I'm gonna give my YS 63 powered Bobcat one more try with a Zinger 11-8 prop
and see what happens. I think it will have to spin about 11,000 to have a chance
at any decent performance....the 12-6 just didn't have any speed. []

FBD.

gen3v8 just a quick observation you have your nose gear strut backwards (coil going wrong way).

That's a theoretical maximum speed of around 83 mph, assuming no drag and no slip from the prop.

In the "real world (tm)", chances are you'll score around 70-75mph in level flight.

You might be better adviced to try a 9" or even 10" pitch -- although there comes a point where you'll actually go slower as you increase the prop pitch.

Ther front coil is in the oppasite direction to normal. The front housing is rotated at 90deg.
Turning it clocwise or counter clockwise gives the same result ,its just up to wich is more convevient in your
application.
Had it been areed engine reverse rotation is no problem as the reeds open on vacuum. But being a rotary valve
it has to be timed with the piston .Turning it 90 deg synchonises the intake timing with a reverse direction.
apc 11 10 good revs lots of prop noise but I didn`t tach. Maiden in 12 hrs

Goodnight Dave

I did my maiden with os 55 ax+11X7 p prop. Pıctures during take off.

Oh I hope it kept going up, would have made a good RATO rotation.

ps, looks great!

Just a quick observation on your rotation...

It appears that not only did you rotate the front intake housing 90 degrees counter-clockwise, you aditionally rotated the carb itself, 180 degrees. This was not mentioned in any of the text I scanned in earlier posts. It was my thought that simply rotating the entire carb assembly would achieve the reverse timing we are looking for.

How does this 180 degree move of the carb effect overall performance? Having the intake nipple in that geometry seems unusual.

Can you enlighten me a bit, please?

I have just pulled the wing panels and fuselage from the plastic bags on my brand new BC and am preapring to rip the covering off to rework the landing gear blocks. The thought of this engine mod intrigues me and I would like to know more.

Happy N'year, y'all....

PM

Hi Folks! I stumbled on this post just yYesterday (I followed Clean) I should have looked long ago since I have wanted one of these Bobcat Jets for a long long time. Clean told me on Christmas day that Nitro Models aka Raidentech finally had a Yellow one that I could get my hands on. As of Christmas morning I've been waiting for the UPS man. Each time I tried ordering one of these, they were always Sold Out! At one point I had actually emailed a manufacturer/supplier in the Philippines and got a response. I would have bet that I could have gotten 10 of you guys to split a mass order from this guy.
---
Dear Mr (FantzyPantz)
Thank you for your Email,

Unit price on the MOQ for Yellow USAF BOBCAT 50 - 51 Nitro Gas is 110.00 USD
Our minimal order is 10 units and maximum order is 50 units, but if this transaction good we can supply 100-200 units per month. If you want order for 50 Units we will give discount 10 % for you.

Payment Option
- The payment via Bank Transfer/ Telegrafic Transfer (T/T)
- All items are in stock and will be dispatch immediately once we received payment
- No delays except for Public Holidays or any unpreventable circumstances which may delay the dispatch

Shipping Information
- Shipping will be calculated at checkout based on your ship-to location.
- Standard shipping is via UPS Ground. The estimated delivery time will be approximately 7 - 10 business days from the time of order.
- Express shipping is via UPS Air. The estimated delivery time will be approximately 4 - 6 business days from the time of order.

Please let me know how many RC do you need.

We're looking forward to hear from you soon.

Mr Johannes Sita
---

Anyhow, I have lots of reading to do here. I started on page 1, then skipped here to the end to make this post, now I'm going back to page 3 or 4 to get caught up.

Rotating the carb does not affect its operation - it just makes it easier to connect the servo to the arm with the front housing rotated.

The "timing" of a 2-stroke engine like ours is determined by when the intake port in the crankshaft opens in relation to the engine reacing top-dead center. In normal operation, the intake port in the crankshaft opens (by passing under the carb. opening) just after the piston is at its lowest point, and closes just before the piston reaches TDC (or there abouts). This allows the crankcase to "suck in" the fuel/air mixture into the crankcase. It is then transfered to the combustion chamber through the cylinder ports on the next down-stroke. When the engine is running backwards, the timing is off just a bit. Rotating the front housing (if possible) adjusts the timing of the port opening and closing to work with the engine turning in reverse.

I'm definately not an engine expert, but this is my understanding. I also believe that the timing of the engine running in reverse with the housing rotated is not exactly the same as when its running forward with the housing upright, but its close enough that it runs OK.

Bob

Yep, I had an OS40FSR that I ran "backwards" on many occasions by rotating the front of the crankcase -- it put out great power and the timing difference was not obvious in the way it ran.

One thing to be aware of however, is that there may be a little extra wear on the piston/rod until the engine settles into its new direction of rotation. The side-loads on the piston-rod are shifted 180 degrees when the direction of rotation is reversed. Once again however, I found no perceptable problems resulted from this.

I just wish more modern engines had a bolt-on front section to the crankcase so we could avoid being stuck with a relatively small selection of pusher props.

Ok then...here I go:

Finished my buddy's Goldberg Sukhoi yesterday so now I can dig into my BC.

I took a piece of 220 grit wet/dry to the fuselage and was amazed at how quickly I knocked the color coat(s) off. Add a tad of laquer thinner and a wide brush and I'll have the entire thing ready for a new primer coat in no time.

I stripped all the yellow covering off and it's true that the blue trim is some kinda inferior plastic that feels like rubber once the clear is peeled back. Anyway, I now have a bare wood structure and an ARP fuse, (almost ready to paint)!

I'm considering a chrome overall with International Orange panels. West Germany had some terrific color schemes on their F-104 Starfighters and others before the Wall came down; besides, I always liked the Iron Cross insignias, lol...

The canopy frame will definately get a masked paint job as well. Normally, I mask the inside and shoot my color coat there rather than on the exterior. However, this one already has the color on the outside so I'm locked in, :-).

The photo of the horizontal stab shows a standard Futaba 3003 servo sitting inside. I don't see the need for a mini servo other than as a weight saver as the amount of casing exposed is quite minimal!

By eliminating the duplicate elevator servo, the weight of the single standard should be acceptable I'd think. Also, why not simply connect the dual rudders together as we do on biplane ailerons? This would save yet another servo and the need for 2-Y harness connections.
Sevo count: 6

I'm also considering inserting a 1/4" birch ply plate inside the fuselage and bolting an aluminum landing gear such as a Halco,(they still make those???) to the bottom of the fuselage and skip rebuilding the wood blocks in the wing panels alltogther. By layering a 6 oz glass cloth over the plate and slathering slow-cure epoxy over the entire thing, strength and rigidity should be possible.

As with most of the stuff I do, I'll post a buncha photos as I move through the BC.

Here's what I did this evening in about 1/2 hr:

PM

I tend to agree with you, Bob....although I have not checked it out myself. All it would take
is someone with a degree wheel to see how the "90 degree is OK theory" would pan out. We
used to cut away rotary valves back in the old days at the motorcycle shop to enhance the
performance of the engines, but we never ran the engines backwards....

Unless the procedure would result in the engine running 100% as well as it did forward....I
cannot see were moving the front housing would be beneficial....unless the prop choice for
an engine excluded any and all available pusher props on the market today.

FBD.

While I am waiting for my retracts to show up I was trying to figure out what I need to do with the wing. So I started laying things out on the wing and I have come up with some questions.

The two black lines together from the servo cutout to the wing root is where the edge of the tube is. The black line along the wing root under the wheel is the thickness of the root rib. The other line by the servo is where the servo horn would line up with the servo in it's cutout slot.

First question is I don't know how long the strut should be. Using the fixed gear as a guide and allowing for the frame of the retracts it does not look like it will be much. I used the fix gear as a guide assuming that is how high it should be. Maybe that is a bad assumption.

Second question is can I use larger wheels to give more height if the strut is real small? The wheel in front of the black lines is 3 1/4 inch. May look funny with the 3 1/4 wheels so 3 inch may look about right.

Third question is I was wondering if I could move the retract further out to where the servo opening is to get more height. Then the servo would be mounted sideways and moved below the retract towards the leading edge. I realize the stance between the two wheels would be wider. Which should improve ground handling.

Fourth and last question. Can the retracts be installed in front of the tube and what would be the drawback to doing so? It may help with balancing moved closer to the center but what would it do to ground handling, etc. Seems like there is plenty of room there to mount them.

Sorry for all the questions but I do appreciate your time in responding. I am sure I will have more once my retracts get here and I need to put in the gear mounts and the support to them.

Max, it's not important where the wheel is when it's retacted, just when it's down - just behind the CG. You may have to bend the legs & mount the retracts at an angle to avoid the tube. Where the big wheel is in the pic is probably the thickest part of the wing, best for accomodating the wheel. - John.

John,
Thanks for your response. The big wheel is right at the cg which is 10 inches from the leading edge.

The carb was reversed for ease of connection.
The induction timing was reversed for prop selection.
Maiden flight was good slight up trim needed.all other inputs were as
throws would produce. When it jumped on the pipe WOW fast

Max,

I've started the installation of the SpringAir retracts in my Bobcat. I will post some pictures soon. I have mounted the retracts out near the servo pockets. I'm going to stay as close as I can to the strut length of the stock gear for maximum prop. clearence. It looks like part of the wheel will actually be in the fuselage, but that should be fine. It is also possible to setup the retracts so that the wheels stay "outside" the wing surface which would simplify installation, but not be as clean...

Bob

Thanks Bob,
I look forward to your pictures. I did not think about going into the fuse but I was wondering about the prop height due to the strut length.

I called Spring Air today and they said my retracts would be shipped today. So by this time next week I maybe able to start on mine.
Have a good holiday.....
Bill

Ok just went to order a Bobcat today, until I got to the shipping charges. $30? No way. Anyone know of another place to order one with reasonable shipping?

Thanks Bob

I bought 2 of them,...received them yesterday,...shipping and handling was $18.43...total of $298.74 delivered to my door.
hmmm,...but then, I'm only about 120 miles from where they shipped from.

Yeah,

mine was $125. + $30. but I had it in 3 DAYS! $155 is still a great price, IMO

PM

Wildchild45177,
Did you go through an RCU link or an e-mail from RCU or did you go directly to their web site? My understanding is if you go directly to their web site the shipping is about $17-$18. I do not know how true it is or why it would be different but that is what I have heard.

For everyone having trouble finding Bobcats, there is one in the classified section with free shipping.

OK, so here we go with the installation of the SpringAir 305 retracts in the Bobcat...

First, we make a 1/4" ply mount to bolt the retracts to. It needs to be large enough to provide adequate area to spread the loads out and attach to the underlying structure (which we will reinforce).

Then we decide where to put the units in the wing. I decided to put them further outboard than the stock gear. I want to make the gear legs as close to as long as the stock units as possible. Even this far out, the wheels will be partially inside the fuselage when they are retracted...

Mark the location of the plates on the lower wing skin, and slice into your new airplane...

More to come...

Bob

Thanks Bob for the pics....
How did you reinforce underneath? Sorry to jump the gun if that is part of more to come.