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push me pull me - 6/5/2004 3:16:17 AM   
yadamabiggs



Posts: 4
Joined: 6/4/2004
From: perth, BAHAMAS
Status: offline 		hiya guys

yadama from australia, here, i 2 am twin crazy, just finished ratting a worldstar40 into a twin now i would like to turn 1 into a pusher puller, any help ideas, pictures etc

greatly appreciated

yadama
       Post #: 1

RE: push me pull me - 6/5/2004 6:25:01 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		As memory serves, there was a thread not too long ago about a bashed "Pushme-Pullyou," but I couldn't find it just now.

Other than that, do a search on "Skymaster," "Mixmaster," "336," and "337." The two numbers are the fixed and retractable gear models, Mixmaster is a nickname of the Cessna Sktmaster.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to yadamabiggs)
       Post #: 2

RE: push me pull me - 6/6/2004 1:34:49 AM   
twinman



Posts: 1628
Joined: 1/19/2002
From: Katy, TX, USA
Status: offline 		Have any pictures of what you have done, and we can get the creative juices flowing. Not my plane, we can come up with all sorts of ideas!!!!!!!!
Twinman

(in reply to yadamabiggs)
       Post #: 3

RE: push me pull me - 6/7/2004 6:35:54 PM   
BattleAxe



Posts: 10
Joined: 11/9/2003
From: Oakland, CA, USA
Status: offline 		Twins are fun for sure and I really enjoy flying them as you do. Here's a photo of my scratch built twin motor plane. Maybe this will give a few ideas for your next project.

More photos and infomation at www.dawnaviation.com

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(in reply to yadamabiggs)
       Post #: 4

RE: push me pull me - 6/7/2004 6:41:11 PM   
Villa



Posts: 875
Joined: 8/12/2003
From: Wilson, NC,
Status: online 		Look for the thread Pusher/Puller to see the SPAD twin engine in Pusher/Puller configuration I designed and built.

(in reply to BattleAxe)
       Post #: 5

RE: push me pull me - 6/7/2004 6:54:47 PM   
Villa



Posts: 875
Joined: 8/12/2003
From: Wilson, NC,
Status: online 		Hi battleaxe
I'm still optimizing my twin. I use Magnum .28 engines and have been using APC 9-6 props. Mine weighs in at 6 pounds, a little more than yours. In the air it does fine, but getting off the ground is marginal. That is why I have been experimenting with different props. The 9-5 Zinger wooden pusher prop did not make the improvement I was hoping for. I have about 3/4 inch between the wing TE and the pusher prop TE. You seem to have a number of inches of clearance. I have wondered if this is causing the rear engine not to rev up properly during the take-off run and in the air. I use 10% Nitro in my engines. What do you use? I will be trying a higher %. My wing cord is 11" less ailerons, and they are 2" What are yours?

(in reply to Villa)
       Post #: 6

RE: push me pull me - 6/7/2004 7:48:07 PM   
BattleAxe



Posts: 10
Joined: 11/9/2003
From: Oakland, CA, USA
Status: offline 		Hello there, I use Thunder Tiger .25 engines with the APC 9x6 props. The rear prop arc is about 3 inches behind the trailing edge of the wing so I do have quite a bit more space than you have on your plane. I must say however, that I don't really see how this measurement affects the rear prop in a negative way. Think about how close the blade tips are in a ducted fan shroud. Yes, the shroud is there to direct the air through the impeller but the closeness of the shroud actually helps. Also, I think it's safe to assume that there is plenty of air coming off the front prop so you should have more than enough air passing through the rear prop. If your plane is like mine, you've probably noticed how effective the elevator is because of all the thrust coming off those two props. I'd bet my last dime that your rear prop is exposed to plenty of air.

If your rear engine is not reving up properly, my thought is that there's something other than the prop's relative position to the wing's trailing edge causing the problem. How does the rear motor run by itself? I usually run 15% Nitro but also run 10% if that is the fuel that is readily available when I buy it. My wing cord is 10-1/2" INCLUDING the ailerons which are 1-1/4" wide.

(in reply to Villa)
       Post #: 7

RE: push me pull me - 6/8/2004 3:06:26 AM   
yadamabiggs



Posts: 4
Joined: 6/4/2004
From: perth, BAHAMAS
Status: offline 		hey guys

thanx for the responses, i'm stilll in the planning stage, but have decided on a world star 40 for the skeleton, going to use 2 os 25's for power and see how we go

battleaxe r u running to tanks or just the 1?

i am in the bush right now, will post some photos as soon as i can...

(in reply to BattleAxe)
       Post #: 8

RE: push me pull me - 6/8/2004 3:49:31 AM   
yadamabiggs



Posts: 4
Joined: 6/4/2004
From: perth, BAHAMAS
Status: offline 		yo battleaxe

love ur site, the boomerang in particular, are u doin kits of the push/pull, cant seem to email u from the site for some reason....
u got any of ur planes flyin downunder????
yadama

(in reply to yadamabiggs)
       Post #: 9

RE: push me pull me - 6/8/2004 9:07:09 AM   
BattleAxe



Posts: 10
Joined: 11/9/2003
From: Oakland, CA, USA
Status: offline 		On the question of two tanks - the answer is YES, I run two different tanks on my twin. This has worked out to be a very good setup because in all the years I've flown this plane I've only had two occassions where I ran out of fuel and went dead stick. Actually, I'm surprised this has ever happened. What are the odds that two fuels tanks feeding one engine each would run empty within 5 seconds of each other?

Running the two tanks also eliminates many problems with fuel flow and pressure. I know of others who have tried using a single tank and had nothing but problems especially when it came to how to run pressure to the single tank. Running pressure from both engines to a single tank is a problem. With both engines connected to a single tank, when one engine quits, it affects the other motor because the mixture changes.

(in reply to yadamabiggs)
       Post #: 10

RE: push me pull me - 6/8/2004 2:22:46 PM   
Villa



Posts: 875
Joined: 8/12/2003
From: Wilson, NC,
Status: online 		battleaxe: My explanation was not clear enough. Let me try again. My rear engine is located about 1 inch above the wing at the wing TE. See http://www.rcuniverse.com/forum/Pusher%2FPuller/m_1806004/tm.htm . The leading edge of the rear prop is about 3/4 inch from the wing TE. So the 9 inch diameter prop DISC is about 60% above the wing and about 40% below the wing. When the clearance was much less, about 5/16 inch, the rear prop screamed like a siren. On the ground both props run about 12,000 RPM. I think the wing TE is interfering with the rear prop. Photo http://www.rcuniverse.com/forum/upfiles/62019/Rp42293.jpg shows the problem.

(in reply to BattleAxe)
       Post #: 11

RE: push me pull me - 6/8/2004 6:12:38 PM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Tony and Rudy:

A single fuel tank can be used with multiple engines, and give excellent results. But muffler pressure and/or header tanks wont do the job.

Using pumped engines, either with built-in pumps or accessory pumps from Perry, the single tank gives no problem. This is my preferred way.

The other way is using Iron Bay or Cline regulators. Works well,

Two reasons I prefer the pumps. Cost is about 1/2 the price of the regulators, and I don't like having the fuel lines running the fuel under pressure.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to Villa)
       Post #: 12

RE: push me pull me - 6/8/2004 9:24:01 PM   
BattleAxe



Posts: 10
Joined: 11/9/2003
From: Oakland, CA, USA
Status: offline 		Bill,

I agree with you totally IF you want to use pumps, one fuel tank can work very well. I'm one of those guys who lives by the rule - Keep it simple. Although I understand and have used pumps on engines in the past, I'm able to get excellent results using two tanks and running pressure to each tank without the added expense and detail of using pumps.

I actully started out using one tank mounted directly over the CG. I figured that would be a great setup - no change in CG as the tank emptied. Then I realized that I could run a single tank dry and kill both motors at the same time. That's when I thought running two separate tanks would lessen the possiblity of loosing both engines.

Isn't this a great hobby? There are always multiple ways of doing things. One way is not right or wrong, it's just different.

< Message edited by battleaxe -- 6/8/2004 1:25:08 PM >

(in reply to William Robison)
       Post #: 13

RE: push me pull me - 6/8/2004 9:48:37 PM   
BattleAxe



Posts: 10
Joined: 11/9/2003
From: Oakland, CA, USA
Status: offline 		Hello Australia,

Yes, I have sent a couple of Boomerangs to Australia. At least a couple of your mates might be flying these birds down under.

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< Message edited by battleaxe -- 6/8/2004 1:51:53 PM >

(in reply to yadamabiggs)
       Post #: 14

RE: push me pull me - 6/9/2004 9:05:19 AM