BillS

By dangerous I should have stated that two rich clicks lowers the take off rpm substantially and the airplane with a .50 is not or barely is at flying speed on grass.

You have a 10% larger engine and I tend to believe that an 11 x 7p would be correct. However with your .55 the 10 x 7p will probably turn 14,000 plus on the ground. If take off is not sluggish it will probably go faster in the air. You picked a better engine size. I have observed substantial heating on a long ground taxi and often a sag on take off which is another reason for a larger engine.

Bill

HeliTB

Thanks BillS for the explanation. My takeoffs are pretty good. I needed to adjust the elevator so that it would level with the top of the horizontal plane instead of the bottom. I believe that takeoffs will be a bit smoother now.

Pit-Viper 1

My Feedback: (12)

All these flight reports and no vids... What gives??? Would be cool to see some flying, especially with the turbine.


Shane

BillS

I also noticed elevator neutral to be strange relative to the horizontal stabilizer and shimmed the rear of the booms up .100� but it did not seem to make much difference. Most airplanes fly faster if the control surfaces are neutral. My Kougars will loose about 8 to 10% top speed when the ailerons are reflexed up.

Canard is back on and ready for more testing.

Bill

cyborg1

Hi guys, need some help on my bobcat setup. I crashed the plane and now she's fixed, but she's gained weight. In the beginning, she weighed about 8 lbs dry, and that was with a tt 50 heli engine and tower muffler. Right now, she's about 10 lbs, and I was wondering if the tt 50 with a macs tuned pipe would be enough to fly her? As it is, the old setup wasn't blisteringly fast either. I have a tt 61 engine available with a hatori tuned pipe, would that be better for the heavier plane[/color]? I wanna maiden it this weekend, and I would appreciate any input from y'all. Thanks!

BillS

I have an 8 lb. and a 10 lb. Bob Cat and am interested in your experience. The 10 lb. one has not been flown with prop. At 10 lb. the minimum flight speed (stall speed) is likely to be 35 mph, which will be difficult to achieve from grass and difficult to land.

My experience suggests that a 61 will be marginal at 10 pounds even with a pipe. Normally 8 lb. airplanes will have engines in the 60-size range and 10 to 11 lb. airplanes will have engines in the 90-size range. However if it doesn’t stall after the first 200 feet off the ground it will probably fly OK but heavy. I believe the strongest engine possible is your best choice.

Good luck and let us know the results.

Bill

I continue to wonder if 100 more sq in wing area wouldn’t make the Bob Cat a much more versatile airplane with many engine and prop setups. For the real finished weight the wing area is simply too small.

cyborg1

Hi BillS,

After doing some research on the engines that I have available, there is very little difference between the 2 engines in HP and maximum RPMs. Both will do 16k max rpm, and the 61 has a .5 HP advantage over the 50. I'll then probably go with the .50 in order to save the additional weight of 12.47 ozs. I'll be trying an APC 11x6p for the initial flight, and then an APC 10x7p to see which gives better performance. As it is, even with my battery pack located right in front of the fuel tank, it still balances a little nose heavy (about 9.5" from the leading edge). It should be interesting to see how she handles. The 50 with a pipe should be able to push max revs, which should be better than the 61. I fly off a cement surface, so she should be able to get up to speed without any problems. I'll let you know how it turns out. Happy Flying!

Xairflyer

My Feedback: (1)

My turbine bobcat started life just over 9lb is now nearlly 10 with various bits added on. I have not noticed and differences in the flying of it. The wing loading maybe higher but it shows no bad tendancies, other than landing faster than I would have liked that is why I have now fitted the spilt flaps.

We would know this better as crow braking, unless you mean to reflex them up quite a bit. We do use this method on our prangster fun fly models, it makes a very steep decent rate, dont know if I would like that on a Jet, but a little bit of crow braking might help, will have an experiment next day I fly it.

Xairflyer

My Feedback: (1)

Has anyone thought of or tried deflecting the rudders outwards to act as an airbrake ?

cyborg1

As far as I know, Opjose tried it, but it pitched up abruptly, working as an elevator

HeliTB

XairFlyer...I saw that someone tried it in post further back. The results from what I remember is "stall stall stall"

Xairflyer

My Feedback: (1)

A friend has a reaper and he said it worked very well, but every aeroplane is different.

Boomerang1

The pitch up is probably due to the very swept back rudder hinge line. In effect it IS acting as an elevator & would be the same problem if the rudders were deflected outwards or inwards. - John.

amcleod

What about mixing in a bit of ELE to compensate?

cyborg1

I was wondering about the retract ready version, which I have. If I leave the wheel wells open (not using the plastic wheel well provided), will there be any adverse effect on flight performance? As it is, my spring air retracts don't retract completely into the wheel well, and almost half of the wheel is hanging in the breeze anyway. Which brings me to another question-can these spring air 301's be adjusted for slack? My front nose gear has quite a lot of slack when retracted, and it makes the gear hang even lower, looking like it's not fully locked in position, when in reality it is.

Xairflyer

My Feedback: (1)

What I done on my AMD hawk was to slightly angle the retract so that it allowed the wheel to retract further, leg will be slightly angled back sitting on its wheels but actually helps with the tracking.

HeliTB

Yeah...I kind did something similar with my retracts mounting block. I used my dremel and sanded them at slight angle so that they retract further. Also flew well with no plastic bay inserts.

You could also bend the wire so the wheels fully disappear.

cyborg1

Well, finally re-maidened my bobcat. Pleased to say that it went well. Had a few hairy moments when I took off, as I adjusted the elevator servo arm to compensate for my previous flight, which required almost full up trim. Since the plane is heavier from the fiberglass repair, I added 2 clicks of up elevator just in case. Well, the plane tracked straight, and I used about three quarters of the runway for my takeoff roll. Near the end of the runway, I applied up elevator, and she shot straight up like a rocket..too much up elevator!!!!!!!!I quickly down trimmed and got her flying straight and level before she stalled. Flew the circuit for about 2 minutes, and concentrated on the landing approach. First actual landing approach bungled, went around at full throttle, and she settled in for the second approach. Spoilerons were a great help in settling down. managed to get her down safely. All in all, a great flight. Speed wasn't very fast with my 50 heli engine and tuned pipe, but I didn't really try for speed, as I wanted to concentrate on landing first. It was probably doing about 90 mph in straight and level flight with an 11X6 apc pusher. I'll try to max it out even further on my next flights. I was wondering if a 10X7 apc pusher qould be better for speed?

BillS

My Bob Cat is 8 lbs and recently changed to an OS .50. I have two flights with 11 x 6p and 2 with a 10 x7p. It lifts off from grass with more authority with a 10 x 7p with maybe 8 to 10% more authority. Lift off with 11 x 6p was slow, scary and once at stall speed.
11 x 6p APC turns 12,500
10 x 7p APC turns 13,500/13,700

In flight with 10 x 7p seemed to require less throttle although both props were OK in the air. I found more reserve power with the 10 x 7p. Will be interested in your findings.

Don’t know.

Additionally over a minute ground run time with a pusher seems to overheat the engine. Often the engine will sag during the take off roll or immediately after take off which is not good. I have started to crank on the runway, quickly check rpm, and go. Also I left the idle deliberately richer than normal.

Bill

Should have also mentioned that I have another Bob Cat that has been sheeted, glassed and painted that will be 10 lbs or more after adding engine and radio gear.

opjose

I fly mine with a GMS .76 and a Graupner 11x8 Pusher Prop.

Initially I too was having overheating issues as the cylinder head is not in the air blast when the engine is running on the ground.

A laser temperature guage helped immensly.

I noted that the head temp at the plug was exceeding 380 degrees F which is MUCH higher than what I should see.

So I adjusted the high end needle richer until the head temp dropped to 280-300 degrees F which was perfect.

This is one of those things where no amount of listening or taching the engine will help. I would not have thought of it if it wasn't for a friend who offered the use of his laser thermometer. After the very first reading I know what was wrong, and within a few minutes I had the engine operating as it should.

I'd suggest doing the same.

BillS

Do you remember the rpm at the lower temperature setting?

First flight today was great. Second flight over an hour later was rich, rich with no change in needle setting and a disaster. Wallowed through a 180 degree turn and was about to go over the pits and parking lot when I aborted and paned into the grass out of sight and far away.

Bill

cyborg1

I've found that using a heli engine with the increased head area works great for pushers. My bobcat starts up, idles, and goes through the tuning process without heating up, sagging, or dying out. If possible, try switching the cylinder head to a heli head that matches your engine. Opjose, thanks for all your input on setting up the bobcat. I'll be flying it more often to get used to it, as I got only 1 flight in during the weekend. I still have problems when aileron banking the plane and applying elevator...the nose still pitches up. The plane is definitely not tail heavy, so I guess it could be the alignment of the booms? I've noticed that the tail booms curve inwards, and it may cause an elevator effect. Would splaying the rudders outward a few degrees solve this problem?

cyborg1

BTW, is there any place to get a replacement canopy for the bobcat besides nitroplanes and raidentech? I ordered a replacement canopy from nitroplanes, but all of a sudden, they cancelled my order and said that it was too big to ship internationally.[X(] I lost my canopy when I crashed it during my first flight, and now I'm using tape to cover the canopy area for future flights. Need Help on this, thanks a lot!!!!

sbrackets

Hey Cyborg1
Read page 135 message# 3354 on this group. Seems that there is a company called Vortex Vacforms who is making canopys for the Bobcat 50.
I hope they can help you, Let us know if they can.

Jim

Boomerang1

Well, my little Bobcat is finally out of the paint bay, from stealthy grey overall to German WW2 camo. - John.