# Why isn't the push/pull twin more popular ? What you say.

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### arj1

##### Well-Known Member
Being tightly sandwiched between two engines that are inside the fuselage and make it resonate loudly is even worse than sitting behind a single engine.
I heard that it is not just that - 337 is just much noisier - people living next to runway particlarly dislike 337 for that reason

#### TarDevil

##### Well-Known Member
Rutan's model 309 had some promise.. but Adam's had to make it fatter, slower, more expensive, etc.

#### Pops

##### Well-Known Member
Supporting Member
The noise never seem to be much louder that most airplane unless the engines are way out of sync. Then it's almost an instant headache from the drumming noise.

Last edited:

#### challenger_II

##### Well-Known Member
Meh.... Go fly in the co-pilot's seat in a B-25 and come talk about noise...

#### Pops

##### Well-Known Member
Supporting Member
Meh.... Go fly in the co-pilot's seat in a B-25 and come talk about noise...
Never been in one, but my grandson got the chance to fly one for a while. Not right, grandfathers should come first

#### PMD

##### Well-Known Member
Meh.... Go fly in the co-pilot's seat in a B-25 and come talk about noise...
Spent enough time between a pair of R-985s to feel the aftermath but wish I had spent some more with a pair of R-1830s just aft of the cockpit when the opportunities were there.

Noise....eh.....what did you say?

#### Bill-Higdon

##### Well-Known Member
Meh.... Go fly in the co-pilot's seat in a B-25 and come talk about noise...
That's quiet compared to a C-123 on takeoff 2 a turnen & 2 a burnen

Last edited:

#### Bigshu

##### Well-Known Member
Supporting Member
You would need enough power to have at least Cessna 150 takeoff and climb performance with one engine Inoperative. That would make it safe to fly. The second engine would make it a blast to fly.
So, with 160 sf wing area, and a 100hp O-200, at 1600lbs MTOW, you're looking at 10lbs/sf wing loading, and 10lbs/hp power loading. That doesn't sound difficult to achieve for a single seater. If you take it down to LSA weight of 1320lbs, there are lots of designs that would be a good basis for a push-pull twin. Use a cruciform empennage like Douglas and Lockheed did for their postwar pusher designs. In fact, if you took the Lockheed model 34 and hung an engine on the nose, you have what you're looking for. Or do the same for Lesher's Teal or Nomad, and again, there you go...

#### Pops

##### Well-Known Member
Supporting Member
So, with 160 sf wing area, and a 100hp O-200, at 1600lbs MTOW, you're looking at 10lbs/sf wing loading, and 10lbs/hp power loading. That doesn't sound difficult to achieve for a single seater. If you take it down to LSA weight of 1320lbs, there are lots of designs that would be a good basis for a push-pull twin. Use a cruciform empennage like Douglas and Lockheed did for their postwar pusher designs. In fact, if you took the Lockheed model 34 and hung an engine on the nose, you have what you're looking for. Or do the same for Lesher's Teal or Nomad, and again, there you go...
10 lbs/hp power loading is nice. I have 11.82 on the JMR and like to have more HP. Maybe change the C-85 to a 0-200.

#### Vigilant1

##### Well-Known Member
Supporting Member
So, with 160 sf wing area, and a 100hp O-200, at 1600lbs MTOW, you're looking at 10lbs/sf wing loading, and 10lbs/hp power loading.
That's 16 lbs per HP, right?

With a twin flying on a single engine, we do have to take into account the drag of an unfeathered stopped (or windmilling ) prop. If stopped, then the drag effectively draws about 4 HP of drag from the good engine at typical climb speeds. Still, with two 100hp engines, it is no sweat to design a single seater that can climb safely on one. A two seater doesn't appear to be hard, either. I think a safe 4 seater (o rmore likely, 2 with a lot of fuel and gear) is probably possible with two 100 HP engines.
The compromise is that, with fixed pitch props, the twin will not be as fast or carry as much weight as a single engine plane with a 200 HP engine and a fixed pitch prop. That's just the way it is if we want to be able to safely fly on one engine with a fixed pitch prop. The props must be of relatively flat pitch in order to allow sufficient engine RPM to generate good thrust at low (climb) airspeeds. That rules out very high speed flight because the props just run out of pitch. With just one engine you can choose a prop with coarser pitch because there's still enough HP at climb speeds to get the job done. With a fixed pitch single, you don't worry about trying to safely climb on 1/2 of the plane's installed HP.
The good news is that, with a twin, both engines working together can still push the plane to fairly good airspeeds when the engines do reach redline. Yes, they may be at 3400 RPM, but they'll be at low manifold pressure, sipping fuel, and living a long, healthy life.
The Rutan Defiant could fly at over 200 mph and it still climbed safely on one engine, all with fixed pitch props.

Last edited:

#### Pops

##### Well-Known Member
Supporting Member
Even my draggy SSSC will cruise 95 mph turning 3250 rpm on the VW engine. Redline on the engine is 3600 rpm. I cruise at 2650/2700 rpm for 80mph.
With the flat pitch climb props for good single engine ROC , then cruise the Beetlemaster at a higher rpm, whatever rpm 22 " of mp gives you.

#### Bigshu

##### Well-Known Member
Supporting Member
That's 16 lbs per HP, right?
Duh, yes! I was thinking about the Zeniths I saw at the Open house last weekend, and my train of thought derailed...Lots of different engines on the various Zenith models, most over 120hp and most aircraft around LSA limits on weight. So, let's say the common power loading for these examples would be around 11 lbs/hp. As you detailed in your example, you could do a one- or two-seater and still have decent cruise with safe single engine margins. I'm wondering if electric constant speed props wouldn't be a smart move. Then you aren't locked into a fixed pitch and can feather the dead engine's prop as needed.

#### Cardmarc

##### Well-Known Member
I like this push pull design. Gotta get me one.

##### Well-Known Member
I like this push pull design. Gotta get me one.
It's had a troubled history - from Wiki:

. The design is owned by Claudius Jr's son, Conrado, who founded Dornier Seawings AG (now Dornier Seawings) to continue work on the project after two previous firms, Claudius Dornier Aircraft and Dornier Composite Aircraft, both went into bankruptcy. Development of the aircraft was put on hold without any production Seastars being completed in 1991.

#### Vigilant1

##### Well-Known Member
Supporting Member
I'm wondering if electric constant speed props wouldn't be a smart move. Then you aren't locked into a fixed pitch and can feather the dead engine's prop as needed.
If the project has a sufficient budget, adjustable pitch props would have a lot to offer. Electrical ones that can adjust a lot (all the way to feather) are priced over $10k. I think the Ivoprop inflight adjustable props are a lot less, but they can't be feathered. Still, they have enough range to allow a higher top speed while also being able to go flatter for good single engine climb. In a centerline thrust layout, being able to feather the dead prop isn't important to controllability, it only affects drag (so climb ability). In that respect, being able to maximize thrust from the good engine at typical climb speeds would be a bigger plus than being able to feather. Last edited: #### dog ##### Well-Known Member If the project has a sufficient budget, adjustable pitch props would have a lot to offer. Electrical ones that can adjust a lot (all the way to feather) are priced over$10k. I think the Ivoprop inflight adjustable props are a lot less, but they can't be feathered. Still, they have enough range to allow a higher top speed while also being able to go flatter for good single engine climb.
In a centerline thrust layout, being able to feather the dead prop isn't important to controllability, it only affects drag (so climb ability). In that respect, being able to maximize thrust from the good engine at typical climb speeds would be a bigger plus than being able to feather.
willfilly nudging
so why not then build constant speed hubs that
full feather,blades are there,its only machine work
that was first done reliably by hand a hundred years ago,how hard can it be?
oil is in the crank already,loose power it goes flat
thinking most of the work is in the govenor
for constant speed,so simplify and put a manual
valve and control cable,what could go wrong?

#### Vigilant1

##### Well-Known Member
Supporting Member
willfilly nudging
so why not then build constant speed hubs that
full feather,blades are there,its only machine work
that was first done reliably by hand a hundred years ago,how hard can it be?
willfilly nudging
that's true i could apply that idea to
the whole plane
by the time I finished them
the rubber trees i planted would
be mature and I could start
working on the tires, hoses,

#### Tiger Tim

##### Well-Known Member
Ah yes, the classic unique home brew twin with unique engines and now unique props…
what could go wrong?

#### dave wolfe

##### Well-Known Member
Wood props. Just rig up lathe cut off tool behind each prop that could be advanced foreward to cut off the windmilling prop blades.

#### Tiger Tim

##### Well-Known Member
Wood props. Just rig up lathe cut off tool behind each prop that could be advanced foreward to cut off the windmilling prop blades.
I’ve read about the last of the big propliners sometimes having to intentionally seize an engine that had a runaway prop in flight in hopes that the sudden stoppage would twist the prop shaft right off and let it windmill away into an ocean.

On our small, maybe automotive powered two-seaters I wonder if a prop with skinny blades like a Warp Drive could be streamlined enough when stopped. It would need a prop brake or maybe just a PSRU ratio that doesn’t allow windmilling.