Twin Super Sportster

[Ricardo]

Hi Guys.
After following the Build threads by Kevin and Dan, I decided to share my latest winter project:
To build a Twin Engine, Glow airplane.
After researching for available ARFs or Kits, I was not happy with the options out there.
I had this Great Planes Super Sportster Kit laying around here for 15 years... And decided: Why not modifying it to be a twin??
So... What follows next in this thread are my adventures in trying to figure this design out...
Hope you guys enjoy the read.

[Ricardo]

This is the original airplane: Designed for engines from 0.40 to 0.46.

First decision: Select the power plant: I chose a pair of OS 30FS.
Typically each engine on a twin should have sufficient power to allow climbing. I may be marginal on this requirement... According to preliminary calculations, I should be around 150W/Kg on single engine condition, which should still allow for a gentle climb. I considered that the twin may end up heavier than the single-engined version.

Wing loading will be on the high end at 69g/dm2. But that is not too far from a standard sport model. Keeping in mind that the nacelles may reduce the effective area of the wing, it will definitely be on the "heavy" side.

[Ricardo]

Second decision: Tricycle or Taildragger?

I chose to go with retracts... But still needed to figure out whether to go with the original Taildragger configuration or to adopt the Tricycle...

Since I have a lot of space in the nose, and the tricycles behave better on takeoff and landing, I chose to modify the kit further and adopt tricycle. On top of that, managing engine asymmetry on a tail dragger is a nightmare...

Next post I will show my sketches with the nacelle layout...

[Ricardo]

Nacelle and nose modifications...

Hand drawn, no fancy CAD here.. hehehehe.

[Ricardo]

Engines ... OS30 FS... Such a beauty..

[Ricardo]

This is the layout for the engines, fuel tank, engine servos, and retract gear.

In the nacelle design, I had two options: Position the tank in front of the wing spar. This had the advantage of keeping the nacelle smaller, since the tank would be embedded in the wing. However, the landing gear would need to be longer, and would take more space in the wing and nose when retracted.

Therefore, I selected to install the tank above the wing, keeping the wing structure un-modified. Landing gear remains short. Also, engine traction line is similar to the original design.

[Kevin Rochon]

Nice project but since it's going to be on the heavy side why no go electric and eliminate the possibility of one engine out, on a twin that spells disaster:eek:

[loflyer2001]

Great project Ricardo and I am sure you have picked the right model
for it. I flew a Super Sportster for years and lost it due to dual rate
selection (my fault).
The pair of OS 30 4-stroke engines are jewels of the glow plug engines.
I have an old OS20 4-s which I will never part from, they run like Swiss
watches.
For the pro and con on electric versus glow....remember one thing,
with glow engine you do not land with the weight of that battery.
I would consider to put inward thrust line on the engines (not a
large amount since they are the 30 size) and the addition of fix
tail fins one on each side of the main rudder on the stabiliser as
seen on some full size old Bellancas that were on floats.
All in all, you have a nice project in your hands, I will be reading
on it and when you succeed, I would be very interested in seeing it fly.
Guy
MAVIP Ile Perrot

[RomanTheBanana]

Very cool project. I like the twin nitro idea, will stay updated! :crazy:

[Ricardo]

Thanks guys for the comments.
Kevin, I selected the Glow power for the challenge... I already have a twin Electric (EFlite Deuces Wild) that is a delight to fly, hassle-free.
But the sound of the twin Nitro...

Guy, you have a valid comment. To address directional stability, I have increased the VStab area by 20%. Will post pictures soon.'

Regards, the engine thrust lines... There are multiple opinions, but I have read some that preach that the engines should be positioned "outwards" by a few degrees. I need to do more research before deciding which way to go on that matter.

[loflyer2001]

You are right....outward they should be.

[drgilo1973]

amazing project

[Burning Head]

That should be a cool re-engineering plane:) great idea Ricardo

[Ricardo]

This is the VStab. Note Area increase (around 20% increase)

[Ricardo]

Also building the nacelles...

[Ricardo]

This is what it is supposed to look like with engine installed:

[Sempai-mj]

Cool, like to be there to see the maiden flight.

[MidnightHeli]

Nice workmanship. Wish I had your talents.

[Kevin Rochon]

As usual nice work Ricardo.

[fbrunet1957]

Very nice work.
I wish I had half your talent and patience.

[Eladio]

I always new there was something special about you !!:)
Bravo !

[Ricardo]

Hi Guys, thanks for the comments. Very encouraging!
The fact that it is -15 outside also motivates me to build....

[Ricardo]

This is the fuselage..
Lots of carving and sanding to get a decent round nose.
At the end, I liked the result.. Looks nice and "pointy".

[Ricardo]

These are the modifications for the retracts.

One nice thing about the nacelles being higher up is the short main landing gear.
It is very short and takes almost no space in the wing.

[Sempai-mj]

The short landing gear give a lot of clearance for the props?

[Ricardo]

Hi Mike, I designed the prop clearance to be in the order of 1.5 in.

[Sempai-mj]

Maiden on May the Fourth be with you!:D

[fbrunet1957]

Maiden on May the Fourth be with you!:D

Do you think the snow will be gone by May 4 ???:confused:

[pierre sarault]

Ricardo,

Thrust lines should be outwards maybe 3 degrees as if one engine should fail, it will be easier to correct with the remaining engine if the thrust is outwards as it will counteract to some degree the yaw induced by the assymetrical thrust.

In 100% scale aircraft , especially piston-engined ones there are multiple examples of that design philosophy; turning the engine thrust inwards will make the thrust assymetry even worse as the strongest engine will force the aircraft into a turn or a spin in the opposite direction to its location, whereas if each engine's thrust is outwards, there will be a tendency for that engine pulling the aircraft away from a turn that would be due to insufficient thrust of the opposite engine.

My 5 cents worth.

Beautiful project and those engines look sweet!

[Ricardo]

Agreed, Pierre. Thanks for the comment!

[RomanTheBanana]

Salut, je sais que ca n'a pas rapport, mais ya t'il des prises de courants au club?:confused: J'ai pas envie de faire un nouveau thread. Mes batteries datent du moyen age et si y'en a pas, je vais devoir acheter des nouvelles, Merci. :D

[bluebird_ca]

Aucune prise de courrant au club amène to générateur portable ou charge tes batteries sur la batterie de ta voiture.

:):):)

[Ricardo]

Here it is the landing gear.
I had lots of problems with electric retracts.
I decided to stay away from them and go with the mechanical Robarts.
Came up with an arrangement that seems pretty robust.
Also decided to use one servo for each leg. This arrangement seems to have worked better in my last airplanes.

[Ricardo]

Also decided to fully sheet the wings. The weight increase due to the balsa is minimal, and due to the nacelles being on the wing, I had to extend the sheeting anyway.
Finished sheeting the lower part and put the airplane together to get a preliminary feel of the CG.
Need to make a big access panel for retract and aileron servo. Will install both in the same wing bay.
Also note a modification on ailerons. Moved away from Strip-ailerons, and installed larger surface ones at the wing extremities.

[Ricardo]

Still a lot to do!
But I was happy with the preliminary feel for the CG.
Will carve some holes on the HStab (pretty heavy balsa there!).
Next will be finishing the wing sheeting, plus access panel for servos.
Then there is a lot of sanding to do....

[Burning Head]

Wow, nice work:cool:

[Ricardo]

This is the wing top view, with servos installed. As you see, six servos instead of one...
Two for retracts, two for ailerons, two for throttle....
Very challenging to fit all. Used smaller hi-torque for the ailerons and throttle.
After the wing is sheeted, access will be via underwing panels, from inside the nacelles, and from the retract bays.

[Sempai-mj]

Nice work Ricardo, lots of stuff in that wing. :)

[Ricardo]

Lots of covering done this weekend. I usually start sealing the tips and hard-to-reach spots...

[Ricardo]

After almost two days work... See the results... The last picture shows, just one nacelle to finish...

Now its just like an ARF... Glue everything together!

[Sempai-mj]

Nice work Ricardo.

[Xavier]

Very nice. Looking forward to see it in the air.

[MidnightHeli]

Very, very nice, can't wait to see the finish product.

[pierre sarault]

Very nice Ricardo, looks like it is going to be a hot airplane!

Also nice to see the creativity, adapting an airframe and improving on it.

Should be nice to hear those 30's singing in unison!

Well done!

Pierre Sarault

[Ricardo]

I am learning a lot with this build... Very challenging..
Now I am on finishing stages, some touches just before glueing everything up.

Chose black and gold. Gold monokote will be here next week, so just black for now.

I can start adding hinges, and finish fuselage with receiver and pushrods installation.

After finishing the wing covering, will install nacelles, engines, and tanks...

Ufff. still some work ahead, hope to have the engines fired up for breaking in soon.

[beto9]

It looks gorgeous!
Otimo trabalho, cara!

[Sempai-mj]

I am learning a lot with this build... Very challenging..
Now I am on finishing stages, some touches just before glueing everything up.

Chose black and gold. Gold monokote will be here next week, so just black for now.

I can start adding hinges, and finish fuselage with receiver and pushrods installation.

After finishing the wing covering, will install nacelles, engines, and tanks...

Ufff. still some work ahead, hope to have the engines fired up for breaking in soon.
Take your time, the weather points to builds.
Great build.

[Kevin Rochon]

Beautiful Ricardo, will be be nice with the gold.

[Ricardo]

Thats it.. Seems to be ready.
Ran the engines, both are broken-in now.

Installed the synchronizer, it is working fine. Keeps both engines at very close RPM.

Maiden next weekend I hope.

[Kevin Rochon]

Amazing looking, hope all goes well.

[beto9]

Thats it.. Seems to be ready.
Ran the engines, both are broken-in now.

Installed the synchronizer, it is working fine. Keeps both engines at very close RPM.

Maiden next weekend I hope.

What is a synchronizer?

[Ricardo]

The synchronizer is a "TwinSynch". It reads the speed from the engines and equalizes them for you. You install a magnet on the spinner and a sensor reads the pulses. It has also some protection features if one engine quits. Also allows you to practice the engine-out scenario, I use an aux channel to put each engine at idle at a time (while still controlling the other engine). It is not mandatory on a twin, but definitely a "nice to have". I has some add-ons such as glow plug drivers (drives the plugs during idle). But the glow drivers I will build myself based on Daniel's design.

[beto9]

Wow! is a "loaded" plane.
Like they say, "In a twin engine plane if one quits the other brings the plane to the scene of the crash".

[Eladio]

Hey Ricardo , are you doing the Maiden Today ?
Make sure your Batteries are well charged !!! :)

[Sunfly]

Very nice Ricardo,
Being addicted to glow engines and most specially 4 strokes I should say this plane should be amazing under many aspects.
When you have suspicions about it to be on the heavy side:
I would think the factor W/kg could be misleading.
Since you run with 4 stroke engines you may find that you will get a surprising
thrust.Since it will turn bigger props there will be a gain of efficiency compared to 2 strokes for the same power.
I have been surprised by many occasions by the 4 strokes when you rotate on the run way (after V1) you may find they will just pull you up before your eyes. Be careful so to get enough speed before the first turn.

I wish I could be there to see it ...one day soon,

Cheers,

Luc