Overpowered

My Feedback: (14)

I started putting mine together and have a few choices of engines in my shop that may work.

With the recent post from Opjose with a GMS 76, I might not be far off on powerplant. There are just too many posts to get my answers so maybe someone can help me with a quick answer

Let me know your thoughts.

MDS 78
ASP 91
Thunder Tiger 80 4 stroke

I know between the heavy enginge and pretty heavy servos I'm going to nead a lot of weight up front.

What props would be advised - looks like 11'' is really pushing ground clearance

Eric

BillS

There are 119 pages of posts answering your questions and many more not asked. It takes a while to read but is well worth the additional information provided. There are many questions answered that may not have been considered.

Availability of pusher props is a strong criteria for engine selection. No need to pick an engine that needs a prop which is not available. Engine weight is also important. Engines above 16 oz. to 18 oz. (with muffler and prop) are likely to require weight up front to compensate. The rpm that 4 stroke engines operate is not likely to produce a speed demon.

The thread is a worthwhile read.

Bill

Stick Jammer

The engine blocks that come with the plane are only about 1/8" short of the clearance needed for a larger engine, not enough to worry about thrust line. You can simply add some 1/8" aircraft ply under the blocks or fab some new blocks. I chose to make new ones out of hardwood because the stock blocks are a little too soft for my liking.

Overpowered

My Feedback: (14)

BillS - Thanks for the reply.

I will skip on the 4 stroke and hopefully someone can help on the engine selection/prop availability on what has worked for them.

I started reading the thread weeks ago (swamped at work keeping me from getting thru it all) , there is a lot of guessing going on early and I hope it starts to summarize on what really works instead of detailed reports on how crashes have been repaired. I want to fly this one right (out of the box), not right by picking and choosing conjecture from others.

It would be great to see a few people post their entire setup (if it flys) including Engine, Rotation if reversed, prop, servos, CG, all up weight, angle of incidence, throws, exponential/D/Rs, Flaps/Spoilers and elev compensation, LG used (stock fixed, retracts, altered, location), Wing attachment, modifications.

Picking and choosing from multiple setups can leave you with the worst combination of flying (or crashing) characteristics. Like cross breeding dogs to get certain attributes - (cross a Lab with a Chiuaua to get a friendly small dog but end up with the wrong attributes of each - a vicious big dog)

Cheers
Eric

Stick Jammer

Overpowered,
Keep reading, answers to all of your questions and MUCH, MUCH more useful information is all here as you progress through the thread.

AGR413

My Feedback: (1)

I have changed some things since then like metal bolts for the booms but here is the review I did and it has most of the important stuff in it.

http://www.rcuniverse.com/product_gu...65&kit_id=4554

mattosan1

[>:]Phantoman, As you said the motor mount is aluminum angle and looks like it will work well. I will know as soon as I can get to the air field and fly this thing. Anyway I have tested this set up several times and all looks to be ok. Matto..


[>:]Stick Jammer, I am taking your advice and have purchased a .46 OS. This engine is scheduled to arrive Mar 3~5. Thanks for the advice. I have 9 electrics and it's high time to get a nitro. Keep you posted... Matto..

Stick Jammer

mattosan1,
Glad to hear your gonna try nitro but you're probably gonna be a little disappointed with a .46 on this plane. You didn't specify if you're getting the .46LA or the .46AX. The OS .46LA will likely never fly this plane. The OS .46AX is a great engine but it's a little short on power for the Bobcat. If you can stop your order and upgrade to an OS .55AX you'll be a lot happier.

opjose

I'll second what StickJammer says on the engines.

An AX .55 will be a much better choice.

Many people are flying the plane with engines up to .76 2C in size.

Team_Monkey

Hello gents, Long time lurker here. I've been keeping pace on the reading while I build my clone.

It's true guys, the major posters aren't kidding. Lot's of good info in 118+ pages.

So the "PlastiCat" is about finished. I need to hookup the rudder pushrods and shrink up a canopy yet.
Here is the build thread
http://spadworld.net/forum/viewtopic.php?t=14650

Sorry I'm at work and can't get to putfile, but I can add short cuts to some pics:
http://www.putfile.com/pic.php?img=7616052
http://www.putfile.com/pic.php?img=7616053
http://www.putfile.com/pic.php?img=7616054

She came out kinda pretty I think.
I'll just lurk again until the maiden. [8D]

AGR413

My Feedback: (1)

Good to see you here TM, welcome to the fray. I keep a look out for new posts to your thread a spadworld. I think Spad jets is a frontier we need to expand in the spad side of the hobby, looks like your setting the bar pretty high.

hapyjac2

My Feedback: (927)

Hey TM,
Good job! keep lurking and keep them Spads a comming.

Hapyjac

www.southfloridajettogether.com

flt lt hurdy

HA...why not go in-between and stick a OS61FX in it...

opjose

Why not go .75 then?

flt lt hurdy

...or Wren 44 Gold...

lol

opjose

Well that's the only way to do it properly!

A bit much for my pocketbook though.

Stick Jammer

The OS .61FX is 5 ounces heavier than the .55AX with just a small gain in power. Five more ounces of engine = more lead up front.
An OS .75AX is 8 ounces heavier than the .55AX and most likely would be unable to efficiently prop.

Strykaas

IMHO, the gain with big props should be marginal... However, I think you could rev it way higher with small props as it surely has a higher fuel throughput. Anyone ?

AGR413

My Feedback: (1)

I have heard the FX motors are better "speed" motors, where as the AX are more torque.

Stick Jammer

I'm not sure that's an accurate description. Any two cycle glow engine gets its power from RPMs. Basically the only difference between the FX and the AX is the new Bi-Metallic Liner which is supposed to increase compression and last longer. At any rate, they are both very good engines.

Wingspam

Hey guys I need some help with my Bobcat.
I am having rough time getting smooth takeoffs with this plane. I have 4 flights on this plane and 3 of the 4 take offs where near death, for the plane.

I am rolling down the field for take off and around half throttle or so the plane will JUMP into the air. I mean really jump into the air, with almost no air speed. So far I have been lucky to maintain level fight until the air speed builds up. Once in the air it fly's great almost hands off...

Can anyone offer any suggestion as to why this is happening. I am assuming it is due to the Cg. It is set per the instructions

It is powered by an Os 46x, stock muffler w/ 11x6 P

Thanks

AGR413

My Feedback: (1)

Well to be completely accurate two cycle glow engines get their power from the the ignition of a mixture of fuel and air. This is a function of how much air and fuel it can efficiently intake and exhaust once it is burned, and how well it translates this energy into mechanical energy. In the case of two stroke engines, different bearings intake and exhaust porting schemes, different stroke length, head polishing or shimming can also affect performance and also affect what the engine does more efficiently produce high RPM with a smaller prop or swing a very large prop at a lower RPM.

You could set up two otherwise identical engines differently one to swing a smaller high pitched prop at a higher RPM, to produce greater pitch speed. The other to swing a large, low pitch prop for static thrust at a lower RPM.

While this may not apply to the two engines mentioned (I was only reporting what I had heard) the concept is sound.

AGR413

My Feedback: (1)

What do your instructions say? The generally accepted sweet spot is 10.3 inches.

opjose

If the model flies well in the air, but you are having problems at take off, it's not a C.G. issue per-se.

Rather it's the wing angle of attack relative to the ground, as the plane rolls down the runway.

Basically your wing is either level or slightly LE down.

Since acceleration pushes the front down, even a perfectly level Bobcat will have this problem too.

You need about 2 degrees of postive wing incidence ( LE slightly higher ).


The easiest way to achieve this is to adjust the gear length or wheel sizes.

I had exactly the same problem, as documented earlier inn this long thread.

Adjusting the angle of attack solved the problem.


BTW: we have gone over this numerous times. It behooves you to go through the entire thread.

Stick Jammer

Hmmm, any idea what happened to my last two posts on 3/3/08? They were here, now they're gone.