Lonewolf9757

My Feedback: (5)

Hello,

I have 2 planes that want to redesign the wings on, changing them from a Dihedral to a Polyhedral (glider wing, with 3 dihedrals ). The 2 planes are the Sig Kadet Sr. and the LT-40. The Kadet Sr. has a WS of 71" with a 6" Dihedral from center to wing tip. I am thinking of changing this to 90" The LT-40 has a WS of 70" with a 3.75" dihedral. This one i would also like to make 90".
What i am trying to accomplish is to turn these 2 planes into basicly powered gliders, very easy to fly, so that i can teach my better half and son to fly them. If i have the basic formulas right. Increasing the wing area will lower the wing loading into the glider range and these will be great planes to learn to fly on. Then, when they are ready, I will put the stock wing back on. I also this this would make for for a great sunday flyer to just putt around the field with.
I guess my questions are, will this idea work ? What degrese should the outboard angles be ? Should the dihedral in the mittle be decreased ? ect...
I am not a designer by any strech of the imagination, i just this would be something different. Any advise, suggestions, or comments would be greatly appreciated.


Thank You in Advance,
Tim
[email protected]

BMatthews

This is a good concept but you will want to approach it with some careful test flying before you pronounce it as ready. You're making the wing larger but not increasing the vertical or horizontal tail areas or the tail moment for that matter. But on the other hand you've picked, by good luck or good planning, a wingspan increase that's not overboard.

The bottom line is that I think it'll work but don't be surprised if the models end up with some quirks to their normally very calm manners.

And FWIW I'd do this on the Kadet. Senior. It's built up and lighter than what I remember the LT being so it should respond better to this mod.

I did the TLAR sketch below for you based on a 90 inch span front view. Don't worry about the center area having less dihedral than the stock wing. There's more dihedral overall and with polyhedral the sharply angled panels being located at the tips gives them more leverage to do their job. This poly wing will be a bit more authouritative at correcting the model from bad positions. It will probably also make the model respond at least as well if not a little "quicker" to the rudder for the same reasons. Test fly and set the rudder travel to suit your students and it'll be fine. It'll be flying a little slower as well so perhaps it'll all balance out. The slower speed makeing the rudder a bit less responsive. Note also that there's only a little difference in the wing span. I feel much less apprehensive about the long span overpowering the rest of the model now.

Good luck with an interesting project.

PS: The poly wing will also be more sensitive to wind in general and cross wind takeoffs and landings in particular. Watch for that. It'll bite them if you're not careful.

Lonewolf9757

My Feedback: (5)

Wow, i ask for comments and Mr Matthews does all that work for me.... Thank You just doesn't seam like enough, but Thank You Sir. I never thought of incrasing the tail area. Should i add the same % I added to the wing, to the tail also ? I plan on puting this poly wing on a Sr. i already have built, but i can always build a new fues. I don't know what you ment by Moment... "You're making the wing larger but not increasing the vertical or horizontal tail areas or the tail moment for that matter" Is this the length of the fuse ? Like i said, I'm no designer. I just thought the new wing on the old plane would slow it down and make it more stable than it already is.

Thanks Again.
Tim
[email protected]

BMatthews

Yes, the "moment" refers to the moment arm which is the length of the fuselage between the 25% point of the wing chord and the 25% point of the stab chord.

Actually I wouldn't worry about the tail. With the same chord as the stock wing you are only changing the wing area by 25%. There's a fine chance that this small an amount will not be enough to matter to the model's stability. But as I said a full test flight series where you put the model into all sorts of attitudes would be in order before you start training just in case. If you find there are some pitch related issues or the model doesn't want to groove in the turns then make the stab bigger in the first case and modify the fin and rudder for the second.

If the model wants to try to tighten the turns and fall into a spiral that requires you ease up on the rudder or even turn outwards to hold it when turning tightly then make the fin and rudder 10 to 15% smaller (very unlikely this will happen). If the model seems to "slide" into turns and hangs tail low when turning then make the fin and rudder 10 to 15% larger.

Once again good luck with this interesting project. If it sees the light of day be sure to post some pics here and let us know how it goes.

tiggerinmk

I'm very sceptical about this idea and whether it will provide any benefit.
Here's where I'm coming from: I've got an LT-40 and a Ripmax Zephyr, both ARF's.

The Zephyr is a lighweight 'old timer' type plane with a 62" span polyhedral wing with a chord of just under 9". The main dihedral angle of the wing when laying on top of the LT-40 wing is about the same, but the outboard polyhedral panels increase the overall effect.

The Zephyr has an all up weight of under 2 1/2 lbs whereas the LT-40 weighs around 6lbs.

In flight, the Zephyr is a slow relaxing plane to fly but it does have some quirks which I feel make it no more easier to fly than the LT-40. The polyhedral wing makes it very sensitive on the rudder, and although this plane has a small rudder only tiny inputs are required. A large rudder movement can easily cause the plane to go into a 'death spiral', this causes me concern for a poly LT as the rudder is quite large.

The LT, as it stands (or flies), is also very slow and forgiving as is far easier to fly than many other trainers. The LT does fly faster than the zephyr but not that much. I think that increasing the wingspan may make the plane too much of a floater and make it difficult to land.

If you haven't already done so, I would recommend flying the planes in stock form first before trying any experiments. The one thing I do think makes a difference with the LT-40 is the choice of engine in regard to weight. I first powered mine with an Irvine 39 then later switched to an OS 46 FX. Although I rebalanced the plane, it now noticably drops its nose when power is removed which it did not do with the lighter engine...

BTW, you didn't mention whether you were going to use ailerons on the polyhedral wing. The Zephyr is 3 channel. I think the main reason this type of wing is used is to induce a roll when the rudder is applied. With the rudder on the right stick, the Zephyr in flight appears to handle very similarly to a 4 channel plane...

Lonewolf9757

My Feedback: (5)

Again, Thank You for the input gentlemen.

I will be making this modification to the Kadet Sr. due to the lower all up weight compaired to the LT-40. The Sr. is designed as a 3 channel. I am thinking about adding alerons to the new wing. Would this compinsate for the rudder efect that has been mentioned ? Is there a formula (say a % of wing area) when adding alerons ? I assume they will be added to the inboard sections of the wing.

I have already started to cut the ribs for the new wing and i will keep everyone posted on the progress of this idea. I didn't mention it before, but i plan to keep the original airfoil and cord. I will only be changing the length of the wing and adding poly to it.

Again, Thanks for all the help on this new project.
Tim
[email protected]

Tall Paul

You can't hurt a Kadet by changing anything 50% !
They're the most adaptable plane there is.
Extending the wing... do it!
My longest wing is 91 inches. Just added two rib bays at each tip. 1365 sq. in.
The biplane version has about 1800 sq.in. of total wing area.
Turns on a thin dime.
The tail areas are generous to start with, there's no need to change them with wing area.
The plane will tolerate much smaller areas there, MOF.
Ailerons will work better with less dihedral. Typcially the kit dihedral is halved.
.
But..
Why do this?
The basic Senior Kadet IS the best trainer there is.
With a buddy-box, it can't get into trouble.
All the world's Kadets..
http://home.earthlink.net/~pjburke1/kadets.htm
and:
http://www.angelfire.com/indie/aeros...ultipix-01.htm

yarray2000

I have a Kadet and I'll design a [link=http://www.rcuniverse.com/forum/Kadet_LT%2D40_custom_symmetrical_wing/m_1184848/tm.htm]second wing to make it more aerobatic[/link]. I'll keep the original wing too, cause it's a great trainer. But I'm sure an aerobatic kadet will be a lot of fun.

The Kadet is a real floater and is about the easiest trainer to learn on.

I think that in trying to make it even more like a glider, it will start to have an unpleasing behavior. It is allready hard to land when it is windy, since you have to force it down because it glides so well. When you have a deadstick, you have all your time to go around the field and land like nothing happened.

This plane wants to fly by itself, allmost like it has a gyro.
It takes forever to do a roll (you have to apply rudder and aileron at the same time).

Some teachers even think that it is a little TOO EASY to learn on as it is.
(making it possibly harder to step to a second plane)

So, in my opinion, you'll work a lot of hours, with possibly inadequate results, the possibility of breaking your plane during testing, all that to change a prefect trainer. If one can't learn on a kadet... one can't learn at all. That's what I think.

BTW: 90" wing is a long wing to transport ! And I tought the 71" on my Kadet was too long :-)