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Spada 3M
- Thread starter Doc J
- Start date
Doc J
Very Strong User
Konrad, mon Vieux!
Unlike the old Redshift, from the start the orginal design of the Spada had parallel sides - no need to change. Note that this means parallel in Z-axis only, and also note that this was not done as a "Hoernerization" it was pure coincidence.
Its interesting, actually - I have not read the book by Hoerner for many years. I don't have a copy, and when I looked for one it was a bit pricy. As I remember wasn't Hoerner offering different fairing arrangements for reducing the different types of interference drag?
In this case there is one thing that we always have to bear in mind when using established theory to design model aircraft, and that is 'scale effect'. Our models can be all sorts of different sizes, but unfortuately the air around it is isn't.
And...There is not too much sub .25 Mach low speed aerodynamic theory there to use, and even less for low speed/small body aerodynamics.
Its difficult for us small size designers, as there is really an immense difference between designing say a 60" model as compared to a 3M or larger model. Some of the bigger size rules get left behind and many times we are reduced to plain old experience and common sense, coupled with the "Well that seemed to work last time" doctrine, as the models reduce in size.
3M is really bordering the lower limits of full sized theory and thats why I have tried to slot in a few trials in the wind tunnel as often I have been allowed to. This has revealed to me relationships and "semi-rules" that existing low speed theory wouldn't help with.
Maybe thats why most larger 3M and plus models fly OK - even if they are a bit iffy in design, whereas a 60" model will be a real pig if its off a little bit.
The design is frozen solid now, so I have every digit crossed that I have it right. One thing I can say is that there has been a heck of a lot of input from many places, not the least from your own good self and most of this that is practical and useful has been incorporated.
You have said that the Freestyler is a better model for F3f, and I guess you are right, but in good hands even the old MK1 Redshift can show a bit of pace. Now what will happen if I have cured all of the control problems with the old model, generally tweaked a couple more parts, and then made a new one with a much slimmer ("Hoernerized") fuselage.
Enter: Spada.
Construction of course can change but only around the designed skin.
Cheers,
Doc.
I like to think of it in very simple terms. Avoid making vacuums at the intersections. With this said, we have seen many great reasons to use vacuums to aid the aerodynamics.
There are a lot of great examples of horrible intersection drag if you look at most any GA aircraft at a local airport.
Hammond is aware of all of this stuff. I think you are trying to teach the professor a grade school subject.
There are a lot of great examples of horrible intersection drag if you look at most any GA aircraft at a local airport.
Hammond is aware of all of this stuff. I think you are trying to teach the professor a grade school subject.
Konrad
Very Strong User
Not sure about that. I’m not trying to take anybody to school. I’m pointing out what I see as potential problems and offer solutions as I a non aerodynamicist understand them.
For example on the mk 1 we discussed mechanical issues with the snakes, V-tail control arms and ballast tube and servo interference.
We’ve discussed structural issues with the premature delaminating of the LE, and ballast tube.
We’ve discussed aerodynamic issues with directional stability and the interaction between the V-tail angle and aspect ratio, front and aft vertical area.
But as you mentioned just because a learned man (professional) has made something doesn’t mean it was done correctly. Take your example of the many issues we can find in GA and transport aircraft.
So here with the mk2 I see a lot of the issues have been corrected. But I also see issues that don’t, with my understanding of Hoerner’s writing and Arnold’s demonstrate performance.
I point out what I see and try to give reference material to suppprt my concern.
For example on the mk 1 we discussed mechanical issues with the snakes, V-tail control arms and ballast tube and servo interference.
We’ve discussed structural issues with the premature delaminating of the LE, and ballast tube.
We’ve discussed aerodynamic issues with directional stability and the interaction between the V-tail angle and aspect ratio, front and aft vertical area.
But as you mentioned just because a learned man (professional) has made something doesn’t mean it was done correctly. Take your example of the many issues we can find in GA and transport aircraft.
So here with the mk2 I see a lot of the issues have been corrected. But I also see issues that don’t, with my understanding of Hoerner’s writing and Arnold’s demonstrate performance.
I point out what I see and try to give reference material to suppprt my concern.
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Hill Hobbit
Very Strong User
The model doesn’t even exist yet, but you’re saying already that it has concerning design deficiencies.
That’s a bit strong methinks…
That’s a bit strong methinks…
Konrad
Very Strong User
The design as shown (CAD). Now I think based on what Doc has said and what I seen in the real 3D world with the Mk1. That this maybe a real concern. Better to find and discuss this while still in the vaporware stage. It sure is a lot cheaper to correct now than after the molds have been cut.
So what is your issue with me voicing my concern at this stage. I wish somebody had said a few things earlier in the MK 1 development!
So what is your issue with me voicing my concern at this stage. I wish somebody had said a few things earlier in the MK 1 development!
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Hill Hobbit
Very Strong User
I would have thought it polite that your ‘concerns’ re the Spada would be better discussed with James via private mail rather than on this open forum. End of.
Konrad
Very Strong User
No, it's done here to drive interest and keep the product at the forefront of the discussion for anyone wanting to get an F3F type ship anytime soon. It is hoped that others will add their input. This is not a sale hype forum, but rather one that encourages active participation in the advancement of the craft.
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Doc J
Very Strong User
Hello Gents.
No need to slap wrists as all constructive inputs are gratefully appreciated - and thanks a lot for all of it and your confidence.
Here's what I think (Hope?)
1. To be horribly honest, I think that the fuselage/wing interference drag is not such a large problem on this model as I have done the best I can to prevent it becoming one, so in fact we are talking about a problem that has already likely been solved.
2. Again, honestly at this scale the whole fuselage/wing intersection interference drag theoretical "Problem" probably isn't.
I do the big Predator type model aeroplanes too, but it really is different to the smaller stuff. Bear in mind that with our little whizzers, the attitude of the model is changing constantly. Its not like even a large drone or a light aircraft where you have relatively long periods of stable flight where these things become more important and need to be addressed.
During my time designing, testing and then making the models, I have found that by far the most important thing to get right is the wing, and so I'll admit, sometimes to my detriment I have concentrated more on that and less on the back bits and the bit that both are attached to. Accordingly, on designing the Spada I did take a very careful look at integrated assembly and cross influences of the wing/fuselage/stabilizers, as I had the Redshift MK1 to go on and it was incredibly useful.
I'm not saying that I made mistakes on the MK1 - it flew OK, but I will say that with hindsight, and the experience I now have, it could have been better. I take heart from the Freestyler series, now up to 6 versions or more. This is an example of very steady development and I’m sure that though the series most of the changes have come from pilot’s experience and inputs rather than aerodynamic theory.
You can make the planes as good as you can but actually most of it's the flying. Watching the racing flights, and having done a fair bit myself years ago, half the time less experienced pilots put in bad times because they are constantly adjusting the attitude of the plane for that they think is a faster line. Actually, if it’s not going to hit anything and its generally going in the right direction, its much faster to leave it alone. Every time you move thse sticks you lose speed - but tell yourself that during a race!
At the moment – maybe until I have a Spada 6 then it’s as good as I can make it and I’m really happy with it. Let’s see how it flies first and then I can start writing down all the inputs from the flyers. Hindsight is a wonderful thing.
Cheers,
Doc
.
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Doc J
Very Strong User
And in turn I do my best to tell you what I'm thinking, and why. I hope is not one-to-one as maybe others will also get something out of our exchanges.
Yes, and that has actually been very constructive overall. It doesn't matter how smart or well-read you are, two (or hopefully more) brains = more horsepower. Others will always think of things that you have not thought of, or forgotten. Even my hero Kelly Johnson used to seek opinions from everyone that he possibly could whatever their status, education or rank. I do try to do the same.
That is true, and yes most of the time I do know most of the theory as I use it every day on Da Big Dumb Planes, but sometimes I forget to apply it, or as I have pointed out, for small-sized MODEL Aircraft, it may not actually apply, or perhaps be of limited effect...But I have learned over the years to be appreciative when someone reminds me of something, or actually wants to know more about it. Nothing like an enthusiastic student.
Frankly, on this size of model you can pay attention to many of the theoretical formulas and rules, and its a good idea to do so; but in many cases those theories may not actually have the same influence that they do on the larger planes - if at all.
Specifically:
If we look at the possible Interference drag on ths model, first, a) we are dealing with a rounded (Trianguloid) section, of a set size as its parallel in plan view and b) we are dealing with a wing root section of a set shape and size as well. To make Mr Hoerner happy we need to joining them in the best way we can. That is what I have done, and other than making longer transitions or smaller blending curves, there is little else that actually COULD have been done.
An thats great, but really Konrad sometimes you are a little bit prickly, and I know its because you care a lot. But possibly a softer approach might let you win more friends and influence more people?
Just a thought.
Doc.
Doc J
Very Strong User
We are fine - I know and understand your enthusiasm and thirst for information and also your sometimes somewhat abrupt manner of imparting it. Maybe occasionally you come across just a little bit 'openly contradictory' or "this is an established fact' rather than 'up for a discussion'? Would that be a good way to describe it?
You are one of the most black and white people I know. You don't have many, if any grey areas. You don't deal in opinions, pretty much facts only and sometimes maybe this stark contrast, instead of assuring people can make them take of offence.
Me? I'm long, long, past the "its my baby and its perfect, so don't criticise it!" stage, so personally I love your minute attention to detail, and your willingness to openly state what you think. But we are all different, and I'm not the only one here.
Cheers,
Doc.
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Doc J
Very Strong User
Hi 2 - actually the Spada is mostly trianguloid (I'm sure I have invented that word) at the sharp end, merging into ellipsoid, (I didn't invent that one) and almost round in some places.
The round cross section remains the strongest so I have not deviated that far.
For interest, the MK1 Redshift "BUFF" fuselage had a lot of round in it so the boom was pretty rigid.
Cheers,
Doc.
Hill Hobbit
Very Strong User
Dear Konrad, please report my posts #26 and#28 to Wayne for being ‘beyond the pale’. I’d also appreciate it if you would kindly tell him that I’m actively suppressing Doc J’s Spada development in this thread.
Thank you
Thank you
Konrad
Very Strong User
That’s a very good point. The tail boom needs stiffness. A round tube while better than a rod flexes too much for any given weight. We don’t need the strength for say, a pressure vessel.
The triangular cross section, like an epee, tail boom might actually be better for the stiffness and strength it offers.
