RE: Nitro models pusher Bobcat?
 

Strange...

My plane gets very mushy before it stalls.

The controls feel ineffective and it wallows about before it stalls, at which point the nose drops HARD.

RE: Nitro models pusher Bobcat?
 

Just curious, is the plane balanced laterally?

RE: Nitro models pusher Bobcat?
 

Very nice, I was interested in the speed so I ran doppler analysis on your video file. Best doppler indicated speed was 118 mph in case your interested.

RE: Nitro models pusher Bobcat?
 

I HAVE to ask...

How were you able to do this?

What did you use for a reference?

RE: Nitro models pusher Bobcat?
 

Opjose,

Go to this link which should take you to the website translated into english from german.

[link=http://translate.google.com/translate?u=http%3A%2F%2Fwww.sprut.de%2Felectronic %2Fsoft%2Fscope.htm&langpair=de%7Cen&hl=en&ie=UTF-8]Doppler sofware website[/link]

Then you convert the audio track from the video to a PCM-8-Bit-Mono-WAV-File. Follow the directions on the website, or you can ask questions in the [link=http://www.rcuniverse.com/forum/forumid_104/tt.htm]Extreme Speed Prop Plane Forum[/link]. There are some very knowledgeable modelers over there and they turned me on to it.

And if you have never heard of it here is a fantastic unit conversion program.

[link=http://joshmadison.com/software/convert/]Convert[/link]

RE: Nitro models pusher Bobcat?
 

AGR413

Thanks for the doppler! I estimated around 120 so I was close. This was at the end of the flight with no dive. My initial goal was 130 so I think that I will get there by changing the landing gear. I can clean up a few other things and make more power but I think 140 will be about the limit because of the thick airfoil

RE: Nitro models pusher Bobcat?
 

No problem man, it is a new toy to me. I'm still having fun with it.

RE: Nitro models pusher Bobcat?
 

Checked the balance again after you asked. Lateral balance is OK. CG was intentionally left at 1/4" to 3/8" forward of 10.3" for the initial flights. Maybe there will be more stall warning as the CG is moved towards 10.3"

Bill

RE: Nitro models pusher Bobcat?
 

Bill,

All I can offer you is my experience with my plane. With the CG a little past 10.5 there was no increased stall indication, just extreme elevator sensitivity. 10.3 is where you want to be. From reading your previous post and then this last one it sounds like you are simply getting too high of AOA and too little speed. The Bobcat is very forgiving but you can't go nose high at low speed to the point that the airflow over the wing is separated from the top of the wing and the bottom is acting like a huge speed brake. I'm not trying to be critical, this may not be the case but I'm trying to read between the lines and apply what I know about this plane. I have never had a stall on landing with this plane. I have almost destroyed it because I had the CG too far back. I always land with power and just nose high enough that the front gear is higher than the mains. Hope this helps.

RE: Nitro models pusher Bobcat?
 

Very cool.

I assume that any throttle changes are going to upset the measurements though.

RE: Nitro models pusher Bobcat?
 

I don't think so, but the real answer is I don't know. Its not an area that I have any expertise in.

RE: Nitro models pusher Bobcat?
 

Having waited 17 days since placing my order, I was pleased today when I finally received my RR Bobcat 50 in silver and orange. Base cost was $99, shipping $155 and excise duty $45. Total cost: $299, only one third of which was for the actual model. <sigh> Hell knows what a set of retracts, a new engine, and whatever other small incidentals I'll need, is going to set me back!

After a quick inspection, everything looks good. I thought for a moment the incidence pin was missing, but I finally found it rolling around in the bottom of the box. Covering very neat, only the tiniest wrinkle here and there; about two minutes work with a covering iron. Instruction book leaves a great deal to be desired! I wasn't expecting much, but I'd hoped I'd at least be able to make out the photos!

Now, I've never built (or flown) one like this, so I have about 1,001 stupid questions I'm going to want to ask. It was 2,001 but I dumped the entire thread to a text file and have read through all 3,001-odd posts, and grepped for anything I needed. So are you guys going to help me get this model together to the point where I can get it wheels-up and clean? I sure hope so!

RE: Nitro models pusher Bobcat?
 

If you really read every post..I'll do whatever I can to help man! I'm not the guy to come to for retracts and there are many around as good as and probably better than me but I admire your spirit!

RE: Nitro models pusher Bobcat?
 

Original: amcleod

Hmmmm......I'm surprised you have very many questions if you read the entire thread, pretty much anything you'd want to know is here. ;)

RE: Nitro models pusher Bobcat?
 

The problem with trying to read a 3000+ post is that once you are done, your head hurts so much you forget all the stuff you just read. I think. I can't be sure, my head hurts.

RE: Nitro models pusher Bobcat?
 

I have indeed read them all., more than once. But there are still questions. For instance:
[ol][*] Is the silver/orange model also covered in Ultracote? If so, what? Plain Silver and Orange?[*] Has anyone dismantled a boom? Either accidentally or deliberately? I'd like to see a photo of what's inside there, because I'm thinking of performing some surgery.[*] The 520W1 retracts seem to be the preferred choice for the RR model. Is there a drop-in alternative that does NOT use pull-pull?[*] The "Medium" air tank has been recommended, but TH says they are "discontinued". Does that mean they are no longer available?[*] Is the HS-125MG really a risk on elevator, due to the small size of the gear-train?
[/ol]
There is plenty said about retracts in the forum, but we are really talking about two aircraft, the later RR version and the earlier version requiring surgery. Posts concerning retracts are not always clear which version is being referred to.

Given what it's going to cost, and how long it's going to take, I would like to get it right! So I'm still hoping for some help here a

RE: Nitro models pusher Bobcat?
 

NONE of them are covered in Ultracoat.

They are ALL covered in "Chinacoat" which is not the same thing.

Yes I've dismantled a boom.

No photos though.

That's up to you.

Even the 520W1 could be set up NOT to use Pull-Pull if you want.

An easy way to do this is to mount a stearing servo pointed down out of the bottom of the fuse, so that you have an exposed control arm.

Then run a control link to the front gear, with a slider on it, and you are good to go.


Probably not, buy I put in a large tank in my Bobcat .52, which fit just fine.


I haven't had any problems with the stock dual servo and rudder arrangement. The combined strength of two elevator servos does fine IMHO.

If you put in a Jet engine however, as people have done, I would not recommend this.

Yup, but was there a question to be inferred there?

Some of our "jet guys" saw ( and loved ) my Bobcat .52.

They said it was a great first Jet trainer, and what they should have purchased it first, as then they wouldn't have cared about crashing it, nor the cost & time involved. e.g. It's cheap, & easy to build.

I agree.

RE: Nitro models pusher Bobcat?
 

Angus, I'm repairing a Bobcat I bought from a friend. The nose retract has the steering servo actually attached to the retract frame (Springair)

What is fitted to this model for elevator is a Hitec HS 5125 MG thin digital wing servo mounted in the right hand boom just under the elevator.

Through the large hole in the boom (fin?) I can see some of the structure, what do you need to know?

The model is turbine powered (MW-44) - John.

RE: Nitro models pusher Bobcat?
 

Thanks for the info, opjose. I'm sure someone said the covering was Ultracoat. If not, anyone matched an alternate covering for colour? I'm considering just using the 520W1's and gritting my teeth over the pull-pull. No question to be inferred WRT two types of aircraft. Just explaining why questions on retracts are not easily answered by searching through the forum.

Boomerang, I don't really like the arrangement of servos in the booms. I feel all servos should be on the inside. And the elevator pushrods are nearly 10" long and operate at an angle. If I knew what was under the sheeting, I'd consider some surgery. If you (or anyone) has photos of what's in the boom under the sheeting , it would save me from having to get one X-rayed! :-)

The 5125s are the same size, weight, torque and (presumably) gear-train as the 125s, but double the cost. They are nearly 2/3rds the cost of the model, each! Since the only concern about the 125s seems to be the gear-train, I probably will not bother with 5125s. I have a couple HS-81MGs that are rated at the same torque as the (5)125s. Two of them will be double the gear-train. And probably two more for rudder.

I must say, it's quite a different beast to [link=http://www.anjo.com/rc/aircraft/bobcat/bobcat.rtf.3.jpg]my first Bobcat[/link] -- the one with 78" span...

RE: Nitro models pusher Bobcat?
 

Hi amcleod

Heres a few pictures of a boom opened up...hope they help

RE: Nitro models pusher Bobcat?
 

Original: amcleod

Most of the thread content regarding the Bobcat are simply personal choices, not really right or wrong. That's the beauty of this type of discussion, read everything and decide for yourself which things will work best for you.

Original: amcleod

The stock elevator servo push rods are actually 7 1/2" long, not really a problem. Take another look at page 99, post 2461. This is how my tail servos are set up, but again, its just another choice. ;)

RE: Nitro models pusher Bobcat?
 

CrashPro: Thanks for the photos. Just what the doctor ordered.

Stick Jammer: I take your point re personal choices. What I'm hoping for is advice, not a definitive guide. Also, I've looked at your set-up, and while I'm sure it works fine for you, I don't like that link between the rudders. Especially if I decide to try mixing in some sort of air-brake function.

RE: Nitro models pusher Bobcat?
 

Original: amcleod

There ya go, exactly my point. You'll get multiple advice on any question and it's usually different from each poster. Again, with all the info available in this thread you get to see what has worked (or not worked) for others and decide what will suit you best. Good luck with your build! ;)

RE: Nitro models pusher Bobcat?
 

I toyed with the airbrake idea...

I modeled it in G3 and found that this was not advisable....

The rudders are angled respective to the angle of attack... so if I turn the the rudders out or in to work as an air brake, they will abruptly pitch the nose up and cause a prop strike.

This does not happen if they operate in unison, but combine them to act as a brake and it does.

RE: Nitro models pusher Bobcat?
 

No it's not.