I'm recommisioning a Hobbico Super Star trainer. It has tricycle gear and as it sits now, on the ground, the nose is a little below level. Maybe I should say the bottom of the wing is lower in the front than the rear. Is this good or bad? I can easily change the gear to make it level, or where ever it needs to be but I don't know what it's supposed to be. I hope this isn't a this vs that type of question, just wanted to have as much in my favor, or the aircrafts' favor, before heading for the wild blue yonder. Everything esle seems square level and true.

From everything I've read a trike gear plane should sit level to give a smooth take off run at the right speed.

You want the wing to be just slightly positive to the ground. Sitting on the runway, the leading edge of the wing should be slightly higher than the trailing edge. With speed, it will fly itself off. If it is negative to the ground, with speed it is being forced downward, onto the wheels, and will abruptly leave the ground with elevator input, at a higher angle than you want.
Are you considering learning without an instructor? (I thought your statement implied that.)
John Agnew

I dissagree with some of the above comments. I found it is always best to have the plane sitting at a slight negative angle of attack when at rest. That way, landing will be much less prone to bounce, take offs easier as you gain adequate flight speed befor rotation to takeoff attitude plus taxi is easier. Main gear placement is critical, you want the main gear to be just a bit aft of the CG, to far back and take offs become a problem.

Well I reckon I'll adjust the main gear so the plane sits a bit positive as the nose gear is maxed out for positive right now. Then later if need be I can lower the nose quickly and easier than messing with the main gear. Last time I flew it I shoulda known better, it was windy and at touchdown a side gust caught the upwind wing and what started out as a pretty good landing turned into a pretty ugly cartwheel. I just might get someone with some experience to hook up the trainer cord until I fly the rusty off. I still can't figure out the fuss though, I never took off without landing.

If the wing is symmetrical, a touch of up AOA is good. If it's a flatbottom, the bottom can be parallel to the ground and you have a touch of up AOA.

I concur, very slight neg to prevent bounce

Grits: I solved the same problem on a new trainer by just going to the next larger size main wheels. The 3" wheels will work better on the grass runway. If you are not flying on a grass runway, going to a size smaller on the nose wheel will also give you the 2-3 degrees nose down attitude.

AERORICH73

Ok, this is not intended to create a stir, but here goes:

If you fly correctly, and strive for perfection, then the main wing should have a slight positive AOA whith the plane on level ground.
This makes for a more realistic takeoff and landing. If you are not into realism, and you like "jerking" the plane off the ground, and require that the plane stay put once the wheels touch, then a slight negative AOA may be what is best for you.

All my planes have a positive AOA, (they are all tail draggers), and I make nice 3 point landings with all of them, (except the Texan).

If you have a negative AOA, the plane is much more prone to being flipped over in the event of a tail wind while taxiing.

It is mainly preference when it comes to the averagte .40 size plane.
Once you are in the air, the plane does not care what configuration your landing gear is.
Some small planes don't have any gear...

Bob

If you are flying of a hard surface runway it is especially good to have a slightly negative angle of attack when all three wheels (remember this is a trike geared plane we are talking about here) or the plane will often be adversly effected by any wind while taxing and can even jump off the ground with insufficient flying speed. putting elevator in to hold the nose wheel down while taxing doesn't help as the plane can not rotate down enough to kill any excess lift. This is especially important for the less experienced flyers so, for best and easiest experience, have a negative angle of attack when a trike geared plane is at rest.

Very nicely put, Rodney. and I understand your logic, but I have one question.
When you think of positive AOA, how much are you picturing?
The typical AOA should be about 3 to 5 degrees. This is usually not enough to make the plane "jump" into the air.
(Besides, I think it just looks nicer and is my personal preference. And it matches my style of flying)

Grits:
You can experiment with both setups, and just use what you like better.

Bob

A level fuselage looks best.. the AOA of the wing will be adequate.
A slight nose down attitude helps taxiing a bit, and lets the plane accelerate to a good speed for takeoff with just a touch of up to lift it off.
In the full scale world...

The incidence angle of the wing in the fuselage is set for cruise speeds. Setting it for takeoff and landings is not the usual practice. Of course, the discussion is ground attitude, but the discussion is pulling in other things.

So back to ground attitude...................

With our models, a couple of degrees here and there aren't going to make a lot of difference.

When you're taking off, if the airframe is down in the nose, it's tail is angled up. Most times, anyway. And what does that do to the AOA of the stab/elevator? And what does being at a negative AOA do? It brings the tail down when the tail starts flying. So you MIGHT get an automatic rotation. Then again........... It's not that simple.

And when you're landing, the wing has to be producing close to it's max lift. And to do that, it's got to have a positive AOA. So until the gear, all the gear, is down, the nose gear is just along for the ride. And the length of the nose strut really only decides when that wheel is going to touch. And unless it's really too long, it will be like the tail wheel. It won't touch until the wing stops carrying enough of the airplane so that the mains have an effect on the attitude.

IF the wing is carried along on the takeoff at an AOA that does not produce positive lift, you COULD be in trouble. Maybe so, maybe not. Try it and see. The beauty of our hobby is that the pilot doesn't die if the builder or designer makes a mistake. The elevator probably will pitch the wing at some velocity down the runway. It might pitch the heck out of it, or not.

BTW, you might consider something about the takeoff situation. The wing is going to lift down, into the mains and nosegear. And the mains probably will compress, and the nosegear probably won't. Should we try to figure out the angles for that? Nah............ go test fly the sucker. Nobody can give you any numbers to use, and certainly can't cover all the bases generally.

Will what you've described wind up as a fatal flaw? Nah...... Worst case is you won't be able to rotate and you'll have to chop the throttle. Then what can you do? Bend the mains and try again. Or put a bigger nosewheel or smaller main wheels.

Maybe this has more to do with the pilots attitude to the ground.

On a trike gear I like slight negative. When you're flairing in and the mains touch as as speed bleeds off you tip forward and the flight is over as the wing loses lift. You can also build up ground speed in preparation to rotation and take-off.

Trainers that have been slapped down a few times get overly squat at the mains and have too much positive incedence. Thay take off prematurely and bounce in as the wing is always trying to lift.

I prefer a level fuse for trikes...

My instructor taught me a long time ago that I was the pilot ... so for takeoffs ill use a little bit of down elevator to keep the plane on the ground and allow speed to build up.... When I have enough I just ease off the down elevator and let the model rise if its a trainer or add a little bit of up elevator for symetrical airfoil wings to rotate the model... When its time to land, the model doesnt know how long the nose gear is... Your gonna touch down on the mains first anyway. Once the nose is down, you should be adding a little down elevator if you think it may be possible to be airborne again...

...just my opinion though.

Da Rock,
This has to be a pretty steep angle for the elevator/horozontal stabalizor not to rotate the plane to at least a neutral attitude.
Either that, or a flying wing configuration, but that's not what we are talking about here.

You also mentioned that the elevator will probably pitch the wing at some point down the runway...
This is absolutely true, onless you made a gross error and have the nose pitched downward 15 degrees or more while sitting in the pits.

I want to side track a little, hope you don't mind... It is relevant.
When I first started to run through this forum, I was slightly anoyed by Mr. Hanson stating that CG does not matter in another forum. He has a great mind, although, not to disrespect Dick, he thinks a little bit out of the box.
He was speaking as the model gets smaller, the rules of aerodynamics gets more lax. You do not have to be so precise in your formulas, and you can be a little more "free" in your design.
I have gained a new respect for Mr. Hanson.

Now, getting back to the ground attitude.
Yes, Meadan, it has a lot to do with "Your" attitude on the ground.
What do you prefer? Are you a novice that like "easy"? Are you an individual that strives for perfection and realism, or just someone that wants to have fun and get into the air?

When you get to the .40 size model, there is a lot that can be changed to make it handle where you are comfortable with it.
If you expect a plane that is on the ground to STAY onthe ground, give it a negative attitude, no more than 7 or 8 degrees.
If you want to have a plane that handles much like a scale plane, then give it a positive attitude on the ground, again, no more than 8 or 9 degrees, (speaking from experience).

Aerodynamics is not proportionate to scale, and transition from ground attitude and flight attitude is a direct result of aerodynamics.
What does this mean?
You can "play around" and deviate from the norm up to a certain extent. And as Da Rock alluded to, nobody dies if the plane augers in. It is, however, an out of pocket expense... Glue, balsa, or even a new kit...

I mentioned in earlier that all I have in my hangar are tail draggers.

There are 4 reasons why this is so...

1. They are easier to setup. You do not have to sinc the nose gear and the rudder.
2. They are lighter than a trike configuration.
3. I don't have to worry about the AOA at ground attitude.
4. I think that they are really cool.

Yes, thay are more difficult to handle on the ground during take off, but so is a bicycle if you have never ridden one before.

Grits,
If your plane sits with a little negative attitude, try it. If you don't like it, change it. If you still don't like it, make it a tail dragger.
(just kidding).
I think it will do just fine.

Go out and have fun.
Let us know how it turns out.

Bob

Keep in mind that runways are only so long.

Keep in mind that when the wing is trying to hold the airplane down and you unstick it with the elevator, you will be in discovery mode. You are about to find out just how well the elevator can pitch the airplane up.

Sometimes they come up nice and easy. Sometimes they rise like PROUD MARY!!

( I once saw a woman attempt to do a Tina Turner impression. When she got to the part in the song where ALL HELL BREAKS LOOSE, she got a bit out of control and fell off the stage. Seems an appropriate image to this discussion.)

Don't know anything about RC, but tricicle gear airplanes for Contol Line Precision Aerobatic competition, where takeoff and landing are scored maneuvers, are generally set up slightly nose down. Bob Palmer told me to have the leading edge of the wing 1/8 inch lower than the trailing edge (0 incidence in wing.) Worked nice for me.

Jumping in 1/2 cocked. As usual.

A-10 sits nose down big time. Engines are tipped up big time.

What happens at takeoff speed with no one on the stick ?

It takes off by itself, if you are busy polishing your boots.

If you use that crummy main landing wire wheel holder on the SuperStar, it makes no difference what the AOA is. The best thing I ever did to my old SuperStar was replace the wire with an aluminium main gear! Then I could set the bottom of the wing to "0" using the nose gear and it will take off when I want it to. And, it lands better!

Stiff landing gear is reuired on a " smooth ? surface " . Any cracks or bumps theat are running the same direction of take off & landing can and do yank the plane around if it has springy landing landing gear.
Sometimes enough to cause cartwheels, left and right. Depends on the wind coming from a foward direction angle.

You can think you caused it . Fast or slow makes no difference. Bad luck.