Talking propellors

[bomber]

and about the link, you saw the point, where one of the guys linked to a lab setup for measuring?

I get an error on page when I press the link on that forum

https://api.viglink.com/api/click?forma ... ab%20Notes

[bomber]

Anyway.... next stop Javaprop

http://www.mh-aerotools.de/airfoils/javaprop.htm

Anybody use ?

Simon

[jwocky]

It means, someone, somewhere in the past didn't look up what the expressions following after those lines actually describe.

See, 1/12*something and 1/3*the_same_something are definitively a difference. The problem is, someone somewhere thinks of "slender rod" as something thing in a physical sense. But actually slender rod means the rod is too thin to produce a significant amount of inertia. Now if the rod becomes for example thicker, it is more of a cylinder, which comes nearer and nearer to the disk formula but with a lot higher mass (because opposite to a disk, it has more mass, it's a cylinder with a length).

Bottom line, one has to be careful with the Internet and taking stuff form there without checking. There is sometimes room for several ways to skin a cat, but any thing that delivers three almost identical equations for the same object only different by a constant factor. that just can't be, unless someoen took somewhere a sloppy short cut.

[jwocky]

Haven't used JavaProp yet, but at least the approach to calculate a propeller blade in segments makes a sense, also when it comes to other calculations (bending, efficiency of prop pitch for example). The simple truth is, you can't calculate anything on a propeller absolute and 100% exact with a reasonable effort, so it's all about an approximation as good as possible.

We have kind of the same problem with lift calculations on wings for example. Aeromatic delivers some value based on wing-surface, but the wing-profile part is out of consideration. And even if we could do a complete mathematical description, it would be hard to handle for daily use. You can't give a pilot a manual that says "just set in some variables and then run those integrals and differentials through your computer". People will hate you and your plane if you say "integral" or "differential".

Here are two thoughts to make our life easier:
1.) Can we automat those calculations? At the moment, we look at the Beagle Pups, but the same problem will pop up with other propellers (and I know, I have some of it with my WWII bombers because for reasons of lazyiness, I used just the JSB internal calculations). And we have planes in the queue for example with counter propellers, in which not so much the problem of inertis alone is interesting but the tension on the whole structure caused by torques in two opposite directions. So maybe, we should think some toolbox here because those are not the last planes we deal with. You don't speak Java by any chance?

2.) When it comes to the Beagle Pups, lets take a little bit the low road for now. You say, the ixx is correct, I say, it's too high. We stuck at a point, where we can't even agree which formulas to use and on what parts. So I would like here to withdraw on some Bomber-wisdom and look for what is intuitive and fun to fly. The enormous torque is not, the plane is almost impossible to handle during take-off and in the air, you use so much rudder and ailerone to compensate for those forces, you can only turn very fast to one side and almost not to the other. So that is neither intuitive nor fun to me, but then, I'm anyway more of a bus driver type of pilot. So, why not involve some with more flying time on small planes and ask for their "how does it feel"?

[bomber]

At one time T4T had a current rated Spitfire pilot on the team....

When we get back up and running we'll get back in touch.

[IAHM-COL]

Can you spell T4T for me?
(Im a newbie )

We have the Orcas for test pilot organization. We send them notification of planes that have bug reports and they are the ones on charge of risking their lifes in the buggy planes

[IAHM-COL]

I am reading this thread with lots of interests
The concepts are way above my head, but I guess I will learn by contact, here



One thing. should I make a branch on the puppy with any modified engine? that way we can just tell pilots test version A and version B and report...

[jwocky]

We are not even at the really juicy things yet ... but I admit, I enjoy going down that mathematical rabbit hole with Bomber. At least, he doesn't shoot my for saying "differential"

But now serious, What we basically talk here is propeller torque, so, in the whole picture of the plane a relative small part. We still have to figure out something more conclusive for the CoG than we have right now. So after we tortures James Thomson a little, we will at some point probably went on to torture Archimedes and of course Sir Isaac Newton

[bomber]

That's actually spot on Jocky.... it's why I called this topic 'talking propellors' so as to focus on just props and not get distracted..

Now I've had my sleep, the kids are walking to school outside my window and I'm ready to start another day of talking propellors ( and grunting as this 6 inch slash across my belly heals)

So let me reply 2) specifically

So I would like here to withdraw on some Bomber-wisdom and look for what is intuitive and fun to fly. The enormous torque is not, the plane is almost impossible to handle during take-off and in the air, you use so much rudder and ailerone to compensate for those forces, you can only turn very fast to one side and almost not to the other. So that is neither intuitive nor fun to me, but then, I'm anyway more of a bus driver type of pilot. So, why not involve some with more flying time on small planes and ask for their "how does it feel"?

I'm not disagreeing that there's an increased workload with high torque and P values, that it's not as easy as flying a jet and even that it's not fun.... although that is subjective and the challenges of flying such a plane could for some be fun.

My opinion however is that you shouldn't fix one problem by 'porking' another.

There are 3 definative areas of development for a prop plane

1) Engine
2) Prop
3) Airframe

For most planes we have some stat's even if it's just top speed at sea level and for some it's ok if their plane matches that.... they call it 'hitting the numbers'. So they change one of the 3 or all 3 to ensure that it does so but it doesn't make the plane correct over it's whole range of operation, but rather just at that point.

Also props developed over a time period... there's a reason constant speed props were designed... to reduce the workload on the pilot. So do people not want that experience of understanding the workload and feeling it reduced as they fly a plane designed to make the pilots life easier ?

High torque is a problem, if at low speeds you open the throttle you're going to notice it because there's simply not enough roll damping to counter it.. this leads to a sudden roll, a differential lift by the wings and a spin.. it's killed more pilots than anything else... Do we not want to experience the problems ?

You have to fly the plane correctly, it doesn't fly itself and that's a feature of a lot of early flight era planes.

Is that not what a simulations all about ?

Airframe designers do a resonable amount of work to reduce the problems by designing each wing slightly different or setting the v-stab at a slight angle, not forgetting the trim tabs that exist to counter torque roll... if we don't have those torque problems we don't have a need to design our airframe to counter it.

I'm not against an easy flight option, I use auto start all the time. These exist in real life up to a point as new designs came along... but more than that we can reduce the p value or put a prop on a plane that reduces it's interia and torque issues.

Totally in agreement with you on it...

But where I dig my feet in is actually wanting a version of the plane that's correct, we use the data available with some extrapolation, where needed as there's never the full set of data. To produce an accurate engine, it's prop and the airframe that flys to the characteristics of the plane... if the planes a pig in real life it should be a pig in a simulation.

Reducing the problems of the plane is then just a matter of hindsight, which we have and is something that we can apply using genuine design methods, or not as required.

Simon

[jwocky]

All valid point ... my point is, I am not flying enough such planes to talk too much about "feel".

That reduces me to some mere technical points. The engine looked good so far, so I was searching the reasons for the too high fuel consumption in propeller and or airframe respectively the balance. Which is kind of not "talking propeller".
So, I think, the torque is too high, you think, it's okay. We have still not enough data to do the exact math, it's all a little bit of guess work here. Still, lets just change approaches for a moment:

you try the approach to put it to pieces, calculate them on their own and add them up
I try to find something for a good calculation in one piece

And no, I won't do it before I get some sleep.