Diherderal in low-wing RET

[dio]

I will just give you a little background before I ask the question. I love to build more than I like to fly.. I have built several high-wing easy goers, and I usually just throw in an inch of dihederal and move on. The fact that these planes have all been high-wingers has amde it simple. I see a plane I like, and I try to make one the best I can. Ususally RET, once full house, but that was ten++ years ago.

I am scratch building a parkflyer for speed 280, small and light, cross between a chubby lady and a Pique 3... All was going well and every time I stopped to really think about what amount of dihederal to use I would put it off. Cant put it off anymore. I wanted to fly it RET as all but one of the planes I have ever flown were that way... comfort level issue... What dihederal "rules" should I be thinking about to figure out how much to use? Does it have something to do with fuselage height? Vertical center of gravity?

Should I stop kidding myself, throw in in inch of diherderal, and make it an aleron elevator and throttle plane and move on?

Here is the body so far.... and half a wing... (unglued) as I have not received your advice yet!


Daniel

[BMatthews]

There's been lots of low wing models that fly fine with RET. If you angle the wings so the tip is about even in height with the top of the fuselage that should produce a fairly fast reacting and aerobatic model. If you make the dihedral so it comes up to the top of the fuselafe sides then it'll tone the reactions down a little but it should still fly well.

Certainly low wingers need a bit more than high wingers. How much more is sort of up to your own taste in how you want it to perform. The more dihedral the stronger the yaw-roll reaction.

I may be erring on the side of too much dihedral and it would certainly fly with a little less than what I've said above but I like positive reacting models. If you find it too spirited you can always reduce the rudder throw until you're looking for that bigger thrill.

Nice looking original design by the way....

[steve lewin]

Perhaps I'm just being particularly thick today, but what's a low-wing RET ?

Steve

[FlyByMike]

Originally posted by steve lewin
Perhaps I'm just being particularly thick today, but what's a low-wing RET ?

Steve
RudderElevatorThrottle :cool:

[Dereck]

Daniel
Your idea of a low winged RET model is great ! This layout works all the better in smaller, lightweight models and really looks different, while being as easy to do as a high winger RET.

One of the nicest published was a freeby plan given away in Model Airplane News called "Beetween" by Randy Randolph. This was around 37" span IIRC (the plan is still on sale by MAN, to see how to do this type of model) and I had many hours of fun with mine. I also "borrowed' the major numbers off the "Beetween" - Randy's a friend of mine and didn't mind at all - for a design of my own.

I looked up the plan for mine, and it has 9.5 degrees of dihedral on each side :eek: This comes up a little shy of Bmatthews suggestion on my design, but would have about followed his rule on Randy's Beetween design.

The one handling "funny" I noticed was sometimes experiencing a slow-down in roll rate if I tried to turn too tightly and pull the nose high. More so at slow speeds, this could cause the model to mush around - the cure was to push down a little to lower the nose in the turn. Otherwise, it was fine to fly.

Regards

Dereck

[Sail 'n Soar]

Sport plane dihedral suggestions in digrees from "R/C Model Aircraft Design", by Andy Lennon:

Wing Position w ailerons w/o ailerons
High 2 5
Mid 3 6
Low 4 7

My general rule is to go a little higher with higher aspect ratios, and a little lower with lower aspect ratio wings. e.g. I go about 7-8 degrees for gliders and I had a great flying AR = 4 mid wing RET with 4 degrees.

[dio]

Thanks for the replies, all. This is very helpful.

I am going to make the "first" wing about 7 degrees. That brings the tips of the wing over what I call my "thrust line". I don't now what you engineering guys call it, but that is a line that I draw lengthwise down the side of the fuse from the prop shaft. I don't know if it has areonautical meaning or not, but when drawing my planes I always use this as a starting point. I don't think I want any more because I don't like the looks of it going to to top of the fuse... I will take AET over a dorky looking plane anyday!

I am going to do this in two steps... I will make this wing aileron enabled, and after I get a few mistakes high I will try to fly RET only. If that works, great, I will just fly it like that. I will take out the extra servo and the hardware to save weight. If not, I can either put more diherdreal in the "second" wing or I can learn to live with it.

I feel a little disheartened over this, because what I really wanted was a simple to fly cool looking parkflyer that is mine all mine... and instead all I am doing is worrying about whether it will be unflyable RET. If I had a little more experience scratching low-wing planes I suppose I would not be so worried about it. And really, 7 degrees of D should make this thing as forgiving as a nun.

When I retire I will have a lot more time to devote to this... just another 20-25 years... Thanks for all of the input.

Daniel

[Ralph Brekan]

This is a great post. I'm building my GWS C47 to fly RET so can taxi on the ground w/a tail wheel (I only have 3-channels now). The nice thng about the C47 is I can "build" the dihedral into the wings as I glue the wing pannels together. I'll definately err on the side of caution and go with 10 degrees so I can recover from 45 degree banks w/o struggle. I'll also have to be careful to put even amounts into each side. Should be an interesting challenge.

[vintage1]

7 degrees seems about rght with most normal layouts.

I tried 5 deg in one model, and it sideslipped into the ground after a long period trying to knife edge out of a gust induced bank. It would turn on 5, but once beyond a certain level of bank it got into a no way out situation.

The wing was taken from an old high wing plane where it had proved totally OK on RET.

So try 7 or more to start with. The key manouver is a barrle roll and a stop halfway. If you can pull out of a vertical bank, its enough.

If not, new wing (and probably new model).

[Zoom]

Daniel
I struggled with the same issues you are on one of my first designs. I wanted a low winger RET and this is what I came up with. It was called the Zoot Scoot (http://rcgroups.com/links/index.php?sid=498277416&t=article&cat=202&id=3921 ). For reference purposes, you can see how much dihedral it had in it, and the flight report will give you an idea of it’s maneuverability. Hope this helps.

- Dave -