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Author Topic: GScholz more ont turbo props:  (Read 6663 times)

Offline hitech

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GScholz more ont turbo props:
« Reply #165 on: January 21, 2005, 05:41:01 PM »
Straiga: Realy want you to bet on this. You name the stakes.

HiTech
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Offline Angus

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GScholz more ont turbo props:
« Reply #166 on: January 21, 2005, 06:20:06 PM »
Hello all.
A humble question.
Do contra-rots have the same pitch for the inboard and outboard propeller?

Pilots note that the contra rots create no torque, or rather that one does not have to keep trimming the rudder to counter it any more.
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It was very interesting to carry out the flight trials at Rechlin with the Spitfire and the Hurricane. Both types are very simple to fly compared to our aircraft, and childishly easy to take-off and land. (Werner Mölders)

Offline Straiga

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GScholz more ont turbo props:
« Reply #167 on: January 23, 2005, 01:21:55 AM »
Well its looks like everybodys waiting on me to respond. I have dug out some info from some old texts but I dont know how to get it from this book onto this post. I can scan it but from there Im lost, Any suggestion? I have good information on Yawing moment coefficients and formulas. So if you can help me get this info on this post I would appreciate it.

Straiga
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Offline hitech

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GScholz more ont turbo props:
« Reply #168 on: January 23, 2005, 09:37:18 AM »
Scan it: Email it to dalea@hitechcreations.com Ill post them for you.

HiTech
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Offline Straiga

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GScholz more ont turbo props:
« Reply #169 on: January 23, 2005, 11:29:57 PM »
Quote
Do contra-rots have the same pitch for the inboard and outboard propeller?


Props on any airplane very in pitch from the inboard to the tip as much as 20 degrees.

All engines will have the same props.

Thanks Hitech let me gather all this stuff I will get it to you as soon as I can. I have a lot on my plate right know so give me some time. I will probable just send you charts and figures I will type in the rest.

Straiga
« Last Edit: January 24, 2005, 01:26:55 PM by Straiga »
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Offline Schutt

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GScholz more ont turbo props:
« Reply #170 on: January 24, 2005, 06:29:04 AM »
This Thread looks a bit clutterd.

1. hitech did say P38 has the props the wrong way round, making for two critical engines.

2. someone else says there are no two critical engines.

3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?

4. torque on twin engined...the overall torque on the plane is around the center of gravity or?
In the famous drawing it is assumed that it is around the longitudinal axis, but that only works if there is such axis, as in a fixed mount and ther is not in a plane....
i think it is around the center of gravity, not around an axis, and when you apply it around that POINT twin engined get a diffrent momentum than one engined.

5. On top of this it is opposed by the stabilizing wings and tail, which makes the inflight behaviour eaven more complicated than just generating a torque around the CoG.
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Offline Straiga

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GScholz more ont turbo props:
« Reply #171 on: January 24, 2005, 01:43:48 PM »
Quote
3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?


Hey Schutt, Misunderstanding, I didnt say that a twin like a P-38 had two critical engines. I just said the P-38 rotation outward is a bad design. Frankly you can have only one critical engine at a time. Now for a four engine airplane this statement is true. The reason why some multi-engine airplanes have counter rotating props is to get rid of the effects when the critical engine dies.

I sent Hitech pages of info thats he is going to post for me so stay tuned. I sending more info also.

Later Straiga
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Offline HoHun

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GScholz more ont turbo props:
« Reply #172 on: January 24, 2005, 02:57:16 PM »
Hi Schutt,

>3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?

I think we all agree on the physical facts, the disagreement is actually just a question of nomenclature. Straiga of course is right that no engine is called "critical" when they are contra-rotating, and Hitech of course is right when the effect of the P-38's engines' sense of rotation is the same as being left with the critical engine on a twin with co-rotating engines.

>4. torque on twin engined...the overall torque on the plane is around the center of gravity or?

Ah, that question aims right at the core of the misunderstanding :-) Torque is not calculated around any certain point, it just adds up. You only have to consider an axis when you convert forces into moments.

>5. On top of this it is opposed by the stabilizing wings and tail, which makes the inflight behaviour eaven more complicated than just generating a torque around the CoG.

I'd say that while the entire system is complicated, the situation with regard to torque is very simple :-) The engines produce torque, something else generates an opposite moment. The side-effects of "something else" account for all the effects the pilots here describe (as I'm confident) absolutely correctly.

I'd suggest that the situation for the twin-engined aircraft is exactly the same as for the single-engined aircraft (on which we all seem to agree), except that due to higher rotational inertia, longer aileron moment arms etc. the rolling moment is much smaller than for the single so that it's submerged in the larger "side-effects" :-)

Regards,

Henning (HoHun)
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Offline Golfer

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GScholz more ont turbo props:
« Reply #173 on: January 24, 2005, 03:04:25 PM »
This whole thread has been a talk of not just torque exisiting (it does) or a twin having more torque than a single (it does, double in fact of a single with the same engine).

It's been about what's the torque do.  Does it have an effect on flight?  The answer is still no, for the reasons described above...there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment.  It all gets thrown into Yaw.

Anyway...I had an idea.  I talked to a buddy of mine, we did our multi ratings together and I am going to make a short video.  Aircraft will be a PA-23 Apache that we have access to.  It's going to be a multi-engine flying for dummies video tape but its going to show exactly what control inputs are used and when.

Now, if anyone has any idea how to get those little sony handicam 8mm videotapes magically transformed into an Mpeg, I am all ears.  We need to have that step figured out before we go burn a couple hundred bucks making the video.
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Offline hitech

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GScholz more ont turbo props:
« Reply #174 on: January 24, 2005, 04:01:15 PM »
Quote
It's been about what's the torque do. Does it have an effect on flight? The answer is still no, for the reasons described above...there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment. It all gets thrown into Yaw.


This is our basic disagreement.
Quote

It's been about what's the torque do. Does it have an effect on flight?


How it effects flight we realy do not disagree on.


Quote
there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment


It is this statment that I say is totaly inacurate.

HiTech
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Offline Golfer

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GScholz more ont turbo props:
« Reply #175 on: January 24, 2005, 04:20:53 PM »
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It is this statment that I say is totaly inacurate.


Well at least we made it through of 4 pages of garbage to wind up where we stood originally and have everyone sticking to their guns.
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Offline jigsaw

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GScholz more ont turbo props:
« Reply #176 on: January 24, 2005, 04:22:43 PM »
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Originally posted by Golfer
Well at least we made it through of 4 pages of garbage to wind up where we stood originally and have everyone sticking to their guns.


That's why I ejected earlier. Turned into a circular conversation.:D

edit- Regarding the video. King Schools has one. Easiest way to make a digital version of your own would be one of the Dazzle  products.

I used it to make my class project video for AVSC 1010.
« Last Edit: January 24, 2005, 04:30:27 PM by jigsaw »
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Offline jigsaw

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GScholz more ont turbo props:
« Reply #177 on: January 24, 2005, 04:25:49 PM »
Quote
Originally posted by Straiga
I just said the P-38 rotation outward is a bad design.


Ever since I first noticed the 38 was built that way I've wondered why. The only hypothesis I've come up with would be that it gets more lift from accelerated slipstream that way. Otherwise, I'm at a loss.
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Offline HoHun

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GScholz more ont turbo props:
« Reply #178 on: January 24, 2005, 04:40:44 PM »
Hi Jigsaw,

>Ever since I first noticed the 38 was built that way I've wondered why.

The XP-38 actually had conventionally-handed counter-rotating engines, but it was found that the slipstream over the centre-wing section disturbed the airflow and lead to elevator buffeting, so from the YP-38 aircraft onwards the direction was reversed.

Regards,

Henning (HoHun)
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Offline jigsaw

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GScholz more ont turbo props:
« Reply #179 on: January 24, 2005, 04:52:00 PM »
Hohun, I'd thought about interference drag with the nacelles and cabin destroying lift, but hadn't thought about  tail buffet. Thanks for the info.
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