SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Feb 14, 2006, 09:46 AM
-plancks only-
Franck's Avatar
The Netherlands, UT, Benschop
Joined Oct 2001
1,082 Posts
Quote:
Originally Posted by jcosta
Here is a Twinstar II from an artist friend...
I like her !! (erm.... I mean the plane 'course (in case the artist should be female))
Franck is offline Find More Posts by Franck
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 14, 2006, 09:39 PM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
Quote:
Originally Posted by Jurgen Heilig
weight is not an issue with a model like the TwinStar II.
This is another area where we disagree. When it comes to powered model airplanes, weight, power, and pitch speed are almost everything - climb rate, acceleration, length of take off runs - all depend on these three.

Even on unpowered gliders, more weight always means a higher sink rate (though there are times when the advantage of faster penetration may outweigh the disadvantage of higher sink rate).

The only models I know of where weight does not cause a performance penalty are slope gliders - the more they weigh, the more wind speed they need to fly, but once that need is met a heavy model can have just as much performance as a lighter one. This, of course, is because the heavy model flying in stronger wind has a bigger power source - the increased wind velocity.

As Treetop says, I have absolutely no issue with folks deciding to choose whatever powerplant and batteries they find appropriate for them. The only part I have trouble swallowing is the "heavy and inefficient powerplants with the wrong pitch speed delivered through a small inefficient propeller are best" bit. I'd rather people know that the stock powersystem, while cheap (you paid for it when you bought the kit) has some significant compromises engineered into it. If you're happy with them, great. If not, there are better options (not necessarily brushless, cheap can motors run at high rpm and geared down to drive a big prop can be very effective and reasonably efficient too).

What I have found through writing WebOCalc is that delivering the same amount of power at the same pitch speed through a small propeller can cost you up to half the thrust you get with a bigger propeller at the same power and pitch speed.. In other words, not considering the motor efficiency at all, simply using a small propeller can be enough to throw away half the available power driving it. (It seems that roughly double the prop diameter - four times the prop disc area - is necessary to get this approximate doubling of propeller efficiency.)

If we assume the big propeller achieves 80% efficiency (I doubt most inexpensive model propellers get this good, but I'm being charitable and this still lets us compare the two systems), that means the small propeller might have 40% efficiency. Add in a direct-drive Speed 400 motor that has 45% efficiency (at full throttle) of its own, and you have a system that probably has about 18% efficiency in converting electric power from the battery into forward motion of the model aeroplane.

Simply using 9" props instead of 5" ones might get you 75% efficiency at the props instead of 40%. Add a 75% efficiency brushless motor (also at full throttle) in place of a 45% efficient can motor, and now you have a combined efficiency of perhaps 56% . Compare that to the 18% of the direct drive Speed 400/small prop setup...perhaps a third as much.

Of course there are some folks to whom efficiency does not matter at all. But for many of us, it does, especially when we're talking about such a significant increase.

-Flieslikeabeagle
flieslikeabeagle is offline Find More Posts by flieslikeabeagle
Last edited by flieslikeabeagl; Feb 15, 2006 at 01:05 PM.
Reply With Quote
Old Feb 14, 2006, 11:08 PM
Honey,just one more thing
spudandretti's Avatar
Rensselaer,IN
Joined Jan 2003
3,098 Posts
Is a twinstar made just to be a twinstar? Going brushless, is there a big difference between going brushless and the standard setup? I could see trying to make , maybe a sportier plane more efficient? Do I make since? I can see trying to do as much as you can for this plane (maybe a brushless person is going to always be brushless), I was always the more is better, but on this plane is it needed? Is the run times better to change it? Is the performance a drastic difference?Bud
spudandretti is offline Find More Posts by spudandretti
Reply With Quote
Old Feb 15, 2006, 12:03 AM
Registered User
Manila Ninoy Intl, Philippines
Joined Nov 2001
1,331 Posts
Quote:
Originally Posted by Jeanseb
Hello there,

I have haerd that it is better to apply a specific coat of some kind of paint on the elapor before applying the definitive paint... Yes this not very accurate.

This is why I am asking! What kind of preparation do you need on the elapor before painting?


Thanks!!!!
1) You sand off the molding bumps with 400 grit.

2) Wipe down the surface to be painted with solvent, I use anhyrous isopropyl alcohol (100%, no water). This is to remove any mold release agent used in the manufacturing process.

3) Multiplex has a new surface prep for elapor called

MULTIprimer #602700

Until now it has been almost impossible to paint ELAPOR® or EPP foam, as the paint soon flakes off. MULTIprimer finally offers the key: once applied, the primer forms the basis for an enduring colour finish with many types of paint. We have had particularly good results on foam with matt synthetic enamels, available in spraycan form from any DIY store.

This is probably what you were referring to.

Haven't tried this yet.

This thread has various posts listing types of paint tried with results etc....
deadduck is offline Find More Posts by deadduck
Reply With Quote
Old Feb 15, 2006, 12:37 AM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
Quote:
Originally Posted by spudandretti
on this plane is it needed? Is the run times better to change it? Is the performance a drastic difference?Bud
Bud, I think that is the a very subjective question, and really, you're the only one who can answer it for yourself.

I find I enjoy my RC planes a lot more if I stick to some fairly simple rules about power, stall speed, and pitch speed of the motor/propeller combination. The stock Twinstar setup does not fit those rules very well, so I'm confident I would not enjoy flying it stock. In the early 1990's, one of my housemates had a Datsun 210B - a nice little car, but very underpowered for the Los Angeles freeway system. I remember driving that car - it took some 30 seconds to get it up to about 65 mph if you hit one of those red lights on the freeway on-ramp (the speed limit was 55 back then, remember). It was very difficult to pass another car - you had to floor the throttle a good 30 seconds before you figured you would pass the other car, and hold it floored while the little car slowly, slowly, slowly gained velocity. If you were lucky and had a clear road, and the other driver did not touch his/her gas pedal, then you might pull off a pass. But most of the time, the only way to get past another car, for instance to change lanes, was to use the brakes, and pass behind the other car. Driving that car on the freeway meant managing precious momentum, because if you lost speed, it took forever to get it back.

The stock Twinstar II power system reminds me of that Datsun. As you can see from Jurgen's videos, if you carefully manage the momentum of the model, give it time to get up to speed, and carefully trade off altitude for speed, you can make it do rolls, inverted flight, etc.. Clearly many folks find this entirely adequate.

For myself, though, I remember my friends Datsun not with fondness for its powertrain, but as a lesson learned: I've done my best to never buy myself a car that badly underpowered. As you'll notice reading through this thread, I'm not the only one who feels the Twinstar's stock setup is inadequate - before cheap brushless motors existed, people were using geared brushed motor setups on their Twinstars to get more efficiency and thrust. It's not the magic word "brushless" that matters - rather, it's that direct-drive Speed 400 setups are always a rather bad compromise: the motor is inefficient at low rpm, the propeller is inefficient at high rpm, and when mated together, neither part is operating efficiently. Put the same Speed 400 motor in a gearbox, run it off a 3S lipo pack, gear it down enough to put a big prop on it that makes the right pitch speed, and it will perform quite well. Or, as I choose to do, use a couple of cheap outrunners instead.

It's your money, your build time, your flying style, so it's your decision!

-Flieslikeabeagle
flieslikeabeagle is offline Find More Posts by flieslikeabeagle
Reply With Quote
Old Feb 15, 2006, 01:31 AM
sensitive artsy type
Treetop's Avatar
Tucker, Georgia, United States
Joined Feb 2004
3,168 Posts
Well I will introduce another factor. I agree that the speed 400 with the direct drive is the least expensive powerplant available, and is probably chosen for this reason. However, most Multiplex planes are built to a size where this system works, and the need for lipos is not there, as opposed to GWS, which according to the guys I have flown with are real dogs with very short flights with NIMH battery packs. So size is an issue, for the smaller park flyers lipos are considered necessary. And I guess having brushless lets you fly them in a little wind.

I agree that a cheap upgrade for the TwinstarII would be geared motors, but an 8 cell Nimh sub c pack, from my vast amount of reading about the Twinstar I, is no problem as far as weight.

Bill Glover uses 4:1 gearboxes with the speed 400s and APC-E 11 x 8.5 props on his Twinstar I. So the upgrade is the cost of the gearboxes and props, and reaches Flieslikeabeagles more efficient state for very little money.

I also notice on my stock EZ Star with 7 cells, that there seems to be no gain in the top 20% of throttle, in other words (it has the same speed 400 and gunther prop as the TSII, except there is only one of them) it seems like the extra rpms is lost to the efficiency of the prop having been maxed out.
Treetop is offline Find More Posts by Treetop
Reply With Quote
Old Feb 15, 2006, 03:26 AM
Registered User
Jurgen Heilig's Avatar
53859 Niederkassel, Germany
Joined Sep 2000
18,786 Posts
Quote:
Originally Posted by flieslikeabeagl
This is another area where we disagree. When it comes to powered model airplanes, weight, power, and pitch speed are almost everything - climb rate, acceleration, length of take off runs - all depend on these three.
...
-Flieslikeabeagle
Oh, I don't think we disagree here. When I said weight is not an issue, I was not saying that it did not have any effect and I just referred to the weight of the motors.

2x73g is only approx. 10% of the total weight of a Twin Star with NIXX batteries. If you really want to save weight, I recommend a Kokam 2s1p 3200 setup.

On a Shockflyer, going brushless makes much more sense. The stock Speed 300 with gearbox weighs approx. 70g and requires a 3 cell setup. That's approx. 50% of the total weight of the model. A brushless outrunner setup using just 2 cells weighs less than half of the brushless drive, reducing the flying weight by over 25%, while providing more power as well. Now that makes a big difference.

Jürgen
Jurgen Heilig is offline Find More Posts by Jurgen Heilig
Reply With Quote
Old Feb 15, 2006, 03:35 AM
Registered User
Jurgen Heilig's Avatar
53859 Niederkassel, Germany
Joined Sep 2000
18,786 Posts
Quote:
Originally Posted by Treetop
...
I agree that a cheap upgrade for the TwinstarII would be geared motors, but an 8 cell Nimh sub c pack, from my vast amount of reading about the Twinstar I, is no problem as far as weight.

Bill Glover uses 4:1 gearboxes with the speed 400s and APC-E 11 x 8.5 props on his Twinstar I. So the upgrade is the cost of the gearboxes and props, and reaches Flieslikeabeagles more efficient state for very little money.

I also notice on my stock EZ Star with 7 cells, that there seems to be no gain in the top 20% of throttle, in other words (it has the same speed 400 and gunther prop as the TSII, except there is only one of them) it seems like the extra rpms is lost to the efficiency of the prop having been maxed out.
Gearing is really not that cheap of an upgrade anymore. The gearboxes on Bill Glovers TwinStar cost much more than a cheap outrunner.

The Easy Star is a rather "draggy design" (= good for beginners). You need a lot of power to make it go faster. Also some speed controllers are not working linear to your throttle stick and may reach full power at 80% of your stick travel.

Jürgen
Jurgen Heilig is offline Find More Posts by Jurgen Heilig
Reply With Quote
Old Feb 15, 2006, 12:52 PM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
Quote:
Originally Posted by Jurgen Heilig
Gearing is really not that cheap of an upgrade anymore. The gearboxes on Bill Glovers TwinStar cost much more than a cheap outrunner.
Exactly! I priced out gearbox setups and direct-drive Speed 480 setups (these are not efficient either), and cheap outrunners, and there wasn't that much cost difference - about $27 for a decent planetary gearbox that would mount in the Twinstar without hanging down below the nacelles, about $16 for a Speed 480, $29 for a 400XT (or $20 on sale). Similarly, a lipo-safe brushed motor ESC that could handle all the current a pair of overloaded direct drive Speed 400's would ask for cost around $45, while a pair of EP Brushless ESC's cost about $56, and a pair of Thunderbird 18 ESC's cost $60 on sale. There simply wasn't that much price difference between these options.

-Flieslikeabeagle
flieslikeabeagle is offline Find More Posts by flieslikeabeagle
Reply With Quote
Old Feb 15, 2006, 02:36 PM
almost slackin
Joined Dec 2005
469 Posts
Exactly what Flies just said. Thats why I'm building my Twinstar with two 400xt's and two brushless esc's. I'll still have to decide on battery power but the motor part is all on its way. What should I use for batteries? Will a single 3150 3 cell be enough?
Piledriver is offline Find More Posts by Piledriver
Reply With Quote
Old Feb 15, 2006, 08:30 PM
Registered User
Joined Dec 2005
6 Posts
Folks,

I need a quick hand with piecing together a TwinStar II setup. I have been flying an Aerobird Challenger for about eight months, so I do not have extra components around to use. I can score the radio, but no idea about what I need as far as:

New motors
Speed controllers (quantity, type)
Batts (I prefer to stay NiMH, not ready for LiPos...)
Props/spinners
Misc

Suggestions appreciated. Money is not an issue, so please help me build the ideal NiMH setup so I won't grow bored too quickly. (BTW, I have searched for this info, but the number of choices/combinations discussed here are mind-numbing to a build-it-yourself-with-components beginner)

THANKS!!!
Quattro03
Quattro03 is offline Find More Posts by Quattro03
Last edited by Quattro03; Feb 15, 2006 at 08:32 PM. Reason: Spelling!!
Reply With Quote
Old Feb 16, 2006, 03:50 AM
Registered User
Jurgen Heilig's Avatar
53859 Niederkassel, Germany
Joined Sep 2000
18,786 Posts
Quote:
Originally Posted by Quattro03
Folks,
...
New motors
Speed controllers (quantity, type)
Batts (I prefer to stay NiMH, not ready for LiPos...)
Props/spinners
Misc

Suggestions appreciated. Money is not an issue, so please help me build the ideal NiMH setup so I won't grow bored too quickly. (BTW, I have searched for this info, but the number of choices/combinations discussed here are mind-numbing to a build-it-yourself-with-components beginner)

THANKS!!!
Quattro03
Motors and props are already included in the kit, and coming from a model like the Aerobird, are more than adequate.

There is no such thing as "the ideal NiMH setup". I would most likely use eight cells GP2200 to keep the model light, others may prefer GP 3300 or even bigger.

A 35-45A Speed controller is fine for the standard motors.

Jürgen
Jurgen Heilig is offline Find More Posts by Jurgen Heilig
Reply With Quote
Old Feb 16, 2006, 06:56 AM
Registered User
Twin-Jet-Crash's Avatar
Norway
Joined May 2004
255 Posts
I would like to get advice on what prop i can use for my TS. It's been lying down for the winter after a crash where one of the props came of.
I was using a 3S LiPo, with the stock props and motors, now I've changed to a 2S-pack and i would like to get better props, to give me enough thrust at the lower voltage.

I've been adviced to try Graupner CAM 6x3, any idea about this?
Twin-Jet-Crash is offline Find More Posts by Twin-Jet-Crash
Reply With Quote
Old Feb 16, 2006, 07:03 AM
Registered User
Jurgen Heilig's Avatar
53859 Niederkassel, Germany
Joined Sep 2000
18,786 Posts
Quote:
Originally Posted by Twin-Jet-Crash
I would like to get advice on what prop i can use for my TS. It's been lying down for the winter after a crash where one of the props came of.
I was using a 3S LiPo, with the stock props and motors, now I've changed to a 2S-pack and i would like to get better props, to give me enough thrust at the lower voltage.

I've been adviced to try Graupner CAM 6x3, any idea about this?
If you have been flying on 3 cells, chances are pretty high that your motors have already suffered. Otherwise the Cam Slim 6.6x3" should work fine on 2 cells and the stock motors (Permax 480 would be even better).

Jürgen
Jurgen Heilig is offline Find More Posts by Jurgen Heilig
Reply With Quote
Old Feb 16, 2006, 07:26 AM
Registered User
Ildefonso's Avatar
Altafulla. Tarragona (Spain)
Joined Jan 2006
21 Posts
Quote:
Originally Posted by Twin-Jet-Crash
I would like to get advice on what prop i can use for my TS. It's been lying down for the winter after a crash where one of the props came of.
When you mount the propos, a small quantity of epoxy applied to the axe of the motor could avoid that props come of.
Quote:
Originally Posted by Twin-Jet-Crash
I was using a 3S LiPo, with the stock props and motors, now I've changed to a 2S-pack and i would like to get better props, to give me enough thrust at the lower voltage.
Another option is to use 3S (11 V) changing the stock motors (400 6V) to 480 (7.2 V) or better for consumption 400 (7.2 v), using full stick motor with care.
Ildefonso is offline Find More Posts by Ildefonso
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
The Mpx Micro-Jet has arrived! (Part II) flieslikeabeagle Foamies (Kits) 57 May 06, 2007 11:32 PM
Discussion MPX Twinstar II in Australia maxy333 Foamies (Kits) 1 Feb 25, 2006 04:25 PM
Yippee! MPX Twinstar II maidened today!! Chetto1965 Electric Plane Talk 10 Feb 08, 2006 02:09 AM
Discussion MPX Twinstar II configuration? Chetto1965 Electric Plane Talk 9 Jan 05, 2006 02:20 AM
The Mpx Micro-Jet has arrived! Jurgen Heilig Foamies (Kits) 655 Jun 05, 2005 04:46 AM