P.R. Racing

Hello guys and gals i'm pretty new to model airplanes and thinking about getting the bobcat 25 and 50 kit. It says it need 8 servos each: which servo do you guys recomend. which engine, prop ect any help would be nice before going and buying things i don't need or getting the wrong things.

Tailspincharlie

I have had a 25 Bobcat and yes it does have 8 servos. You should use HS 81's for the elevator and rudders and standard for the ailerons, throttle. You also need 18" extensions for
the elevators and rudders. It flys well with a OS 32fx really flys fast we clocked it at 107 MPH.

You will need the same servos for the rudders and elevators except they will be HS81's with the metal gears. I am running a Maxnum 52 with a 10x7 pusher prop. I still have it and it is very fast also 124 MPH. If your not really experienced I wouldn't go with these plane unless you have plenty of help.

Tailspincharlie

opjose

There is a huge thread on this plane in the RC Jets section.

PLEASE take the time to go through that thread.

P.R. Racing

Hello Tailspincharlie thanks for the info but what prop are you using on your bc .25 and opjose thanks for the rc jet info but ot's almost all bobcat 50

Migul

P.R. Racing

Hey were can I get the OS 32fx engine and are the hs 81 servos the same as standered mini servos and mini servos?

Tailspincharlie

I used a 9x6 apc pusher prop and you will have adequate clearence for the prop to the ground. You can order a OS 32fx engine fron Tower Hobbies for about 160 bucks there not cheap but well worth the money. You use standard mini servos.

I hope that that helps. Tailspincharlie

Tailspincharlie

I meant the standard servos are futaba 3004's you need 4 of them and 4 std. mini servos.

P.R. Racing

Hey Tailspincharlie thanks but what mini servos what number i mean, and do you hav any oic of your bobcat or what other hint can you give me.

Thanks Miguel

opjose

You may want to go through it anyway...

Things like angle of attack, elevator trailing edge zero setting, relative C.G. and spoilerons all come into play for the Bobcat .25 as well.

The best prep I had for the .25 was having built and flown the .52.

P.R. Racing

Thanks i did get some info in the jet fourm. I called towerhobbies to ask about the o.s. 32 fx and they told me it was discon. but the do have the .32 sx do you know the diffens between them and also what engine prop do you recomend for the .50 bobcat

Again thanks for all the help

P.R. Racing

Is the O.S. 55ax abl a nice chose for the bobcat .50??

opjose

The O.S. .55AX would be a good choice for the .52 bobcat.

Many are are also flying it with the Tower Hobbies .75 engine ( 2.2bHP ).

I'm flying mine with the GMS .76 ( 2.5 bHP ) ( current availability "late march" made by the same company that manufacturers the SuperTigres and T.H. engines ).

I would venture to say that the .75 or .76 may be a better match to make this a fast and powerful plane, not that the .55AX is a slouch either...

But to get the same performance levels out of the .55AX ( 1.75 bHP ) you need pipes, etc. so you have a somewhat greater expense for about the same or less performance.

Slap a Graupner 11x8 Pusher prop on the .75 or .76 and you have a great speed demon that scoffs at this thing called gravity.

The OS .32FX is the predecessor to the OS .32SX.

OS seems to have changed the liner material and the carb design in the SX, inproving both over the older .32FX.

The .32SX is getting a bit long in the tooth now though.

The bHP specs are identical for both.

P.R. Racing

ok opjose what about the O.S. 75 ABL engine? with an 11 x 8 zinger ??

opjose

Nothing wrong with that!

However AFAIK Zinger does not make any 11x8 pusher props.

You will need to use a pusher prop on this plane.

Graupners are the only 11x8 props that I have found.

I also cut down a 14x7x3 prop to about 12x7x3, but I found it about equal to an APC 11x7x2 Pusher in overall performance but lower RPM's and unloading in the air, so I went back to that until the Graupner's came in.

The Graupner is faster, but the plane is very good with the APC 11x7P.

P.R. Racing

opjose i was looking at the tower hobbies catalog and yes zinger makes an 11x8 pusher wood prop item number for $3.79

opjose

Yeah I looked again and found it.

It should be fine, though remember that the prop will be spinning at fairly high RPM's.

fll owen

OPJOSE. I was just reading your comments, as I just ordered the Bobcat 50 51 ad your info was very useful on the engine choice and performance. How do those Tower Hobbies engines stand up?
Also, with that engine and performance, what servos are you using on the elevator and rudder for that type of speed? Someone mentioned in another reply to us metal gear servos. HS81S I think they were stating.
Not familiar with that number, so I dont know who makes that servo. I think you comments on the prop choices are also good, And specific place to find those props easily the Graupner 11/8 P or the APC 17/7p?
Thanks Owen

P.R. Racing

This is going to be my set up :

Bobcat .25
O.S. 32 SX engine with a 9x6 zinger or apc prop

Bobcat .50
O.S. 75 AX ABL engine with a 11x8 zinger prop

Still need some help on the servos to use and tank size, extentions??

opjose

On the Bobcat 50 I used Hitec MG 225MG servos for the rudders and the elevator. I did NOT join the two rudders together as some have done.

I also used the stock setup for the elevator. I haven't had problems with it, other than the small caveat about what the actual "zero" point should be of the elevator...

I've used the Tower engines on many planes and they have held up very well. Parts can be had easily from Tower. I even purchased a used 3D plane from someone who had flown the .75 Tower engine it had for three years. The engine felt like it had lower compression as it was very easy to turn over... however I found that there was nothing wrong, and I flew it two more seasons, before moving it to another plane after I lost this one ( 3D Passion .60, the tail tore out due to a bad glue job by the seller...). It's ready to go in a .60 extra now...

The caveat with them is NOT to touch the needles as they come. Monkey with the needles and you'll be spending some time getting the engine dialed back in again.

The factory settings seem to be best to get it running initially. These engines do not come into their own until they've burned at least a gallon of fuel. After two tanks they break in enough to start tuning them.

Here's another caveat with these pushers...

The cylinder head tends to get HOTTER when the plane is on the ground because of the pusher prop.
When I went to tune up my GMS engine on a Bobcat 50, I seized it due to the heat. Fortunately it was not damaged, but this was a bit scary.

I was having a hard time getting the engine tuned until a friend pulled out a laser thermometer and aimed it at the engine head just below the glow plug.

It was reading about 400 degrees on a hot day, which is too much...

So after reading here that the head temps should be about 280 or so, I richened the engine until it hit 280+, and ran the plane this way for three tanks.

After that I had no problems tuning it for better performance. Note that you want it richer than you would normally set a tractor plane.

The engine unloads quite a bit in the air, and you will be tempted to go for speed at first. Resist the urge.... you want it RELIABLE first... speed comes later!

Re: Where to get the props.

Almost everyone sells APC ( Tower, Horizon, etc. )

Graupner's are another matter, I ordered mine through Hobby-Lobby. They have them in stock.

opjose

You'll be impressing everyone at the field.

I've found that many of the big jet guys at our field now believe, after seeing mine fly, that this is the way to go for someone interested in getting into Jets.

They believe it's the perfect intro, since it's low in cost, and you can afford to make mistakes with this setup versus 20K+ jet planes...

I often hear "not bad for a prop", and they all come over and look.


See above for the .50 servos.... I used cheap but powerful 130oz/in, TowerPro ( aka Hextronics ) HG5010 standard servos for the ailerons. Nitroplanes also sells these as their high torque analog servos.

For the .25, the larger micro servos work well, preferably higher torque ones, lest you strip gears too easily... I believe I used Hitec HS81's for the ailerons... and I've replaced the gears twice already... but this was due to inadvertently landing in the grass...


On the .50 I used the provided tank, facing forward. The .75 at FULL throttle will fly just more than 8 minutes with it.

Since I never fly at constant full throttle I set my timer for 8 minutes, and start looking to make a landing when it goes off.

It would be simple to install a slightly longer tank. You can cut the formers if you want w/o loss of structural integrity...

The turbine guys REMOVE THEM!!!!!! AND THEN fly with Turbines installled!!! Wow...

I cut the former at the front ( my front ) of the tank at the top, to make it easier to place and remove, and to facilitate getting foam in around the tank.

I'm awaiting on a glow engine for my .25, but I've flown the .25 with TWO 11v 3S 3900mAh packs in a 3S2P 22v configuration. This makes the plane fairly heavy, more so than what I would get with a glow engine, which is why I want to try a .32 in it with the default tank.

The provided tank should be fine for WOT 8minute+ flights as the .32SX consumes about .5oz/min at WOT once the engine is fully tuned.

opjose

To the both of you...

Make sure you set your planes up for Spoilerons. This REALLY aids bringing the Bobcat's down.

You'll be surprised at how fast this thing rolls at full deflection when it is at speed.

The little .50 SCREECHES at full deflection in a roll, because of aileron turbulence.

It sounds much like a 40% plane at full deflection... quite impressive for a small plane.


Remember that the "zero" point of the elevator is when you approximately have the TRAILING EDGE of the elevator control surface even with the TOP trailing edge of the elevator wing trailing edge, itself. It will appear to be slightly deflected up when the stick is centered.

Don't forget about having a positive angle of attack when the plane is sitting on the runway.



And view the on-line videos, paying particular attention to the landings. You'll see the pilots bring it down fairly quickly on approach.

P.R. Racing

Thanks opjose i'm planing on buying a futaba 7c 2.4ghz computor radio are the sevos that nitroplane sell or the ( aka Hextronics ) HG5010, Hitec MG 225MG compatable or do i have to stick with futabas? the receiver is a r617fs 2.4ghz fasst rx 7 channel

fll owen

Thanks for the follow up info.
I remebered that I had a Supertiger 75 sitting around and I may try that to start. That was a pretty finicky engine to get tuned right, so I may opt for the Tower hobbies.
Seeing that I dont have the model as yet, I guess there are some options on the rudder and elevator set up as you mentioned???
I have a smaller electric one and had to make several modifications to the CG position, horizontal stab position and engine size,as even that one required a bigger electric brushless than stated. Now it flies OK, so I hope this one is not as tedious. Great point on the engine heat, will look for that.
Where did yours balance with the larger engine? The weight on the ST and Towers engine varies by about 3 ounces.
Did you have to change the engine mounts to facilitate the larger engine and prop size?
Saw one before, where I think it was the same model, the guy made his own aluminum mounts as he said the wood mounts were not adequate.
Thanks again

fll owen

The idea of using spoilers seems great. How does the plane react with them deflected? Real drastic pitch down or mild, and does it cause any problem in the flare?
What deflection angle are you using?
I have a JR 9303 and and 7202 , think they can be configured for the spoilerons.

fll owen

Looked at RC Jets but did not see thread as you mentioned.