Twin/triple for magnum 91 4s
05-08-2008, 07:57 AM
#1
Senior Member
Thread Starter
My Feedback: (18)
Join Date: Jan 2004
Location: Formosa, ARGENTINA
Posts: 2,370
Likes: 0
Received 0 Likes
on
0 Posts
Twin/triple for magnum 91 4s
I am looking for a project for two magnum 91 4 strokes. I am willing to build from plans or to do a kit bash. This will be my first twin and I want something pretty docile but capable of big loops, inverted flight and otherwise basic acrobatic flight. So I am thinking along the lines of a high wing plane with little or no dihedral.
I also want to leave the nose open for a possible third engine (either as part of the original build or added later). Most likely it will be a .25-.40 2 stroke.
I have been looking around and come up with very little. I emailed Bruce Tharpe about the BTE twin flying king. Although its too big for my maggies he is willing to let me scale the plans to fit.
Are there any other planes or plans out there already suited to this project?
Also, if I decide to scale the flyin king or bash a kit plane, what size plane should I be looking at for 2 90 sized 4 strokes?
I also want to leave the nose open for a possible third engine (either as part of the original build or added later). Most likely it will be a .25-.40 2 stroke.
I have been looking around and come up with very little. I emailed Bruce Tharpe about the BTE twin flying king. Although its too big for my maggies he is willing to let me scale the plans to fit.
Are there any other planes or plans out there already suited to this project?
Also, if I decide to scale the flyin king or bash a kit plane, what size plane should I be looking at for 2 90 sized 4 strokes?
05-10-2008, 10:25 PM
#3
Join Date: Jan 2002
Location: Redwood City, CA
Posts: 763
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
These are about the right size, I think.
[link=http://www.rcmmagazine.com/store/store-plans-catalog-tem.html?item=plans
l-1330&sid=0001CRD0A5NOUXAaZM9B2I0]RCM Sea Twin[/link]
[link=http://www.rcmmagazine.com/store/store-plans-catalog-tem.html?item=plansl-1336&sid=0001CRD0A5NOUXAaZM9c8R0]Or RCM A-26.[/link]
[link=http://www.rcmmagazine.com/store/store-plans-catalog-tem.html?item=plans
l-1330&sid=0001CRD0A5NOUXAaZM9B2I0]RCM Sea Twin[/link][link=http://www.rcmmagazine.com/store/store-plans-catalog-tem.html?item=plans
l-1336&sid=0001CRD0A5NOUXAaZM9c8R0]Or RCM A-26.[/link]
05-10-2008, 10:55 PM
#4
RE: Twin/triple for magnum 91 4s
For your desired characteristics a bash of the Senior telemaster would fit the bill closely.
I would suggest forgeting the idea of three engines as that would be excessive. As well as reducing the thrust disymetry with the loss of one engine. Ordinarily a good thing but since you need to learn how to control an airplane on one to properly round out your skills, it just won,t happen if the airplane is too benign.
John
I would suggest forgeting the idea of three engines as that would be excessive. As well as reducing the thrust disymetry with the loss of one engine. Ordinarily a good thing but since you need to learn how to control an airplane on one to properly round out your skills, it just won,t happen if the airplane is too benign.
John
05-11-2008, 12:12 PM
#5
My Feedback: (2)
Join Date: Apr 2002
Location: Strathcona county,
AB, CANADA
Posts: 5,394
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
An alternate opinion: Triples are highly under rated. They make an excellent training platform prior to jumping into twins. :
In an engine out situation, there are a number of advantages
-you only lose 1/3 of your power, not 1/2, leaving a very comfortable margin to complete the flight and land
-if an engine quits, AOTBE, you have a 33% chance that it would be the center engine, leaving a perfectly symetrical twin still flying
-you have a 66% chance (again AOTBE) that it will be one of the wing mounted engines, in which case, the center of thrust distribution from the remaining 2 engines is much closer to the fuselage centerline than a regular twin, so assymmetric thrust is greatly reduced. This enhances your ability to maintain control of the airplane and bring it in for a safe landing.
There is some downside.
-you have a 50% greater chance that any one engine will quit (having 50% more engines)
-The propellors are closer together, and you have to be VERY careful when starting that last engine that you keep your hands well clear of the 2 spinning props.
-you are much busier on start up getting all three engines up and running.
However, all that pays off once you get airborne because you are not constantly straining your ears to reassure your self that both engines are still running (in a twin); you lose the concern of losing an engine at the worst possible moment, so you can relax and enjoy flying....you can be more daring, trying manoevers that you wouldn't be comfortable doing in a twin - snaprolls, hammerheads. low slow high alpha passes, spins, etc..
As John mentoned above, engine outs are a benign situation, and that is a good thing, as it builds your confidence when flying multis. So how do you develop your skills to handle an engine out in a twin (besides lots of flight sim time..)? The way I did it was to put a separate throttle on a separate channel for the center engine (operated by a slider lever on my Tx). I can idle the center engine in flight, and fly it as a twin as desired ( or a single
) In the event of a wing engine quitting (I've had one), I can slowly bring back the center engine to see how the airplane behaves, having the surpreme comfort in knowing that if things go south, I can firewall the center engine and recover....
In an engine out situation, there are a number of advantages
-you only lose 1/3 of your power, not 1/2, leaving a very comfortable margin to complete the flight and land
-if an engine quits, AOTBE, you have a 33% chance that it would be the center engine, leaving a perfectly symetrical twin still flying
-you have a 66% chance (again AOTBE) that it will be one of the wing mounted engines, in which case, the center of thrust distribution from the remaining 2 engines is much closer to the fuselage centerline than a regular twin, so assymmetric thrust is greatly reduced. This enhances your ability to maintain control of the airplane and bring it in for a safe landing.
There is some downside.
-you have a 50% greater chance that any one engine will quit (having 50% more engines)
-The propellors are closer together, and you have to be VERY careful when starting that last engine that you keep your hands well clear of the 2 spinning props.
-you are much busier on start up getting all three engines up and running.
However, all that pays off once you get airborne because you are not constantly straining your ears to reassure your self that both engines are still running (in a twin); you lose the concern of losing an engine at the worst possible moment, so you can relax and enjoy flying....you can be more daring, trying manoevers that you wouldn't be comfortable doing in a twin - snaprolls, hammerheads. low slow high alpha passes, spins, etc..
As John mentoned above, engine outs are a benign situation, and that is a good thing, as it builds your confidence when flying multis. So how do you develop your skills to handle an engine out in a twin (besides lots of flight sim time..)? The way I did it was to put a separate throttle on a separate channel for the center engine (operated by a slider lever on my Tx). I can idle the center engine in flight, and fly it as a twin as desired ( or a single
) In the event of a wing engine quitting (I've had one), I can slowly bring back the center engine to see how the airplane behaves, having the surpreme comfort in knowing that if things go south, I can firewall the center engine and recover....
05-11-2008, 06:14 PM
#6
Senior Member
Thread Starter
My Feedback: (18)
Join Date: Jan 2004
Location: Formosa, ARGENTINA
Posts: 2,370
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
Tell me about the plane in the pic.
I plan on building the plane to fly on the two engines. The reason for the third engine is to have a novelty, something different to carry to fly-ins. Also, I am sure 2 four strokes with a 2 stroke mixed in will have an interesting sound.
Unless I come up with something else that really catches my eye, I am leaning towards taking the twin flyin king plans and scaling them down. I am still a little unsure about what size to scale to.
I plan on building the plane to fly on the two engines. The reason for the third engine is to have a novelty, something different to carry to fly-ins. Also, I am sure 2 four strokes with a 2 stroke mixed in will have an interesting sound.
Unless I come up with something else that really catches my eye, I am leaning towards taking the twin flyin king plans and scaling them down. I am still a little unsure about what size to scale to.
05-11-2008, 07:36 PM
#8
Senior Member
Thread Starter
My Feedback: (18)
Join Date: Jan 2004
Location: Formosa, ARGENTINA
Posts: 2,370
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
thats what I thought but I was wondering what size engines, the plane seems awful small to have 3 props turning
05-12-2008, 12:49 AM
#10
My Feedback: (13)
RE: Twin/triple for magnum 91 4s
Hi Guys,
Here is one with four ASP .15's. I tried four .32's...way to much power, four OS Max 10's...not enough power and three engine flying was a night mare with the OS's, and the ASP .15's...when running, fly it really quiet well. I'm not real happy with the ASP .15's and getting four to run is a lesson in patience. Four OS .15's is the ticket for this converson. I've well over 50 flights on the airframe, and a delight to fly. Dual main gear tires, and spring loaded trailing beam nose gear. You need to keep power up on landing, for she glides like a home sick falling brick...but the glide is very managable, just a very steep approach.
Soft Landings always,
Bobby of Maui
Here is one with four ASP .15's. I tried four .32's...way to much power, four OS Max 10's...not enough power and three engine flying was a night mare with the OS's, and the ASP .15's...when running, fly it really quiet well. I'm not real happy with the ASP .15's and getting four to run is a lesson in patience. Four OS .15's is the ticket for this converson. I've well over 50 flights on the airframe, and a delight to fly. Dual main gear tires, and spring loaded trailing beam nose gear. You need to keep power up on landing, for she glides like a home sick falling brick...but the glide is very managable, just a very steep approach.
Soft Landings always,
Bobby of Maui
05-12-2008, 07:36 AM
#11
My Feedback: (26)
Join Date: Aug 2003
Location: El Paso,
TX
Posts: 677
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
I have one of these still in the box, and two Magnum .91 4's ready for it, http://www.nitroplanes.com/giscce310sc6.html
Also have the Hobby Hangar OV-10 Bronco, with the retract kit. Good candidate for the .91's...http://www.hobbyhangar.com/test/acc.htm
Remember, two motors will generate more thrust that an equivalent size single...sooo, two .91 four strokes will pull like a OS 2.00 single and close to a Saito 2.20 four stroke...so size your plane accordingly.
Also have the Hobby Hangar OV-10 Bronco, with the retract kit. Good candidate for the .91's...http://www.hobbyhangar.com/test/acc.htm
Remember, two motors will generate more thrust that an equivalent size single...sooo, two .91 four strokes will pull like a OS 2.00 single and close to a Saito 2.20 four stroke...so size your plane accordingly.
05-12-2008, 07:49 AM
#12
Senior Member
Thread Starter
My Feedback: (18)
Join Date: Jan 2004
Location: Formosa, ARGENTINA
Posts: 2,370
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin/triple for magnum 91 4s
ORIGINAL: Prop_Washer2
Remember, two motors will generate more thrust that an equivalent size single...sooo, two .91 four strokes will pull like a OS 2.00 single and close to a Saito 2.20 four stroke...so size your plane accordingly.
Remember, two motors will generate more thrust that an equivalent size single...sooo, two .91 four strokes will pull like a OS 2.00 single and close to a Saito 2.20 four stroke...so size your plane accordingly.
