tucson

My Feedback: (1)

I have now 30 flights on my Avanti and have worn out a set of tires due to my brakes locking up and causing flat spots on my tires. Very frustrating as I have tried Vaseline , light oils, and others, lightly coated on the inside of the wheel hub.

I fly off a hard surface runway and it is tearing up my tires with this problem.

What are other pilots doing to prevent this problem? I am using the same air tank with approx 100 lbs of pressure I use for my gear. Maybe that's the problem. I am also using a jet tronics electronic valve.

It appears the size of the brake disk surface could be to large to give smooth stopping power. I have also used a air restrictor on the brake valve.

Any thoughts? I have had 6 jets and never seen this bad of a brake problem before.

Thanks,

Stan

wfield0455

My Feedback: (7)

Stan,

I usually use a separate air tanks for my brakes and gear and I tend to run about 20% - 30% less air pressure on the brakes. This has helped with my other jets but I haven't gotten around to assembling my Avanti yet so I can't say if it will help with the Avanti or not yet.

Is the Jettronics valve you're using the 2 button, low loss, proportional brake valve? How are you activating it, down elevator? If so, if you plugged a servo into your brake channel, would you get travel from center to 1 extreme of full travel in both directions? Just wondering if perhaps the control pulse range is "compressed" and making smooth braking more difficult.

Kevin_W

My Feedback: (1)

My brakes work great with the UP-6 valve.
The retracts, on the other hand, have been a constant problem.
I am in the process of changing the out for Electron retracts. I had to do some machining on the struts, re-position the main gear mounting blocks, and completely re-engineer the nose gear mounts and gear door.
It will be worth it in the end though to have reliable retracts.

tucson

My Feedback: (1)

Hi Wayne,

I just hooked up an external air tank with an air gauge tied it directly to each retract to see how much pressure was needed to completely lock the wheel from turning.

At 30-40 lbs of pressure I was able to turn the wheel with moderate pressure. 60 lbs took a lot of pressure to turn the wheel, to much in my opinion, 80 lbs and above was very difficult and acted as if it was fully locked.

The Jetronics valve I am using is the on off only valve. I realize the pulse valve would work better, and might have to go to one for this brake assembly.

The pressure test I did is telling me I need to add a small air tank and run low pressure to get this system to work.

I really would like to use a electric brake system as what I have heard they are fully proportional. I don't know if there is one that would fit into the Avanti wheel hubs. Maybe some one has already done it.

Stan

wfield0455

My Feedback: (7)

Hi Stan,

Well it sounds like you understand what's happening now. That Jettronics valve you're using can be made to operate in pulsed mode (proportional) can't it? I realize that will make it use much more air but since it sounds like you would need a separate airtank anyways, that shouldn't be a problem..

I like the sound of electric brakes as well but at approximately $250 for the brakes and controller, if you need to drop another $150 - $200 for wheels it starts getting kind of expensive. Since I haven't built my Avanti yet, I'm not sure what it comes with for wheels. The Electric brake unit that Dreamworks sells says it's designed to work with the Intarico split rim hubs. I'm speculating but I suspect the most important thing about the hub is there are bolt holes to mount the brake disk onto. Maybe someone that's looked at this already will have more info..

tucson

My Feedback: (1)

Hi Wayne,

Another thing I have noticed is that the brake pads they are using appears to have soaked up some of the oil or grease I put on the inside of the hub. Now that is preventing the pad to slide as easily as a new pad. They appear to stick.

I have another new set of pads and they slide smoother on the inside of the hub then the oil soaked ones. I did remove any trace of oil or grease on the hub with acetone.

If you get a chance take a look at your brake set up and see what you think.

Stan

wfield0455

My Feedback: (7)

Hi Stan,

Todd at Dreamworks once told me not to lube the brakes so it's something I've never done. I've always just played with the air pressure and the brake valve (I've always used proportional valves) to get them so that at full on they won't quite lock and I've never had a problem. I just fished the gear out of the kit and pulled the Wheel from one of the mains. It looks pretty nicely made to me but unfortunately, I don't have one of the Intarico Split rim wheels that the Dreamworks ProBrake Electric brake conversion kits are designed for to compare it against. I'm guessing that if you were willing to do enough work and modify things slightly, it could be made to work but I doubt it would be a drop in replacement. If I get a chance, I may send an email to Dreamworks asking if they've looked at the Avanti S landing gear to see it their ProBrake Electric brake conversion could be made to work with it or not..

tucson

My Feedback: (1)

Wayne, Todd's brakes at least the ones I have used in my flash work differently then the Avanti. The Avanti uses a brake pad where Todd's uses a rubber that expands with air pressure. To me the size of the brake pad is over kill for the weight of the Avanti.

Anyway the reduction in air pressure with another air tank will probably work much better.

Let us know what Dreamworks says about an electric conversion.

Stan

Kevin_W

My Feedback: (1)

I believe that Dreamworks electric brakes use a brake pad that presses on the wheel hub just like the pneumatic brakes that come with the Avanti. He may even have one that is the same diameter. The biggest problem is the way the Avanti's brakes are attached to the struts. The axle appears to be press fit through the brake hub and into the strut.
It would be very difficult to remove that axle without the proper fixture, and even if you could you would have to make sure that the electric brake hub you were installing had exactly the same dimensions as the original, otherwise the axle length will be incorrect and the bearings in the wheel will either bind when you tighten the screw, or the wheel will be able to slide laterally on the axle.
The strut/brake/wheel combination is on the Avanti is very well designed and precisely built, but it is not readily adaptable to other products without doing a fair amount of machining.

I ran into similar problems when I decided to swap the pneumatic retracts for electric. The top of the strut that fits in the stock retract is a weird size, so I had to cut it off, drill it out, and make a steel adapter to fit between the strut and the retract's pivot block.
I contemplated electric brakes too, but the amount of work to modify these struts, or the expense of buying new struts and wheels, made me decide against it for now.

wfield0455

My Feedback: (7)

What you describe is the same is installed in my Boomerang XL, an O ring that expands against the inside of the drum due to air pressure.

Looking at the install instructions for the Dreamworks ProBrake conversion, it appears completely different than that and much more similar to the Avantis brakes. The instructions show that you remove 3 of 6 screws the screws from the Intairco, split rim hub and attach a steel brake disk inside, held in place by the 3 screws that were previously removed, From there it appears the new electron brake mechanism simply slides inside the hub and acts upon the steel disk that was installed. From reading the instructions, it really looks very similar to the Avanti's brake setup but I don't know if there would be enough room inside the Avanti's hub to accept the new brake mechanism or whether the hole pattern in the Avanti's wheels would line up properly, etc. Still, it looks like a possibility.

wfield0455

My Feedback: (7)

Kevin,

Excellent information, I had already replied to Stan saying some of the same info before I read your post. A couple of questions if you don't mind..

1) You mention that the top of the Avanti's struts is an unusual size. Was it too small or too big? It would seem that it it was too big that it should be simple enough to turn it down slightly slightly and if too small, perhaps a simple bushing could be machined. In the worst case it could be cut, drilled and replaced with an adapter as you suggested.

I only quickly disassembled the brakes on my Avanti this morning and also noticed there was no obvious way to remove the axle. Still as you suggested, the axle should be able to be pressed out and a new one machined to the correct length to replace it, as long as everything else will fit inside the hub. Even if the holes in the Avanti's rim are spaced differently than the Intairco hub the Dreamworks brakes are designed for, it appears the brake disk is a simple steel plate, drilled to match the bolt pattern of the Intairco hub. It sounds easy enough to make a replacement if someone really wanted the electric brakes. I'm very interested in your feedback as you have obviously had more time to think about this than I have and some of my assumptions may be totally incorrect.

tucson

My Feedback: (1)

Hi Kevin,

I have the same problem with the gear also. It seems every 4 flights or so I had to go and tighten the retract screws. A friend let me try a space age mixture that works better then the normal blue lock tight. It has helped.

I think I will stop here as I do not want to start redesigning the Avanti gear system. If a replacement set of gear will fit the Avanti wing I might be interested..

As far as brakes are concerned, I will continue to play with that till I am satisfied.

The plane does fly great though, don't you think

Wayne,for now I am just going to stick with the pneumatics for brakes, between trying to learn the Jeti transmitter and the brakes I am going into overload

Stan

Kevin_W

My Feedback: (1)

Wayne,
The top of the strut is considerably smaller than the standard 1/2" that most suitable retracts accept (I am using Electron retracts BTW), I don't remember the exact measurement, but I would guess it was around 14mm.
Unless you have access to large lathe, machining the top of the strut is more difficult that it first seems since you will have to mount the bottom end of the strut into the chuck.
I racked my brain for quite a while to figure out a way to mount them on my little Harbor Freight lathe. I finally figured out that the hole through my 4 jaw chuck was large enough to accept the entire strut, and I could push it through the back side, but then the bottom part of the strut would prevent me from mounting the chuck to the lathe. I ended up making some 1.75" aluminum block standoffs to go between the chuck and the lathe. This allowed the fat bottom part of the strut to stick out the back of the 4 jaw chuck with clearance to still mount the chuck. I just had to put the strut in the chuck, then mount the chuck to the lathe, then center it, before I could do any cutting. (I'm sure that probably sounds confusing, I can post pictures this evening if needed).
At any rate, once the strut was chucked into the lathe, it was very simple to do the machining.

As far as the axle/brake/strut assembly, I think it is press fit, but I am not 100% sure of that. It could be that the axle is threaded into the strut, but I didn't want to risk damage trying to disassemble it. A press fit seems like the most likely scenario though.
Switching to the Electron retracts is a fair amount of work, and my shop time is rather limited, so I decided to just concentrate on that aspect of the project for right now. Once that is done I might look more closely at electric brakes.

Instructor

My Feedback: (16)

I had to cut a dual wall pipe that was given to me for a shorter application. When I went to center the outer pipe to the inner pipe, I was stuck for ideas. A friend came up with this idea. Get some 3/16" aluminum pop rivets and insert them from the outside. When they are collapsed, you will have about 3/16" between the two pipes. Worked just fine with my pipe....

Larry/Instructor

kev-o

My Feedback: (1)

Sorry for the late replys here.

Festo makes a valve that you can vary the rate of flow to the brakes they work well. I would try that and see what you think I used them on a few planes on the past and had great results. As for the gear hanging up. As I do on any build I completely disassemble and lube everything and use fresh BLUE locative and have had great results down to about 35-40 lbs. I get 3 cycles each way easily and have got as many as 5 with no issues. We need one cycle up and one down. I top up air every flight. I had close to 30 flights in mine as well but all from grass so far it's a great airframe.

Kevin

tucson

My Feedback: (1)

Hi Kevin,

Thanks for the info on the Festo valve. My gear cycles down to 35-40 lbs as well. The problem I had was screws not staying tight even with blue loctite.

The brakes have been my biggest problem. The plane is great.A *****cat to land. My favorite plane to fly.

Stan.

Kevin_W

My Feedback: (1)

Stan,
I just noticed this line from your orignial post about your brake problems.
I don't think using a restrictor on the brakes is a good idea. A restrictor does not restrict the pressure going to the brakes, it just restricts how quickly that pressure can move through the air line.
Remember that the air lines going to the brakes are a two way street, the air is delivered to the brakes from the valve at high pressure, then when the valve releases that air reverses through the line to exhaust back at the valve. If you have a restrictor in the line it will slow the rate at which the exhaust air can move out of the brakes, and that could cause a significant delay between the valve command and the actual release of the brakes.

tucson

My Feedback: (1)

Kevin,

Never thought of it that way. Sounds logical. In addition to using a separate air tank with a much lower pressure I will also remove the restrictor.

Stan

tucson

My Feedback: (1)

as a follow up to my brake problem this how it turned out

Additional air tank for brakes. Pressure set at 45 lbs, Two flights today perfect stops straight away.

I did replace the brake pads with new ones. I had put a light coat of oil on the inside of the wheel hub with the old pads,. The pads absorbed some of the oil and caused the pads to stick.

Not a good idea to lightly grease where the pads ride when the brake is applied.

Anyway it works perfect now. No more ground loops when I apply the brakes.

Stan

Instructor

My Feedback: (16)

Hi Stan,

I don't want you to think I'm trying to be smart here, but my vocation was an automotive mechanic. When we had a customer bring in their car saying the brakes grabbed, the first thing we looked at were the pads or the rear lining. 9 times out of 10, we would find grease on them. Replacing the pads or rear lining, plus the wheel seal to keep the grease off the new brakes, solved the problem every time. If the brake pads of your Avanti are similar to brakes used in the auto industry, keeping then clean is the right way to go. I have used silicone grease on O-ring brakes to keep them from grabbing, but not on any brake that uses a pad or disc....

Larry

tucson

My Feedback: (1)

Hi Larry,

Thanks for the info about brake pad usage..

This was the first time I used a brake pad in any of my jets.

All my brakes in previous models used an O ring which I did use a light grease on.

This was a learning experience for me about the use of pads.

They work great now.

Stan

wfield0455

My Feedback: (7)

Kevin,

I just noticed that in addition to and e-brake upgrade package, Dreamworks also offers an e-retract upgrade kit. You basically disassemble your retract side frames and replace the air cylinder with their actuator. Did you look into this at all when you were messing with the Avanti's retracts? It looks like it may well work but I'm not certain how standardized the retract units are.

F1 Rocket

FYI
I have a complete set of retracts/brakes and thrust vectoring pipe for the Avanti S. Please PM me if interested.

Kevin_W

My Feedback: (1)

Wayne,
I have seen those too. They will not work with the Sebart retracts. The electric atuators work by turning a jack screw, the slider in the retract is threaded onto the that shaft which then moves back and forth to actuate the pivot block. The jack screw remains the same length inside the retract mechanism. The design of the Sebart retracts makes it impossible for them to work with that jack shaft in there.
Believe me, it would have been much easier to convert this thing by using the stock retract assemblies, but none of the commercially available electric coversions will work with them the way they are designed.
Modifying all the gear mounts to accept the Electron retracts was the only way to go.

1moparman1

My Feedback: (28)

Just got one last week, cant wait to start on it