The Good, the Bad and the Ugly

[Konrad]

In this thread I was reminded of the work by Hoerner and how Arnold applied these principles to his exquisite full size racer the AR-5. It is real important to control this junction drag as it goes up geometrically as a function of the lift coefficient. Read it will slow you down in a turn, just what we don't want in an F3F racer.

I thought I'd look at some of my racers and see if these principles are being used in our slope racers. Well as you might expect the answer is yes and no.

I have the great TUD Freestyler 5, the horrible Simprop Sagitta and the middle of the road Redshift mk1 fuselages on my bench, so I'll use these to show what I see.

The Freestyler is consciously following Hoerner's ideas with the front fuselage changing from the triangular cross section to a straight sided parallel box section at the wing fuselage junction back to the very rigid triangular cross section for the tail boom. I call this the Good.

At the other extreme we have the horrible (but ever so sexy looking) Simprop Sagitta. It too has the triangular cross section fuselage. But rather than bringing the side to effect a 90° or greater junction at the wing intersection. The designer kept the sides slanted under the wing. This allows for the vortex to really clamp on tight almost bring the ship to a stop. In top view we can see the fuselage's radical taper from large at the front and small at the rear of the wing junction. These B.U.F. (Big Up Front) profiles at the wing to fuselage junction are to be avoided at all costs if one wants a low drag ship. Read fast and fast turning ship! The Simprop Sagitta is what I call very bad design. Heck, the designer didn't even try to address these issue with the expanding radius fillet! (This just shows that if model looks good and sexy it still won't fly right!)

Now the Redshift fuselage isn't near as bad as the Sagitta's. But when it comes the fuse design it looks like the designer was just phoning it in. The fuse has the large cross section at the LE edge of the wing to fuselage junction with the fuselage taper resulting in a smaller cross section at the TE of the wing to fuselage junction. This BUF wing junction sets up a large drag nozzle. Now this fuselage does not have any of the less than 90° issues we saw in the Sagitta. So to my mind this is just typical of most fuselages and a bit ugly. The designer has admitted that he didn't spend the time he might have otherwise on the fuse, as he really was excited about his wing.

Having flown all three here is what I noticed. The Sagitta looses a lot of speed in a turn. Much more than you would expect. I thought back then that this was as a result of the rather low aspect ratio wing (for a glider) and that she was a bit small at 2 meters. I now think that along with the low aspect ratio this fuselage to wing junction might as well be a drag chute thrown out in the turn.

The Redshift and Freestyler are both 3 meter F3F racers and are designed to turn well. When looking at the performance and what contributes to this performance it can be difficult to separate all the variables. Both turn well, meaning keep their speed in the turn. While the Freestyler-5 has the aerodynamically much better fuselage. This fuselage can't make up for its rather short aspect ratio wing. But she goes where you point her.

The Redshift mk 1 has no problem overcoming the wing junction issues as that great 18:1 aspect ratio wing really really pulls through the turns. And does so, so quietly!

 

[2MUCH2DO]

Honestly, I think you may be much ado about nothing here. Look at the shinto also, similar to your redshift. These gliders are literally any given sunday winners.

 

[Konrad]

I love the Shinto with her high aspect ratio wings.
In the hands of a competent pilot even a Strega can be found on the podium.

"Much ado about nothing", so true this is a hobby.

But that is the consensus that the wing junction is only a few percentage point of the over all drag of the flight. But what a lot of designer overlook is that this drag goes up by a cubic function of the coefficient of lift. So what looks like "much ado about nothing", when cubed it starts to become a significant issue. See how Arnold controlled this in his record breaking AR-5. His coefficient of drag was thought to not be possible (practical, in reach).

Now when you see (fly) a plane like the Sagitta turning compared with a straight fuse sided 2 meter you know something is going on.

So if all that one needs to do is expand the rear of the fuse over the wing junction a bit, to eleminate or lower this drag, why not?

Yes, I'm always looking for that incremental improvement.

 

[Doc J]

"Supercritical" takes on a whole new meaning...

I'm watching this with interest.

From my side, when I designed the Redshift I was mad keen on trying out my new wing ideas, and possibly (I hope) due to that attention to detail, I may have done that bit OK. I wish I'd paid as much attention to the other bits, but I didn't.

As I always say, hindsight is always a wonderful gift to be born with.

At the world F3f champs in Rugen Germany a few years back when the Redshift came out in public, almost everyone asked "does it stall on landing?"
"Nope" was the answer.

The 'Redshift team' there had enough info on the wing design to let the other curious flyer know what I was trying to do, and in flight they saw that it was working. Though quite possibly, some of them did cast a jaded eye over the V-tail configuration and the chubby fuselage.

But...Now look how many new models are featuring higher aspect ratios and lift-specific wing planforms!

With a pretty long history of Redshift anaylsis on both contruction and flight characteristics, I had a lot of good solid information, some of it backed up by actual testing, and that is exactly why I condone and encourage constructive criticism. Armed with that, on the new model I really have paid attention to EVERYTHING I know that can make it light and strong in construction, and a good, fast, and obedient flyer.

Yes, there are things that I know, and things I have discovered during testing that I could have incorporated on the new design, but have not, but its really only because they are bit too radical to be commercially viable. Unfortunately if you want to sell your planes; and I do...I'm begging you! you have to follow fashion to a certain degree even if it is a stupid dumb animal.

One day I'll have the time and the financial ability to make special non-commercial models that will either prove the new stuff or not. But for now its a bt of a risk that I don't want to take.

Let's see where Konrad's GBU analysis takes him. I'm hoping my new plane can be in the GOOD band.

Cheers,
Doc.

 

[Konrad]

Any variable that has an exponential effect is super or hypercritical in my book, but I don't think I made that statement.

We have had high aspect ratio (18:1 plus) F3F gliders for a long time before the Redshift. I'm thinking the Shinto and Fosa. But what the Redshift has is a very benign stall. This allows us to really push the glider in the turn*. Or have little or no fear in the landing zone.

You lost me with the term "GBU".

* The few times I drove the Redshift into a high speed stall during the turn all that happened was the turn opened up. One time I did get into a spin and because I think the V-tail is a bit shy on area I had to actively get out of the spin.

 

[Doc J]

Any variable that has an exponential effect is super or hypercritical in my book, but I don't think I made that statement.

We have had high aspect ratio (18:1 plus) F3F gliders for a long time before the Redshift. I'm thinking the Shinto and Fosa.

The orginal Redshift was designed in 2003. The first mockup was made in 2004 and went down with all hands due to a stupid battery mistake on my part.

But what the Redshift has is a very benign stall. This allows us to really push the glider in the turn*. Or have little or no fear in the landing zone.

You lost me with the term "GBU".

The Good the Bad and the Ugly. Actually its a divison of the Russian secret police, or was that GRU?

* The few times I drove the Redshift into a high speed stall during the turn all that happened was the turn opened up. One time I did get into a spin and because I think the V-tail is a bit shy on area I had to actively get out of the spin.

Sure. I think any model can be forced into a stall, normally by over-enthusiasm (!). I bet you don't get it so often now you are so much more experienced.

Cheers,

Doc

 

[Konrad]

The first I saw of a Hammond Redshift was in early 2016. This had a bottom wing and ugly expanding radius fillets. (What do you define as the core design concept that makes a design a Redshift).

Yes all aircraft can be driven into a stall. I do it on purpose to find the corners of the flight envelope. This is just part of my flight test routine.

Now I do cut back on this with all my racers going back to the 80's. As you say in the heat of battle I'm (we) are all often excited and show over enthusiasm.

This is a free racing hint if anyone wants it. Cut down on your throw to the point that the racer feels dead/dull in race trim while sport flying. In the heat of a competition you don't want a ship to be flighty. (I recently learned to use super high expo to tame the beast. In the past I used rates).

Got it GBU, my appologies to the spaghetti westen and Clint Eastwood.

 

[jure]

Got it GBU, my appologies to the spaghetti westen and Clint Eastwood.

I thought that the source was " Brutti, sporchi e cattivi", by Ettore Scola , very famous film , Festival de Cannes director's category winner (1976).

wiki link

 

[Doc J]

I thought that the source was " Brutti, sporchi e cattivi", by Ettore Scola , very famous film , Festival de Cannes director's category winner (1976).

wiki link

View attachment 12396

Since its a spaghetti western, I thought they were types of pasta...

 

[Konrad]

There is a new glider coming out. In the sneak peek CAD drawing I see some issues that concern me. These drawing are of the 3D model, and without cross section views I can't be sure of much. But as shown I see the dreaded less than 90° junction at the front of the wing leading edge. This looks a lot like what we see on the Sagitta. It's not clear but it looks like the cross sectional area at the rear of the wing junction is smaller than the cross sectional area at the front of the wing junction. I suspect it is looking at the side view taper. Now if the cross sectional area at the rear is less than that at the front I'd like to see an expanding radius fillet to be compliant with Hoerner's writings.

Now I do love the geometric strength of the large LE radius.

 

[Hill Hobbit]

Toes and thin ice come to mind here…

 

[Konrad]

This is a reference to what?

 

[Hill Hobbit]

Konrad, Konrad, I’m an adult and so are you. No personal attack or pretence for bickering etc intended (none of my posts have ever been made in that fashion), but I really shouldn’t have to explain to a fellow adult the reasons for what I’ve just said.
Goodbye.

 

[Konrad]

To communicate you do have to explain things. I’m not looking for your reasoning (I assume there is none). I’m just asking for the meaning of the phrase you posted.

 

[ORRich]

There is a new glider coming out. In the sneak peek CAD drawing I see some issues that concern me. These drawing are of the 3D model, and without cross section views I can't be sure of much. But as shown I see the dreaded less than 90° junction at the front of the wing leading edge. This looks a lot like what we see on the Sagitta. It's not clear but it looks like the cross sectional area at the rear of the wing junction is smaller than the cross sectional area at the front of the wing junction. I suspect it is looking at the side view taper. Now if the cross sectional area at the rear is less than that at the front I'd like to see an expanding radius fillet to be compliant with Hoerner's writings.

Now I do love the geometric strength of the large LE radius.

View attachment 12404
View attachment 12405

Qq: how do we know anything about the enhancements. Are these models tested in wind tunnels? Or sim software?

Just curious.

 

[Doc J]

There is a new glider coming out. In the sneak peek CAD drawing I see some issues that concern me. These drawing are of the 3D model, and without cross section views I can't be sure of much. But as shown I see the dreaded less than 90° junction at the front of the wing leading edge. This looks a lot like what we see on the Sagitta. It's not clear but it looks like the cross sectional area at the rear of the wing junction is smaller than the cross sectional area at the front of the wing junction. I suspect it is looking at the side view taper. Now if the cross sectional area at the rear is less than that at the front I'd like to see an expanding radius fillet to be compliant with Hoerner's writings.

Konrad, even I am getting slightly over this constant search for problems. Frankly, if you look hard enough for trouble, you will find it.
In this critique it appears to the untrained eye that you have discovered catastrophic problems with a new model design that will severely affect its performance and therefore saleability, and as you know that is not true.

Let me say this with absolute certainty: The things you mention as problems in actual fact will have no effect whatsoever on how the model flies or how fast it is. This design is developed from a model which is already on a par with most if not all current F3f models, and has been improved from there.

The fact of the matter is that you are using full sized theory on models which are fractional in scale compared to the subjects that were used to delevop said theories. I have said this before - there is little useable low-speed aerodynamics theory, and if you get down in size to our minute models then most of what is available changes or simply does not apply.

This is understandable because you personally have no other theories to go on, and you don't have access to the test results provided by actually testing the model's critical components. As I have said before this is a model that has had everyting well thought out, based on four decades of model design, and the things that go against full-sized theory here either don't apply, or do not have any influence.

I love discussion, as I have often mentioned, and also constructive criticism, but this strikes me more as judgement; almost as if I have to pass your examination to get the 'Konrad seal of approval'.

Please do remember, all: This is what Konrad Konrad categorizes into "good", "bad" or "ugly" ONLY.

You are asking me not only to reveal scalable CAD details of my next model, now you are also asking me to also furnish the detailed theories that led to its final design. With the situation right now and the very real possibiity of plagurism, these are not a reasonable requests.

Cheers,

Doc

 

[Doc J]

Qq: how do we know anything about the enhancements. Are these models tested in wind tunnels? Or sim software?

Just curious.

Hi Rich.

Wind tunnel = yes in parts.
SIM = Yes - BUT the SIM results are to be taken with a very, very, large pinch of salt as at thse sizes they are not accurate to real model flight.

Cheers,

Doc.

 

[ORRich]

Hi Rich.

Wind tunnel = yes in parts.
SIM = Yes - BUT the SIM results are to be taken with a very, very, large pinch of salt as at thse sizes they are not accurate to real model flight.

Cheers,

Doc.

The reason I ask: I’m an avid F1 fan. I watch how teams spend tens of millions in wind tunnel testing to shave the extra tenth on a lap. Amazing stuff because teams are within inches of each other on a three mile lap. This year the top 10 drivers are within 4/10 of a second during qualifying which is amazing.

But. For all those tens of millions spent in the wind tunnel, you will invariably see a car that had contact with another car and lose the end plate of the front wing for example. And by the book, that driver should be like ½ a second slower due to the damage but he’s actually ½ second ahead of the field and winning the race.

Point is in our hobby you can get good but don’t let perfection get in the way. I don’t even fly coordinated turns and doubt the best pilots do so either 100% of the time.

 

[Wayne]

Gentlemen - Time for me to dial in this thread a bit.

Konrad you are pushing peoples buttons, your words are being received as less than friendly.

If you care to discuss this further, by all means do, but please take it down a notch.

 

[Doc James Hammond]

Y

The reason I ask: I’m an avid F1 fan. I watch how teams spend tens of millions in wind tunnel testing to shave the extra tenth on a lap. Amazing stuff because teams are within inches of each other on a three mile lap. This year the top 10 drivers are within 4/10 of a second during qualifying which is amazing.

But. For all those tens of millions spent in the wind tunnel, you will invariably see a car that had contact with another car and lose the end plate of the front wing for example. And by the book, that driver should be like ½ a second slower due to the damage but he’s actually ½ second ahead of the field and winning the race.

Point is in our hobby you can get good but don’t let perfection get in the way. I don’t even fly coordinated turns and doubt the best pilots do so either 100% of the time.

You are right Rich. It all really depends on the flying (driving) Actually you can do everything you can do to make the model the best it can be. But in the end it’s the guy on the sticks that makes the difference.

Cheers,

Doc