skywagn180

I will try it this weekend. My plane will certainly show a difference if there is one. I already have elevons on a switch. I can turn them off and on. For some reason I never tried what you are suggesting before.

Aussieflier

If you watch some footage of delta aircraft taking off you will see that a very high AoA is required for take off. Even with the later designs incorporating close coupled canards the minimum AoA at lift off is about 16deg. With the Northstar the maximum AoA prior to lift off is clamped at the point where the main hull and tip floats are both planing on the surface of the water. If you draw a line from the step in the hull to the bottom of the tip floats and then compare that to a line drawn at the angle of incidence of the wing you will find that it is about 5deg. So 5deg is the maximum achievable AoA prior to lift off. It is about 1/3rd of what is normally considered the minimum. Adding up aileron will not increase the AoA in this case, in fact it will effectively reduce it.

If we want to increase the lift of the wing so as to achieve a shorter or slower take off run we have only one option, we have to increase the maximum achievable AoA. This can only be achieved by increasing the depth of the hull or reducing the height of the tip floats, the latter is less desirable as it would allow the wing to come in contact with the water creating drag. Making the hull deeper required some careful design. If you were to only increase the depth of the hull at the step you would be increasing the AoA of the hull relative to the water. This will cause loss of roll stability and the model will want to keep digging the wing tips into the water. In boating this is called chine walking, where the boat is trimmed too high and the boat looses roll stability and starts to walk from side to side. The hull needs to be designed to plane while the rest of the aircraft is maintaining the optimum AoA for lift off. If you draw this up ( as I have already done ) you will see that the design is pretty ugly, looking less like a jet and more like a Grumman Goose. There is also a down side to this remedy. If you now have the wing at this increased AoA while the hull is planing during your initial acceleration, you have much higher drag caused by the wing. We all know that the quickest way off the ground is not to hang onto the elevator from the start.

What can be deduced from all of this is that in Laddie's original design he was able to take all of the various limiting factors and come up with a workable design that is easy to build and does not require a computer, or canards, or leading edge flaps to maintain reasonable stability in flight. It does need to have a high take off speed. What Laddie has done is to take the various limitations of combining a delta with a sea plane and sort them into a workable compromise, that is what good design is all about.

In all of the forums there is one statement that is continually repeated and quite rightly so, if you want to make a better Northstar, make it lighter.

Cheers, Lionel

LADDIE

Lione, I agree with you statements. Personally I do not see any benefit making the ailerons into elevons on the NS. The area of the ailerons on the NS is too small to make them effective as a elevons. The elevons on my delta wing “Arrow� which has same size wing as on the NS are almost twice size.
But, I do not see any harm trying them as elevons after the model was flown in aileron mode.
Laddie.

alasdair

Laddie,
I am surprised I have to disagree with you but, having flown three Northstars with and without elevon mixing, I have to recommend elevon mixing for vastly increased manoeuvrability in flight. Without elevon mixing, just the elevator, I never dared to try a bunt (outside loop) from the top. With elevons, how tight do you want?
A great many Northstars turn up at all the splash-ins here. They are often the most numerous model (only eclipsed by ARTF Seamasters). (I bet you wish you had a $1 for each one built)
Most of us here use elevons, and many increase the size.
I used more movement for pitch than for roll (maybe 50% more)

Aussieflier,
I take your point. There may be a case for unmixing the elevons for takeoff. I never tried.
However you left out one very important effect of deflecting both ailerons up. Yes, you get extra drag, and reverse camber does bias the lift down BUT

add in a number 4, reverse camber, so far aft on the section, adds considerable pitching moment (Cm) to the section, and in this case it acts Leding Edge UP.

My point is that there are plus and minus points for up elevator, and up aileron, but only bonus points for up canard. It is not just lift we are after. If it were then I could see an argument against elevon on takeoff.

What we need is Pitching Moment, nose up,and lift at the front is better valuethan downforce at the rear. We need to get the nose up to increase AoA on the wing.
When your NS is planing on the tails of the tipfloats, downforce from up elevator will try to push them deeper into the water, increasing their drag.

Has anyone tried a step on the tipfloats to bring their planing point forward a little?

Aussieflier

Alasdair,

Actually if you read my post again you will see that I have not missed the point that the reflexed ailerons provide a downward pitching moment. Of course this is quite true when the aircraft is in flight. It is also true when a delta is taking off the ground.

A full sized delta on tarmac rotates at the main gear, a point just behind the C of  G. The tail of the aircraft has enough ground clearance to rotate to more that 30deg nose up. The elevons create a downward force well behind the point of rotation and so the tail goes down unhindered and the nose rises to reach the optimum AoA.

In the case of the Northstar taking off water, we have a different scenario. The aircraft rotates at the step in the hull until the tip floats come back into contact with the water, and a maximum AoA of about 5deg is achieved. At this stage the point of rotation moves rearward from the step in the hull to the rear edge of the tip floats. Once this situation is reached, the elevators are the only means of providing a downward force rear of the point of rotation. The elevons are applying a downward force in front of the point of rotation and working against the elevators. Effectively the elevons are trying to clamp the aircraft to the water.

Try this experiment: Fix your elevators in he neutral position and try to take off using only elevons. I will bet the you discover that a much higher take off speed is required, if indeed the aircraft will take off at all.

I don't know this for a fact, but I would  not be at all surprised if this is why the Arrow does not have tip floats. The design probably needing to trade the ability to rotate for poorer water handling characteristics. Aiding to achieving a faster but less popular design.

As before, I do agree that elevons would offer a benefit to those pilots wanting to push the aerobatic capabilities of the model, but perhaps it would be a benefit to use only elevator during take off.

A canard will offer a small advantage but perhaps not as much as you may think. Again, in the case of a full sized aircraft the canard only needs to offer a small amount of force to rotate the aircraft because the aircraft is rotating around it's C of G. In the case of Rafale, Euro fighter, Saab Viper, all of these aircraft are balanced behind the centre of pressure and as such during most flight conditions the canard is actually holding the nose down and forcing the airflow to remain more laminar to the wing. With Northstar trying to rotate at the tip floats we would be asking the canard to lift almost 25% of the weight of the plane, so we would need a canard that is about 25% of the wing area of the wing or greater. The C of G would then need to come way further forward, followed by then needing to mover the step in the hull forward, this would put the tip floats even further behind the point of rotation and thus reducing the AoA while planning, and we would be back where we started or worse off.

What we need is the ability to achieve a greater AoA on the wing when the hull is planning. That is exactly why conventional designs make better seaplanes, flaps are used to increase the angle of attack and the long tail with elevators are used to maintain the stability under flaps.

The real answer is a hydro vane to lift the nose out of the water.

Cheers, Lionel

Aussieflier

Sorry, I forgot to add.

A hydro vane in water only needs to have 1/1000 of the same plane ( wing) area at a given velocity to achieve the same lift as a wing in air. So only a very small hydro plane would be required and it would add very little drag while flying. Naturally, this is a whole new science to understand and get working, but it's a decent challenge.

Cheers, Lionel

Aussieflier

I am getting old, my fingers work faster than my brain.

Correction, I should have said hydrofoil not hydro vane.

russram

There is a lot of good science coming through and here is my penny's worth following on from Auzzyflier. From watching the America cup racing lately why don,t some try putting foil's on the tip floats and maybe hull centre to get the NS above the water surface and with the correct foil angle the AOA would be easerly attained. From a Kiwi the country of inventions Cheers Russell NZ PS i have built 4 NS over the last 20yrs and still enjoy flying them

Aussieflier

Something like this might work.

russram

That is spot on a Lake Buckaneer doing just what the north star needs some one give it a go I not sure about the landings with foils down maybe they need to be retractable

Goldenduff

Or at least with suspension. An actuator would be easily installed instead of lead in the nose!!!

Aussieflier

Apparently the foil aids quite significantly in softening the ride through the rough as well as getting hull up out of the water quickly. I have ridden in a large hydrofoil boat here in Vietnam, I can say for sure that the ride in the rough improves substantially as the hull leaves the water. At first glance the foil gives the impression that it would hook up on landing and create problems, evidently that is not the case when the geometry is correct. The steep dihedral in the foil acts to both stabilize the rolling motion as well as to work a dampener. The lift provided by the foil is relative to how much of the foil is submerged. So on landing the initial bump is said to be quite soft.

Cheers, Lionel

russram

So to get into the nut and bolts of this the foil needs to be forward of the step and well underwater to get good lift it maybe that i shall have a go at this [&:]

LADDIE

Alasdair.

Thank you for changing my thinking about the benefits of having elevons on the North Star.
I am learning something about NS that I did not know.
Laddie.

Cougar429

My Feedback: (3)

I hate to say this, but it's starting to sound like the description of an elephant, (ie. mouse designed by committee). In most cases supplemental add-ons only correct for a deficiency in a basic design or try to expand a performance limitation BEYOND the intent of that original design.

Examples of this premise are widespread, such as replacing the tires and bolting a blower, (supercharger) on the family wagon, to Vortex Generators glued to the wing on your 172.

In the case of the NS there have been a lot of little tweaks, some intended to improve performance and others just to see if and how it would work. Personally, as a card-carrying tinkerer I love reading what others have come up with.

Also, in the case of the Northstar I believe a deeper step or redesign of the fuse bottom may be a simpler method of achieving a higher AoA during water ops. It would allow better rotation before the floats came into play and perhaps reduce drag. If and when I find another NS kit I will incorporate a few of these, just to see "if and how it works".

A good example is present here with the Seamaster, one of the best water ops birds I've ever seen, (even considering the flat bottom). That hull closely follows what is common to full-size birds.

p.s. This was early in the covering process as I was still trying to work out the scheme.

LADDIE

Here I go again. Here is a reason I shaped the bottom of the fuselage and the height of the step as you see on original NS. In my mine I figured that I rather let the model to pick up lot of speed before lifts off then having the air trapped underneath of the wing making model just jump out of the water before it had a flying speed. At the same time I wanted the wingtip floats be in contact with the water until air born. Again, someone might prove me being wrong. But that is fine with me.
If someone out there did modified the bottom, let us know how it worked out.
I am happy when someone is modifying basic design with idea to make the design better flying, nicer looking and so one.
Laddie.

Aussieflier

Cougar429,There is a reason why we are not all driving model T Fords, it is because people with vision worked together to discuss and implement possible options for improvement. In it's day the Model T was the latest technology and sold in unmatched record numbers, even today some people still own them for nostalgic reasons. But nobody drives them as their daily rides because they have very poor handling, they are uncomfortable, have very poor engine performance, need to be hand cranked, and don't stop well. The fact is that if you made a new model T today, it would not even come close to meeting the minimum design standards for a motor vehicle. What Laddie is saying is, I am sure, exactly correct. He has designed the model for high speed take off. What we have been discussing are ways to take off at a slower speed, or with less power, or with more weight. So we are not talking about improving the design for the purpose of that which it was originally intended, but to perhaps change the design criteria a little and look at modification that might work. On my own ( as yet untested ) Northstar, I have built a Vee bottom with chines and raised the step as well as altered the planning angle of the hull to maintain a higher angle of attack on the wing. It is a yet to be proven modification, it may be better or I may discover that I have released a whole new bag of problems.If you actually draw up a Northstar with enough step to get the AoA to 16deg you will see that it looks just like a Pelican, I know, I have one on my drawing board. Now I am drawing one up with a hydrofoil and rounded bottom on the fuselage, it look's much more elegant and streamlined. Somebody, I forget who, stated in a post earlier in this thread that what we want is better aeroplane and not a better boat. Having pondered this for some time I now think that they were right. Would it not be better if we had a perfectly streamlined fuselage and a very unobtrusive hydrofoil system to get it airborne? From what I have been reading, no step in the bottom is required at all. There is actually a lot of work being done around the world right now on this very subject.Cheers, Lionel

Aussieflier

This fuselage would never get out of the water without the Hydrofoils.

alasdair

What IS that? Is it real, or a clever bit of photoshop work?

Aussieflier

It is the Akoya. It is real, although that photo may be worked up a little.

Go to this site and you can find a lot of information about it. At the moment they have flying prototypes but are not yet in production.

There are also some video footage of take off and landing.

Cheers, Lionel

http://www.seaplaneinternational.com...-on-the-water/

Aussieflier

Also here: http://www.lisa-airplanes.com/

Cheers, Lionel

Cougar429

My Feedback: (3)

Aussieflyer, it was not my intention to start a philosophical discourse on progress or problem-solving, just to point out some of the add-ons posted were beginning to look just like the name suggested, (bolted on rather than integrated into the original design). This is for Laddie, as well-not to suggest the basic NS design was flawed, just that a slightly deeper fuse and step would perhaps have been a more elegant solution, (and easier, from a structural standpoint) and better able to deal with the inevitable weight growth that drives the fuse deeper into the water.

As one who cannot remember EVER building a kit to stock, I thought your version absolutely beautiful even sans covering and await a report on water handling with that hull mod. One of the biggest problems with flat-bottoms is the tendency to skip unless the landing is perfect, (difficult if on anything but glassy surfaces).

p.s. I used to be elbows-deep in solutions to the first gen emission regulations beginning in the late 70's. What came out of Detroit, and what Japan sent here at least, was increasingly complex and EXTERNAL to the basic engine design, (where the term "Lipstick on a Pig" became common....I will NOT tell you the military designation, at least in public!). Examples like these drove my comments regarding attempts to alter or solve what was an inefficient system to start with. As a bit of info, most of these systems were fixed, ie. not able to deal with environmental changes very well.

Aussieflier

Cougar 429,

Firstly, thanks again for your complements regarding my Northstar, and secondly, you are correct, we should focus our energy on the topic.

The Vee and hull lines that I have implemented on my model were indeed intended to reduce the tendency for the model to skip. I have an 800 gram battery under the canopy that I don't want to punch through the bottom of the fuselage. I did a fair bit of reaserch on planing hulls and I made my modifications as best I understood what was required. Having since read a lot more about boat design I have come to understand more about why the model skips. The problem is not just that the bottom is flat, there is another problem. Please note that the area of the hull that I am talking about is everything forward of the step. On most modern planing hulls, the widest point in the bottom hull is the very rear at the transom, many hulls are parallel for the rear 25%. The Widest part of the bottom of the Northstar is much further forward. This works well for making the fuselage streamlined from an airflow point of view but not so great for stable planing.

When the ride conditions force the hull deaper into the water, such as a heavier landing or hitting a small wave, the rear part of the planing section on the Northstar sinks deaper into the water than the front. The rear being narrower more easily displaces the water and the area further forward less easily. This allows an increase in angle of attack for both the wing and the hull resulting in the model exiting the water. After realising this I added Chines to the hull to create more lift at the step. If you look at most flying boats, EDO floats, etc, you can see that they are usually widest at the step.

If we made the hull wider at the step there would be many benefits. The model would have more boyancy further back and so it would more easily get up on the step as the hull loading and less there is actualy less drag. It would skip less. It would plane at a lower speed. It would have better lateral stability and the tip floats could be made smaller, shorter or perhaps eliminated. Now there is a penalty in that there will be extra drag while flying because of the wider step creating a partial vacuum at high speed. There are some manufactures experimenting with retractable steps. What the are actually doing is retracting a part of the fuslage behind the step line in order to creat the step for take off. I was looking very hard at this option when I came across the use of hydrofoils.

Hopefully I will get my Northstar into the water next week, maybe I'll even get it into the air.

Cheers, Lionel

skywagn180

Well I have an update on the 8 lb. Northstar that couldn't get off of glassy water. I went to the lake today armed with .025 aluminum, various sheet metal tools and tape. I stood around with cutters and let my brain run wild. The photos will show what I came up with. Initially the angles were a little too aggressive, but it took off the first run on glassy water full of fuel! After the embarassment of failing to get it up about fifty times last float fly, today felt good. Lol. I used a kicker tab on the main step for lack of a better term. That solved the planing issue. It planes much sooner now. The other issue I was having was with the tip floats causing directional control issues and creating a lot of drag. I solved that with kickers that have an addition tab longitudinally with a slight toe in. The plane tracks dead straight now. I don't really even need a water rudder on plane. It's nice. All takeoffs were with elevator and elevons. I ran out of time to try an elevator takeoff. On wheels they are pretty sketchy at this weight, so I wasn't looking forward to trying it anyway. Since the pics, I have reduced the size of the main hull tab and reduced the angle of all three. I ran out of time, but the last couple takeoffs were very nice and reasonable. At this point my experimental tabs need some refinement, but the results are very good so far. I will continue to improve and experiment with them and report back when I have it perfected. A funny thing we noticed is that these tabs seem to have substantially reduced wing rock in flight! Wow was that interesting. I assume it is the tip tabs helping with that. I am happy with the takeoffs now. The tabs also made it much harder to bounce. Landings were nice and smooth with all the extra hardware. A very exciting day overall. Again today, the Northstar got people excited as it flies like a dream even on the tiny .46. It's a screamer. Hopefully a video will surface soon. I think some were filming it.

Aussieflier

skywagon180,

That is great news, well done. Some friends of mine were suggesting that the wind rocking could perhaps be exaggerated by the large flat area on the back of each float, it was one of the reasons that I tapered the back of mine. I wonder if anybody else has notices changes in stability with their tip modifications. I can tell you for sure that in F3A the wing tips are super important for accurate flying.

Can you give an estimate of how much room you need from near stationary to actually taking flight? And also if you had any headwind?

Cheers

Lionel