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how much is too heavy?

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Old 01-27-2013, 08:13 AM
  #1
chadxp1
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Default how much is too heavy?

Just finished building by Simple Flier (kit) and it came in too heavy. Kits calls out 5.1lbs. Mine wieghs 6lbs 3oz. I wonder if this is too much? I can do a couple of things to remove a little wieghts but I would rather not. (everyone knows this feeling). Does anyone know of a genral rule of thumb on precentage of wieght planes should try to be within in regards to wieght? Also would it be any advantage to go with lipo over my NiMh? I would have to have some type of voltage regulator with the lipo I guess as I need to be at 6Volts.



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Old 01-27-2013, 08:23 AM
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Default RE: how much is too heavy?

Typically speaking all the kit makers were a little light on weigh estimates. I am thinking I would head out to the field and fly it. As for lipo's, I got rid of all my nicad packs and switched to lipo and a Castle regulator. I was having to many nicad packs fail to keep screwing around with them. Good Luck, Dave
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Old 01-27-2013, 08:37 AM
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Default RE: how much is too heavy?

I would expect the stall speed to be a bit higher but otherwise the plane will likely fly fine.

Personally, I like Li-Fe rx batteries. If the servos can handle 6.6 volts, no need for a regulator, and they charge fast and don't self discharge.

Only negative is their voltage remains pretty much the same as they discharge, so recharging them and looking at how much it took to bring them back up to full charge is about the only way to determine their state of charge.
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Old 01-27-2013, 09:03 AM
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Default RE: how much is too heavy?

Quote:
ORIGINAL: chadxp1

Just finished building by Simple Flier (kit) and it came in too heavy. Kits calls out 5.1lbs. Mine wieghs 6lbs 3oz. I wonder if this is too much? I can do a couple of things to remove a little wieghts but I would rather not. (everyone knows this feeling). Does anyone know of a genral rule of thumb on precentage of wieght planes should try to be within in regards to wieght? Also would it be any advantage to go with lipo over my NiMh? I would have to have some type of voltage regulator with the lipo I guess as I need to be at 6Volts.

For once I agree with Agar, that is about kit estimates concerning weight. It is, I suppose, a marketing thing.

Beautiful flying machine. Since I have no clue as to the size and weight you actually have I will just say some points in answer to your ??s concerning rule of thumb.

For airplanes with under 800 square inches wing area, a good general of thumb is not more than 1 pound per 100 sq. ins. wing area. All have flown heavier but it can get tricky. Ove 800 squares it seems OK to go a bit more weight per 100 square inches. You have a long nose-moment arm and a relatively short tail-moment arm. I sugest you not get too slow on approaches or quick-on-the draw when rounding out.

One item that I use frequently is some form of washout for most all airplanes, especially heavy ones. I can't really determine where the end of your ailerons are. If they do continue to the end of the wing I suggest that you cut them about 5-10% of length at the tips and glue the small cut-off portion to the Trailing Edge OF THE WING WITH ABOUT 2-3 DEGREES up. If that is impractical, then at least TAPER the last 15 to 20% of the ailerons Trailing Edge to at least only 50% of the aileron's main chord at the tip.

This "washout" will make landings and tight turns far less subject to the old "Tip Stall" thing that sends many machines to an early grave, or at best a rebuild.

Edited to add: As far as batteries, I still like Nicads and Nmih. I use a number of Lithuim Ion. The Lit. ION is as stable as a Nicad. Charges hang in there. I don't do electric models and I don't assist fire-ball recoveries of Lit. Polymer.
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Old 01-27-2013, 09:48 AM
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Default RE: how much is too heavy?

Thanks all to the replies.

Hossfly, I calculated my area of the wing to be around 520 in.sq. The plane weighs 6.2 lbs. so Im overwieght. I did not inlcude the under belley of the plane/wing in the calc but if I did I would get a little more.

Attached is a better pic of my aileron. It is tapered to the end. it would meet the 50% rule if I use the flaps as part of the aileron. However I planned on deploying the flaps when landing. With that I would not meet the 50% rule. I have my radio programmed to have a few options with the flaps. 1. fully deployed/ do not travel with aileron, 2. travel with aileron full tiume, or 3. fully deployed/travel with aileron. Im scared of the tip stall as I have already destroyed one kit (RV-4) due to this.

I looked at the life batteries. Im going to get some as I too dont trust my Nimh.

Hard to tell from pic but my ailerons due taper to the end


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Old 01-27-2013, 10:01 AM
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Default RE: how much is too heavy?

As Dave pointed out, the kit makers may have stated the weight of there prototype planes but during the true manufacture of them they may have used a lower grade of wood and a much lighter engine. A kit built plane that was built according to the plans usually comes out weighing more then stated on the box. Fly the plane and see how it handles, It will probably be just fine. I test all new planes up high to see if there is a stall or wing loading problem before I try landing. To date I have only had one plane with a stall problem due to weight. It was a prototype ARF and so over weight I was surprised it got off the ground. I liked it so much I gave it away, it was a 30% Extra Patty that wasn't excepted for production by Tower. Had some great features but it was a true pig in the air.
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Old 01-27-2013, 10:27 AM
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Default RE: how much is too heavy?

Grey Beard, thanks. Im starting to feel more comfortable hearing everyones opinions. I must have a calculated the wing area wrong as I checked the plans and it stated 610 sq.in of wing area. This is good news.
Also I took a good look at the wing tips. There looks to be washout already built in to the wing as the leading edge is pointing lower than the wing root! (the wing has a slight twist) more good news!

Thanks again. Chad
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Old 01-27-2013, 10:52 AM
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Default RE: how much is too heavy?

Over in the kit building forum you can pull up a wing load chart I posted several years ago when a lot of people were freaking about wing loading. It doesn't really tell you much but it's easy to use. Only reason I ever know what the loading is on one of my planes is so when someone asks I can tell them. I really don't give it a lot of thought but some people just have to know? Mike liked the chart so much he put it on a sticky?
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Old 01-27-2013, 11:11 AM
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Default RE: how much is too heavy?

OK first as everyone has indicated you are freaking out for no real reason, it would be rare indeed anytime a kit build or an arf comes out as advertized, that is in most every case BS. The simple fact of the matter is the manufacturer has a vested interest in not telling the truth.

Now you re measuring your wing area incorrectly, for all normal wing area calculations the area through the fuselage is included. Average chord x wingspan tip to tip thats it. Also the chord measurment will include any flaps or ailerons in trail.

If you have a bit of taper (leading edge, trailing edge, both or even eliptical) just midspan average to find that very simple measurement. all you gotta do is measure the chord half way out between the fuselage and the wing.

Now you can multiply the span by the average chord and you have your real wing area. But thats only half the information and not of much help in trying to get an idea of how the airplane is gonna fly. To finish the job you need to calculate wing loading and only then through yours and others experiances here we can begin to get a good idea as to how your airplane is going to fly. Wing loading expressed in ounces per square foot of wing area. That will be the magic number and its so easy to obtain.

It can be arrived at in just a few minutes but its a challange to write out and I have done it here many times but its
not worth it unless you are interested, so ask if want the simple calculation. Even if you will simply post the true span tip to tip including the fuselage and the (mac) average chord along with the actual weight in pounds or ounces without fuel I will post back with your actual Wing Loading. Thats the magic number that every designer will strive to acheve or improve as well as giving all the rest of us an idea as to the types of performance to be expected.

Now having typed all that (the only reason I did is because you seem to reallty want to learn and I like that) Ya'll need to chill just a little reflex the trailing edge of your ailerons up a smidge simply by extending the clevis a few turns Boom ya got washout baby and go fly that airplane.

The NImh are fine shoot heck thats all I use and reading these forums one would get the idea they are unsafe and that is just not true.



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Old 01-27-2013, 01:28 PM
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Default RE: how much is too heavy?

Hoss, we need to drink a beverage in celebration. After all these years you and I agree on something. Thanks, Dave
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Old 01-27-2013, 04:38 PM
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Default RE: how much is too heavy?

Quote:
ORIGINAL: JohnBuckner

OK first as everyone has indicated you are freaking out for no real reason, it would be rare indeed anytime a kit build or an arf comes out as advertized, that is in most every case BS. The simple fact of the matter is the manufacturer has a vested interest in not telling the truth.
DItto.

Fly the plane.

I have a Tiger 120 that needed over a pound (in fact, 18 oz.) of nose weight to make the CG. I thought it would be way to heavy. It flew like any of the typical Goldberg Tiger aircraft, it flew just fine.

So, as stated, just fly the thing. If it were electric, that would be different because more calculations would be needed to pick the right power system (Battery pack, ESC, and motor). According to the OP, and the picture provided, the power is glow, so it probably will only make a difference in a slightly faster approach and landing speed.

My simple advice is keep it simple and stay away from LiPo and regulators. Go with NiMh or LiFePO4 packs and fly the plane.

CGr
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Old 01-27-2013, 07:48 PM
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Default RE: how much is too heavy?

John, I would like learn the wing loading. Thanks. I will be away from the plane for a few days while at work. When I get back I will post the data you need. I will get the formula from you too so I can give it a go.

Chad
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Old 01-27-2013, 09:31 PM
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Default RE: how much is too heavy?

For the flaps I wouldn't bother with having a setting for them to move with the ailerons. You will however be giving yourself another safeguard against tip stalls by using them as flaps. Deployed flaps effectively change the incidence of the wing at the root, so the wing will tend to stall there first. A root stall just drops the nose instead of dropping one wing.
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Old 01-28-2013, 03:30 AM
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Default RE: how much is too heavy?

Who sells the kit?
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Old 01-28-2013, 03:54 AM
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Default RE: how much is too heavy?

There is a 25.4% increase in weight going from 5.1 lbs. to 6.3 lbs.
The wing area on the Simple Flier is 610 sq in.
The wing loading is 23.8 ozs./sq/ft 6.3 lbs.
The wing cube loading is 11.6,

Your flight characteristics should be in line with warbirds and racers if that is what you seek. By the way, nice looking job on your build.

Bob
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Old 01-28-2013, 08:14 AM
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Default RE: how much is too heavy?

OK great Chad I will go over how easy it is to find a wing loading. That wing loading is of course your guide as to what to expect from your airplane. It does of course require a judgement call on your part as to what is going to an easy flying slow trainer like airplane or perhaps a hot rod. That will come with experiance as your progress and learn. This is why many manufacturers but not all do list their projected wing loading right on the box. Something that was almost never done in the past but it is such a useful tool more and more customers are demanding it.

Looks like Sensei ran his own numbers for you and there you go but I am going to walk you through the simple steps its easy to remember and do anytime quickly

You need the wingspan in inchs and this is tip to tip including through the fuselage area. You will need the average wing chord if any tapers or elipses are involved use the chord measured at half way from the fuselage to the wing tip. And you need the total weight ready to fly but without fuel measured in ounces.

As you already know its then simple with this info to multiply the span by that average chord to arrive at the wing area and expressed in square inchs.

Now we can get to the 'rest of the story'

Divide this total Wing Area (in square inchs) that you have already arrived at by 144 (this number never changes and is what you use each time) The result will be the Wing Area in square feet.

Now that we have the Wing Area expressed in Square feet and we have the Total Weight expressed in ounces the last step is easy: simply divide the Total Weight by the Wing Area and the result will be that magic number that is quite a useful tool.

Get into the habit of computing the wing loading of all your airplanes and you will soon have surprisingly accurate benchmarks for your own prediction.

John
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Old 01-28-2013, 09:27 AM
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Default RE: how much is too heavy?

With the wing loading at or below 24 oz. per sq. ft. you should have a great flying sport plane. It will land a little faster than a trainer but it should fly great. At 30 oz. per sq. ft. and above landing can get dicey.
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Old 01-28-2013, 01:55 PM
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Default RE: how much is too heavy?

According to this wing load calculator your plane will fly in between a "scale" plane and a "racer". At its suggested weight it comes in at the bottom of the Scale category. So depending on what type of plane it is it might not be too over weight.

http://www.ef-uk.net/data/wcl.htm

Update I found the specs for your plane and it says the wing area is 610 so that puts it at current weight in between the Aeobatic and Scale catagories. It should fly good there unless you need it to be a trainer. At suggested weight it is at the bottom of the aerobatic catagory.

http://www.ef-uk.net/data/wcl.htm

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Old 01-28-2013, 05:26 PM
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Default RE: how much is too heavy?

I may not pay any attention to wing loading but that is a very good web site with some good information.
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Old 01-28-2013, 06:02 PM
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Default RE: how much is too heavy?

Like everyone has stated the proof is in the flying. I scratch built a Sweet Stick a year ago and with my usual extra bracing and and extra heavy wood it came out at 6.5 pounds. At least 8oz over the weight listed on the plans. I had no choice but to fly it. Guess what? It flies just fine. I like it better than my GP Sweet Stik with a 4oz lighter wing loading. My sweet Stik has a 22oz wing loading and takes off just as fast and lands just as slow as the bigger GP stik. Plus it feels so solid in the air. Its a real pleasure to fly in spite of being a lardbutt.

I think you are worrying too much about nothing.
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Old 01-29-2013, 02:52 AM
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Default RE: how much is too heavy?

Heavier planes fly fine. They handle the wind better and go just as fast. About the only thing it compromises is acceleration and vertical climb.
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Old 01-29-2013, 07:29 AM
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Default RE: how much is too heavy?

The worst thing that can happen is unexpected pitching and roll on a maiden flight. The less experience the test pilot has the more precarious this becomes. This is not a put down but it sounds like you are not that experienced and maybe it would be wise to seek the help of an experienced pilot for the maiden. He could trim it for you and let you give it a go some 3 mistakes high. If it proves too much of a challenge for you he can take it back and land it. Maybe a small dent in your pride but you will still have the airplane to fly after gaining enough confidence.

Like the others have said how something will fly might surprise you even though it may appear too heavy. Years ago if you told me that a 14 ft span with a .65 would lift and fly a 46 lb all up (including payload) model I would have thought you were out of your tree.

[youtube]http://www.youtube.com/watch?v=g8xC-pE6RoA[/youtube]

Give it a shot if you lack the confidence then its no shame to ask for someone with more experience to help you test fly it.

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Old 01-29-2013, 10:52 AM
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Default RE: how much is too heavy?


Quote:
ORIGINAL: sensei

There is a 25.4% increase in weight going from 5.1 lbs. to 6.3 lbs.
The wing area on the Simple Flier is 610 sq in.
The wing loading is 23.8 ozs./sq/ft 6.3 lbs.
The wing cube loading is 11.6,

Your flight characteristics should be in line with warbirds and racers if that is what you seek. By the way, nice looking job on your build.

Bob
Bob, please explain the wing cube loading. I now see it used in a lot of reviews and have asked a lot of people just what is it and what does it tell you? So far no one knows or they have tried to baffle me with BS?
Gene
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Old 01-29-2013, 11:09 AM
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Default RE: how much is too heavy?

Read this for an explanation.

http://www.theampeer.org/M1-outrunne...unners.htm#CWL

Bob
[/quote]
Bob, please explain the wing cube loading. I now see it used in a lot of reviews and have asked a lot of people just what is it and what does it tell you? So far no one knows or they have tried to baffle me with BS?
Gene
[/quote]
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Old 01-29-2013, 11:23 AM
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Quote:
ORIGINAL: Lifer

Heavier planes fly fine. They handle the wind better and go just as fast. About the only thing it compromises is acceleration and vertical climb.

You leave out the most important factor and it most certainly is compromised any time you increase the wing loading of any fixed wing Airplane.

And that is the stall speed will be increased and that is no BS and should never be summarily dismissed.


John
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