BillS

but too much positive angle of attack will turn a hot landing, or even a normal not stalled landing into a bouncing tip stalling unhappy time. I have had a few of the “bouncing tip stalling unhappy time” landings. Idle speed too high seems to aggravate the bounce even with zero AOA. It is difficult to get a 75 engine with 11 x 8 pusher to slow to landing speed. Incidentally my airplane flies very flat and lands long when the engine has quit. With smaller engines (had three) on the airplane it lands much better. However the take off with smaller engines was always without enough reserve power and sometimes scary.In addition aileron down by less than 1/16 inch has a big effect on the take off. Aileron reflex down pushes the nose down. The most successful flights have been with slight aileron reflex down for take off and to adjust to neutral flight when in the air.There seems to be a very delicate balance between engine size, prop size, AOA, CG, and aileron reflex without much margin of error.Bill

exciter900rr

I'm with you on the small margin of what works! It'ss making more and more sense to me that the airframe/planform is pretty sensitive to deviations in the spoileron C/G AOA department....
For clarifications sake, could you post some of your specs for us on your "known good" setup? ie. all up weight,C/G location AOA difference form LE to TE, and also clarify your "reflexed down"? ailerons?

Excuse me if I misunderstand, but to reflex and aileron, wouldn't it be going up? and to camber would be going down? Flaps vs. Spoilerons? I just wanna get some actual numbers that work, rather than "a visible amount" or "a little bit" or "around this many"...... I have read this thread start to finish, almost 3 times now, and there are a lot ofvaguemeasurements and angles floating around.
After some posts, I actually felt like I had become less intelligent having read them.... lol...

bottom line is, this is one sexy airplane, and seems to have a good deal of "punch some holes in the sky" factor- I sure would like it to remain in good health and enjoy it rather than thrashing it every weekend.
Someone had posted that the manual would have been more informative and less confusing if written in chinese. I whole heartedly agree!
Thanks all!
KM

BillS

“known good” set up is a questionable statement.Weight 8 pounds without fuel.AOA = zero degrees when sitting on the ground.GC is approximately 10 1/8”.Engine TH .75Prop 11 X 8 pusher13,000 max rpm.I find that ailerons down less than 1/16” makes a difference during take off. Aileron must be adjusted to neutral after take off for airplane to fly level at speed. Leap off ground seems worse when ailerons are neutral. Down ailerons push the nose down. Seems backwards.I have landed with more than 1/8” up aileron reflex but it was with a smaller engine and probably does not apply to the current .75 engine, which has a higher pitch prop.Idle speed of 3500 rpm is likely to produce a bounce. At 3000 rpm landings are generally without bounce. The airplane flies very flat with a dead engine. It has never bounced when the engine was dead but lands long.Ground run time and taxi time makes a difference in how the engine runs. Will test with slight positive AOA soon to determine if ‘leap of ground’ is reduced.Bill

exciter900rr

Thanks Bill-

I would be cautious with the AOA increase, and probably try it in 1/8" increments as not to get too far behind the 8ball... it will take off oh so sweet, but I just can't get the image of the plane in the air on that last bounce........ Unfortunately, I have yet to experiment with the spoilerons, and will be doing so this weekend, weather permitting. I'll be reducing some of the throw on them just in case...
The Bobcat is all fixed up now, minus some covering repair on the bottom of the wing where the retract twisted. After athoroughinspection on the gear block failure, I have noted that I'll just re glue the block into the wing, fixing the cracked light ply with thin ca and a bit of carbon fiber tow. the wing and the block absorbed a tremendous amount of stress, and failed in the most appropriate area IMHO..
The Robart 501 main aluminum housing actually was bent, pinching the trunion. (aluminum block that pivots and the gear leg goes into) If I was to beef up the gear block area too much, I'd be afraid of it failing the spar, or more of the wing itself..

Soooo, We'll see how "round two" goes on sunday...

KM

BillS

The main wheels were changed from 3” dia. to 2 5/16” which will probably represent 1/2” or so AOA change. With the TH .75 there seems to be plenty of reserve power at lift off so I should be OK. I will use about 1/32” aileron down and some down elevator trim on the initial flights. ‘Leap off ground’ cannot possibility be worse. After the last series of big bounces I decide to stop repairing the fuselage. Either learn how to fly it or destroy it.Bill

exciter900rr

Well, I decreased the AOA, and have had better results, but will go further to almost 0/0 AOA.... it still just wants to jump and bounce on landing, and it's hair raising to say the least!
I have gotten the engine tuning sorted out, and it's running MUCH better!
I had two flights on sunday, where I got some impressive looking speed out of it, and was finally able to evaluate trim and C/G withoutworryingabout the engine.
Crashpro had taken some video, and extracted a few clips with the fastest passes. He then posted them in another forum for Doppler readings, and got a best speed of 145 mph out of a shallow dive. Very impressive, but I'm a bit skeptical that it was exactly that fast. ifdefinitelyfelt and looked like it was over a hundred, but a buck forty five? might be pushing it.... However, I understand it is pretty accurate....
I'm going to try an un-sprung front gear leg, and smaller low bounce main wheels next, along with moving the C/G back to 10.25". This plane is proving to be challenging, but a bunch of fun!
www.rcuniverse.com/forum/m_8814477/tm.htm

BillS

From a design standpoint I have always thought the mains were too far back on the Bob Cat. Sitting on the wheels on the bench it takes a lot of weight on the stabilizer for the Bob Cat to rotate. I use fixed gear and moved the mains forward so I can’t give you a comparison weight. I located the mains about 2 1/2” behind the CG.

I also fly Kougars and they stick like glue on landing. The Kougars are all set up with a negative AOA with mains 3” or so behind the CG.

Bill

opjose

That is why I use the spoilerons. The decreased lift prevents the bouncing...

Yet I can still keep my positive AOA for takeoffs and not have the "stuck to the ground" problem.

exciter900rr

OK well, Noted.

Last thing I like to do on maiden flights is throw all the switches and crap. There is another one at our field that takes off and lands just dandy without all that jazz.
I am not saying that there is nothing to be gleaned from the spoilerons, (they're programmed in and ready to go in my TX) just not on your first flight- and with a runway like ours, you got room! hot landings are cool by me for first flights, but the pogo stick thing has to go! He He!

chuckie099

Hi All,

Just bought the yellow / red bobcat from Colchester A1 models in the UK along with a set of spring air type retracts (although not made by spring air) Can't wait to get this thing flying! I'm going to use an ASP .62 which came out of a recently deceased WOT4.

 

I’ve followed the thread so far with great interest and taken on board many good tips…thanks to all!

 

I’ve got a question tho.. Has anyone experienced any quality issues with the airframe / wing construction (poor captive nut fitting aside) my 2 wing panels seem different towards the trailing edge close to where the booms fit. One panel has a straight trailing edge along the whole length and the other has a slight return close to the boom. Also one of the ailerons does not fit nicely, I cant get it to line up straight between the wing tip and inboard trailing edge. If I get the trailing edge of the aileron to line up with wing tip I end up with a considerable downward reflex towards the inboard trailing edge. I can go for a ‘line of best fit’ by re-hinging the aileron but the whole aileron will sit diagonally across the wing resulting in the outboard end of the aileron sitting slightly low to the bottom of the  wing and the inboard end being slightly high.

 

I would kike to sort this out myself, I recon it will be difficult to return the model to the shop as it is not ‘as new’.

 

Any comments would be greatly appreciated.

 

Thanks,

 

Chuck.  

chuckie099

Oh Another question...

How much of a chore is it to assemble the model at the field with the removable wings. I didn't consider this when I bought the plane!

is it self jigging or will I need to check all measurements before each flight and manually adjust everything so its square??

Thanks,

chuck.

exciter900rr

Im off to the field right now, but wanted to reply first- I would imagine it's definitely a chore to assemble at the field, but if you have and extra hour for assy & dissasy, then it's ok. lol not a good idea, as you have to run air lines, and 6 servo leads from the wings to the fuse, and usually, end up bringing the wires up front under the servo tray. it's up to you how things index and line up since they pretty much leave it up to you how the wings will be joined (without gluing them together on the tube to the fuse).

On the first post, Iwould check to see that the aileron is not warped by sighting down it from tip to root, and hopefully it is! then just twist it in the correct direction and warp it back into place while shrinking it with the heat gun. this should work for a warped control surface. The trailing edge at the booms is clipped on mine, and appears to be the norm from the few I've seen, and the various other pics I've seen. hope this helps a bit, and rest assured, others will happily pitch in and help on this thread!!! good luck! I'll try to post pics of the inside when I get home this evening.

KM

chuckie099

Thanks for your reply KM,

I'm off to the workshop to hopefully find a twisted aileron (doubt it tho..I hope I would of spotted this already)

Concerning rigging at the field, in order to transport it in one piece I will need to get my old knackered death trap of a van back on the road which seems a false economy!! So I think I will have to resort to field assembly. I am fairly happy with all servo and airline connectors as I will have a loom assembly which I can easily access through the removable belly hatch. It’s more the geometry of wing, stab, booms, fuz I'm concerned about.

Looking forward to some pics, I'll post some of my efforts also.

Hope you had / have a great flight. I'm off to the field this evening for some raptor action!!

Cheers,

Chuck.

Xairflyer

My Feedback: (1)

I would say it would fit in most cars fully rigged so long as you can fold down the seats, fits very easily in my estate

chuckie099

Well I took the plunge and found line of best fit for the aileron, its not perfect but will be ok. Thanks for the advice KM, the aileron was slightly out of true and a gentle steaming got it a much better fit. the real problem seems to be with the wing panel being slightly off...it looks like they ran out of  decent wood in <place><country-region><country-region><place>China</place></country-region> and found some scraps to finish the wing with!!

progress slowed when I spilled a load of thin CA all over the wing so spent the rest of the evening cleaning everything up, I then went to the flying field for some light relief and blew a hole in the piston on my Raptor Titan resulting in its first auto....thank goodness for corn fields!!

Thanks for your input Xairflyer, I have an Audi A4 Avant (estate) so hopefully will be able to transport the plane complete.



I would post some pics but cant figure out how to... any advise?

Chuck

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Xairflyer

My Feedback: (1)

Simple really just use post reply and not the fast reply, it then has a link to attach pictures.
Best resize them first

bri_877

I just got one of these from a guy at our field who now thinks it's going to be too hot for him. I've heard something about pinning the rudders as they aren't all that functional. Any fact to this? The other thing on my mind is what is the best retact to use thinking that I fly from a grass field? Planning to use an OS 61 or a Supertiger 61 depending on which one I can find a more suitable muffler/pipe for as neither have any exhaust on them at this time. Thoughts on this? Anything else I should be thinking/watching for? Thanks guys.... bri

chuckie099

Cheers Xairflyer for the picture advise.

Right, got another problem.... the instructions suggest the wing bolts are 4mm however the captive nuts in mine are only 3mm and they are not put in straight! has anyone else ended up using 3mm bolts? they seem a bit on the small side for a 150mph plane! A

Icould always try hammering the captive nuts out of the root and replace with 4-5mm jobs but would prefer to avoid this if anyone could tell me they have used 3mm without any trouble and the fact the bolts are not straight wont be a problem.

Thanks.

Chuck

chuckie099

exciter900rr

Yeah- The elevator extension was a pain, but since I opted to recover the whole airframe, it made it a bit easier to route things. Also, one thing that made the wiring easier was the fact that I had bulk servo wire to solder and extend all the wires with no bulky connectors to snag on things once I was pulling them through tight areas.

One thing that's tough with these planes is the fact that there are a few variants of them. some have different hardware, and some have hatches in the underbelly. Some also were built by people who care, and others were not. lol! When mocking up everything, I noticed about a half an inch of difference in the height of the rudders- this made it an easy decision to block them in and delete their existence... I had planned to drill a couple of 1 1/2" lightening holes in the rudders since they were solid, but forgot and got carried away with the covering- good thing I did, as I was way too nose heavy with a traditional layout! The 5cell battery is now along side the fuel tank. I intend to open it up, and take some final pics of things soon, but I have a few other projects that have been consuming my time.... I think everyone knows the drill.. lol!

LOOKINGGOODchuckie!
BTW- if the wing mount bolts are angled somewhat downward, I would at least try to mock up the plane with them the way they are, as this may make it easier to get to them through the hatch.
I had to cut my own hatch in the bottom, and when I showed a few club members that have, and have had bobcats, they said it was how they come. Sheesh! ....and I was really proud of my "great idea"!

KM

chuckie099

so you are running 6v? I was planning on doing the same as I'm only using standard Futaba 3001's on the ailerons....I recon I need the 6v to give me enough torque. do you find the increased current draw at 6v to be an issue? I'll be driving 8 servos (4 mini and 4 standard size. only 6 in constant use) was wondering what capacity to go for?

I've talked myself into tolerating the 3mm wing bolt as I recon the torsional and bending loads will be easily taken by the ali wing tube and piano wire joiner. the bolts only need to stop the wings falling off!! (I've also read on another thread the wings are pulled inwards towards the fuz by arerodynamic forces in flight)

looking forward to the pics of yours when time allows, if you did a stearable, retractable nose wheel a pic of that assembly would be a great help!



Brilliant idea with the belly hatch by the way.... all us newcomers to the bobcat are forever in your debt!!


Cheers,

Chuck.

exciter900rr

Yes I'm running 6v, and to be honest, I've never even given the current draw a thought. As a rule, I always put more battery thannecessaryin my birds. I had a low voltage reboot once in a .91 powered edge, and a reboot in a T-rex 450 heli both with devastating results....... now, the more Mah, the merrier! BTW, I run a 2000Mah 5 cell pack in the bobcat. I also have made 2 TX packs and 4 rx packs (2 5s and 2 4s) 2450Mah in capacity from the rechargeable energizer aa's found in the home depot and lowes without issue. you just use them as any other cell, and wire the packs just like normal, soldering tabs to connect them. I believe I just read somewhere that the "formula" to shoot for is, 50Mah per servo, per hour. and even though two are part time use, they are still holding center so you count them too. that equals 400Mah usage. however, I would feel confident using the 5 cell 2000Mah pack for a typical day flying. then at the end of the day, take and discharge them and take note of how much Mah was left. this number when subtracted from the total capacity will be you typical usage. it's one of those "just so you know" things.....

The steerable nose wheel is kind of a joke, but works just fine once you've spent an entire day cycling the gear and re adjusting- lol- The trick is to leave a good amount of slop in the pull pull cables, otherwise they will not allow the gear to lock down, and well- you know what happens then...... the cables have to be routed in a manner so that they can be pushed out of the way when the gear retracts, and not bind the gear in the up position. cause if it's stuck up, well... then you also know what happens next..... a picture is worth a thousand words, so I'll try to post some up.
I am not saying by any means that this is the only way to do it, just the only way I feel confident doing it in this application. I am a carpenter by trade, and what I would call "VERY mechanically minded", so I have tried to make things function as well as they can. in the case of the nose gear, I tried a few different things, and essentially gave up after it worked well rather than trying to clean it up more and refine it. Y'all should see my sketch pad! Ha ha!

Did yours come with the belly pan pre cut? if not, and you decide to do it, I'll throw a tape measure in the pic for reference.

KM

exciter900rr

here's some photo's of the install, and the nose gear- also, how I cleaned up the wing servo's as well. and my bottom hatch..

chuckie099

Wow thats a cool colour scheme! thanks for all the pics they really help a lot.

I found myself in Spain then Portugal on a last minute business trip this week whichhas kept meoutof thework-shop. Going to getback on it now tho, theundercarriage is next...again nothing is simple the wheels do not sit in the stock wells very nicely so I recon I'll end up lining them with balsa instead.

I'll post an update at the end of the day after I've done something....

exciter900rr

Good idea with the wheels- another thing you could do is go a bit smaller on the wheel size- I think I'm at 2" mains and nosewheel- the stock wheel wells will hold onto the wheels if the gear legs get bent even slightly aft, and then once the landing timer goes off, you'll invent a few new words while trying to get the mains down....