It's all about balance.

Oldenginerod Mon Dec 31, 2018 6:50 pm

Just running some theories through my head. A while back I built a "The Cadet" 1/2A racer. I never got around to rigging up the hardware or mounting an engine. Not sure which engine I'll use. I do know now that it will need to be a Cox because I was thinking of using this plane for the Speed challenge. If I want real fast, I could use my Tach Race winning Silver Bee, but it might end up having too much overhang. I'm not all that keen on fitting and removing a multitude of engines to get the balance and power figured out. It just uses wood-screws to attach the engine, so the less swapping the better.

So here's my theory. The landing gear is right at the firewall and just forward of the leading edge. If I were to weigh the tail of the aircraft with the gear sitting on the deck, would that give me an approximate engine weight to aim for. I know the CG should be probably an inch back, so is there a formula I can use to calculate an optimal engine weight, or should I just give in and start bolting engines on and checking the balance for each? Or, just thinking, maybe just tape the engine in place for the weigh-in??

ticomareado Mon Dec 31, 2018 8:01 pm

Tape.

Oldenginerod Mon Dec 31, 2018 8:31 pm

Yeah, thinking back, I was just over-thinking it wasn't I? Guess I just wanted an excuse to use my scales and pretend I'm clever.
I just thought of the tape thing when I had nearly finished my post. Probably should have just deleted it before making a fool of myself. Embarassed

ticomareado Mon Dec 31, 2018 8:43 pm

Think nothing of it. Go listen to a little tune.

https://www.youtube.com/watch?v=HQHnO6NoHFQ

**944_Jim** Mon Dec 31, 2018 10:16 pm

So you want to use a scale, eh?
How about weigh all of the prospects and then trying the lightest, then the heaviest? Compared CG between the two.
Nose heavy isn't awful for a speed event. Although I do recognize the easier it lands, the more often you get to fly it!

Good luck, and tell us how you work this out.

KariFS Tue Jan 01, 2019 2:38 am

Tape is the most straightforward, but you could do it with a scale and some geometry too.

The latter would be an interesting excercise. I’m not sure if the weight of the tail alone is enough though Huh...

Maybe if you support the plane from the wings at the desired place of CG, make sure the fuselage is horizontal and weigh the tail then. After that you need the horizontal distance from CG to the tail where it rests on the scale, and the horizontal distance from the CG of the plane to the CG of the engine, which I imagine to be a little aft of the cylinder on a long-tank bee. Then you can work out the desired weight of the engine.

Of course, calculations should be verified, so I’d weigh and calculate just for fun first, then do the tape thing.

If you just want to ”get it done”, then just skip the calculations, grab your favourite engines and start experimenting Smile

getback Tue Jan 01, 2019 7:49 am

I find it best to pic the desired engine you want to use then weight it , that will give you an idea of what tail length and thickness , width to work with . If the plane is in the building stage you have the option . Tanked or not will make the difference to Very Happy

Iceberg Fri Oct 16, 2020 9:20 pm

Have built a plane from scratch and was trying to get the perfect balance. I have it from the proper point in the wing about an inch back. Should a plane with motor and all with tank empty be just slightly slightly heavier in the tail or the nose? I am going for the tail.

I seem to remember the plane should be ever so slightly tail heavy but almost nothing correct?

Thanks
Iceberg

davidll1984 Fri Oct 16, 2020 9:47 pm

Remember that a plane nose heavy wil fly bad a plane tail heavy wil fly once m'y humble opinions Smile

Oldenginerod Sat Oct 17, 2020 3:58 am

I figure that the time that you most need the plane balanced is when the engine cuts, meaning at the end of the flight. That way your glide will be good for landing. So, best to balance it with an empty tank and expect that it will be slightly nose-heavy with the tank full on launch, but under full power that should pose no problems.

getback Sat Oct 17, 2020 5:55 am

25 % of the wing width is what i was told and use , seems to work fine if tapered use the widest part of the wing >>> I was reading on this till i realized it was 2 yrs. ago Rod you ever finish this plane ?? Very Happy

Iceberg Sat Oct 17, 2020 7:32 am

Oldenginerod wrote:I figure that the time that you most need the plane balanced is when the engine cuts, meaning at the end of the flight. That way your glide will be good for landing. So, best to balance it with an empty tank and expect that it will be slightly nose-heavy with the tank full on launch, but under full power that should pose no problems.

This is what I understand too. So my plane right now is just a few grams heavier in the tail with empty tank. However with full tank ever so slightly nose heavy so I think this will be pretty good.

Thanks Oldenginerod!!

batjac Sat Oct 17, 2020 4:57 pm

You didn't say whether this is a control line or an RC plane. If it's an RC plane, 25% is good. If it's a control line, 15-20% is good. That's what I build all mine to.

The Well Balanced Mark

NEW222 Sat Oct 17, 2020 6:10 pm

Iceberg wrote:So my plane right now is just a few grams heavier in the tail with empty tank. However with full tank ever so slightly nose heavy so I think this will be pretty good.

While it MAY be alright, I would not fly it like that myself, and I am sure many others would not either. You want it to be slightly noseheavy with an empty tank, not full. So add something to the nose to give it a bit of extra weight. If it is as minor as you say, assuming Bee type engine, I would add a washer or two behind each screw holding the engine to the firewall. Also if there is a wooden noseblock you can also screw in a screw or two into it for weight, drill a small hole and fill with BB's and seal with epoxy. If whatever you are planning on flying has landing gear and it is ahead of the center of gravity, another easy thing to do is wrap each gear leg with a bit of solder for weight to bring the nose slightly down. Ways to remedy this are plenty and most very easy.

Iceberg Sat Oct 17, 2020 9:42 pm

Got to fly maiden flight today. It flew really quite good. Extremely light so any wind sent it all over but easy to recover and with empty tank it landed perfectly. Slightly tail heavy. Ready board with clear tape covering everything to keep fuel spray off the paper. Really flew stable and steady.

Thanks
Iceberg

NEW222 Sat Oct 17, 2020 11:49 pm

Glad it flew good for you, but may fly even better if properly trimmed. Now seeing what you got, another quick thing you can do to add weight would be to put,glue a washer or two on the outboard right side cowl inside by the engine should you decide to try it. By using glue, you could also easily pop it off if you do not liek the way it flies then.

getback Sun Oct 18, 2020 7:40 am

Glad it flew to your liken Very Happy

NEW222 Sun Oct 18, 2020 9:48 am

Iceberg, do you happen to have a weight of your plane without fuel? I am just really curious as I have one as well, but built it to the plans using coroplast. Never thought of foam and was wondering what the weight differences between ours actually is. I am suspecting that yours would be quite a bit lighter.

Iceberg Mon Oct 19, 2020 10:41 am

I don't have the weight right now but will track down a scale and send you. I put a coin under the wing outside. The plane is very very light and held up like a winner on the flight. I had to use a counter weight of a mini bag of sand in the fuselage just being the wing to balance because the silver bee I used was making the front too heavy. I was pleased with the sand trick as you can let a few grains out at a time to get the perfect weight distribution. Wanted to send a video but can't on the forum? I think it might really do well for acrobatics as on fast steep dives it pulled out almost instantly with up elevator when I tested it. Flight speed was also pretty good. But if a side gust hit it was interesting it was fluttering a bit but with responded almost instantly back with a correction of elevator. So really decent actually.
Thanks
Ice

NEW222 Mon Oct 19, 2020 7:31 pm

So, since I had asked about weight, I thought it was only fair to weigh mine as well. As I said it was porky, I was really curious. Built as per plans, landing gear and all as well as made from coroplast. With a Cox Babe Bee installed, it came in at 6.9 - 7.0 ounces. I was honestly floored at that, as I was thinking it was a lot heavier. The only things not weighed or currently attached are my lines and handle as I will be tying my line directly to the bellcrank.

Iceberg Tue Oct 20, 2020 10:54 am

Hi New 222
I weighed the plane this morning. Silver Bee including control lines 7.1 ounces or .44 pounds or 190 grams if you like metric. Everything included except the fuel.

Flew a few times today and got almost 60 rounds on a tank.

Pleased with everything.

Thanks
Iceberg

NEW222 Tue Oct 20, 2020 5:01 pm

Nice. I am now very surprised in the basic weight difference of nearly nothing. I still stand behind my thoughts that mine made of coroplast would be much heavier than yours. Glad it flies well and that you are able to go flying. Just started snowing here now.....

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