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  • November 19, 2017, 02:49:27 PM

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51
Having built a few planes designed for .35s and putting up to a. 76 in it I can say this.....

A plane wants thrust and a good balance point;  thats it. 

Getting dirty with torque and trim is more important than trying to factor 1/4" difference in nose length for a given engone weight..

Its just not THAT important. 
52
Open Forum / Re: Tom Morris takeapart system
« Last post by PJ Rowland on Today at 12:56:13 AM »
Dave.  This is only a local rule for USA domestic travel.

I know this because when going international the planes (oversized cargo)  get taken on a different plane. This is how much luggage gets lost for fliers. 

It sucks if your in the USA because you cant really go domestic then international with a large item unless you depart from an international terminal.

Steve..  give Herb a dingle on the dog and bone
53
Open Forum / Re: Equal or unequal wing panels
« Last post by PJ Rowland on Today at 12:12:35 AM »
I think there are far more things you can do to an airframe to make it fly better than worrying about the lift differential.

For what its worth Ive calculated it and yes if you compare the outboard tip to the inboard tip there is a distance difference. Thus a minor speed difference. If you want to get completely technical ; to do it properly the entire wing needs to have the thickness percentage altered from inboard to outboard in a linear manner.  This is somewhat impractical but would yeild ( for example..  Inboard tip at 1" outboard at a reduced percentage.

I dont think it makes as much difference as you think it does vs talking about it. 

Brett is correct when you move the wing your moving the thrust line and stab.  But what if you build on the assemtry into the stab also..  Trust me it doesnt make it "the next big thing"

I think* (rarely)  how the airflows around the system is more critical than many other ideas.. as Igor eluded to the wing doesn't always see all the air....



54
Open Forum / Re: The Imitation
« Last post by Dan McEntee on Yesterday at 11:15:32 PM »
Someone asked me if the Imitation was profile-legal.  I'm not sure how I came to be an expert (maybe just because I can't keep my mouth shut?) but here's the NW Profile rules as pertains to the Imitation.  Note that profile is not a national event -- your rules may vary, so make sure to check.

3. Airplane: Any profile airplane is allowed.
3.1. The engine may be mounted in any configuration -- side-mounted, upright or inverted.
3.2. Doublers or triplers and cheek cowls are allowed, including faired spinners, but the fuselage must meet the "profile" definition of maximum 3/4" thickness by the trailing edge of the wing/flap hinge line, and the engine must be fully exposed from lugs to plug.

4. Engine: Any engine up to 15cc/.91cu.in. Electrics allowed per AMA Stunt Rules.

3: Yup.
3.1: Yup.
3.2: Yup, yup, yup (1/2 inch, not 3/4 inch), and yup (in fact the engine is fully exposed in the 'real' Imitation)
4: Yup.

Were I going to build one (and oh, man, am I tempted!) I might swiss-cheese the fuselage and laminate on some 3/32" balsa sides, or make a BIG cutout, fill it with foam, and ditto the balsa sides.  This should be far more rigid, and lighter to boot -- if you don't take the weight of glue into account.  Cover the outside with silkspan or CF veil, and it should make a nice rigid assembly. 

Note that it's a lot more work, so it turns a "knock it out quick" project into something longer.

Note, too, that this may not be legal in your area -- I understand that 1/2" wide behind the wing is the limit in some places. 

Finally, note that it's also not wise at all if you're still Sir Crashalot of the Knights of the Round Circle, because a cool laminated fuselage is way, way harder to repair than a solid hunk of wood.  If you fly Profile because you're not world class but are too good for Advanced, and you just NEED some trophies, then it's probably worthwhile.

     In my opinion it doesn't not qualify as a profile, and everyone gets hung up on the  "3/4" behind the trailing edge of the wing"  part of some rules that describe a profile model. Hells bells! There are some full fuselage designs out there that are that narrow behind the fuselage!. What denotes a profile model in my opinion is what takes place in front of the trailing edge, and on a true profile model the engine is mounted sideways. This has all been "discussed" before in other threads but in our contests here, it would not be allowed because of all the build up in the nose and the upright or inverted engine. The whole purpose of this design, as I see it, is to get you beyond the typical profile with simple construction and to ability to easily change out power plants for experimentation. That is what attracts me to the concept, having a decent looking, good flying "mule" to check out different engines in.

    So, add me to the list Mr. Griffin!

   Type at you later,
   Dan McEntee
55
1/2 A building. / Re: Houluzko Venturies?
« Last post by Target on Yesterday at 11:10:36 PM »
That's just it; I have no idea what they look like!!
56
Building techniques / Re: Twister kit question
« Last post by Dan McEntee on Yesterday at 11:03:50 PM »
It looks like those two options are good then. Do they add a lot of weight? I am trying to build this kit as light as possible. Tim

   As it has been mentioned, no need to get hung up on weight just yet at this stage. That is one reason I usually advise keeping modifications to a minimum until you get some time in the air and get some experience to learn what the modifications are for and that in itself helps keep weight in check. It's more important to built a straight, accurate air frame. The half ribs and shear webs (which I think aren't necessary but if installed only need to go out about half way on each wing)  won't add but a few grams of weight. The Twister air foil is capable of carrying a fair amount of extra weight. I have seen Twisters bastardized  up to 50 ounces or more and still fly a pattern. One legendary example is a dimensionally stock Twister that was built entirely out of pine but the late ( and I think great) Jason Pearson and his Dad. I think it weighed around 55 to 60 ounces and was powered with a .35 or .40 FP the last time I saw it fly, and Jason flew that in contests! And did well with it! They did it just to prove a point I think. You can search on the forums here for more information on it. Something like that takes some careful flying when it gets too heavy, and that is something we all have done and you will to eventually in the process of learning.. You just can't build a light airplane at first, you have to learn HOW to build a light airplane and what it takes to do that. As Brett mentioned, there are several elements involved in building up weight in a model and no one thing will make an airplane lighter. It starts at the beginning and has to be monitored through the construction right up to the final finish, and learning what to do and watch for takes time and experience, but you will get there. Jason Pearson was quite a guy and great modeler who was tragically killed in an ultralight airplane accident. We are holding our now annual Turkey Shoot contest tomorrow that he instigated here, and I believe his wife is supposed to come up and attend tomorrow. We miss him a lot.
  Type at you later,
  Dan McEntee
57
Building techniques / Re: Show me your stick!
« Last post by Trostle on Yesterday at 11:02:47 PM »
Keith,

You have some really great models there. Are they still around today?

Those models have wings similar to mine.

Let's put that "stick" wire or whatever issue behind us, for a moment.

Here's my question:

Just run the leadouts through the wing and out at the tip. Will the model fly and be controllable if this is done?

Charles

Charles,

Yes, those models are on the wall with the several other models built for the Tucson 1/2A multi-engine profile scale contests.  The B-47, 39" span,  was built earlier for a contest in Los Angeles (the Black Sheep Squadron), then it flew at the 2000 Nats in Profile Scale where it placed 3rd. It has two Norvel .049's.  The Tu 95 has four Norvel .061's, 56" span.  Both to 1/36 scale.

Now, to your question about just running your leadouts through the tips.  Go back several posts on this thread.  The CG of the airplane determines where the leadouts MUST be, even if it is inconvenient to NOT put them through the wing tip.  If the leadouts are behind the CG in an extreme way, the model may fly but it will yaw seriously to the outside of the circle, it will put the leadouts in a serious bind and the model may be uncontrollable, even if it gets off the ground.

For your model, the leadout position at the wing tip should be maybe 3 or 4 degrees behind the CG position.  You might be able to use slightly less, like 2 degrees, but 3 or 4 degrees will be safe.  For scale/sport flying, that would be adequate.  Only when you are looking for refined response/maneuverability for stunt flying would you want to experiment with less line rake.  If you are using a throttle and anticipate a lot of taxi maneuvers and slow flight, you might want to have slightly more line rake.

As I explained earlier, the Tu-95 has the CG slightly behind the wing TE at the center section and the leadout guide holds the leadouts about 6" in front of the tip LE edge.

Keith
58
Open Forum / Re: The Imitation
« Last post by Brett Buck on Yesterday at 10:25:41 PM »
There's absolutely no reason that you can't build this airplane in the upper 40's/low 50's ounce range with completely conventional approaches. All these crazy weight-saving schemes are unnecessary. The problem, if there is one, is the *rigidity*. My full-fuse Imitations and other similar-sized models from the ST46 era were between 45 and 52 ounces, which is plenty light enough, considering the available power.

    For those without piped engines, build it normally, put on a 46LA (power and repeatability we could have only dreamed of in the 80's) and it will be in the low 50's. That's *plenty* good enough, if everything else is right. I flew one of my full-fuse versions with everything from 35FP to a 40VF.

    David won the World Championship with what amounts to the same wing at *66* ounces, and many NATs since.

      Brett
59
Open Forum / Re: The Imitation
« Last post by Mike Griffin on Yesterday at 10:13:10 PM »
"Were I going to build one (and oh, man, am I tempted!) I might swiss-cheese the fuselage and laminate on some 3/32" balsa sides, or make a BIG cutout, fill it with foam, and ditto the balsa sides.  This should be far more rigid, and lighter to boot -- if you don't take the weight of glue into account.  Cover the outside with silkspan or CF veil, and it should make a nice rigid assembly.  "

Stay with me on this Tim.  Ted, Eric Rule and I are working on a built up very rigid fuselage that is going to meet your requirements.  I think you and everyone else is going to like it.

Mike
60
Building techniques / Re: Twister kit question
« Last post by Brett Buck on Yesterday at 10:06:50 PM »
It looks like those two options are good then. Do they add a lot of weight? I am trying to build this kit as light as possible. Tim

   I wouldn't worry about things like this. Where you get in trouble with weight is in the finish, hardware, and the excess use of plywood. A few small bits of ribs will not make a consequential difference in the weight, but will slightly improve the aerodynamics (and appearance). Don't make them with the grain vertical, put it fore/aft as per normal. Use light-medium balsa (6-7 lb) B or C grain.

     It's much more important to make sure you radius the leading edge as blunt as you can make it, basically, carve/sand a smooth arc from the ribs on the top to the ribs at the bottom, and symmetrical. A razor plane will speed this up dramatically.

      Brett
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