RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)  
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RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/30/2007 11:15:56 PM   
normandouellette


 

Posts: 369
Joined: 3/12/2007
From: Laval, QC, CANADA
Status: offline 		Counter rotating props:

Yes counter rotating props are better. Standing behind the aircraft the left engine prop wash rotate and is divedrted to the right. This is why the left engine is called the "critical engine because the prop wash that gives "authority" to the rudder in a sudden engine failure and disables the airplane at lower speed to react positively aigainst a sudden undesired "Yaw" that will take it to a spiral dive. This is the reason why that in the case of an engine failure the engine you do not wish to lose in a low airspeed is the left one. If the right engine prop wash was rolling towards the center of the tail instead of towards the right side in the "air" it would give the rudder authority. This is why you whant the right engine to counter rotate. (you may stand behind any full power aircraft and you will notice how the prop wash is diverted to your right...at 5 feet your left hand has no wind and the right one gets all the wind (and grease if you run glow!)...I love this grease BTW.

If you are running electric the chance of a single engine failure is very little. If you do not counter rotate, this will imply a little right rudder action to maintain the aircraft on a straight axis once airborne and this is all...neglectabe. Unfortunately for me with glow engines the probabilities are higher and Saito or Os do not produce a counter rotating engine in this class...so a gyro might be my savior in this event!

Also counter rotating engines help the aircraft to fly "Clean" meaning it does not need rudder or aileron correction to fly coordinated and thus increase the airspeed and reduce drag. Counter rotate if you can.

(in reply to nemesis4u)
       Post #: 226

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/30/2007 11:21:36 PM   
p39


 

Posts: 256
Joined: 10/8/2002
From: New Ulm, MN, USA
Status: offline 		All what you said was more prevalent in a single rudder airplane.... like the A-20. With the twin tail like the B-25 the problems with one engine out were minimized

(in reply to normandouellette)
       Post #: 227

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/30/2007 11:33:12 PM   
flaviosi


 

Posts: 248
Joined: 3/2/2007
From: Rio de Janeiro, BRAZIL
Status: offline 		Timothy Thompson!

quote:

no contrarotating props


They don't charge you by word! Come on! Elaborate that! Why not?

Flavio

(in reply to timothy thompson)
       Post #: 228

RE: Top Flite B-25 ARF (Tecnical, tips, sugg... - 10/30/2007 11:46:24 PM   
normandouellette


 

Posts: 369
Joined: 3/12/2007
From: Laval, QC, CANADA
Status: offline 		P39

You may resume it the way you whant but the convergent propwash it help in using both rudder. Also why not have the use of both rudder if you can? This is an information site. Misinformation like resuming all is wrong because there is two rudder may lead some to conclude that counter rotating props are useless. Well all I reported is not made up by myself and please if you pretend some information is not to your liking try to overlook it and avoid misinforming some who may need it. thanx.

(in reply to flaviosi)
       Post #: 229

RE: Top Flite B-25 ARF (Tecnical, tips, sugg... - 10/31/2007 12:08:57 AM   
timothy thompson


 

Posts: 2761
Joined: 6/19/2004
From: saginaw, MI, USA
Status: offline 		The 25 had a large tail area and didnt need contrarotating props . The P-38 had small rudders and contrarotation made a very stable platform as a fighter-bomber. slipstream had a large effect on the big rudders of the 25 so contrarotation was not needed. Also inline engines (allison) were easier to convert back in the day they didnt have the cam issues radials do. It had to to with ignition timing.

(in reply to normandouellette)
       Post #: 230

RE: Top Flite B-25 ARF (Tecnical, tips, sugg... - 10/31/2007 12:15:48 AM   
p39


 

Posts: 256
Joined: 10/8/2002
From: New Ulm, MN, USA
Status: offline 		Norman- by "resume" I'll assume you mean presume... and what I was reporting was based on the full scale aircraft. Not a model.

(in reply to timothy thompson)
       Post #: 231

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 12:23:34 AM   
krproton



Posts: 533
Joined: 8/5/2007
From: Champaign, IL, USA
Status: online
quote:

ORIGINAL: nemesis4u

krproton ,

WHAT SIZE AIR TANK did you Use?

OK,,, I am going to use the 2 3/4 nose and 4" main ROBART WHEELS... Like the look better than the stock foamies...
Ordered the ROBART GEAR ALREADY... of course it is backordered....

I will add the bombbay... and some release mechanisms...

planning on a modified colorscheme.....

THANKS,

TOMAS



Hi Tomas.

I cheated, but didn't tell anybody until now. Originally, our show model got two to three cycles per charge. Therefore, when I built my model, I used the next-larger Robart air tank (I forget the size--I can find out). I would have to guess I could get about ten cycles! But this is crazy. But now that the levers and hinges have broken in on our show model, we probably get about five cycles per charge--plenty.

Should anybody decide to go to a larger tank, I suspended mine from the top of the fuselage bulkheads above the fiberglass tubes for the wings. Problem is, this made it a little tight for installing the nose steering servo--this doesn't effect the servo at all, it just makes fitting your hand and a screw driver a little tight when you mount the servo. You could mount the nose steering servo first though.

But truly, I have learned my lesson and the standard air cylinder (recommended in the manual and mounted in the front above the nose gear) is sufficient.

There you have it.

And yea, I have to admit the Robart wheels (you've selected the correct size) look a lot better than the stock foamies.

Keep us all updated on your build.

Tim


< Message edited by krproton -- 10/31/2007 1:20:21 AM >

_____________________________

Tim Lampe
Hobbico R&D

(in reply to nemesis4u)
       Post #: 232

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 12:44:19 AM   
normandouellette


 

Posts: 369
Joined: 3/12/2007
From: Laval, QC, CANADA
Status: offline 		Air Tank

Hey ho I shoulg go on with my build but the tank fits perfectly in the front, those holes are 100% and I will also have the medium tank installed for the gears...the front one will be to actuate the bomb bay and the brakes. For those interested the pn# of the medium tank by robart is: "Medium Pressure Tank #191" the brakes are pn# 140SET include the electronic gadient valve and all you also need to fit whit this is the wheels Pn# 13840A2 aluminium main wheels... I know it is nuts but those wheels and brakes will honor the TF B-25 and help it stop on a paved runway. The noze wheel is not yet available in 2.75 but according to robart will soon be. yeah my front air tank will be useful. Now i have to stop chatting and adding weight if I whant to be airborne this week end. Ps (I have plenty of power with my 82's)

Servo Wire,

You may run two 48 inch servo wires through the tube to the back pulling them (with the connectors offseted) with a cord and voila! nothing hanging around.

(in reply to krproton)
       Post #: 233

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 1:24:00 AM   
krproton



Posts: 533
Joined: 8/5/2007
From: Champaign, IL, USA
Status: online 		Hi Normand.

The primary test pilot of the B-25, who is building one of his own (from a leftover prototype), is also going to use the brakes. Really cool! I think he has chosen to use an additional tank, rather than replacing the intended one in the nose with a larger one.

This is a good option.

Tim

_____________________________

Tim Lampe
Hobbico R&D

(in reply to normandouellette)
       Post #: 234

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 1:45:05 AM   
kthmarks


 

Posts: 28
Joined: 3/11/2006
From: , GA, USA
Status: offline
quote:

ORIGINAL: normandouellette

.Ps (I have plenty of power with my 82's)



The Saito 82's fit.....no problem? Pic's would be great!

_____________________________

Keith Marks
AMA 49064

(in reply to normandouellette)
       Post #: 235

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 2:01:53 AM   
normandouellette


 

Posts: 369
Joined: 3/12/2007
From: Laval, QC, CANADA
Status: offline 		Oh yeah pictures coming soon; by friday and straight pipe with vp30 perry pumps. I have a pair Saito 82a GK on there and if you go to the previous thread about the 11th or12th posting there is a description of the prop and engines research I've made since TF announced the B-25. I should stop interupting my buils every time I hear the "ploop ploop" of the e-mail but what the heak I'm having fun.

(in reply to kthmarks)
       Post #: 236

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 2:28:38 AM   
sgoen


 

Posts: 50
Joined: 5/16/2005
From: South Bend, IN, USA
Status: offline 		Well, I ordered my Top Flite B-25 today. The hobby shop said it may not come in till the end of November or middle of Dec. now.

(in reply to normandouellette)
       Post #: 237

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 3:09:20 AM   
timothy thompson


 

Posts: 2761
Joined: 6/19/2004
From: saginaw, MI, USA
Status: offline 		more pics i added the square hatch, The round cover is where the crew would go to get into the cockpit or waist gun section. Its all styrene from evergreen. I have not patterns as its all scratch built. I have added a lot since these but its too dark to take good pics ill add them tommorow

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< Message edited by timothy thompson -- 10/31/2007 3:17:03 AM >

(in reply to Hellcat716)
       Post #: 238

RE: Top Flite B-25 ARF (Tecnical, tips, sugge... - 10/31/2007 12:24:48 PM   
mike-rc


 

Posts: 63
Joined: 2/13/2004
From: Port Washington, NY, USA
Status: offline 		I guess you are not very familiar with modern electric power. The power does not decrease as the batteries run down. You just have to know how long you can go. As your fuel runs out your CG is changing also.
I will work on the levers today. I will let you all know when I have them. I figure about $10.00 a set.

(in reply to Hellcat716)