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Old Nov 10, 2013, 10:03 AM
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Tucson
Joined Nov 2009
949 Posts
On rough CG: The Silence Twister has a real advantage, starting out as an RC model before being made into a full-size experimental.

With an empty tank, the plane balances right about the 30% cord. This rough balance is very close to perfect. Kudos, Seagull. And with the gas tank mostly in front of the CG, I should be a little nose heavy for takeoff with a full tank. I will probably watch handling for a couple dozen flights as I run down the tank, to see if a little nose weight is needed for stable landings.

(I put tail feather servos in the rear cockpit servo mounts. 3 pushrods, no pull-pull. 60g servos -- Solar 200 series. Pick the speed you want, if you use these. 222 are faster, 223 are slower.)
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Old Nov 10, 2013, 11:25 AM
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Keller, TX
Joined Aug 2005
299 Posts
Quote:
Originally Posted by wuest3141 View Post
Thanks for the gas tank comments. It's definitely not a standard approach, but I had 4 x 24 oz tanks sitting around, and it does negate the complication of using a timer on the radio.

(RCFVR) I'm trying to think through the comments on gas usage in 2-stroke engines and displacement. The numbers that I came up earlier this year (as to displacement) are:

20 cc = a cube with 2.71 cm on a side ( a cube root of 20.0)
= a cube with 1.05 inches on a side
= a 1.05 cubic inch engine (20cc = 1.22cu inch disp)

30cc = a cube with 3.1 cm on a side (a cube root of 30.0)
= a cube with 1.2 inches on a side
= 1.73 cubic inches (30cc = 1.83 ci)

A .90 cubic inch engine = a cube with 0.965 inches on a side
= a cube with 2.47 cm on a side
= 15.069 cc (.90 ci = 14.744 cc)

.
You might be overthinking this stuff.
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Old Nov 18, 2013, 08:17 AM
Registered User
Tucson
Joined Nov 2009
949 Posts
You're right, about maybe overthinking the power equivalent. But coming from the electric side of the fence, I always design power systems for pounds of thrust (150 watts of power will accelerate 1 pound of plane straight up).

So a 10 pound plane needs 10 x 150 watts (effectively to the prop) or 1500 watts or 1.99 horse power to (just) do vertical aerobatics. It is better to add 30-50% power, so the engine can be run and fly the plane at 70% power. This gets you up to almost 3 horse power.
So a 10 lb plane really needs about a 30cc gas engine to fly well.

This is not a simple equivalent of cubic inches, as the nitro engines tend to get more power out of a cubic inch than the gas engines. So, I see 20cc gas engines as about equivalent to .90 size nitro engine, and a 30cc gas engine as equivalent to about a 1.25 nitro engine.

At my elevation (Tucson) I loose a pound of thrust for every 10cc of a gas engine. At sea level you may get 6 lbs of thrust per 10cc of DLE gas engine, but at Tucson, you only get about 5 lbs of thrust for every 10cc. That means that a 20cc gas engine just will not fly a 10lb plane well here, so I have to go up to the next bigger size engine.

The weird thing, to me, is that the nitro engine manufacturers often don't list the power metric of their engines, although nitro engines may differ in power greatly, for the same displacement. The new 20cc Evolution gas engine has no power rating, and I have no idea how to properly fit it to a plane for adequate power. Or, compare its power to nitro engines.
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Old Nov 18, 2013, 09:38 AM
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Keller, TX
Joined Aug 2005
299 Posts
Quote:
Originally Posted by wuest3141 View Post

The weird thing, to me, is that the nitro engine manufacturers often don't list the power metric of their engines, although nitro engines may differ in power greatly, for the same displacement. The new 20cc Evolution gas engine has no power rating, and I have no idea how to properly fit it to a plane for adequate power. Or, compare its power to nitro engines.
HP is easier to calculate from the watts involved in electric propulsion, Not so easy on the fueled engine side. Our planes fly on thrust rather than HP, and best thrust is realized with larger props at lower rpms. With fuel powered engines the highest HP is arrived at with smaller props at higher rpms, but those are not the props that best fly the plane. The manufacturers do not use a uniform measure of "power rating" their engines, but tend to throw out some horsepower number that is usually meaningless as to usefulness for comparisons.

It can be daunting to try comparing power ranges between engines and electric motors. Probably the most useful would be to compare thrust produced, but this is often not readily available.

Good luck!
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Old Dec 03, 2013, 08:11 PM
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Tucson
Joined Nov 2009
949 Posts
The Seagull Silence Twister flies like a Spitfire. It will pull full vertical loops with a 20cc gas DLE (at Tucson elevation), with good lateral control in the loop. The plane flies fast, and carves, but don't slow it down too much.

With the DLE 20cc gas engine and a 24 oz gas tank, the Twister flew a little tail heavy. The retracts that come with it don't quite track straight, if you are going to use them for fixed gear. They may add a bit of yaw on take off. Ground handling is good, if you add about 60% exponential to the rudder. With a 15 x 6 prop, the engine idles but will not move the plane on the runway (good for ground handling). Hold full up elevator to taxi, and blow some air over the tail to taxi.

I never could get the wing attachments to work, so epoxied one wing on, and taped the other one on for the maiden flight.

My overall rating of this scale plane is that it is a nice flier compared to WWII scale fighters, but it is not the slow aerobatic plane that its full-size relation is. It is a fast flier, and gets a bit hinky when it is slowed down. I think that the ARF is a good deal, but it is not quite the slower, "carving" aerobatic plane that I was looking for.

Hope that this information helps some of you.
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Old Dec 04, 2013, 07:30 AM
Closed Account
Joined Dec 2006
4,258 Posts
I too had looked at this thread and thought what is a Hanger 9 ARF doing in this Scale Fuel Planes forum. Further confusing things was the O.P.'s reference to Seagull, which I took as a reference to the Horizon Hobbies Hanger 9 manufacturer by the same name, to confuse me even more is the fact that Horizon Hobbies does have an ARF called the "Twist".

Oh, well, I think I finally understand. However, I am easily confused!
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Old Jan 08, 2014, 05:45 PM
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United States, OR, Central Point
Joined Jul 2008
11 Posts
Yo wuest3141! Thanks to you, I now have a fairly good idea on what to expect. I picked my Twister up right as they were going out of stock and I sure am glad that I did, because they went from the typical 'back ordered' to 'no longer available' really quick...
Its been a month now, so I have to ask, have you gotten much air-time with your Twist since you last wrote? And if so, did you find any new 'idiosyncrasies' with her or can I expect to get good, and then relaxed flying it? I am building a Seagull Edge 540 and the Silence Twister, as winter projects because its the 'rainy season in Oregon now. And here is a question for you!
I have 2 engines that I can't decide which is going to go in what: A tried and true Magnum 1.20 4 stroke, and a OS 1.20AX that accelerated my GP Revolver 70 straight up in unlimited vertical and bigger than Montana loops. And get this: Through a ton of experimenting, I settled in on a Master Airscrew 14 X 9 3-blade prop for both of these engines for the past 7 years with awesome results, plus they look really cool... The 9" pitch develops incredible speed, and the low-end torque made both of these engines work well for my large float planes. (I have my own 2 acre pond next to my 440' grass runway, AND I just retired... )
All's that to say, I am leaning hard towards putting the OS power-house1.20AX in the Silence Twister and try to break the sound barrier with it... Well, you get my drift, right? I want to end with saying THANK YOU for all your input. Good stuff, and I hope this thread keeps going. It seems that either no one in the US bought these, or they are sitting on the shelf collecting dust? (I know they weren't available here for a long time, and then they were here and gone again in no time too...
I await to hear more from all you guys, as I would be BUMMED if I accidentally over-powered this thing, or too, didn't make it as nice (fast) as it is capable of going, right?
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Old Jan 11, 2014, 12:44 PM
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Tucson
Joined Nov 2009
949 Posts
My Twister had a 20cc gas DLE engine, putting out 10+ pounds of thrust at Tucson, Arizona elevation. I think that a nitro 1.20 is about this equivalent. A 2-stroke 1.20 should wuup this plane through vertical aerobatics.

Once you solve the build weirdnesses that I encountered (how to clamp the wings on, how to get a steerable tail wheel, etc.) you will have a fast flying Spitfire, that looks good. What you will NOT have is a model of a full-sized plane that does slow, graceful aerobatics! The wind slickness and the weight of the Twister make it a FAST plane, like a WWII scale fighter.

When you kill the throttle and point the Twister straight down, it will pick up speed! It is not an Extra that will keep speed down for slow aerobatics! Fly it fast, until you get a good feel for how it reacts. And be careful with spins. It will accelerate straight down, with no power, so you will not have as much time as you would with a modern aerobatic Extra.

I also am building a Seagull Edge 540 (60 size) , and waiting for an ASP 1.20 4-stroke to put in it. This should easily give full vertical aerobatic power for this plane. I ripped an Evolution 20cc gas engine out of this plane, because the engine ran worse, the longer I ran it (exactly according to the break-in procedure in the manual). The REALLY FAT airfoil of the Seagull Edge should keep aerobatics quite slow, compared to the Twister.

I am also trying out a Seagull Super Chipmunk (55 size) with an ASP 90 4-stroke glow. I don't know that I will get quite vertical aerobatics, but should get sport aerobatics in a wonderful looking scale plane. I will leave notes on what I encountered in the fuel scale area.

Some of these Seagull planes are hard to find, but go on the internet (ebay) and there will be little hobby shops that will sell them. I bought the Twister, the Edge, and the Super Chipmunk from advantagehobby on the internet. The ASP 4-strokes I am buying from Taiwan (I got a .52 for a Smith Miniplane, and it has lots of power and runs better and better, the more time I put on it).

Good luck flying the Twister!
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