prop clearance for twins

[lloyd schultz]

This message from lloyd schultz <lsefly@earthlink.net> brought to you by EFLIGHT!

Anybody have any formulae or SWAG as to how close two props can be
placed? It seems there might be a "too-close" distance where the inflow
to either prop might interfere with the inflow to the other, etc.

I intend to do a twin with the motors as close together as possible, and
have never seen anything written about this?????


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[PMisuinas@aol.com]

This message from PMisuinas@aol.com brought to you by EFLIGHT!

Actually, since nearly all the prop thrust is not from the propeller pushing air, but is from the airfoil of the prop "pulling" the model thru the air, you don't need to worry about separation. In fact, there is at least one full scale aircraft where the props overlap--the engines are mounted in the nose and staggered, with one a bit ahead of the other, and the prop arcs overlap considerably as a result. It's a high wing civilian cabin model (a Tri-Pacer variant or something like that I think--been too long since I saw the picture). So mount them in the model as you will--should not be an issue...Pete M

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[Steven Grimshaw]

This message from Steven Grimshaw <n7vqw@mac.com> brought to you by EFLIGHT!

This reminds me, there is a helicopter that has overlapping rotors
mounted at an angle and are sync'd so they do not hit each other. It
is designed specifically for lifting loads so close props must not be
to detrimental.

Just an observation as I am no engineer or designer or expert or
scientist or know it all.

On Monday, May 19, 2003, at 03:09 AM, PMisuinas@aol.com wrote:

> This message from PMisuinas@aol.com brought to you by EFLIGHT!
>
> Actually, since nearly all the prop thrust is not from the propeller
> pushing air, but is from the airfoil of the prop "pulling" the model
> thru the air, you don't need to worry about separation. In fact,
> there is at least one full scale aircraft where the props overlap--the
> engines are mounted in the nose and staggered, with one a bit ahead of
> the other, and the prop arcs overlap considerably as a result. It's a
> high wing civilian cabin model (a Tri-Pacer variant or something like
> that I think--been too long since I saw the picture). So mount them
> in the model as you will--should not be an issue...Pete M
>
> *** Any complaints or problems? Send an email to monitor@ezonemag.com
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I wonder how much deeper the ocean
would be without sponges.

Steven Grimshaw N7VQW
Richfield, Utah
N7VQW@mac.com


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[John B Swetland]

This message from "John B Swetland" <jbswetland@earthlink.net> brought to you by EFLIGHT!



> This message from Steven Grimshaw <n7vqw@mac.com> brought to you by
EFLIGHT!
>
> This reminds me, there is a helicopter that has overlapping rotors
> mounted at an angle and are sync'd so they do not hit each other. It
> is designed specifically for lifting loads so close props must not be
> to detrimental.

Sounds like the Kaman H-43 "Huskie"

Used for aircraft crash rescue/fire fighting in the US Air Force way back.

John S.



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[Rick Page]

This message from Rick Page <rick-page@shaw.ca> brought to you by EFLIGHT!

At the other extreme there are contra-rotating props on the same shaft so I
wouldn't be concerned about it. Its not that there is no interference --
just not a big deal for our models. Unless you are using a slowflight prop,
it should be able to handle the loads.

Rick.


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[Steven Grimshaw]

This message from Steven Grimshaw <n7vqw@mac.com> brought to you by EFLIGHT!

I happend to see a couple in use last year fighting forest fires here
in Utah. Looked like an upside down egg beater but sure could haul
water back and forth. Burned a lot of fuel too, seemed to go back to
base about every hour.


On Monday, May 19, 2003, at 01:13 PM, John B Swetland wrote:

> This message from "John B Swetland" <jbswetland@earthlink.net> brought
> to you by EFLIGHT!
>
>
>
>> This message from Steven Grimshaw <n7vqw@mac.com> brought to you by
> EFLIGHT!
>>
>> This reminds me, there is a helicopter that has overlapping rotors
>> mounted at an angle and are sync'd so they do not hit each other. It
>> is designed specifically for lifting loads so close props must not be
>> to detrimental.
>
> Sounds like the Kaman H-43 "Huskie"
>
> Used for aircraft crash rescue/fire fighting in the US Air Force way
> back.
>
> John S.
>


I wonder how much deeper the ocean
would be without sponges.

Steven Grimshaw N7VQW
Richfield, Utah
N7VQW@mac.com


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[Scott Asmussen]

This message from Scott Asmussen <asmussens@shaw.ca> brought to you by EFLIGHT!

> I happend to see a couple in use last year fighting forest fires here
> in Utah. Looked like an upside down egg beater but sure could haul
> water back and forth. Burned a lot of fuel too, seemed to go back to
> base about every hour.

I would take a guess and say the Heli's you saw were the Kaman K-max
helicopters

http://www.parkbull.com/snakingfire/kmax/

they are very impressive to watch in flight

Scott


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[Rick Page]

This message from Rick Page <rick-page@shaw.ca> brought to you by EFLIGHT!

>Anybody have any formulae
You asked for it. They call it the "overlap interference factor".
http://www.enae.umd.edu/AGRC/Aero/AHS2002_Griffiths.pdf

There is an interesting homebuilt tandem helicopter. Not quite available
yet.
http://www.lafhelicopters.com/EN/index_en.htm

I think you would be getting more interference from the fuselage if you get
the prop tips too close rather than from each prop.
There's an interesting review of the numerous twin configurations:
http://www.me.wustl.edu/~aiaa/AIAA_2001_Nov_85x11.pdf

Rick.


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