Detlef Kunkel

Mitch,

I dont have a stock of spare parts.

The pushrod- problem is sorted out when you frequently lube your ex-valves, and normally these engine run for many hours without significant wear.

mitchilito

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Hey Detlef, I can't believe it but I"m finally installing my landing gear into the wings. I't been at least FIVE YEARS since I built them!!! I'll try to get a video up in the next day or two. They are coming out nicely, I think. We'll see if they hold up. . . . . (not as nice as your new ones of course)

With the maiden flight looming on the horizon I have a question: What kind of elevator trim is required on this airframe with flap deployment? I'll have three position flaps - up, takeoff and full (landing) flaps.

Detlef Kunkel

The Bearcat is almost as neutral as a P-51.

But (just my personal preference) I dislike the instable situation between push and pull on approach, so I also select a little downtrim with flaps ( 4-5%)

Better keep up speed than to park the A/C in 4 meters of height.

You see on the video- it comes in perfectly ( although a little tail heavy which we correct at the moment, building lighter elevator & rudder)

mitchilito

My Feedback: (7)

Hey, thanks for the info Detlef. This will give a little more confidence for the maiden.

I think I’d like a little up trim tendency to start but I agree with you about setting her for a nice downward glide on final approach.

Detlef Kunkel

Hi Mitch,


any news of the mighty Bearcat?

In between it is getting pretty cold here.





Maybe to add a little motivation, the 300 is ready from rebuild. Featuring some modifications. I cannot resist :-)




Yesterday evening, the second 300 from a friend ( and also Bearcat jockey) made its first turns on my test bench.

It will be powering the sister ship of my B-Cat.

The two engines are totally similar build up and modified, as the BCs are as well.

They really shoud show exactly the same performance. The difference is a slightly differend blue coulour and a 14 instead of a 13 on the fuselage.


Hopefully next year, a meeting of those two would be great

mitchilito

My Feedback: (7)

Great video, Detlef. And what a run stand you have! Wish I lived closer. . . . . .

I finally started tackling the COCKPIT detailing. We all know that this is a slow process. It's slowing me down more than I counted on. . . . ..

Keep those videos coming!

mitchilito

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Any news on your newly finished Rare Bear Detlef? Howz it working?

I took a break to put a jet together. Modern AFR products are kind of "instant gratification" nowadays. Especially when compared to something like our Bearcats! Only took about a week to finish. Then I went right back to work on the Bear. I installed a super light weight wire tunnel to get all the wires and air lines to the front. I still have to tackle the cockpit kit but that really is the very last thing now.


The clear tube started life as a neon light protector tube and the foam bulkheads are 1/2" EPP foam. Weighs nearly nothing.

Amazingly empty looking tail!

Here's a Quick Look at my shiny new Jet:

​​​​​​​

You Tube

Detlef Kunkel

Hi Mitch,
the Bear has received some reworks and improvements.

First of all, the repaired and highly modified 300, then I am still working on a new (lighter) elevator. Need to move the CG more to the nose, without adding a single gram to the A/C.

Need to straighten the original rudders to make them worth making a mould of it.

They are pretty twisted in any 3 W BC I know.

Will take some time until that is done. Will be ready in springtime I hope.

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Last week, I did some reworking on my T-33 ( onboard cmpressor, new steerable drum brakes) and the last days I spent on the Phoenix engine. Was running on the test bench yesterday with the new bigger reduction drive.

It is turning a 37-25" Prop now. Man that makes some wind..

mitchilito

My Feedback: (7)

Wow, I see you are on a quest for the PERFECT Bearcat! Keep up the good work -

mitchilito

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Well, I finished and flew the MB339 (a FANTASTIC toy IMHO) so it's back to work on the 'Bear. Here's the maiden. Who's the old geezer in the vid??


I spent a BUNCH of time setting up the landing gear SEQUENCER in my Spektrum DX18 transmitter. I have three functions: Gear, Doors and Downlocks and it has been an interesting process to get it all working together. I've programmed a lot of controllers/functions over the years on this and that but this sequencer really challenged me! I'm going to have the cockpit to detail and it will be maiden time.

An interesting point about this radio setup: I'm only using a 10 channel receiver but this aircraft requires FIFTEEN separate functions! But you'll also see I"m using an Aura 12 pro stabilization system (I wouldn't fly without one nowadays). So I harvest all the channels available on the receiver and get the other functions out of the empty Aura ports - that can be set up to use any and all available channels coming out of the transmitter (Spektrum DX18).

mitchilito

My Feedback: (7)

Exciting times in the shop today! I finally saw the landing gear that I made 6 years ago work for the first time!! Still needs some tweaking but I'm very happy with the sequencing and power of operation. Plus I got to see the bear on its gear for the first time!!

Detlef Kunkel

Nice movement- and nice moment :-)

6 years....I cannot believe it

mitchilito

My Feedback: (7)

Rapidly running out of things to do to the Bear!

View from the back. You can see I removed one of the three switches I originally installed. It was going to switch a separate battery for the pump and ignition but they are now each on their own Techaero kill switch. In place of their own battery I increased the two main packs to 6000mah 2s lipos. That ought to do it!

View from front of 50 ounce fuel tank and main and auxiliary air cylinders. I considered an onboard air pump but after gear cycle test I can get two cycles with PLENTY of reserve with this setup so no air pump needed.

mitchilito

My Feedback: (7)

I saw your awesome flight on YouTube Detlef. What a machine! You asked about my progress:

I had a big setback on my Bearcat's progress - although it's actually a huge upgrade. Kind of a long story:

I fly only Spektrum equipment and have been disappointed lately they didn't have any power-management receivers that would work with the Flex Innovations stabilization systems I've come to love (once you fly with one there's no going back). Until lately the best option was to use the power management Aura 12 with the 10 channel Spectrum 10100T receiver. Using this set up you can actually get 16 usable channels. This is the route I went with my new Horizon MB339 jet - which I love BTW. As you see in my earlier posts above this the setup that I also chose to put in my 'Bear. But then I maiden flew the MB339 and was terribly dissatisfied with the amount of receiver/satellite FADES I had: in the thousands!

While all the above what happening, Horizon released their new SYNAPSE powersafe receiver/stabilization system. It was just the ticket for my big-plane needs but it definitely wasn't optimized for my DX18 transmitter SO: I scrapped ALL my current RC equipment and bought a new Spektrum iX20 transmitter (love it) and TWO Synapse systems ($500 apiece!).

I yanked the receiver and Aura out of the jet (after only 4 flights) and installed the synapse in its place. It's an entirely different setup process but very much easier than the Aura. The Synapse and the iX20 transmitter seamlessly communicate in all aspects of setup and operation which makes it such a pleasure to use. Bottom line, after flying it in the jet I LOVE it. The system has twice the satellites and the fades are now in the double digits which is fantastic for a jet.

Here's what the new setup looks like in my MB339:



SO: I bit the bullet and tore the Aura system out of my totally setup Bearcat and just now am in the process of installing the Synapse. What a turn of events! But overall I'm very happy. I was NEVER satisfied with the limited receiver setup for my precious 'Bear.

Detlef Kunkel

Small update from my BC II


After some drawbacks with the BC, i finished mine TODAY for the third time.

I experienced elevator flutter, made a new elevator and have the rear tube enlarged to 20 mm now, 2 servos in the elevator instead of wire driven from inside the fuselage.
Another thing that I learned to fear was the vibration level of the 300 combined with the very hard carbon wing. NOTHING is absorbed here, and the vibration level in the wing was deadly. Not much or quiete high, simply deadly.

I did not expect problems here, but I was wrong before...

I re- balanced the engine, reworked that, and the engine performed A LOT smoother. On my test bench, like a monster brushless now, not more. How happy I was ( it was A LOT of work)


Then back in the airframe, the Vib level was significantly lower, but the frequency did not change. Clear, as it is the interaction of excitation (motor) and natural frequency (airframe, and especially the carbon wing as my surprising problem child. You all know a tuning fork? it doesn't matter how hard you hit it, its frequency is always the same. the wing is nothing else.
Although the motor now runs now balance-free, the excitation of each ignition as a torque impulse is of course still present. And precisely because the carbon wing absorbs nothing at all, it still vibrates well above the level of an identical BC with Moki 250. I had an extremely bad feeling about simply continuing to fly with the great hope that everything would be fine. Not a good strategy for operating fast airplanes.

I have now decoupled the engine with an intermediate plate and 6 rubber elements. It's supposed to run for the first time today.

If it doesn't work again, I'll slowly throw the beast in the dustbin.

gow589

My Feedback: (1)

I tried rubber isolators on an a Stinger 125cc twin. The engine actually shook horribly. I hard mounted it and it was fine.

Detlef Kunkel

You have hit a resonance point with your bearing. This happens again and again, then the geometry of the soft attachment, excitation by the engine, damping by the rubbers was not optimally selected. It can take time to find the optimum solution.

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BTW last night the Moki 300 was started again in the BC.

The result was good to very good; the decoupling of the airframe is not overly strong, but sufficient that there are no longer any harsh vibrations.

Especially in the aileron servo area, where there used to be really deadly frequencies, it has now become much softer.

I am extremely satisfied.


And on the other hand, the engine doesn't rock up at any speed, it stands quite still and even the ignition cables don't vibrate much either.

It was a lot of work, but the life expectancy of the cell should be much better now.

Even the total take off weight is not exceeding the magic 25 kilogram level. Beyound that, you have a lot of trouble here.

Was a hard way to get rid of some nice features in order to stay below 25. It did as you can see :-)



Let me be very clear: what I had here was the unfortunate combination of a pretty hard carbon fiber cell with a really powerful engine.

A friend of mine has the 300 in a balsa airframe and he doesn't notice anything.

It is so soft that it absorbs everything that the motor introduces in terms of frequencies.

mitchilito

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That's great news, Detlef. Now I don't have to fly to Germany and hide in your dustbin!! How about some more flight videos. . . . . . . .

I've been working all week on my Bear as well. I had her almost ready to run/taxi and ran into a landing gear snag. I'll be posting in a day or two with pictures.

Detlef Kunkel

What is a landing gear snag?

Did you damage the BC??

mitchilito

My Feedback: (7)

No. I'm doing the final install of all components and when I got the gear in I did one final pressure check and it leaked - AAAARGGGGG!

As you all know, I remanufactured a set of Century Jet gear for this project and changed almost every single piece. EXCEPT the downlock cylinders. I was hoping to nurse them along long enough for the maiden but they had other plans! These little cylinders really were total crap so I bit the bullet and manufactured my own set of mini-cylinders as well as the mounts. Many of you know that the smaller the item is, the more challenging the machining/manufacture is and these were no exception. I think it took every single tool in my shop to get these done! Another challenge was the fact that there is VERY little room for these actuators once the gear folds up.

Cylinders and mounts

Here are the old cylinders. Glued together (unserviceable), 1/16 soft wire rods (!) etc. New cylinders 1/8 hardened steel rods, MUCH bigger pistons etc.

Those two little mounts statred out as a 2 inch round piece of solid aluminum rod.

Installed on the elbows.

Here is my super-technical, high-tech drawing.

It took every minute of one week to make these little devils. Now, time to mount the engine and run!!

mitchilito

My Feedback: (7)

I installed the engine last evening. I think I really like the "quick engine change package". I used a 5-connector Ashlock connector block and two Festo tube disconnects to hook up EVERYTHING on the firewall. We'll see how that works in service - but it makes for an amazingly simple engine service package.

mitchilito

My Feedback: (7)

Detlef, out of curiosity, what size tires are you using on your bearcat? I've got 5.5 inch tires on mine and they seem a bit big.

Detlef Kunkel

5,5 is perfect in my eyes
For greasing the valves I use high temp teflon ptfe spray

Normal oil does not stick to nothing, the spray is a bit sticky
Nevertheless your Firewall will be pretty scale with a nice oil cover.
Had a stuck valve ln a 180 last week. Valve covers are no reason to purchase a Valach- but a GOOD idea anyhow
Best regards my friend

mitchilito

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So you spray the high temp spray into your exhaust guide manifold? I think I like that idea!

mitchilito

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I wanted to take the Bear out to our little field here for running/taxi tests. That's when I realized I couldn't even transport this beast without some handling equipment. This is my answer to storage/transport. This cradle will be the hoist sling as well as the transport/assembly cradle.


Top two bars are removable. I used hot sand (for the first time) to soften the PVC pipe for the U's. Boy did that work well. The cradle U's will be padded with foam tubes and wrapped with black athletic tape.