invertedthoughts

I picked this up used today and Iwould like to know what model it is if anyone has any idea?It has a .61 size 2 stroke in it and the wing span is 47"and the fuselage is 35"and the wing from leading edge all the way back to rear of aileron is 19" .

JohnBuckner

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Profile Hots

John

Gray Beard

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Profile YAK.

delman

Su-Do-Koi by Morris Hobbies

scale only 4 me

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I think delman wins

invertedthoughts

Thanks Delman!


Any idea on the suggested throws and CG location? I can't seem to find this information on the web anywhere.

drbenz

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Not sure about that. I had a su-do -koi and it had a much wider fuse. Mine was a 60 size. Did it come in different sizes? It definitely looks like a Morris hobbies product though....

Gray Beard

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The fun of the profile, do a little cutting and sanding and it can be whatever you want it to be.

invertedthoughts

Still haven't maidened it as I'm leary of where to set the center of gravity.

scale only 4 me

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one of many,, http://www.scaleaero.com/CG_Calculator.htm

Gray Beard

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That's one of the calculators I have in my favorites file, it works so well I have used it on planes and never moved the CG. If the address was posted as a sticky we would loose most of the Where To Set CG questions.

invertedthoughts

Thanks for posting that, Iam trying to figure the calculations and am having trouble finding this value:Enter %MAC Balance Point (do Ihave to take the wing off to find that balance point?The wing is epoxied on the fuse unfortunatly)

JohnBuckner

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The Profile Hots also a Morris kit is almost identical save for the deep nose that ship has to give it sorta maybe raidial engine look of the Sukhoi.

I have no doubt it is one of the many inovative for their time Morris kits along with the imaginitve names for their ships. Only one I ever built was the first Balsa Nova.

Many of his airplanes were early examples of what is now called 3D. However back then well before the internet (or at least widespread use of it) those types of airplanes were called 'Fun Fly' airplanes not 3D. Competition events for them were called Fun Flys and it was not the same as fly ins which were a non competition fun gathering.

An alternative method to balance an airplane like that is quick and easy. But first let me suggest with a ship like that I would start out a 25% MAC. Now before everyone starts yelling at me, true for most of the 3d stuff you will be using more aft CG's even up to around 34% aft. However this will present a lot more problems to folks who are not that accomplished with that type flying. A lot of airplanes are crashed in their early flights because of this. Its far better to start at a more forward 25% mark and back into the aft CG's a little at a time. Sorry only just my opinion.

Now back to the very easy way to acheve that 25% mac point to balance at. It is called mid span averaging. You only need a ruler or perhaps some string, Heck you can even use your fingers.

All you need to do is find the point that is half way between the fuselage and the wingtip and at this point measure the chord of the wing including the aileron. That is the distance from the leading edge to the training edge out there beween fuselage and the wingtip. This is your MAC (mean aerodynamic chord).

You only need to divide this by four and that will be the distance back from leading edge at this midspan point that is the 25% point and is your target for a good first flight. You may project this point straight or at a right angle to the fuselage up to the fuselage to make it easier to understand or use a balancer.

No this is not precise engineering data that is why it is called averaging but it is quick and easy even at the field or when some walks up to you with an airplane. It is the system that has been used for years in certain competitive venues that had rules based on wing areas. It was used for pre event testing of comformance with the rules. This method also automatically makes reasonable allowance for the single or double tapers of many wings.

Its worth investing a couple of minutes investment in thinking it out and trying it. You will never agonise over a mystery airplane CG agine.

John

scale only 4 me

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John gave good advise,,

Use 25% to start,,
Just measure "A" at the fuse side,, that will be close enough,, adjust from there to you liking

Good luck

invertedthoughts

OK, figured out that MAC (thanks to John Buckner) is the percentage of root chord at the desired spot the plane will balance at. I figured 25% using the calculator graciously posted and it gave me: 4.75" and at 30% it gave 5.56 and at 33% it gave 6.05.


Using the averaging method posted by Mr. Buckner it gave me 4.1" so very much inline with the calculator.


Only variable is that the wing tip is not straight at the tip but rounded and increases in distance at the midway point (between the tip chord) So I did the best I could with very limited knowledge and experience.


The CG is currently set at 4.5" so I think I'll bring it back a little bit more and see how Ilike it. 4.5 just seems awfully far forward on a wing that has a root chord of 19"

root chord: 19"
tip chord 13"
sweep distance 1.5
half span 22.5
%MAC balance point: 25%
balance point at root chord: 4.75

invertedthoughts

Have it set at 5" back from leading edge measured at the wing root. Maiden in the morning, will post pictures and flight report.


Thanks again!

invertedthoughts

Maiden went well, put 3 successful flights on her and she flies great. Very reactive due to the short-coupling. I might bring the CG back a little further as now it basically flies very stable and docile. I want to HOVER THIS THING!

daveopam

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If you fly it till the tank is nearly empty, and it does not act tail heavy. Then ease it back a little. There will be a time when it acts funny as it burns fuel and you will know it's too far aft.

david