olecr

Yes it’s definitely too soft. I also flies on grass and the plane was crazy to handle in takeoff.
The way I stiffened the springs was that I took a shims on both sides of the spring and put an ordinary fuel tube inside the spring. That make the spring much stiffer.

Kraftei

Hi Jesus,

unfortunately I know exactly how you feel, because looking at the last seconds of your video, I felt watching a replay of my maiden flight but with one difference: you had a couple of minutes fun with her while mine died after 10 seconds on her maiden flight, already on the first turn - destroyed in seconds

What happend :
after a very smooth take off I throttled down to about 70% of the 120N engine (the BF 100 really gave her a punch - Wow what an engine!).
My measurement to correct the thrust axis and to move the tank into the CG absolutely succeded in very impressive way!
The climbing was really flat and smooth and she felt really well behaving at the stick.
At a height of about 150 ft I brought her in a very slight big left turn with very little left aileron and little elevator.
Not wanting to risk an elevator stall if it would have been necessary to pull a bit more for a closer turn, I decided to maintain the left turn with left rudder while I wanted to "support" the left wing by giving very carefully a little right aileron. But as soon as I did this (once again: i did this very carefully and with very little travel!), still beeing in a big left turn, she immitiadely snapped (!) to the right into a spiral spin untill the impact - It happend in a second so I had no chance to recover her :-(

Neither I nor the other pilots around couldn't believe what we saw. We all agreed that this was a typical tip-stall but none had an idea why it happend!
Speed was absolutely OK and CG was about 140mm totally empty (tank was exactly IN the CG, with filled hopper CG was apprx. 138mm)
With the flaps full down (which have not been activated on take off) I also mixed 2mm aileron up. The installation was very neat (so obviously no technical problems) so what did I wrong ???

Obviously either she's a real beast or I wasn't skilled enough for her (or probably both)

Anyway, very sad! She was a real beauty!


kind regards

Holger

causeitflies

Holger,
Was a beautiful plane, sorry for the loss.
I think the cross controlling is what did you in. It needs to fly through the turns, not skid.

Ron101

My Feedback: (22)

I have one of these in E power... mine seems to fly well. I only have 3 flights due to power system problems.
My old setup was 23.5 pounds, had tons of power on 14s ...... but I had two ESC issues and a fire

I swapped out to a much lighter 12s setup and I'm now 21.5 pounds loaded and ready to fly... I moved the CG to 135mm and reduced the flaps to I think about 15 mm
I had a huge amount a flap at first (all I could get) and it did some strange things, I think it was blanking out the elevator

so I'm really excited to get it back out with the new setup, I know when this plane is dialed it flies really sweet... I watch Pablo flies his for many flight at California jets a few years ago and knew I had to have one. I went with full gear doors and a cockpit. I think it I ever do a new one I'll strip it down to bare bones like Pablo

his is 20 pounds loaded and flies killer..... so maybe it's just a wing loading issue

look how well his flies

[youtube]http://www.youtube.com/watch?v=oVXJKfagL10&list=FLZs_85GBgFakA1dJ1oKqyhA&index=7&feature=plpp_video[/youtube]

EDFCrazy

I noticed in this picture Holger that your nose strut seems to be bent back very far. i wonder what had happened and if this had pushed up against any batteries that might have been in the nose area.

I see you moved your tank closer to your cg, now with other people that have not done this, i wonder if you were then tail heavy with your tanks full? Reason i say this is because people measure there cg before they fill there tanks but then add fuel before they fly, with other people tanks more forward then yours, that would make there planes slightly more nose heavy and with your tanks not forward of the cg your did have this extra nose weight.

Kraftei

HI EDFCrazy,

The bended nose strut is simple to explain.
I changed the springs of the main struts to stiffer ones so that they came about 25mm higher than the nose.
To correct the negative angle I had to made a new nose strut bolt on the lathe.
This resulted in a perfect angle ( which I saw on the very easy, smoth take off), but the longer bolt was simply to soft (standard steel) to stand the force on it, so that it bended on the ground tests. (The inductively hardened bolt was yet to come. Please see the pics of the old / new bolt and the measures of my new one below).
The CG was absolutely perfect on 138mm with empty tanks. With filled hopper it was even a bit more nose heavy. The main tank was exactly in the CG and filled or not hasn't had any effect to the CG. I tested this before.
I think it's just the aerodynamical design of a hawk with it's narrow tips that can cause some problems.
I explicitely choosed the GJC version with the vortex generators and it's straight tips, which are normally the better ones than the round ones (the are supposed to be even more critical).
However all these measurements absolutely make sense but you should always be aware: hey, it's still a Hawk !
Obviously the requirements of this plane and my skill didn't fit together hovever I still do not know what my major fault was! If a plane behaves like this and reacts that critical to a stall you must be honest to yourself and think if it's really that what I want or do I just want to relax and have fun with a plane that sometimes can forgive a pilots mistake (who is free of making them)?
I obviously wasn't honest to myself. I only saw this beautiful Hawk and wanted to have her.
Hmm... now that I again looked at the pics I could cry and understand why I was fascinated by this beauty!
Not to make the same mistake twice I decided to set my sites lower and to realize something proven.
I'm just about to finish an nice small Aeronaut F9F Panther with a Lambert Kolibri T-20 microturbine. My size - my skill

Holger

hooker53

My Feedback: (106)

Ron that thing sounds almost like a turbine man. Ha. Ha.

Ron101

My Feedback: (22)

I love the good old dynamax, they sound really sweet.... they have a nice jet sound to them and there quiet
we had no idea how nice they sounded back in the nitro days

Felix Barrao

At last, I re- maidened the T-45. Everything was perfect. Here the maiden flight video.

http://www.youtube.com/watch?v=w6bxK...1&feature=plcp

The landing could be better, but not bad for the maiden.
Now, I have make a new brakes with an 2,5 mm o-ring instead the original 6 mm. Now is more progressive, and start to brake with a little pressure.
I´m finding too a stronger springs for the main legs. They are too soft.

ecocopter

Felix,
what is your weight of the T-45?
I'm dry at 9.3 kg

Volkmar

madmodelman

Felix, it's absolutely crucial you stiffen or pack your mains springs! Before you know it you will get into a porpoise and thump your gear through the wings, don't ask how I know!

Felix Barrao

The dry weight is 9 Kg.

I´m going to install a harder springs in the main gear, the actual ones, only with the wight of the plane go to the limit.

Regards

ecocopter

9.0kg that is light

Yesterday we did our maiden, no problems:



Regards

Downwind3Zero

My Feedback: (10)

Couple of questions:

Where is everyone's CG? The manual says 120mm but I'm reading anything from 100 to 140.
My mains compress completely when standing even after putting stronger spring in there. How does your Hawk sit?

Chris

Ron101

My Feedback: (22)

140 mm was to tail heavy for me
I moved it forward to 135mm maybe even closer to 130mm and it feels much better for me...now mine is electric so there is no fuel to burn and CG stay the same through the flight for me

I opened up my main struts and addes a 1/2" spacer to tighten up my springs... that solved the problem and I don't bottom out. The plane still sits a little nose up for takeoff

ecocopter

If you have the CG too much back, you will have the tip stall problem.In the instructions there is the note of 120 CG empty.
If you have your fuel tank in front of the 120mm CG, than you are safe.

paulsf86

My Feedback: (52)

For turbine version, UAT full of fuel, main tank empty and landing gear down, CG at 143mm back from leading edge at center section works very well. Too nose heavy and the airplane will bounce like a rubber ball on landing, you just run out of elevator with it too nose heavy. Prooven with over 140 flights on my T45, first flights too nose heavy and almost destroyed the airplane. Maintain power at slower speeds using speed brakes with flaps to avoid tip stall. Square wing tips and vortex generators from Global Jet Club help slow speed flight.

Paul S

Xairflyer

My Feedback: (1)

120mm is too nose heavy, the last one I setup I made it 135mm with a full UAT and it flew very well, still would require a good push on the stick while inverted, so could still go back a bit yet but 135mm is a good starting point.

Important to have your flap angles set correctly with some up elevator trim. Plus reflex on the ailerons is a must as it transforms how a hawk flys at low speed.
I also had a small AMD Hawk and they were well know to tip stall, I spent a lot of time with CG, control surface setting and aileron reflex and mine never showed any tendency at all to tip stall.

Aileron neutral is also important on any plane not just a Hawk, many guys dont seem to spend any time on this and more times than enough both ailerons are slightly down, this reduces the washout in the wing, if anything set ailerons to always be on the high side of neutral rather than the low.
Also after the ailerons are trimmed in flight, the one that is now low will cause that wing to tip stall first, so try to get rid of the trim by adding weight to the light wing and checking your flaps are perfectly level as this may be what is causing the roll.
On fullsize light aircraft along with trim tabs we would also deliberately set one flap slightly up to help correct the trim.

Seinfeld

Hi All

I recently received a warning advice from my GJC Rep that the Jet Legend has changed the design of the T45 and BAe Hawk Elevator Stabs to a composite material called Airex Foam and that these new stabs are not up to the same standard as the old balsa / glass construction and should not be used under any circumstance as it could cause total loss of the airframe.

Has anyone else received this advice or experienced an issue with the stabilisers ?

I've just finished by T45 that I purchased in July and I have the airflex stabilisers - the main wing is also made of this material

Need less to say I've responded to my GJC Rep and waiting for a fix.

cheers, Michael

Ron101

My Feedback: (22)

Good info zairflyer, how much up reflex did you run on the ailerons? and did you keep it like that during the whole flight or just landing?

Xairflyer

My Feedback: (1)

Only on flap settings and normally only on full flap, I always start off at about 5mm, straight away you increase the washout so makes it more stable in slow turns.
The amount of reflex depends on model and really needs to be increased gradually as it will also change your elevator trim, so you dont want to introduce a lot at once then be fighting the nose pictching up or down on finals.
I also when setting up a new model have the crow braking/reflex on a switch so if I dont like it I can turn it off, once I am happy with the setting I deactivate the switch.

smeegarn

Michael,

I had the same advice from Jeremy at GJC in relation to the elevators so have shelved mine. He indicted that a couple of models had been lost as a result of the new materials, so good advice until a fix is found. I am about 1/2 way through my build but would like a resolution soon.

Peter

Downwind3Zero

My Feedback: (10)

Thanks a lot for your replies to the CG question and the great information!! I'm in the last steps of completing the Hawk. Maiden should be in about 2 weeks.
Ron, well aware of your EDF Hawk from the forums on RCG.

Regards, Chris

Hughes500E

My Feedback: (16)

Holy smokes, read all 53 pages LOL

I still have questions but not many! GJC modified the wing tips to be square...... I'm not sure what this means exactly or how I can modify mine if I need too?

What is reflex? Never heard of this term!

Thanks

FILE IFR

Reflex is sometimes referred to as 'crow'. It's when both of the ailerons slightly deflect up to create a poor man's washout of the wing chord..... This helps keep the airframe a little more stable during slow speed flight.