Stick Jammer

Sorry, All Up Weight. (flying weight with empty tank)

ExcaliburIII

BTW don't put too much elevator throw in this thing or you will find out about high speed stalls and the snap roll that follows which is immediately followed by rekitting and subsequent weight gain caused by gluing all the little pieces back together. Don't ask how I know because it makes me use the acronyms FUBAR and DF over and over.

Rich

Stick Jammer

Good advice. Although it does appear that a fairly good amount of high rate elevator is necessary for landing. Anyone know how much?

NM_Mark

My Feedback: (8)

LOL - I did the same thing, but fortunately I was high enough to recover from the OMG moment. I think I have 13mm in each direction, but plenty of expo to help smooth it out.

Mark

AGR413

My Feedback: (1)

If you get the CG back where it needs to be you won't need much to land, the most important thing with this plane is to establish a good glide slope without getting the nose up too high you can't flare and drop this plane or it will bounce and bend the landing gear.

patzane

As this is a very long thread it a lots to read. I was looking to purchase one of these and need a few questions answered if someone can help please.

How many servos do I needs and what is the best servos to use per surface?

What model and size engine will give the best profrance. I like speed so I want to rip the sky. Also what prop.

Looking to order one tonight as well as get the things I needs for the plane tonight from tower

omega-RCU

AGR413 and others, thanks for info about wights.
Is there anyone on the thread that's flying the Bobcat Electric?

This configuration is ontop of my list for now
Motor: Hacker A50-12L, CC Phoenix 85HV, Flightpower EVO 3700 mAh 10S1P, APC 12x8 E Prop.

With MotoCalc this would give me 10 lb of thrust, 92 mph prop speed and a ready to fly wight of 8.5 lb.

PointMagu

My Feedback: (11)

patzane,

For each of your 3 questions there are 3 pages of answers.

I wouldn't shortcut to anyone's individual answer. I'd compare what's being used, flown and what those results are to make a more informed decision as to what may be best suited to your needs.

Personally, I just can't see the economy in using 2-rudder servos and 2-elevator servos. I installed a HiTec MG125 aileron servo into the horizontal stab for the elevator. I'm driving the rudders with a Central Hobbies, carbon fiber connecting rod pushed by a JR standard servo mounted inboard on the starboard tail boom. If I could figure out how to couple the nose gear to these, I'd dump that servo too. More servos=more current drain on the battery pack, more weight, more wiring and more headaches, (IMO, of course).

Engine choice is highly debated here. You'll see everything from turbines to electric. Ducted fans, .46's, .50's, .61's, .75's, .91's, etc.

What I like about the Bobcat is the ease with which powerplants can be swapped out. I plan on bolting up an MVVS .40 with tuned pipe for my solo. Once I have the plane trimmed out, learn it's characteristics, I have an OS .61 pumper that I'll tinker with next. Speed is fun but flying the plane and not the prop is where I've been most my life. Hanging an anvil of an engine on the butt of this plane doesn't appeal to me so, "light is better" holds true here as well. Another argument for reducing that servo count...

Prop clearance is another limiting factor. You can only go so far as to prop size and then, selection of a pusher style within that diameter to get the pitch you may want. There are lotza variables.

Once more, another argument for reading through the various posts regarding the topics you are most focused on to see whats working best for other folks.

Enjoy your Bobcat, whatever decisons you make to get her to perform.

PM

Stick Jammer

While I am all for weight savings, reducing the amount of servos in this example doesn't really save any weight. A Hitec HS-85BB servo weighs .67 oz. each, 1.34 oz. per pair. One standard servo on either the starboard or port side for rudders weighs more than a pair of HS-85BB,s but does save some money. Modifying the stab to accommodate an HS-125MG and routing the wire is a bit of a headache. The single HS-125MG weighs .84 oz. as compared to (2) HS-85BB at 1.34 oz. but the HS-125MG is 6" farther behind the CG so I'm not so sure there is much if any weight savings there either. I personally wouldn't trust a single HS-125MG to handle the elevator as it is a mini servo and has the same torque rating as a single HS-85BB. I do agree with keeping the powerplant on the light side, seems the OS .55AX is a pretty good choice for the money.

PointMagu

My Feedback: (11)

patzane, Stick Jammer has reinforced my observation that to listen to a single source rarely provides you with the best solution to your questions, lol...

Thanks, Stick Jammer!

To focus upon any single aspect of a project without considering the entire picture, can be misleading. I fly standard servos on all my aircraft with the exception of my Goldberg Sukhoi and Kaos 90. I'm a sport flyer, fly weekends as a rule and don't compete. In my world, hanging 4-standard servos behind the engine doesn't compute. I spent $125 on the Bobcat. If I can't use the equipment I have on hand, I'll spend abit additional to get that item or two. The HiTec MG125 is a classic example. Torque on the 125 is similar to standard servos that I own and as I've never experienced a failure using them, I have confidence that this one will perform in similar fashion. The only way I'll know that is to fly the airplane and see. So in my world, without buying the lightest, torque-E-ist and smallest footprint servos out there,($$), using the one HiTec 6" behind the CG rather than 2 standards in each boom, does save me weight. Total ADW, (all-up dry weight) is my goal. Wing loading should be as light as possible. Balance does play a role in this as adding lead to the nose contradicts my aim. So hanging the one servo further back does present it own unique situation.

I acknowledge that there are better, faster AND lighter solutions to flying the Bobcat. I'd be a fool to think otherwise.

My post is but one of many...

PM

Stick Jammer

True, the torque ratings are close but the HS-125MG is a mini servo which would be my concern.

This is very true and I'm all for using what you have but the Bobcat's stock design is for two mini servos on elevator. The stock locations would need to be cut larger for two standard servos which I agree is too much weight back there.

As you stated, that's one of the benefits of this site, lots of info and opinions!

patzane

So the elevator use 2 mini servos.
What about the rudder alir, thro, frist wheel.

Also do the OS 61 has more power than the Tower Hobby 75. I think I seen that somewhere on here

I just order this plane last night and expect to be here wed.

Stick Jammer

Plane is setup for eight servos. Two mini's on elevator, two mini's for rudders, two standard for ailerons, one standard for throttle, and one standard for steering the nose gear. As PointMagu mentioned, some are using one standard servo for rudders with a link between them and some are doing mods to the stab and using one servo for elevator. If you go with the stock setup of two servos for elevator you'll need a reversing Y harness or enough channels so you can mix them to reverse one side. You'll need lots of servo extensions also or cut the leads and solder your own using servo wire (this is what I did). Tail boom servos need about 36" added and aileron servos need about 24". I know it's a lot of reading but you might want to go through this whole thread as there's lots of good info about every part of this plane. It's a nicely built ARF but there's a few areas that need some tweaking.

Darrel Patterso

Anyone having problems with just using muffler pressure, with stock fuel tank location, or would adding a pump be of any advantage?

NM_Mark

My Feedback: (8)

OK, I have a question about the thrust line, and need some opinions. I think I need more downthrust on my Bobcat (pointing the engine towards the ground). It flies fine, but when I chop throttle, the plane noses straight for the ground, so I have to hold quite a bit of elevator to land.

Also, it does a strange thing as I climb out - the nose points up, and increases the angle of attack unless I hold some down elevator. As soon as I build up some speed, it starts flying normally - at least, until I cuts throttle, and bare down on up elevator. Is the angle of attack thing a trait of this model, or is it also related to the engine thrust line?

My CG is around 10.75" back, with an OS 46 (slightly underpowered), with a 11x6 prop. When I invert the plane, I need to hold quite a bit of down elevator for level flight.

Thanks, Mark

CrashPro

My Feedback: (1)

My friend Serge mounted an O.S. .61 on his Bobcat, I went with the Tower 75 on mine. With APC 11x7 props, in straight and level flight, I'm able to walk (not run) away from him. Best I've got on the radar gun so far is 110 mph. We've both since mounted .91's on our Bobcats, his with an .O.S. , mine with a Magnum. We have a couple different props to experiment with today. We're starting with 14x7 three blade Master Air Screws cut down to about 13". We also have 16x10 three blades cut down to 12" Will probably end up cutting that one down to 11" or less, will know after todays flights. Temps around 80 degees and 4 mph breeze right down the runway forecast for today. Its 5am and time to load up the trailer and get ready to head to the field. Will post results of the prop experiments later on today, maybe some video too.

MMallory

My Feedback: (1)

Darrel,

You shouldn't have a problem unless your line constricts. If it does, use brass tubing to route the lines back from the tank (keeping the clunk toward the rear of the plane).

NM Mark,

Yup, it sounds like your thrust line is off. Set your wing to zero on your bench and put a level on your prop shaft to check.

Stick Jammer,

Pylon racers use the Hitec 225. Go with the metal gear version for extra durability. Also remember this is a copy of a plane designed around a lot more weight than we are building into this.

Speed will be a function of drag more than engine size (given the limited availability of pusher prop sizes). If you really want to do it right, the servos should all be moved inside the plane and retracts should be fitted with doors.

I still think the best engines are the reversed Jett's, my YS 45 seems to do a good job as well. Anyone considering different engines should do a search on the pusher F16 (Combat Models if I remember correctly). This subject was hashed to death years ago. The YS was always the winner back then but now we have more engine options. The key is getting to more prop solutions.

Mark M

PointMagu

My Feedback: (11)

I was looking at Morris Hobbies website for an unrelated product when I stumbled upon this:

http://morrishobbies.com/product_inf...cd29bcf93e9ef1

$129.00

PM

Stick Jammer

The HS-225MG is a fine choice but the stock servo bays need to be slightly enlarged. They also weigh 1.09 oz. each as compared to .67 oz. for the HS-85BB and are a bit more expensive. The torque rating is slightly higher for the HS-225 at 54 oz. compared to the HS-85 at 42 oz. I would think two HS-85BB with a combined torque of 84 oz. is more than adequate for this application. It's quite possible that a single HS-225 on elevator may suffice but it's not my first choice. I'm not a real big fan of metal gears in these smaller servos as the small pinion gear is still nylon and is usually the first thing to strip anyway. The metal gear version of either of these servos will also develop slop much faster than the nylon version. True this platform was originally designed for a lot more weight but that is with a turbine strapped to it. This plane is also quite a bit smaller than the design it was copied from. I usually try to keep any plane as light as possible without skimping on quality or going to extremes to lighten it. There is no doubt this plane will fly very nicely with a multitude of combinations, it's all about what makes each pilot feel the most comfortable.

Stick Jammer

NM_Mark,
I have not flown mine yet but I'm guessing this is not a plane that lends itself to chopping the throttle until the wheels are just about to touch down.


Does the plane leave the ground at a very shallow angle or does it tend to jump into the air at a steep angle? I could be wrong but it doesn't really sound like a thrust angle problem if it flies fine with some speed. If this were the case it should keep pitching up the faster it flies.

MMallory

My Feedback: (1)

Jammer,

My experience with the 85's is they are not nearly as durable as the 225's. It could be the pitch of the gears, I don't know. I would not put an 85 on a major control surface on a .40 or larger sized plane. But, as you said, do whatever makes you feel comfortable.

Mark

NM_Mark

My Feedback: (8)

I flew it again today with an APC 10x7 prop, flew much better, but still keeps pitching up as you angle the nose up. For instance, it just lifted off the ground on takeoff, did not "jump" into the air. I do have a positive angle as it sits on the gear, so if I build up enough speed, it lifts off by itself. As I climb out, I have to hold down elevator to keep the climb angle the same, or else it keeps pointing skyward (till it snaps).

I had an aborted landing (sudden 20 MPH wind, happens in the mountains on occasion), and as I was climbing out near stall speed, I has holding almost full down just to keep the nose halfway level to build up speed. Then, the motor quit as I was coming around the downwind leg. I got it down, but practically had to hold full up elevator to land. Definately bumps up the heartrate a bit [X(]

Mark

CrashPro

My Feedback: (1)

Update on the prop experiments:

Well, Serge and I went out to the field this morning with great expectations with our new .91's and 13x7 three blade props.
We were a bit disapointed....best we got out of this set up is 82 mph [:@]
I then tried the 16x10 (cut down to 12") not any faster. Duane smoked our *****es with his delta wing again. Next week we're gonna try 13x8 Zingers and 14x6 (cut down to 13) APC props.
Hey APC,..are you listening?....we need a wider variety of pusher props.
Heres a short video of Serge and Duane today. As you can see the delta wing is very clean with the retracts and doors. Its powered by an old O.S. 61 with reversed crank so he can use any prop he wants.
http://home.dc.rr.com/maurie/BobcatvsDeltawing.wmv

Stick Jammer

MMallory,
I totally agree with you on not using a single HS-85 for any control surface on a .40 size plane but two of them on this elevator should be more than enough to do the job and hold up. It's not a 3-D aircraft and the throw at high speeds is very minimal. Several pilots have posted using two HS-81 servos which have quite a bit less torque than the HS-85,s. With two HS-85BB on the elevator the linkage is extremely tight with no slop whatsoever. This is definitely what I would look for in this plane as any flutter of the elevator will most likely end in a re-kit.

Wayne22

My Feedback: (2)

Zinger makes an 11-10 pusher.......the 91 should have enough grunt to turn some decent R's with it........