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RE: Nitro models pusher Bobcat? - 8/20/2006 8:50 AM   
topper5


 

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From: SPRINGVILLE, UT, USA
Status: offline 		just a quick reminder to all that are setting up a pusher prop, no mater how you do it make sure your fuel clunk is to the back of the tank, i got my tank in and realized my clunk was in the nose of the tank and my first flight would have ended up in a quick dead stick.

KNOWCRASH: the fact of the balancing my tail heavy bird scares the h... out of me, to get it balanced on the 175mm CG is gonna be a nightmare, kinda like flying a winged anvil, take off will be fine but landing will have to be FAST because anvils don't float.

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RE: Nitro models pusher Bobcat? - 8/20/2006 3:10 PM   
knowcrash


 

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Status: offline 		topper 5: i did the same but luckily a fellow modeller said i should turn the tank around for that same reason. also, i was lucky that the plane would not take off because too much nose heavy. has anyone actually flown one of these? i'm taking mine to the field today and i hope it doesn't come back in a body bag. btw i took the 91 off and put a K&B 7.5 w/pipe to help the balance.

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RE: Nitro models pusher Bobcat? - 8/20/2006 4:28 PM   
G-ROOKIE


 

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Hi Knowcrash!

When you get to the field check every thing and give us an update asap. Also take some pic's of it taking off and landing. One more thing, which way did you position your fuel tank ?

Thanks again and good luck on your flight today.

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RE: Nitro models pusher Bobcat? - 8/20/2006 5:10 PM   
rhklenke



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quote:

ORIGINAL: knowcrash

hay guys has any one checked the CG on the bobcat (WITH OUT THE MOTOR), just for fun i checked mine (RETRACTS & RADIO INSTALLED) and I'm so tail heavy it's not funny,

i put mine together with a 91 magnum xls and i could not put enough weight in the front to balance at the recommended cg. can anyone enlighten me on this. seems like the instructions are way too far forward.


Ah, now the Achilles heal of Nitroplanes comes out! There is a thread in the Seaplane forum about the Nitroplanes Seawind and guys were raving about how much better it looked than the Great Planes one. Then somebody tried to fly it... Turns out, it won't fly (or flys like crap, if at all). In fact, in the only picture of the Seawind on the Nitroplanes site that shows it off the ground, you can clearly see the feet of the guy standing behind it that just threw it!

I hope it works out with these things, but it may be that it looks much better than it flys...

Bob

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< Message edited by rhklenke -- 8/20/2006 5:17 PM >

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RE: Nitro models pusher Bobcat? - 8/20/2006 7:47 PM   
kmtranmd


 

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Status: offline 		Test flight report please. And share with us your set up if it worked out well for ya.

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RE: Nitro models pusher Bobcat? - 8/20/2006 9:37 PM   
Canardman



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Status: offline 		I have mine ready to fly, I had to add 1.5 pounds of lead to the nose. Now I fear having a wing break off in flight. I'll let you guys know how it flys this week.

Specs:
O.S. 61
hitec 645mg on wings
hitec 225mg on ele,
Hitec 225bb on rudder
futaba 3004 on steering and throttle.

< Message edited by Canardman -- 8/20/2006 10:08 PM >

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RE: Nitro models pusher Bobcat? - 8/20/2006 10:01 PM   
EASYTIGER


 

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quote:

ORIGINAL: booker-RCU

quote:

ORIGINAL: mr_matt

Sorry maybe I am on too many "Ignore" lists :-) I will try again.....

Do these models have flat bottom (Clark Y) airfoils?


Thanks!!



Yes they do.

Galen




That's the smartest question ANYBODY has asked.
With a flat bottomed airfoil, the plane may trim out and perform dramatically different from the original Bobcat. Be prepared!

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RE: Nitro models pusher Bobcat? - 8/20/2006 10:08 PM   
mr_matt



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Status: online 		Hi G-ROOKIE and B58,

First before we get all lathered up, I would never recommend that anyone buy one of these models, for a prop or otherwise. Many of these new ARFs look like they have never been even test flown, and I would never buy a kit that had never been flown to my satisfaction (and not just one tentative flight, but demonstrable consistent flight performance)

I think the incredibly low prices on these planes are very seductive, but given the relatively massive investment needed for ANY turbine to put on the plane, I think the low kit costs makes this false economy.

As a strictly technical exercise, I believe this plane (if it is the one I saw at my field) could be flown with a JetCat P-60. With internal modifications, I think the plane could hold well over 40 ounces of fuel yielding a 6+ minute flight time. On the other hand, I have no idea how difficult it would be to balance, and in turn how heavily loaded it would be after balanced.

As stated, I would look at this strictly as a technical challenge, NOT as a good way to spend hard earned hobby dollars. There is no free lunch, and the quality TURBINE models in this hobby can be easiliy identified just by going to a flying field. It is just like when you are deciding on a turbine.....take a break from RCUniverse and go to a jet rally and you will see what really flies and who is really having fun.

Regards,





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RE: Nitro models pusher Bobcat? - 8/20/2006 10:14 PM   
EASYTIGER


 

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quote:

ORIGINAL: rhklenke

quote:

ORIGINAL: knowcrash

hay guys has any one checked the CG on the bobcat (WITH OUT THE MOTOR), just for fun i checked mine (RETRACTS & RADIO INSTALLED) and I'm so tail heavy it's not funny,

i put mine together with a 91 magnum xls and i could not put enough weight in the front to balance at the recommended cg. can anyone enlighten me on this. seems like the instructions are way too far forward.


Ah, now the Achilles heal of Nitroplanes comes out! There is a thread in the Seaplane forum about the Nitroplanes Seawind and guys were raving about how much better it looked than the Great Planes one. Then somebody tried to fly it... Turns out, it won't fly (or flys like crap, if at all). In fact, in the only picture of the Seawind on the Nitroplanes site that shows it off the ground, you can clearly see the feet of the guy standing behind it that just threw it!

I hope it works out with these things, but it may be that it looks much better than it flys...

Bob


That is one cheesey photo!
But I don't think all is lost.
I think a LOT of these planes end up in the hands of modellers who NEED a full instruction manual and need their hands held.
These kits don't provide diddly in the way of documentation. Part of the price, I guess. But you will find that most of them build and fly just fine, I've had a few of the Nitromodels planes, can't beat them at the price. Can't speak about this Bobcat, have not had one yet, but chances are it will fly just fine. Yes, it might need noseweight, and yes, it might be up to you to figure out the CG and throws and such, and yes, you might need to check certain aspects of the construction, but if Great Planes sold it, yes, you might get much better support...but it sure ain't going to be $129! And you might STILL have problems.
Other side of the coin is it's a SUPER bargain at $129...unless it folds a wing on the first flight. Then it's not such a great deal!
But I think chances are the plane will fly fine.

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RE: Nitro models pusher Bobcat? - 8/20/2006 10:53 PM   
EASYTIGER


 

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quote:

ORIGINAL: mr_matt

Hi G-ROOKIE and B58,

First before we get all lathered up, I would never recommend that anyone buy one of these models, for a prop or otherwise. Many of these new ARFs look like they have never been even test flown, and I would never buy a kit that had never been flown to my satisfaction (and not just one tentative flight, but demonstrable consistent flight performance)

I think the incredibly low prices on these planes are very seductive, but given the relatively massive investment needed for ANY turbine to put on the plane, I think the low kit costs makes this false economy.

As a strictly technical exercise, I believe this plane (if it is the one I saw at my field) could be flown with a JetCat P-60. With internal modifications, I think the plane could hold well over 40 ounces of fuel yielding a 6+ minute flight time. On the other hand, I have no idea how difficult it would be to balance, and in turn how heavily loaded it would be after balanced.

As stated, I would look at this strictly as a technical challenge, NOT as a good way to spend hard earned hobby dollars. There is no free lunch, and the quality TURBINE models in this hobby can be easiliy identified just by going to a flying field. It is just like when you are deciding on a turbine.....take a break from RCUniverse and go to a jet rally and you will see what really flies and who is really having fun.

Regards,





Good points...there is a bottom line here, which is you are guinea pigging putting a turbine on this plane, and the ultimate price COULD be a smooshed $2500+ turbine engine when it hits the dirt. That's life on the bleeding edge. Big difference between putting a pusher prop on it and a turbine, risk-wise.
Me, I think pretty much ALL of these models ARE indeed flown in China before being released...but I'd be pretty sure nobody tested it with a turbine.

My guess is the plane with be fine with an MW44, but that remains to be seen.

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RE: Nitro models pusher Bobcat? - 8/20/2006 11:03 PM   
B58


 

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Status: offline 		As in my earlier post, pusher glow first. And I am using an OS 91FX. That is comparible weight wise to a Wren 44, and the power shouldn't be too far off. However, it is about $2300 less of a risk. I would not suggest anyone do the turbine on this until some of them are flying. The quality does look pretty good, and it seems well engineered. But such things as one screw on each side of the fins to hold the stab, fairly short wing tube, question of cg, these are all things that need to be worked out. I am going to reenforce the forward boom mount screw also. another week or two and there will be some experiece some folks can pass on to the rest of us. I do have two of them, and they arrived in good shape and look very good for the price. Bob

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RE: Nitro models pusher Bobcat? - 8/20/2006 11:38 PM   
knowcrash


 

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Status: offline 		rain delay on my test flight today will be next weekend before i get to try again. someone please fly their's first and give us an update.

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RE: Nitro models pusher Bobcat? - 8/21/2006 12:56 AM   
topper5


 

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OK well it looks like mine will be ready Tuesday or Wednesday, with my ys-45 and tuned pipe stretched up the side, and a 2400ma C cell battery stuffed in the nose it comes surprisingly close to balancing, just a few more small issues with my retracts and working out my canopy hatch latch and ill be air-borne.










< Message edited by topper5 -- 8/21/2006 1:04 AM >

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RE: Nitro models pusher Bobcat? - 8/21/2006 3:33 AM   
jimbo1846


 

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Status: offline 		Nitro models was holding a second kit for a friend and he canceled & I got it.

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RE: Nitro models pusher Bobcat? - 8/21/2006 7:19 AM   
G-ROOKIE


 

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Status: offline 		Make sure you guy's move everything forward and try putting the fuel tank in the first bay area not in the rear. Aslo make up your nose weight with a larger battery. Anything with twin booms is always tail heavy.

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RE: Nitro models pusher Bobcat? - 8/21/2006 8:08 AM   
eaticus


 

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Status: offline 		I am not sure if this is appearant. I think the CG location as indicated (6.9 inches) may assume that the plane is balanced with an empty tank. (My JHH Mirage has tank aft the Aero Center and the instruction indicated to balance plane with a full tank)

Based on calculation from http://jef.raskincenter.org/published/balance_point.html , Aerodynamic Center should be 9.74 from L.E. of wing root. Based on graphical solutions, Aerodynamic Center should be 11" from L.E of wing root (assuming 25% chord). Attached is a picture illustrating my graphical solution (aero experts, please make necessary corrections.) Therefore assuming balancing with a full tank, the CG should be between 9.74" and 11".

Thanks

Dave



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< Message edited by eaticus -- 8/21/2006 8:38 AM >

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RE: Nitro models pusher Bobcat? - 8/21/2006 8:12 AM   
CARS II


 

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Status: offline 		All this talk and no flight report yet.

Man, is any one going to fly one of these airplanes soon?

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RE: Nitro models pusher Bobcat? - 8/21/2006 3:08 PM   
flyrcjets



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Status: offline 		I hear you Carlos..all sold out and nobody's flown one!

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RE: Nitro models pusher Bobcat? - 8/21/2006 3:20 PM   
G-ROOKIE


 

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Status: offline 		I have a friend that has one arriving today by fedex. He will have it build and up in the air this week and i will let you all know, he is using a OS 61 fx.

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RE: Nitro models pusher Bobcat? - 8/21/2006 4:56 PM   
EASYTIGER


 

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ORIGINAL: CARS II

All this talk and no flight report yet.

Man, is any one going to fly one of these airplanes soon?


So true, but on the other hand, who wants to drop everything to build an ARF pusher prop just to please some people online?

Something to consider, also, is that you might want to cut back part of the rear fuselage to get the engine further forward if you are trying to balance with a turbine....

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RE: Nitro models pusher Bobcat? - 8/21/2006 5:55 PM   
knowcrash


 

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Status: offline 		11" from leading edge instead of the 6.90 makes alot more sense when actually trying to balance one of these things. 6.90 from trailing edge would seem closer to this measurement. on the other hand i have very little jet experience. that's why i love these forums.

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RE: Nitro models pusher Bobcat? - 8/21/2006 8:00 PM   
Bob.R


 

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Status: offline 		FWIW, I believe the graphical technique shown below is more accurate for wings with a high taper ratio. Setting the cg at 25% of the MAC is usually a safe number for a prop sport plane. As for this pusher BobCat.........I would think 25% would be close, but a number of factors enter into the calculation.

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< Message edited by bobber -- 8/21/2006 8:17 PM >

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RE: Nitro models pusher Bobcat? - 8/21/2006 8:08 PM   
1Eye



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quote:

bobber replied . . .
. . . I believe the graphical technique shown below is more accurate for wings with a high taper ratio.

Good catch! The other component that needs to be taken into account is the (slight) amount of lift from the fuselage that's forward of the MAC reference. As a result, if you use 22% MAC for the CG location, it more closely approximates that of the instructions - my 2¢ worth. (I'm not an aerodynamicist, but I did stay at a Holiday Inn a while back.)

Mike


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RE: Nitro models pusher Bobcat? - 8/21/2006 8:25 PM   
Bob.R


 

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Status: offline 		Mike, I'm not an aerodynamicist either - should have thrown in that disclaimer. You are right about the fuselage effects. Also, pitching moment from the flat bottom airfoil and elevator size and its location relative to the wing MAC enter into it. I have measured the Composite BobCat, and as I recall, the recommended CG is around 23% MAC. However, I don't think you can blindly use that number without comparing all other factors.

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RE: Nitro models pusher Bobcat? - 8/21/2006 8:34 PM   
1Eye



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quote:

bobber again:
. . . You are right about the fuselage effects.

Heh, heh, I found that out the hard way when I arbitrarily extended the nose on one of my ByroBlaster Enforcers - the jet was extremely pitch sensitive (doh) and the CG had to be move forward to compensate. I think the CG location for the NitroModels rendition is pretty darned close.

The 1st of the 2 yellow-flavored ones I ordered arrived last week. What a great thread! We're going to have fun with this airframe.

Mike


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