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Old Sep 04, 2012, 10:36 AM
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Nice.
Today I taped an 808 HD keychain cam on the canopy facing backwards, to video what I had hoped to be cool smoke trails from twin smoke bombs fitted to the wingtips.
Even doubling up the smoke powder "loads" they only lasted about 10 seconds, and twice the "bombs" fell out of the holders I bolted to the wings, but for a little bit it was cool
The RJ barely seemed to notice the extra weight of the cam and bombs, with the 2826 motor and 1.3A 3S nano-tech she SCREAMS.
I did finally experience the dreaded "death spiral". On her 3rd or 4th flight of the day go up for a majestic tail slide about 300' up. Instead of just flopping over as usual and tightening up she started to spin and flip crazily. Tried juicing the throttle, pulling back, both, nothing worked. &@^!. Luckily she pancaked into some tall, relatively fluffy grass right next to the runway. No damage - checked out the controls and tossed her right back in the air.
what KV motor, im kind of new to this but i copyed the 2826 number and there were several options, could you please link the motor you use.
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Old Sep 04, 2012, 12:35 PM
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harly - it's a 2826-6 2200kV, bolts right up to the stock mount (after you pry it out), running the stock prop.
http://www.hobbyking.com/hobbyking/s...dProduct=12919
Seems these are OOS 90% of the time, I should have ordered 2 it's a little powerhouse. Tried one 4S pack, but it's too much for the motor the thing was red hot when I landed. No ill effects though, and on 3S is really as fast as I'll ever need it.

Here's how I mounted smoke bombs to the RJ. Found that little plastic cups for dremel cut-off discs are perfectly sized to wedge in a bomb.
Just too bad there's only ~10seconds of smoke per bomb.
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Old Sep 04, 2012, 07:51 PM
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Cool thanks Kurt
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Old Sep 06, 2012, 03:21 AM
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I just bought a Radjet 800 (not flown yet) and have been reading this thread with interest. Lots of really useful suff on this thread although it takes a while to get through.

I did read with interest the discussion on the 'death spin' that the Radjet can get into. As well as being an RC'er I am also a 1:1 flying instructor and an aerospace engineer.

In the 1:1 world, there is a standard recovery technique which works for 95% of aircraft which is:-

Power to idle
FULL opposite rudder
Move control stick forward

Hold until the spin stops, centralise the controls and recover from the dive.

Clearly this doesn't work for the Radjet.

However, it should be noted that there are aircraft that are cleared with a recovery technique that differs from the standard due to unusual spin behaviour. Some aircraft (PA-28 for example) are not cleared to spin at all. All recoveries include the use of rudder.

There are many things that can affect spin behaviour; a couple of dominant characteristics are:-

Center of Gravity - has a significant effect on spin and recovery behaviour. A mor rearward c of g will make an aircraft easier to spin, and more inclined to stay in the spin. I noticed that the c of g being recommended on this formum is substantially further rearward that the designer recommends. Maybe the spin behaviour was a consideration when they were selecting the design c of g for this aircraft.

Wing Planform
Delta type have a center of pressure movement during deep stalls very different to what you get with a conventional 'straight' wing. It is likely that the 'death spin' is caused by the aircraft getting into a very high angle of attack situation, with very low airspeed and some yaw component. For a delta wing aircraft this can be unrecoverable (again exacerbated by rearward c of g).

Distribution of mass.
Aircraft with long noses etc (like the Radjet) have a tendency for any spin to flatten out as the rate of rotation increases which increases the depth of stall and again delays recovery.

Fin surface area and distance from c of g
Aircraft with a small vertical tailplane, only a short distance from the center of gravity (like the Radjet), due to the limited aerodynamic effect and the small lever arm having little direction-restoring effect. the rearward c of g exacerbates this again.

So having read the posts etc, although the Radjet does seem to be a great aircraft, it does have all the design features that may make it prone to an unrecoverable spin.

In the full-size certification world, an aircraft that has difficult recovering from a spin will typically have some additional fin area added as far back as possible (usually below the empenage). there are many example of this in 1:1 world. I noticed that somebody did try this earlier in the thread and reported good results. The other easy change would be to use a more forward c of g, but this would be at the expense of other handling traits that benefit from the more rearward position (catch-22).

There is little you can do about the distribution of mass - maybe remove the tip-tanks and keep the nose nice and light (although I appreciate the desire to beef-up this bit to help with 'arrivals-gone-wrong' may help a little.

One poster mentioned about leaving the controls neutral and using power to get out of the condition. This is very unconventional from a 1:1 point of view but when you have an aircraft with such a huge Thrust:Weight ratio you can pretty much throw conventional aerodynamic theory away. Using power to get out of the 'death spin' has been proven to work well for a very overpowered aircraft.

One thing that I haven't seen discussed in this forum is 2D thrust vectoring. I would imagine that 2D thrust vectoring in the pitch-sense would work well on this aircraft - and would probably provide enough pitch authority at low/zero airspeed to recover from the 'deal spin'.
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Old Sep 06, 2012, 04:04 AM
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Actually, I am thinking about putting a 2D Thust Vectoring system on my Rad but I haven't been able to find an appropriate swivel mount on the internet. Anybody seen any?
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Old Sep 06, 2012, 04:23 AM
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Originally Posted by Simon1013 View Post
Actually, I am thinking about putting a 2D Thust Vectoring system on my Rad but I haven't been able to find an appropriate swivel mount on the internet. Anybody seen any?
The only Rc plane with a Prop ive seen that has any kind of thrust vectoring would be the E-Flite C-Z Scimitar.
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Old Sep 06, 2012, 06:56 AM
Radio? Screwdriver!
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RadJet 420 or 800?

Sorry if this has been done to death - I'm sure it has but I can't find any posts on it!

Looking to get a RadJet, but not sure to get a 420 or a 800. If your only getting one, which one would you get?

I'm tempted with the 420, but the 800 is slightly cheaper and hence looks better value. The 420 is easier (as smaller) to throw in the back of a car for impromptu flying, however I believe the 800 is faster?

Out of the two, which one would everyone go for - for a back of the car ready to go type job?

Which is the more fun out of the box (i.e. no mods)? Or just different types of fun?

So many questions.

Cheers,
Si.
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Old Sep 06, 2012, 07:24 AM
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The 800 is not big at all. So its size should not be any issue.
It flies pretty fast stock.... and then faster with the prop change..... but then it can still fly at almost walking pace too!!! So you can fly it anywhere really.

I haven't had the 420, but I don't see any reason I would want to either.
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Old Sep 06, 2012, 07:45 AM
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Great post Simon! Very interesting reading.

Quote:
Originally Posted by Simon1013 View Post
Actually, I am thinking about putting a 2D Thust Vectoring system on my Rad but I haven't been able to find an appropriate swivel mount on the internet. Anybody seen any?
I've also done a bunch of thinking about this, and unfortunately haven't found any pre-made 2D vectoring motor mount.
Was planning on doing something like this guy's home-made:
http://www.wattflyer.com/forums/showthread.php?t=61024

I bought a couple nose-wheel mounts, MG servo and a few various linkages but haven't got around to fabbing anything up yet.

Last night took off the smoke-bomb holders and had a really nice flight with the RJ 800 last night at the local school. Didn't try any tail-slides, just big sweeping loops, snap rolls, low fast passes and high-g turns. Big grin on my face afterwards
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Old Sep 06, 2012, 07:48 AM
Radio? Screwdriver!
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I thought about the 420, as it kinda looks a good size to squeeze in my girlfriends car (MX-5/Miata) when we're going back to her parents for the weekend. But then if the 800 flies better, then I'd rather go for that. The 800 does look like it would make more sense - but then when ever has buying planes made sense?

What's the recommended Prop over stock on the 800? Would I have to extract and replace the ESC from the PNF version to a higher current version for it?

Cheers,
Si.
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Old Sep 06, 2012, 12:32 PM
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well i officially give up on my radjet. tried to fly it again today...with the predictable result. rolls to the left the instant it leaves my hand,goes nose down and hits the deck. it just will not fly for me.
i have tried everything suggested to me over the last couple of pages ranging from putting in some throttle/aile mix to throwing it tilted to the right to throwing it hard at almost full throttle at 45* up ...i have tried everything i can think of and everything that has been suggested to me,but no joy.
3 attempts today and 3 crashes,the last one pretty much snapping the cockpit in half. i could fix it but to be honest i don't think there is any point. the thing is rapidly becoming more glue than foam.
think i will just pull the electronics off and chuck it in the bin....where it belongs!

ive never had so much trouble trying to make a maiden happen before! luckily i had my mx 2,anx and a couple of wings with me so the trip to the field was not a complete waste of time.

bit gutted really but i guess i should of known it was jinxed from the start what with all the hassle i had from the point of placing the order to getting it to my door. should of seen it coming!
it seems im not destined to join the ranks of the radjet owners after all. seemed like a good idea at the time. alas,it was not meant to be for me.
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Old Sep 06, 2012, 01:56 PM
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Quote:
Originally Posted by Simon1013 View Post
Actually, I am thinking about putting a 2D Thust Vectoring system on my Rad but I haven't been able to find an appropriate swivel mount on the internet. Anybody seen any?
ive seen a funjet with a set up, simular to what your looking for . do a search for it on youtube or here . its an old video.
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Old Sep 06, 2012, 01:58 PM
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Originally Posted by mrmurder1975 View Post
well i officially give up on my radjet. tried to fly it again today...with the predictable result. rolls to the left the instant it leaves my hand,goes nose down and hits the deck. it just will not fly for me.
i have tried everything suggested to me over the last couple of pages ranging from putting in some throttle/aile mix to throwing it tilted to the right to throwing it hard at almost full throttle at 45* up ...i have tried everything i can think of and everything that has been suggested to me,but no joy.
3 attempts today and 3 crashes,the last one pretty much snapping the cockpit in half. i could fix it but to be honest i don't think there is any point. the thing is rapidly becoming more glue than foam.
think i will just pull the electronics off and chuck it in the bin....where it belongs!

ive never had so much trouble trying to make a maiden happen before! luckily i had my mx 2,anx and a couple of wings with me so the trip to the field was not a complete waste of time.

bit gutted really but i guess i should of known it was jinxed from the start what with all the hassle i had from the point of placing the order to getting it to my door. should of seen it coming!
it seems im not destined to join the ranks of the radjet owners after all. seemed like a good idea at the time. alas,it was not meant to be for me.
i hate when that happens to me. it happend with a staggerwing, no matter what i did or was recomend for me to do , the plae would just go up and then back down and crash.
im looking into getting one of these in the near future i hope i dont get on with bad ju ju
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Old Sep 06, 2012, 04:51 PM
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im sure you will be fine sandman. others are having great success with their radjets. don't know what it is about mine,there is no reason i can see as to why it shouldn't fly and i have gone pretty much as far as i can or am willing to go to make it fly. but there comes a point with these things when you just have to say enough is enough. today was that day for me and the radjet.

i still want a jet. i want that speed rush. thinking of going down the edf route. hopefully with more luck than ive had with the radjet!!
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Old Sep 06, 2012, 05:14 PM
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Originally Posted by SimonChambers View Post
Sorry if this has been done to death - I'm sure it has but I can't find any posts on it!

Looking to get a RadJet, but not sure to get a 420 or a 800. If your only getting one, which one would you get?

I'm tempted with the 420, but the 800 is slightly cheaper and hence looks better value. The 420 is easier (as smaller) to throw in the back of a car for impromptu flying, however I believe the 800 is faster?

Out of the two, which one would everyone go for - for a back of the car ready to go type job?

Which is the more fun out of the box (i.e. no mods)? Or just different types of fun?

So many questions.

Cheers,
Si.
hi i own both and like them both but its taken me a few crashes and setting up and was not until i put front canards on the 800 would i find it user friendly and now its one of my favorite planes.
The 420 flew perfectly and is easier to fly and land right out of the box and even tho its not as quick as the 800 it feels quick being so small plus it can fly alot slower with out falling out of the sky when compared to the 800.

im not trying to say that the 420 is better, just easier.
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