DUCMOZ

Well, tested and it looks like I have not been able to fix the entire area. So, the tank had to come out. I have masked a band all around the seam and sanded lightly, unfortunately I am out of Aeropoxy. Will order some tomorrow and Aeropoxy it all around. Hopefully that would take care of it. Maybe end of next week will be ready again. If not, will have to order a new tank.

Behzad

Blancr

Canopy Latch
In my 'canopy latch' bag I have these components:

There is already a brass tube installed in the fus to accept the pin so I'm wondering how the designer of this approach imagined the other three items would be used - particularly the odd sized nut. It's perfectly straightforward to assemble a linkage but I'm just intrigued by the seeming unrelated nature of these items.
Grateful for any thoughts.
Bob

Dave Wilshere

B

The nut goes onto the length of wire to give you something to pull against. The tube with notch can be used to secure the canopy latch open, makes the cockpit easier to remove single handed...

D

Blancr

ok - thanks Dave.
B

DUCMOZ

Okay guys, I flew the plane. The takeoff and flying was straight forward. It hit the 5 minute mark and it was all well. I lowered the gears, all okay, lowered the flaps, all okay for about 10 seconds and then the plane went if to a shallow dive. I pulled on the elevator but nothing happened. Went to full throttle and pulled again still nothing. At this point It was about 15 feet in the air. I tried to bring the flaps up but nothing happened so it hit the soft grass with the nose. I had full Airlons and power control.

frame is total. The turbine, tank, pipe, fin and gears are fine. I just broke the soft landing gear covers. Sad ending to a long build for this project. I will be probably take the covers off the gears and sell them and go to Something else.

Behzad

jws_aces

My Feedback: (33)

DAMN!! I am so sorry Behzad...I know the feeling. You may not know but I lost mine at Ky jets. I have a flame out at the 6min mark and made a perfect landing but had a on board fire that I not sure how it started. I have a really good idea but not sure.

I had close to 160 flights. Even with the fire in the middle the elevator leads didn't burn and I landed it. It burn completely. I did mange to salvage the landing gear. I have rebuilt them and they are ready for the new one.

I couldn't remember did you have the elevators in the rear?

I hope you try again. I am starting on my second one hopefully this week.

Did you salvage the cockpit? Canopy? Maybe I could get that from if you don't build again.

DUCMOZ

Hi Jeff

thanks. My elevator servos were on the back. They seem fine with one having a damaged gear which I am mostly sure it happened in the impact. I had 89mm landing flaps. I could understand that it would want to make it nose down a little but not at the cost of full elevator. I have to make a work trip tomorrow but I will check stuff after I get back. Unfortunately, the cockpit and the canopy were both destroyed. I spent a lot of time on them and nothing is left. I think I am done with the hawk. Maybe a Tomahawk 3.5 viper or a Mibo A10 once I lose my mind again!

Behzad

Blancr

Hi Behzad

I'm so sorry to hear your news especially after the great effort you made to create an outstanding plane. Do you think you will be able to find the cause?

Bob

lavi rider

My Feedback: (6)

One thing that might be the reason for elevator control loss is that the servos were not perfectly matched along their entire travel perhaps just end and mid points . Just my two cents ... Sorry for your loss .

jseppanen

Sorry for your loss Behzad!

Sounds exactly the same i had with my carf/sg Hawk in JWM 2013 in Switzerland. I had servos in front. The long pushrod was intact after the crash. And so was both servos. I made about 15 flights with the plane before the crash - it had absolutely no need for flap to elevator mix. Balance point issue if there is need for a lot of up elevator with flap in this Hawk. Speed is also a factor of course...In my case I have no other explanation than a total loss of signal or power of the whole plane. No control on any surface for several seconds...

I'm still (very) slowly building another one. Love the way it flies!

jws_aces

My Feedback: (33)

WOW! I spoke with Mike Haddox and he lost his on the 3rd flight. Simular loss of elevator control. He had the servos up front and had a new rod built and felt like that was not the failure.

I don't know if any one of the crashes involed the use of a Matchbox. I ran my straight to the receiver and use 2 channels. Yes I adjusted the end points to match. I plan on doing the same on my new bird.

Sorry for all the bad luck. This is a awesome jet to fly and that is the reason I am doing it again.

jseppanen

Yes, this is interesting! And a bit scary too!

I didn't use Matchbox or anything similar. Two servos, two channels, Orbit Powerjack with two 7008 receivers (not redundant)...small rx batteries becouse of the 20kg JWM weight limit. And my guess is these batteries were not up to the task of delivering power (although tested with 20A short time) to all the servos when lowering the flaps in final turn of the first competition flight! My next Hawk will have nice large LiFe rx batteries...

For those interested, I still occasionally fly my Skymaster 1:4,75 Hawk. Well over 300 (400?) flights in 7 seasons, stopped counting at some point. It has pretty similar elevator servo system with dual servos at the back. No need for flap to ele mix. Never a problem. Even if opening flaps in higher speed. Of course wants to dive a bit until speed slows down but easy to control.

jws_aces

My Feedback: (33)

I only use Life with the powersafe Spektrum receiver. The only time I had a scare was the first flight with the Cortex gyro. I use a lot of expo and when I was one the downwind to base turn I thought it was going down until I finally move the sticks far enough to give it enough elevator. I had to take out at least half of my expo.

Once I got it adjusted I never saw anything close to that again. I use the 4700mah zippy life packs with no issues. I swap them out about every 5 flights with fresh charged ones just to be safe.

I installed mine just behind the main doors so I could remove them.

jws_aces

My Feedback: (33)

I also wore out a 1.5 SM hawk and I don't remember have to mix the elevator for flaps. Now I use flight modes and retrim after flaps deployment. My flight mode switch is my flap switch so it remembers each setting for each position.

If you do this make sure you are up high when you deploy the flaps because the trim goes to center and if you have a lot of up trim the bird will dive hard until your retrim.

I don't think this is the cause of the crashes but it is something to consider if you had to trim it alot without flaps and you are using a flight mode.

jseppanen

Yes, that method works! I use a bit different approach. On first few flights I have FLAP to ELE mix trim in left dial pot. Adjust it to my liking and then after couple of flights transfer that amount permanently to the mix and get the trim off the LD (18MZ). Normally use that to trim nose wheel.

Someone should measure current flow to elevator AND flap servos in flight! And when opening flaps at bit higher speeds? I'd like to know for sure...

jws_aces

My Feedback: (33)

I do a test on the ground is simular to a full size to check movement and batteries. I do a full control movement and watch my battery volts on my telementry. I also have alarms set that is the batteries fall below 5.5volts it will let me know. I know the telemtry works because I fly a lot of 1/5th scale electric warbirds with full telementy on the power packs 12s and AMP pulls and they are spot on.

I used 8711s on my entire bird. I really don't think amps is the problem unless you are binding the flaps with too much travel. I know mine did'nt travel as much as I felt they should have but I was limited by the servo arm travel in the wing.

jws_aces

My Feedback: (33)

If there was any kind of current flow during flight the Alarms would have sound also I check the Min and Max readings after flight. The telementy will record those of the batteries, GPS info also.

That is another way of monitoring the batteries (life)

DrScoles

My Feedback: (18)

Behzad is probably the most detail oriented and cautious jet guy I know. Slim chance he missed anything. Just sucks.

jseppanen

Yes DrScoles, seeing the work he has done, that's easy to believe! It was a really nice Hawk! Really sucks, I know!

My SG Hawk was consuming 300-400mAh per flight, which I consider pretty normal. Nothing was binding anywhere. Rf signal loss for some reason is the leading theory in my crash case...will most likely never know for sure. After that I've flown lots of flights with different planes with the same tx. At least with 6014 receivers the radio link has been bullet proof. Waiting for my first R7018SB receiver so I can do some testing with that.

As for rx batteries, I have tested many LiFes and even the quite small 2100mAh Nanotechs can easily sustain constant 20A for almost all capacity (at good voltage). Servos would burn first. But I really like 2300mAh A123's for their over all robust design and reliability.

Btw. I did't use the kevlar tank provided with the kit, weight issue mainly in JWM plane. Five liter PET water "bottle" suits perfect in place (no surprise!). Weighs a fraction of the original and they are STRONG! After atomizing front fuselage all the way to wing bending the wing tube, fuel tank was in perfect shape. Found that about 30 meters in front of the wreckage. Thrust tube and dented JB220 was halfway between plane and fuel tank...

jseppanen

Couple of pics of my plane. Before and after. No worries, a new one is under construction and hopefully survives a bit longer...

DUCMOZ

Hi Guys, first, thank to many of you for your comments about the loss of the Hawk. Now, to just clear some questions up, my history is that I started building ducted fan jets in 1988 with. BVM kits while I was very involved in pattern. Without exaturation i can say that I built most of BVM and old yellow aircraft kits and now doing the newer modern models. Also don't have any problem to say it if I messed something up. In this case, as I mentioned, I was using the servos on the back with two linkages as the modification called for after the first crash due to the old linkage system problem. I did about 40 minutes of testing on the stab by working the servos and measuring the temperature of them. It started by having about 30 degree temperature gap but at the end, they were running at 4 degree difference consistently and that satisfied me. Although draggy, the plane flew well for five minutes and then things went bad. While flying, a good friend took some great pictures and just sent them to me. We have three shots from the time I went on flap to the time that the plane touched the ground. I can clearly see that the flaps are down and surprisingly the elevators are in neutural position while I was pulling as far as the stick goes up. From this, I can say that something went bad on the back and it was not flap issue.

I had to make a Work trip today but since the back of the plane is intact, I could see last night that all wires are in perfect condition so we can rule that out (they were nicely routed and are in heat resistance material) I was using a powerbox competition and two Li-ion packs for receiver which are still perfect and fully charged. When I get back, I will test the servos and the powerbox and report. But, as you can see, there are too many of these going down for similar causes. It is a shame as the model is nice and it deserves better. In my case, i only can spend one hour here and there and it took me form May 2013 until now to finish it so it is needless to say that looking for another one would be not so wise unless someone smarter than me jumps in and redesign the elevator part of the plane.

Thanks again and I will report as I find out more.

Behzad

AKB

My Feedback: (6)

Hi Behzad
Very sorry to hear about your loss. I have lost quit a few lately as well and it sure is rough at the start as you well know. But the one thing for sure is, after you have been in this for quit a while, somewhere we get the senseless reason to do it all over again. Hope to see you in Princeton in the fall and we can talk about our ones that got away on us.

Alan

jws_aces

My Feedback: (33)

I have no doubt that you have more experience than I have when it comes to building jets. I don't want to say anything to create an argument but the one thing that bothers me about your set up that I have read about is that you were using the Powerbox. I have not used one and I no where near an expert but I have seen a number of jets go in with loss of control and they were using Powerbox units.

I use the K.I.S. method of building. "Keep it simple" The less you have to use the less chances of a failure.

I have to ask was the elevator mix done in radio or the Powerbox? I do know there is not a issue with this design of the elevator.

I have way to many fights to prove that. I have let at least 10 different people fly mine. I would still have if not for a festo filter. Yes after so many wonderful flights I added one after I was told I should always have between the pump and turbine..I would rather have a flame out and have to send my turbine back for repair instead of having to sit there and watch it burn to the ground.

if you have a festo filter in your jet rip it out!

I just got my new one today and can't wait to get back up in the air.

lets us know what you find out.

Again, Sorry for your loss I know how you feel and I hope you find a reason to build another one.

jws_aces

My Feedback: (33)

You know something just hit me....Did you guys wrap the pipe under the servos with heat blanket? I did on mine. Maybe that overheat the servos if you didn't have any thing protecting the servos.

I know in the manual it shows the pipe hold down with nothing on the pipe. I also used Tams pipe that is a double wall pipe and cools better.



Just another thought.

David Gladwin

Very sorry to hear of your losses, guys, and the number of Hawks which have crashed in this way IS worrying. I personally have seen two, Jan's at Meiringen and another at J Power a couple of years ago.
What is the common component as equipment and installation configuration varies ?
That has to be the large stab, bearing, it is quite stiff. So I wonder if you guys had lubricated it as the heat from the tailpipe may have dried it out leading to seizure. If these components experience heat differential expansion, leading to stiffening or seizure, is also possible. I will test mine for that . That is my number one suspicion.
Second, for those using front servos, is the brass tube pushrod bearing, mine can be lubed via the dummy GST exhaust.

On my two Airworld Hawks, the servos are hard mounted in the rear of the fuselage and are protected from heat by a balsa sheet cover, above the pipe, faced with Wren foil faced heat blanket, measured temperature rise using my old JPX probe, is negligible. It's worth protecting the bearings and, if used, the rear servos, weighs little and is easy to do.

With the hard mounted dual servos, matching them at centres and ends is not good enough. I measured the amperage throughout travel and needed to adjust at several intermediate points to get exact matching, otherwise current draw could be significant. The Weatronics system allows this to be done VERY precisely. The data recording facility of the Weatronics system would vey likely have pinpointed these problems, I just can't speak too highly of this radio and the data recording shows that total current on the ground is around 1.5 amps, and about 3 (servo driven gear doorts closed) in flight. The time of highest current draw, briefly 9 amps, is when the flaps are moving to full down position.

After the JWM ( flying my 8 year old AW Hawk) I will test fly mine. My servos are front mounted JR. 6311 HVs, Weatronic 12-22 with dual Powerbox batteries. I also replaced the screws supplied with the small ball links on the stab. " rocker", the originals were too loose, and created too much slop in the stab.

Finally Festo filters! The usual plastic Festo filter is designed to be used in gaseous VACUUM applications and must never be used in onboard fuel pressure applications, that is WAY outside the design specs. That has been discussed many times on RCU and I made a note about this problem in my column in RCJI.

Perhaps we will never know the real cause of those unfortunate crashes but I do think the bearings are the prime suspect.

If if there are any SG Hawks at Leutkirch I will discuss installation with pilots, perhaps we can get to the cause of the problem.

David.