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

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Vigilant1

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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.
In a light twin with fixed pitch props, there's a really good chance that the dead engine won't windmill anyway at the best speed for staying aloft/climbing.
Well, at least if the dead engine is still making compression.
If it's a problem, the brake set from a mountain bike could be used to stop the spinning and not do further damage to the engine. Spring loaded, just release the cable. If it deployed by mistake somehow, just keep applying the throttle until we burn through the brake pads.
 

Tiger Tim

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In a light twin with fixed pitch props, there's a really good chance that the dead engine won't windmill anyway at the best speed for staying aloft/climbing.
Anecdotal, but I’ve found light piston singles with fixed pitch props windmill at best glide speed. I assume the same engine and prop on a twin would do the same.
 

Vigilant1

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Anecdotal, but I’ve found light piston singles with fixed pitch props windmill at best glide speed. I assume the same engine and prop on a twin would do the same.
Thanks. I shouldn't have spoken so broadly. The specifics are probably important, especially propeller length. I've read many accounts indicating that it is very hard to get fixed pitch VW installations to windmill (shorter props=lower torque to get the engine through compression strokes). Bberson is able to get his Limbach to windmill by using the installed adjustable pitch prop, cycling through the settings.
"Regular" airplane engines seem to windmill. I'd guess props turned by a PSRU and engine probably do not windmill (unless there is a clutch of some kind).
 
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Bill-Higdon

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Anecdotal, but I’ve found light piston singles with fixed pitch props windmill at best glide speed. I assume the same engine and prop on a twin would do the same.
This brings up an interesting thought the Yamaha snowmobile conversions use a clutch, should they also have a brake to stop the prop from spinning in case of engine shutdown in flight?
 

Vigilant1

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This brings up an interesting thought the Yamaha snowmobile conversions use a clutch, should they also have a brake to stop the prop from spinning in case of engine shutdown in flight?
Some of the PSRUs for the BMW opposed twins used a sprag clutch of some type. I recall reading that the prop windmilled and significantly affected glide performance. Good, I guess, if you want a steep glide angle, otherwise not so handy.
 

raytol

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Hoffmann make a simple 3 position prop with climb, cruise and feather as their settings. The added complexity of fully adjustable pitch may not be required. I would only like a mechanical pitch change system.
 

wsimpso1

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Being as this forum is about homebuilts, I shall restrict my answer to homebuilts.

At OSH most years, ALL of the twin engine homebuilts present are Defiants, push-pull twins. Once in a while we will see a Cri-Cri, and there is an RV with two Corvair engines that showed up in 2021. I must question if that is really a reliability upgrade over the Lycoming install it replaced.

From that sampling, I must opine that within the homebuilt community, the push-pull is popular.

I suspect the big issue is simply that having more than one engine is unpopular, both in Experimentals and in store-boughts.
 

DaveK

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That Red engine site says it’s a diesel burning Jet-A, but also says it burns hydrogen, mentions hybrid, but seems to be a turbo diesel only. Marketing hype?
 

PMD

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That Red engine site says it’s a diesel burning Jet-A, but also says it burns hydrogen, mentions hybrid, but seems to be a turbo diesel only. Marketing hype?
It is fairly easy to use hydrogen as a supplemental fuel with compression ignition engines, but still using the liquid fuel injection to trigger the combustion event. Running on pure H2 requires a return to spark ignition in most cases. Hybridization will be mentioned because in the fantasy world of the Euroweenies idiotic governments will shell out millions in subsidies if you mention hyrbridization or even hundreds of millions if you are going full stupid and pretending you will make a BEV.

While some of the biggest players in the actual aviation businesses of Europe have clearly stated they consider the immediate future to be SAF, they have also agreed that the long term future will include hydrogen - just not many people know in what form that will be. Full electric is totally dismissed except for the shortest of duration missions, but some sort of hybridization may have some practical applications - only if because the use of large M-G set could boost takeoff power but also run a large suite of...uh....let's just be polite and call them military things.
 

DaveK

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back in the day it was bleeding a bit of CNG into the diesel intake. But doing that with hydrogen just seems like a loser, low density, easily leaks, two fuel systems, etc. Didn’t make sense with CNG, still doesn’t with hydrogen. But getting off topic of push pull.

Honestly I’d think push pull with rear engine with folding prop makes some sense. Low workload, engine dies, prop folds. And I say engine out climb isn’t as important in a push pull. If you can maintain altitude to get to a landing spot it’s better than being a glider. Without the controllability issues it would be more like single engine procedures in my mind.
 

Turd Ferguson

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It's hard to find much info on the Gemini. Dave Ganzer reportedly was going to offer plans, but I don't think that ever happened. I'd like to have a set.
As I recall, there was no interest.

If you search the Canard Zone forum there are old articles, photos, line drawings with dimensions and comments from people that had first hand knowledge on the plane. Plus a lot of speculation which is entertaining to read.
 

dog

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That Red engine site says it’s a diesel burning Jet-A, but also says it burns hydrogen, mentions hybrid, but seems to be a turbo diesel only. Marketing hype?
they have a partner with caravans who is doing the hybrid idea,could work now in certain markets
like taxi drivers with a prius
short heavy hauls would be spendy with a turbine
and hauling cargo is going to help with getting
approval to move people
looks like they are targeting the small turbine market,and those players are all going to have
money and very sharp business sense
now two v12 turbo diesels @550hp each is
a whole different kind of pushin and pullin
 
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I wonder about that, too. Single-engine ops are much simpler and safer when all the thrust remains on the centerline.

The C-337's had a reputation for being a maintenance hog and for not being as fast as people thought a twin should be, maybe that has hurt the cause. (The speed complaint rings hollow to me-- the 337:is faster than a Seminole an carries more). Neither of those shortcomings were the result of the push-pull layout, but were due to other design decisions made by Cessna.

Maybe the challenges of asymmetric single engine operations get insufficient consideration from the buyers of twins. After all, we are all above average pilots and would never allow ourselves to be caught below Vmc
to compete with a baron that had probably It only had hp continental engines on it. Why would anyone expect the more hp on tap?
 
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to compete with a baron that had probably It only had hp continental engines on it. Why would anyone expect the more hp on tap?
Darn computer. The 337 only had 225 hp/engine and they were continentals to boot. (maintenance hogs) You should not expect it to preform with aircraft that had probably 100 hp more available.
 

challenger_II

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To get apples to apples (a bit of Golden Delicious to Granny Smith, but in the ballpark):
Compare the useful load and speed range between the 337 and the Piper Seneca. The Seneca does have 220hp turbocharged engines, as compared to the 210hp engines on the 337.
Also, the Seneca has a bit better aerodynamics due to the low-wing configuration and the 337's forked tail. The Seneca is somewhat faster; however, the useful load is only slightly more.
 
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