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Build to fly not to crash?

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Build to fly not to crash?

Old 02-20-2011, 04:00 AM
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longdan
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Default Build to fly not to crash?

I'm interested in getting a few peoples opinions on this subject - the old saying build to fly not to survive a crash. And if it relevant anywhere, it's here in 1/2A.
I'm well aware that too much weight is detrimental to a plane flying well. But weight is necessary - we need some structure to actually have a plane to fly. And that structure, in the form of wings, fuse,engine, electrics etc carries some weight.
But going back to the old well used adage of ' build it to fly, not to crash', I'd like to expand on that - 'Build it to fly more than once, whilst keeping weight to a minimum'.
Where do you draw the line?
I could build a 1/2A that would fly fine, survive high G turns, and be the lightest plane you ever weighed, but it would be bare wood, glue would be water based, balsa would be swiss-cheesed with lightening holes and battery would be made from cells from a rechargeable 9V. It would fly once, but be unsuitable for a second flight.
I just wondered where people drew the line between lightness and longevity.


Old 02-20-2011, 05:46 AM
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ocelot31454
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Default RE: Build to fly not to crash?

That is a very good question regardless of whether your building an R/C, C/L or free flight model. That said, I think you have to balance structural intregrety with looks and mechanical ability. Kinda like building a house. You can't expect the air frame of a model that was built for rubber power to accept a glow or electric to fly well, if at all, let alone surive a crash. The reverse is true of a model that was built to hold a .25 and has a .049 installed. Thats why the designers specify the engine size range and the plans call for certian material thickness. The varing factor is if you do any major modification to the model ie 3/16 balsa where it calls for 1/8, 6oz tank where it calls for 4oz, Hard wood whaere it calls for ply etc. to allow for for those changes.
There are alot of models out there that were designed for engines that either are not available or are hard to find. Replacing it with a different one that is readily available will probably result in having to changebulk head position, Engine mounting procedure etc. To maintain astectic or scale appearance you might have to lengthen the cowel which is giong to change the weight because of theincrease in material. Increase the weight and you more than likely are going to have to increase the engine size which means you have to re-inforce the engine mounting. There are a lot of variables, and one change can lead to more in order for things to work out right.
The idea isn't to draw a line as to what can or can't be donebut have fun doing what your doing. I personaly don't believe in the word "CAN'T. I do believe that there are things that shouldn't be done. But the choice ultimately rests with the builder in how much work and money he/she wants to invest in their model.
Hope this helps
Old 02-20-2011, 06:27 AM
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Default RE: Build to fly not to crash?

To my experience, build as light as possible and it will both fly and crash better. Of course, the engine has to be sized appropriately and again, you don't have to put a huge lump up front if the plane is super light to get awesome performance..

As examples: My Little Extra weighs about 28 ounces ready to fly. The plane has done cartwheels and everytime, that resulted in a broken nylon wing retainer bolt (As designed) and very little else. Years ago, I mildly cartwheeled a Great Planes Super Sportster .40 which was built a lot "tougher" and it required weeks of repairs (Never flew again..)

- As you may have seen on other posts, a few weeks ago it went straight-in lawn dart style from about 75-80 feet due to an aileron servo failure. I flew it again the SAME DAY after minor repairs (Flew it again yesterday [8D]).

As another example: The C/L combat wing I scratch built with my son. I built it as light as possible ( 1/16 balsa everywhere) Balsa spars , " swiss-cheesed " with lightening holes in just about every flat surface. The only hardwood on the entire plane is on the beams holding the motor mount (Those are also wrapped in Carbon Fiber). If flown over a normal grass surface, the thing is almost crashproof. It will littrally go in lawndart style at full speed and bounce off the grass. (Watch it bounce in the "Bloopers" at the end of this video [youtube]http://www.youtube.com/watch?v=4vzPJtNqvvI[/youtube]

My last "Extreme" example: Back in the eighties I bought a used Ugly Stick (40 bucks with engine + radio) that had been built "To survive crashes" the thing was really heavy, with a glassed fuselage. It was like a P-47 Thunderbolt and would out-dive just about anything with a .40 until one day when the Tower Hobbies radio became ineffective during a flight. The plane got into doing loops at full throttle and eventually cratered-in at full throttle: Everything broke including the engine crankcase. There was not one piece of the fuselage bigger than a dollar bill at the scene of the crash.
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Old 02-20-2011, 06:30 AM
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Mr Cox
 
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Default RE: Build to fly not to crash?

Definitely build to fly it and, perhaps more importantly, build it correctly without taking any stupid shortcuts. To me lightening holes in balsa, that are so common in ARFs for instance, are totally wasted. The weight savings are only marginal and are not worth the weakening of the structures that they give. Balsa is a highly directional material and properly built-up structures will be both lighter and stronger than the lasercut shortcuts.

Another thing, to-days planes are so much lighter compared to what they used to be, that is just a phenomenal development. I learned to fly on a 150 sq inch plane, weighting 22oz and powered by a BabeBee. Today one can build the same plane with fullhouse controls and it will only weight about 10oz.

Old 02-20-2011, 06:41 AM
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Default RE: Build to fly not to crash?

I kept the Balsa I took off the plane and that equals to the weight of all the ribs on one wing panel: I'd say that it's not insignificant.

I'm currently building a Herr Star Cruiser trainer for my kids and the weight taken off by "swiss cheezing" is currently equal to the weight of 2 servos..

As for the holes making the structure "Weak" : Watch the video..
Old 02-20-2011, 06:48 AM
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Default RE: Build to fly not to crash?

My first plane was one of those PVC pipe fuse jobs with foam wing. It was so heavy it would not fly!

A good fairly crash proof flyer is the classic Balsa USA Stik 40 Plus with that wood crutch fuse. Very solid and, if needed, very easy to repair. And flies well if you use the ailerons. I used a Saito 56 4 stroke.

Cheap. $65.95 for the kit and a very easy build. See it at http://www.balsausa.com/store/product.php?id_product=53


Tom
Old 02-20-2011, 07:03 AM
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Default RE: Build to fly not to crash?

Perfect timing for this topic. i'm just finishing my first attempt at a "big", lite-weight .074 powered plane. The model is a Mountain Models "MINI FLASH". Considering the fact that I hold the self proclaimed title of "WWB" (Worlds Worst Builder), I'm not burdened 'bout looking for some fine line of what can, & what can't be technically accomplished. It's my lack of building skills that is the limiting factor. On this project, I went through a rather steep learning curve. Most important; This is not a typical HOB kit.!!!!!! My heavy handed "dumb fumbling" was the greatest challenge. (Broke both fuselage sides, one trailing edge, & a couple of ribs, just during assembly. Things got worse while applying the covering to the wing.. Should have gone with lite silk span, but instead, thought that I'd be safe with some lite shrink covering. (Can't remember the name, but the label says "made in England"). Well, two or three attempts at this, & more repair to the twisted & warped wing, (plus an almost unlimited amt. of profanity) & the dang thing is covered. Next one of these (I've got another waiting, plus have the thin "speed wing" ) will have some 1/8x1/2 balsa strips between the ribs & against the trailing edge. NOT because the structure needs it, but it's gonna make life a lot easier, during assembly, considering my crude building skills. Right now, dry weight, minus dope, is 13&7/8 OZs. Obviously a skilled builder could shave some weight off that, but I'm gonna add 'bout 1/2 OZ, so as not to make the finished product look like it's been through a few dirt naps; even before it's first flight. ..................... George K.
Old 02-20-2011, 08:05 AM
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Default RE: Build to fly not to crash?


ORIGINAL: R/C Phile
I'm currently building a Herr Star Cruiser trainer for my kids and the weight taken off by ''swiss cheezing'' is currently equal to the weight of 2 servos..

As for the holes making the structure ''Weak'' : Watch the video..
Well, I'm sticking to my opinion that any built up structure, when built correctly with the wood grains in the right direction, will always beat any swiss cheesing version of wood.
Don' take my word for it, just study any indoor free-flight planes where weight really does matters, you will never find any swiss-cheesing there...

The video cannot be view as it contains illegal material... Music?
Old 02-20-2011, 08:17 AM
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Default RE: Build to fly not to crash?

I love a 1/2A RC plane to weigh 12 ozs or less. At that weight the climb performance is very good and most designs are very hard to stall. A 12 oz plane that has a control malfunction flown over a grain field most often won't even reach the dirt.
At 14-16 ozs the larger airframes are still good flyers, you just lose the spectacular performance that you would have if you kept it at the 12 oz threshhold.
Just by using simple, proven construction methods that have been demonstrated over the years at this forum, there's no reason for anyone to be building any lead sleds...unless that's what you want.
I also agree with Mr Cox about lightening holes in balsa. If you are using good balsa, it takes a big pile of "holes" to add up to a substantial savings and the structure is much weaker. Worse, try piecing all the splintered fragments back together after a crash. Lightening holes in heavier wood, especially plywood is a different story. I will hog out a plywood firwall and plug it with balsa and punch holes in ply doublers if it seems like a good idea for the plane in question.
Old 02-20-2011, 09:24 AM
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Default RE: Build to fly not to crash?

Ok, well done!

You're forgetting to chalk the grass, and I forgetting the name of the bossa nova piece?
Old 02-20-2011, 11:47 AM
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Default RE: Build to fly not to crash?

My planes are built up and around 19oz. This one is #9 It has well over 450 flights, and 50+ hours in the air powered, over the last five years, still will fly this year. The other is #8, has over 45+ hours powered, this year is it's seventh flight season, has 445 flights on it. This plane is also around 20oz. Also ready to fly this year, it's eight season.

These are all built up, and have dowl rods on the leadine edge of the wings. Lots of trees here.

The proof is in the airtime, not the age of the wood.
Old 02-21-2011, 04:33 PM
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Default RE: Build to fly not to crash?

I usually err on the side of tough. Most of my stuff is overpowered so performance isn't normally an issue.
Old 02-21-2011, 05:05 PM
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Default RE: Build to fly not to crash?

Since "1/2A" can mean many things, I break it down a bit farther for power/weight requirements. For wingspans between 30" and 37" I have the best luck staying around these numbers for sport models.

Cox bee's, SS, and medalions: 10 to 13oz
Cox TD: 12 to 15oz
Norvel 061: 13 to 16oz
Norvel 074: 14 to 19oz

I fly these mostly from an uncut rough field, so landings can be a bit abrupt, always no-gear belly landings. Hitting the occasional dirt mound or small bush and at these numbers the planes hold up just fine. If I was flying only from the club field, I could go lighter built.
Old 02-22-2011, 05:04 AM
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longdan
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Default RE: Build to fly not to crash?

Thanks for all that input. Certainly some food for thought there.
R/C Phile - I wish my yard was big enough for some of that action. Takes me back to when my dad bought me a cox c/l plane for christmas when I was 8 or 9. Though as I recall, he had more fun with it than I ever did.

When I'm building, I seem to get into the habit of just adding a little bit of strength here and there, and there, and a bit here, oh, and mustn't forget to reinforce that bit, and a bit of glass won't go amiss there, a bit of tri-stock on those corners, etc. And before I realise it, I've added a couple of ounces. Then when it comes to flying, and it doesn't perform so well, I ask myself if all that reinforcement was really necessary.

Though I did build a DNU a while back, and I told myself I will build it exactly as per plans, and it came out at about 13 oz ready to fly with a TD .051, which is probably the lightest plane I have ever built. Its still in one piece, though probably a bit heavier now due to a few repairs. I've thought to myself - if I had added my usual reinforcement to this plane, would I have needed to make those repairs? The answer is yes, I would still have had to repair it. And probably make it even heavier if I had to glue more wood (the extra reinforcement) back into place as opposed to just gluing the unreinforced fuse back together.

This winter ( coming soon - Southern hemisphere here) I have several projects I want to get built - I have 3 sureshark kits - a 1/2A and 2 x .15 sized ones. Plus some bigger stuff that doesn't belong in this forum.
As I said, for some reason, I keep glueing in bits of wood to make the planes stronger, but I am going to use all the willpower I have to resist that temptation on these builds.

Happy flying all.

And my heart goes out to all the families of the victims of the massive quake we had today. Mother nature is a *****.

I see RCU doesn't like the B word. My apologies.
Old 02-22-2011, 10:02 AM
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Default RE: Build to fly not to crash?

I have learned over the years to hopefully build structurally sound and reinforce where needed to allow for that, not a crash. Wish I could remember how may firewalls and landing gear blocks I have seen come off without a crash. Those are two high stress areas that need reinforcement in many cases. I have a Cermark 1/4 scale Pitts that as I was assembling it, I cut the covering off on the front to reinforce the landing gear, firewall and cabane struts. These were all weak areas where I read other modelers had failures. Many hours of flying mine with no problems and minimum weight gain. These rules also apply to my 1/2 A's.

John

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