Twin pusher design questions (twin props facing backwards)

[duckduckgoose]

I have a project in mind for a large twin boom pusher design but I'm not sure if one motor will do the job, which leads me to wonder if a twin pusher design is common or effective?I understand that twin tractor setups are far more common, and maybe I will go down that road, but I'd like to have the motors attached to the fuselage instead of the wing like the A10 has its jet engines. Thanks

 

[Hai-Lee]

Something like this perhaps. https://outerzone.co.uk/plan_details.asp?ID=5932

Have fun!

 

[duckduckgoose]

Something like this perhaps. https://outerzone.co.uk/plan_details.asp?ID=5932

Have fun!

YES! Thanks. wow thats a real throwback but the general design is there. now i just need to design the motor mount

 

[Hai-Lee]

YES! Thanks. wow thats a real throwback but the general design is there. now i just need to design the motor mount

You could also take a look at the FT Sea Otter Motor mount and pylon for some ideas or inspiration!

Have fun!

 

[OliverW]

I have a project in mind for a large twin boom pusher design but I'm not sure if one motor will do the job, which leads me to wonder if a twin pusher design is common or effective?I understand that twin tractor setups are far more common, and maybe I will go down that road, but I'd like to have the motors attached to the fuselage instead of the wing like the A10 has its jet engines. Thanks View attachment 135401

One of these buzzed our RC field last week. I was the only one who knew what plane it was lol

 

[quorneng]

duckduckgoose
Unless you already have the motors there is no particular reason why a single bigger motor cannot be used. For the same Watt output a single likely to be a bit lighter and will certainly be more efficient, giving longer flight times.
A really high power twin with counter rotating props does have the advantage there is no resulting torque on the air frame but then you are in trouble if for any reason one motor fails - unless you go for a tandem twin like a Cessna Skymaster.
Its really a matter of what you are trying to achieve.

 

[duckduckgoose]

duckduckgoose
Unless you already have the motors there is no particular reason why a single bigger motor cannot be used. For the same Watt output a single likely to be a bit lighter and will certainly be more efficient, giving longer flight times.
A really high power twin with counter rotating props does have the advantage there is no resulting torque on the air frame but then you are in trouble if for any reason one motor fails - unless you go for a tandem twin like a Cessna Skymaster.
Its really a matter of what you are trying to achieve.

Yeah I have a few sunnysky 1250 KV Motors which might be enough ( wingspan will be 2m) but yeah it's starting to look fairly complex. Might start with a single pusher setup and see what happens. Maybe even a push pull configuration like the Cessna Skymaster

 

[quorneng]

duckduckgoose
Its not the wing span that matters so much as its weight along with the aerodynamic efficiency of its air frame.
If we assume your motors are Sunnysky x2216 1250 kV they are capable of delivering 230W each.
A typical "light aircraft" plane configuration will fly quite adequately on 100 W/lb so if your plane weighs say 2.2 lbs (1 kg) it should manage quite nicely on just one.
On the other hand a plane with a really efficient air frame, like a modern glider, will only need half that power at the same weight.

 

[duckduckgoose]

duckduckgoose
Its not the wing span that matters so much as its weight along with the aerodynamic efficiency of its air frame.
If we assume your motors are Sunnysky x2216 1250 kV they are capable of delivering 230W each.
A typical "light aircraft" plane configuration will fly quite adequately on 100 W/lb so if your plane weighs say 2.2 lbs (1 kg) it should manage quite nicely on just one.
On the other hand a plane with a really efficient air frame, like a modern glider, will only need half that power at the same weight.

Ah ok well in that case it's probably going to be fine. I'm away working and Im just excited to get started building it and see it succeed and a little nervous about flying a plane so big. It will probably end up somewhere in the 1.5-2kg weight range with fpv gear and a 500g 5000mah 4s lipo onboard. Anyway thanks for the help, I really need to learn more about wing loading and lift equations haha

 

[quorneng]

duckduckgoose
That sounds like quite an ambitious project.
I hope you have some experience in building and flying larger, heavier planes or you might be putting some serious time and money at risk.

 

[duckduckgoose]

duckduckgoose
That sounds like quite an ambitious project.
I hope you have some experience in building and flying larger, heavier planes or you might be putting some serious time and money at risk.

Haha yeah pretty ambitious, I've built a 165% sparrow with was pretty big as well as an explorer but I'm pretty unconcerned about it, foambord and hot glue don't cost much and I already have all the electronics. It may end up only being 1.5m (2 sheets of FB instead of 3) depending on its 'ridiculous looking' factor. But yeah im using an extended simple cub wing plan and it's pretty much a larger version of a plane I have already built the FT Smoothie https://forum.flitetest.com/index.php?threads/ft-smoothie-simple-cub-tiny-trainer-twin-boom-blend.59162/

 

[jpot1]

Go for it. I don’t think it matters forward facing or rearward. For the nacelles you can use the approach of score cuts with gorilla glue for strength. That is what I did on my 737 nacelles.

 

[duckduckgoose]

Go for it. I don’t think it matters forward facing or rearward. For the nacelles you can use the approach of score cuts with gorilla glue for strength. That is what I did on my 737 nacelles.

View attachment 135523
View attachment 135524

That looks awesome! Did you use plans?

 

[duckduckgoose]

I've started the build for anyone interested https://forum.flitetest.com/index.p...om-plane-with-extended-simple-cub-wing.59329/ thanks for the help!

 

[jpot1]

That looks awesome! Did you use plans?

No, done from three views. Plans eventually.

 

[duckduckgoose]

Hi all, just wanted to update you on the project.
Big Bird took to the skies today and as it turned out 1 motor had enough Power. The AUW is 1.8kg with a 2.25m wingspan. I had it at 1/2 - 3/4 throttle so I'm sure it has more to give. Cheers for the advice