If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Question about center-line push-pull engine configuration
Hello all,
I am currently brainstorming/daydreaming of a twin design. I would choose a pair of Rotax 912 or Jabiru 2200 or 3300. Considering the place configuration of two engines on a twin, I am just wondering what are the pros and cons of center-line push-pull design. There're far less such configuration than side-by-side engine configuration among twins, so I think there must be a reason. The biggest (if ther's any other) advantage of push-pull design seems obvious: the center line configuration eliminates the torque effect when one engine fails. So what're the cons? Besides the heating issue of the rear engine, I can only guess it might be the efficiency issue. The front engine disturbs the air flowing through the rear engine. If it's true, how big is this disturbance? Say if the side-by-side two engines' efficiency is 200, what's the possible number for push-pull configuration, 180,160,150? If the number is no lower than 150, I think it's tolerate for my use. Thank you very much in advance. Shin |
#2
|
|||
|
|||
Balance is one issue. The wing wants to be near the engine (look at pushers
vs. pullers - pushers are rear wing, pullers are front wing). So you can't just stick another engine on the tail of a standard config plane. Thrustlines are another issue. If you are flying and you lose the front engine, do you nose up? Nose down? Ditto for the rear. Google for the Cessna Skymaster to read up on the pros and cons. Then go to www.scaled.com and look at some of Burt Rutan's designs like the Rutan Bommerang for some out-of-the-box thinking on twins. One might ask - why do you want two engines? - More power? Get a bigger single engine. - More reliability? Get a more reliable single engine. There are many alternatives to continental and lycoming one the scene now. People have been saying this for years, but it's really true now. Since you are thinking about a new design (experimental) you don't need to wait for FAA certification to use an engine. I haven't checked the NTSB database (you certainly could - www.ntsb.gov/ntsb/query.asp), but from googling other peoples discussions, it seems the accident rates for singles and twins are the same. Enjoy the argument that's about to start, or check the archives of this newsgroup for basically the same argument, only repeated every few months... "Shin Gou" wrote in message om... Hello all, I am currently brainstorming/daydreaming of a twin design. I would choose a pair of Rotax 912 or Jabiru 2200 or 3300. Considering the place configuration of two engines on a twin, I am just wondering what are the pros and cons of center-line push-pull design. There're far less such configuration than side-by-side engine configuration among twins, so I think there must be a reason. The biggest (if ther's any other) advantage of push-pull design seems obvious: the center line configuration eliminates the torque effect when one engine fails. So what're the cons? Besides the heating issue of the rear engine, I can only guess it might be the efficiency issue. The front engine disturbs the air flowing through the rear engine. If it's true, how big is this disturbance? Say if the side-by-side two engines' efficiency is 200, what's the possible number for push-pull configuration, 180,160,150? If the number is no lower than 150, I think it's tolerate for my use. Thank you very much in advance. Shin |
#3
|
|||
|
|||
who was that masked man?
|
#4
|
|||
|
|||
Thank you very much for your advice and information, Mr.x. So seems
efficiency not a big issue. good to hear that. Shin "x" wrote in message news:2URwc.62186$Ly.20810@attbi_s01... Balance is one issue. The wing wants to be near the engine (look at pushers vs. pullers - pushers are rear wing, pullers are front wing). So you can't just stick another engine on the tail of a standard config plane. Thrustlines are another issue. If you are flying and you lose the front engine, do you nose up? Nose down? Ditto for the rear. Google for the Cessna Skymaster to read up on the pros and cons. Then go to www.scaled.com and look at some of Burt Rutan's designs like the Rutan Bommerang for some out-of-the-box thinking on twins. One might ask - why do you want two engines? - More power? Get a bigger single engine. - More reliability? Get a more reliable single engine. There are many alternatives to continental and lycoming one the scene now. People have been saying this for years, but it's really true now. Since you are thinking about a new design (experimental) you don't need to wait for FAA certification to use an engine. I haven't checked the NTSB database (you certainly could - www.ntsb.gov/ntsb/query.asp), but from googling other peoples discussions, it seems the accident rates for singles and twins are the same. Enjoy the argument that's about to start, or check the archives of this newsgroup for basically the same argument, only repeated every few months... |
#5
|
|||
|
|||
This topic has been discussed over the last year a few times. I've
been the main agitator on this topic as of late. Been playing with some models in X-Plane, read all about it below: http://inline_twin.tripod.com/concept.html I think one of the main reasons for left/right twins is that for structural purposes, you like to put your heaviest componants near the main wing spar so you don't have to build such a heavy structure to support the engines. The engine loads are applied directly to the wing spar instead of showing up as bending loads at the wing root. The reason I was interested in the twin arrangement was in the pusuit of composit reliability (fail soft) and cost. An idea analogous to the cross coupled brake system in your car- Critically important, dirt cheap, rarely inspected. The idea was to use 2 small motors to fly 2 people. This is in contrast to almost every twin was designed to use 2 power plants powerful enough to lift 2 people, so they were large 4 or more seat aircraft. As far as efficiency, its true the rear engine is living in the turbulance of the front prop. This is one of the reasons the Mix-Master is so loud. This is part of the reason why in my designs I've tried to get them as far apart from each other as I can. But there is also an advantage of living the the accelerated air of the front prop, and that is the idea that you can accelerate the air in 2 stages, instead of all through a single prop disk. Similar to reason you use a 2 stage turbo for high altitude boost. The larger the difference between the velocity of the air infront of and behind the prop disk, the lower the efficiency of that prop. You might end up with a design that puts a large prop in front and smaller one in back (which is nice for ground clearance as well). Regards "x" wrote in message news:2URwc.62186$Ly.20810@attbi_s01... Balance is one issue. The wing wants to be near the engine (look at pushers vs. pullers - pushers are rear wing, pullers are front wing). So you can't just stick another engine on the tail of a standard config plane. Thrustlines are another issue. If you are flying and you lose the front engine, do you nose up? Nose down? Ditto for the rear. Google for the Cessna Skymaster to read up on the pros and cons. Then go to www.scaled.com and look at some of Burt Rutan's designs like the Rutan Bommerang for some out-of-the-box thinking on twins. One might ask - why do you want two engines? - More power? Get a bigger single engine. - More reliability? Get a more reliable single engine. There are many alternatives to continental and lycoming one the scene now. People have been saying this for years, but it's really true now. Since you are thinking about a new design (experimental) you don't need to wait for FAA certification to use an engine. I haven't checked the NTSB database (you certainly could - www.ntsb.gov/ntsb/query.asp), but from googling other peoples discussions, it seems the accident rates for singles and twins are the same. Enjoy the argument that's about to start, or check the archives of this newsgroup for basically the same argument, only repeated every few months... "Shin Gou" wrote in message om... Hello all, I am currently brainstorming/daydreaming of a twin design. I would choose a pair of Rotax 912 or Jabiru 2200 or 3300. Considering the place configuration of two engines on a twin, I am just wondering what are the pros and cons of center-line push-pull design. There're far less such configuration than side-by-side engine configuration among twins, so I think there must be a reason. The biggest (if ther's any other) advantage of push-pull design seems obvious: the center line configuration eliminates the torque effect when one engine fails. So what're the cons? Besides the heating issue of the rear engine, I can only guess it might be the efficiency issue. The front engine disturbs the air flowing through the rear engine. If it's true, how big is this disturbance? Say if the side-by-side two engines' efficiency is 200, what's the possible number for push-pull configuration, 180,160,150? If the number is no lower than 150, I think it's tolerate for my use. Thank you very much in advance. Shin |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
V-8 powered Seabee | Corky Scott | Home Built | 212 | October 2nd 04 11:45 PM |
Diesel engine | Bryan | Home Built | 41 | May 1st 04 07:23 PM |
Tecumseh Engine Mounting Question | jlauer | Home Built | 7 | November 16th 03 01:51 AM |
CAD outline of Rans S6S instrument panel? | Rob Turk | Home Built | 2 | October 21st 03 09:27 PM |
Corky's engine choice | Corky Scott | Home Built | 39 | August 8th 03 04:29 AM |