P. Richards

My Feedback: (3)

Cermark MB 339 give me a brake

After watching the superman 11 video I noticed that the MB 339 prototype did not have brakes, I also noticed that the plane landed without flaps both turbine and ducted fan versions.
Is it possible that because this jet lands slow that the brakes are needed for extremely short runways only? I know that some jets have a problem with residual thrust and therefore brakes are just a fact of life can anyone elaborate on this.







P. Richards
Mach 2 Jets
Flight Demonstration
Technical Representative

eb2fly

My Feedback: (2)

I know that there is a rule for turbine aircraft to have a rudder (like everyone uses them), but I thought that the AMA had a mandatory rule about brakes on turbine aircraft too. I could be wrong about that. Flaps are optional and only needed for aircraft with high wing loading to add lift at slow speeds and a little drag to help with the effect of risidual idle thrust. I have flown the Cermark MB339 with Ram 500 for power and it can land without flaps as long as it is reasonably light. It is a terrific flying aircraft.

Eric Baugher

EASYTIGER

My Feedback: (119)

You do NOT need brakes for AMA if the plane will stand still at idle thrust. And plenty of them will.

patf

My Feedback: (4)

if this is the plane I think it is, from superman 11, this was Yves prototype he flew at the event changing from turbine to DF during the day. the plane had a bit of trouble slowing down to land with the residual thrust of the turbine and landed very long, once the gear touched it was no big deal at taxi.

P. Richards

My Feedback: (3)

BVM makes a 2 1/4 sport wheel and brake that is tried, tested and true. I guess these would make a welcome addition to this project.













P. Richards
Mach 2 Jets
Flight Demonstration
Technical Reprensentative

rcav8tr

Hi P. Richards

Trim makes a 2.3" wheel and brake set which will work as well. Let me know if your interested.

Ed

P. Richards

My Feedback: (3)

Thanks Ed but it's Too late BVM wheels and brakes are already enroute.













P. Richards
Mach 2 Jets
Flight Demonstration
Technical Representative

P. Richards

My Feedback: (3)

I am proud to say this plane flys great. It is rock solid stable and very comfortable in the air. After 1 flight logged we will go through everything and make sure we have no defects. Jet Cat P80 turbine operated flawlessly.










P. Richards
Mach 2 Jets
Flight Demonstrations
Technical Representative

Thud_Driver

My Feedback: (1)

Have about 97 flights on mine with a P-80. It will sit still at idle without the brakes on, a smidge above idle and it rolls - this on a dry lakebed. No brakes and you'll have one hand tied up holding the airplane during a Jetcat engine start. Without a helper, an engine start emergency will get exciting.

Even on no wind landings the airplane can be slowed down very nice. However, I flew six flights one day without the brakes working and it was only that I was on the lakebed that I was able to handle it. The residual thrust at anything but a dead slow landing will cause the airplane to roll out quite a bit. Taxi back had to be handled by constantly turning to burn off speed and I had to catch it before the the pits.

Unless you have a grass field, a large runway, or a smaller engine, I wouldn't go without the brakes. They just make a pleasant aircraft that much better. I'm using Trim wheels and brakes.

booker-RCU

My Feedback: (43)

Thud_driver
Did you do any of the modifications recommended by Tam? How is your's set up? (servos, Gyro, retracts ect)
Our local club has a 350' grass runway. Would it fly off that with a Ram 500?
Thanks,

Galen

Thud_Driver

My Feedback: (1)

Yes I did all the mods, there is a more complete set of answers in one of the other threads (do a search) but here is a summary:

1. Put the carbon fiber rod across the horizontal tail.
2. Sand off all the paint on places to be glued.
3. Use aeropoxy inside the fuse around all the tail formers and doublers.
4. Take the bolts out of the spar holders in the fuse and replace them with 6/32 bolts. You'll have to cut into the bottom of the fuse to do it. Then aeropoxy the spar holders down good.
5. Put 1/4 ply vertical shear webs under each hardwood gear mount (that's 2 per side). Make sure you put a thin ply plate on the upper wing surface (inside) to take the load from the verticals. You have to cut into the root rib to get at all of this.
6. The wing, stabs, fin are all fragile, try not to handle them.
7. I made two lite ply plates, 2"x4" and expoxied them to the fuse side for servo mounts for the rudder and elev. Location right at aft bulkhead at rear of hatch.
8. Used carbon fiber pushrods for rudder and elev. Had to file open the holes in one of the aft bulkheads to get a clean run (look inside the tail and you'll see the lightening holes).
9. Mounted the wing servo's on the access hatch and used 4-40 hardware and robart horns.
10. Springair 3/16" gear at first - causes the airplane to act like a pogo stick mostly on landing. Absolutely find some sort of gear with oleo's. I'm using Eurokit struts now. Fixed the problem, but I can't retract the gear until I mod the wing.
11. Airtonics Stylus. 161's on flaps & elev. 102's with EMS bearing kits on everything else. Tower TS-10's on brakes and gear. No gyro. 45 degrees of flaps - 2" deflection at TE at root.
12. Cg is 1/2" behind forward hatch line. I seguence the fuel so that the saddle tanks feed the large tank forward for a forward Cg on landing to reduce the bounce tendancy. I used batteries to make good on the Cg.
13. Make sure you use a BVM UAT.
14. There isn't anything to glue hinges into in a lot of places. I used Probond Polyurethane and robart hinge points. Drill hole, squirt water in, squirt glue in, use hinge point to plug hole, hold surface hinge line down so glue puddles and foams around hinge point. Painful, but worked.

There were other things too. Make sure you do the spar holder mod first, else it's really hard to do. I waited 20 or so flights and it was hard. But the fix made a serious roll trim problem go away - the spar holder had shifted on the bolts and gave an incidence problem on one side.

I still don't trust the wings so I try not to horse it around. Don't cut holes in the stabs and mount servos there.

Thud_Driver

My Feedback: (1)

350' grass with RAM 500??? My takeoff on the dry lake bed with P-80 is ~100 - 125 feet. I can land, usually within +/- 50' or so. On no wind days, I'm in idle from the middle of the base turn, too high, too fast and it's long. You can probably manage better with the smaller engine. I hope you have somewhere to go when the 350' runs out because I think you will be out there sooner or later, but not very often.

rcav8tr

Hi Gents

Are you sure the kits you purchased are ARFs? They sound more like semi-kits to me, with all the mods you have to do! You'd be better off buying the original kit!

My $02 CDN.
Ed

BernieG

I thought ARF means Almost Ready to Finish, anyway !!! ;-)

Bernard

booker-RCU

My Feedback: (43)

Thud_Driver,
Hey, thanks for the great comments. I've copied them off and put them in a file for future reference. If the wind is blowing right I have a good overrun. The other end is a ditch and then a hay field. Not so good!!
Thanks again,
Galen

Thud_Driver

My Feedback: (1)

Well, compared to an actual kit, it is an ARF. While I didn't keep close track, I figure around 60-70 hours which includes the mods and figuring out where to put everything. In fact, the mods took a significant portion of the hours. Inclusion of the engine mount formers that they eliminated, which couldn't have cost even a buck, would have saved 6 or 8 of those hours. Another 6 or 8 went into fixing the wing mounts. Roughly 3 weeks out of the box to flight and that's not bad.

At least I didn't have to paint it, which is at least 40-50% of the build time for me. Actually I did have to put some paint on it. In the desert here, with deep blue sky, the airplane is really hard to see. So I added a bunch of extra white stripes on the wings and tail.

My kit had the number 006 on the box and was in the first batch. Rumor was that later kits would have a bunch of these mods in them. I'd be interested to hear if that happened.

Since the thing flys so effortlessly, all the swear words I used during building were wasted. This bird is doing for me exactly what I wanted which is to get a lot of turbine time quickly and without a ton of down time. 97 flights since July 17 with 2 weeks out of town and a couple other interuptions isn't bad either.

P. Richards

My Feedback: (3)

My MB339 cockpit

P. Richards

My Feedback: (3)

check this out

P. Richards

My Feedback: (3)

front view

Thud_Driver

My Feedback: (1)

P. Richards

Curious, getting any bounced landings out of the wire gear struts???

jks

P. Richards ,
Nice cockpit and panels. Did they come with the kit, or.......?
Jim

P. Richards

My Feedback: (3)

No bounce on landing I have approximately 1 and a half degree of
positive angle of attack and this provides me with smooth take offs and landings. The only thing I have to remember is to slow the jet down.

P. Richards

My Feedback: (3)

The cockpit panels that come with the kit are fairly cheesy Rick Meyer located a picture of the actual cockpit and copied them onto his printer and as you can see it came out good. Sorry I don't know what website he found.

randykrul

My Feedback: (2)

I think I talked to you at Fresno about the mods to the MB339. I started on mine, and the question is which strut, part Number etc. did you get from Eurokit. They have some for 12 lb models and some for 20 lb models. Did you get the same strut for the nose gear as well? Have you made the retract mods yet? Any helpful tips in doing this?
Since I am building I would prefer to make retract modifications now.
Between this post and Tam's web site I think I have a pretty good picture of all the mods needed. Mine will be powered by a JDE54 ( 12lbs ) so I don't think I can overspeed this model, plus the engine is really light so I can keep the overall weight down.
Thanks For Your Input, hopefully saving any structural mishaps.
Randy Krul

Thud_Driver

My Feedback: (1)

Yes I was at Fresno on Saturday only and probably did talk to you. What you saw was:

15082/000 on the mains
15072/000 on the nose

http://www.eurokitplane.com/retractf...ize1.htm#15080

These were the smallest trailing arm units they had for the size tires I was using: 2.5" mains, 2.25 nose. All the axles are 5/32". Took about 4 weeks to get them, but they are holding up fine and the price is great.

I outlined a new retract cavity on the wing the other day and it looks like almost 1.5" longer with some other bumps as well. Would have to cut a rib but that's probably not a big deal. You might want to mold up new gear wells

Three suggestions: (1) Drill out the mains to take a 3/16" wire if you're using Spring Aire HD. I haven't bent mine hardly with 5/32" but I think it needs a bigger pin. (2) You might want to use the nose gear style (072) all the way around if you're willing to use smaller tires. I think they're strong enough, particularly with the lighter weight you'll have. They can be shortened about 3/8"-1/2", but you might not be able to drill out for 3/16". (3)The 082 mains could be shortened down 1/2" IF you have a retract unit which will take a 1/2" strut and IF that retract unit has a bottom which will provide an end cap for the strut spring.

The airplane isn't real fast. I went through the traps at Fresno at 140mph, gear down, not much dive and probably at full power but since I don't know which pass it was, I can't say for sure what the power setting was. I was running close to flat out all day since it seemed so slow compared to everbody else.

The mains are going to come off and go onto my Top Cat soon. I'll retofit a set of smaller units later. They've made all my landing probems go away.

Good luck, after Wed am, I'm gone for two weeks.