg
Thanks for the ever interesting points of view and words of wisdom!
Last edited: