# An argument in favor of multi-engine design

### Help Support HomeBuiltAirplanes.com:

#### Topaz

##### Super Moderator
Staff member
Log Member
It's interesting seeing the different perspectives. Multi-engine commercial pilot prefers multiple engines - more the better. A glider pilot (me) prefers one simple engine and good gliding capability so that finding a spot to land is much easier. For some, "landing out" is a disaster. For others, "landing out" is an annoyance, and a case of your buddy's favorite beer because he brought out the trailer.

I see the point being made here, and it's fine, I suppose. Me, I'd much prefer the simplicity and low weight of a single engine, and a bit more span, which helps out in everyday flying, too. To each their own, I guess.

#### blane.c

##### Well-Known Member
HBA Supporter
I think it boils down to speed. As a high time fighter jet pilot once told me "speed is not your friend" , speed is also expensive. One of the expenses of speed is a higher wing loading with a corresponding reduction in glide distance and a higher landing (impact) speed. If you are thinking cross country cruiser (me) then speed correlates with fuel economy and distance. If you want some reasonable options when you are in close proximity to the earth then multiple engines become a possible solution. This forum is a more cost effective way in both time and money to explore possible options than many other methods.

#### bmcj

##### Well-Known Member
HBA Supporter
[As a high time fighter jet pilot once told me "speed is not your friend" /QUOTE]

Not what I would have expected. The typical fighter pilot mantra is "Speed is Life".

#### Sockmonkey

##### Well-Known Member
The typical fighter pilot mantra is "Speed is Life".
Only when you're being shot at.

#### Jerry Lytle

##### Well-Known Member
Here is a twin engined Piper Cub, similar to the twin Tripacer by the same party.

HBA Supporter

#### blane.c

##### Well-Known Member
HBA Supporter
[As a high time fighter jet pilot once told me "speed is not your friend" /QUOTE]

Not what I would have expected. The typical fighter pilot mantra is "Speed is Life".
Yes but he was talking to me.

#### blane.c

##### Well-Known Member
HBA Supporter
The married fuselage designs did not have much success?

#### nerobro

##### Well-Known Member
Log Member
The married fuselage designs did not have much success?
No. you end up with a whole buttload of interference drag, and the front of the airplane looks to air, almost as if it's solid...

#### Winginit

##### Well-Known Member
Offered as an unproven spur of the moment thought. It would seem to me that for a decent looking design something with a twin boom tail design and both engines mounted on centerline would be a good design for a homebuilder. The rear engine could be moumted directly to the fuselage or elevated
slightly for ground clearance. In the event of an engine out, the dynamics of thrust would still be on the centerline of the aircraft and be easier for the pilot to deal with. Something like a modified version of the Sadler Vampire.

https://www.youtube.com/watch?v=gtbk8SllXng

#### blane.c

##### Well-Known Member
HBA Supporter
Offered as an unproven spur of the moment thought. It would seem to me that for a decent looking design something with a twin boom tail design and both engines mounted on centerline would be a good design for a homebuilder. The rear engine could be moumted directly to the fuselage or elevated
slightly for ground clearance. In the event of an engine out, the dynamics of thrust would still be on the centerline of the aircraft and be easier for the pilot to deal with. Something like a modified version of the Sadler Vampire.

https://www.youtube.com/watch?v=gtbk8SllXng
Thinking to the extent possible not introducing "both yaw and pitch moments" is probably best. So elevation wise everything pretty close to the cg line. I am thinking twin boom more from an Aesthetics point of view than any other reason. This would place the engines on the booms in tractor configuration, but I am still puzzling over tractor or pusher for third engine. I am thinking it will probably be tractor because I do not want to put it overhead for the above stated reason and the extra weight of reinforcing a rear firewall/bulkhead for 10g's in order to mount it directly behind the cabin may be a deal killer for that arrangement. I like the idea of the look of the third engine in pusher aesthetically it is the better option for me.

HBA Supporter

#### bmcj

##### Well-Known Member
HBA Supporter
Offered as an unproven spur of the moment thought. It would seem to me that for a decent looking design something with a twin boom tail design and both engines mounted on centerline would be a good design for a homebuilder. The rear engine could be moumted directly to the fuselage or elevated
slightly for ground clearance. In the event of an engine out, the dynamics of thrust would still be on the centerline of the aircraft and be easier for the pilot to deal with. Something like a modified version of the Sadler Vampire.

https://www.youtube.com/watch?v=gtbk8SllXng
Yes, an excellent configuration for a designer to work with, but possibly less than optimal for the passengers who are likely sitting in a short fuselage between two nearby noisemakers.

#### Sockmonkey

##### Well-Known Member
Doing a tandem wing lets you keep both close to the centerline and makes it easy to use a cross-shaft for one engine to drive both props if you feel the need.

#### Winginit

Of course if money is no object you could use 3 of the small Turbojet engines like Sonex uses. A mere $55K apiece. #### timberwolf8199 ##### Well-Known Member It would seem to me that for a decent looking design something with a twin boom tail design and both engines mounted on centerline would be a good design for a homebuilder. I've often thought that a P-38 built in reverse would be an interesting ride. That is, push-pull engines on the center pod and cockpits on the booms. Unfortunately the separation of passenger from pilot is not likely to be popular and asymmetric loading for pilot only operation have always seemed like big enough issues to prevent me from letting it get beyond a passing thought. #### blane.c ##### Well-Known Member HBA Supporter Yes, an excellent configuration for a designer to work with, but possibly less than optimal for the passengers who are likely sitting in a short fuselage between two nearby noisemakers. Isn't eventual deafness for pilots and their friends and family's just a given anyway? Seriously though, how do you significantly lessen the decibels of the propulsion package without adversely affecting performance. #### blane.c ##### Well-Known Member HBA Supporter Of course if money is no object you could use 3 of the small Turbojet engines like Sonex uses. A mere$55K apiece.
Money is an object, I am thinking three Geo's or Subaru's, considering the cost to weight to HP to fuel burn ratios.

#### blane.c

##### Well-Known Member
HBA Supporter
I've often thought that a P-38 built in reverse would be an interesting ride. That is, push-pull engines on the center pod and cockpits on the booms. Unfortunately the separation of passenger from pilot is not likely to be popular

Depends on how obnoxious your passenger is ... could be very popular for some ... like a mother-in law apartment.