EDF Vampire T11

[Piers Bowlan]

Excellent job Nick, hope it flies as well as it looks. Nice floor too!

Here is my foamy Durafly ARF Vampire from HK. Hope to have a flying shot of it soon.

[RickenBangler]

Finally finished the dreaded cockpit / fuselage interface and I'm quite pleased with the results!
The rest of the cockpit structure will be built on top of this...

Though I have all the bearers in for the gear, I'm now seriously considering making this a bungee launcher as
a) it will be a considerable weight saver and
b) access to a long enough tarmac runway is a bit of a pain, whereas we have plenty of long grass around here.

I think I need to make a decision on this soon... any input gratefully considered!

Piers - it's not raining, so stop playing with that tractor and get the foamy thing flying - camera batteries are charged

R

[Nick Chudley]

Lovely stuff Rick. As you can see, I still have to do my cockpit.

I'm a big fan of bungee launchers..

 

 

I'd like to help, but I doubt if you need it. I think your wheels are bigger than mine. Here's my Vampire maiden from grass..

 

You'll see it was a pretty scary ride.. Pitch control was about right, but the roll control was much to fierce for me. I guess I'll have to swot up on exponential for my Spectrum. Any advice will be appreciated. Presently the ailerons move 12mm up and 8mm down. p'raps I could just reduce that by about 40%?

 

Nevertheless, I'm a very happy flyer today!

Edited By David Ashby - RCME on 13/08/2012 08:20:26

[Piers Bowlan]

Maidened the Durafly (HK) Vampire this afternoon. Interesting! No shortage or omph on 4s but I think the C of G was a tad too far back as it was a roller coaster ride even when I switched to low rates (7mm up and down with -30% expo). I think I was also a bit too enthusiastic with setting up aileron differential as the model was yawing strongly in the same direction as the roll. I don't think directional stability is the model's strong point with those small fins, particularly at low speed. Maybe that is why they made them bigger on the full size T11/T22? In the end a gentle touchdown was effected- into a bramble bush. Glad you weren't there Robin! No harm done apart from a few cuts and a bruised pride - in future I think I will stick to gliders! Will report further after a few changes.

[Mark Powell 2]

 

Nick,

It did look a bit scary, but it flies very well. I would certainly reduce the aileron movement by about 40%.

A warning on using expo for the ailerons. Problem is, it softens the control near the centre. as of course you want. But then you move the stick a bit further as nothing much seems to have happened, and it all comes in at once. So I never use expo on ailerons.

I do find it useful on elevator. For example, I have got an old 76 inch span AirSail Auster AOP9. It has a short moment arm, a small tailplane, and is sensitive on elevator. Reduce the elevator movement and then you haven't got enough elevator to flare properly at low speed on the approach. So I have about 30% expo which calms it down in normal flight, but I still have full movement for the flare. Works fine. But never on ailerons.

PS: One thing about expo. It is best for resolution to have as much movement as possible on the servos. But you end up with a short servo arm and and a long horn on the control. Fine with small control movements, but at full movement the servo arm has moved through a large angle and the horn has moved  through a much smaller angle. So you have 'reverse exponential', making it over sensitive at the centre. Adding expo on the transmitter does not give you 'real' exponential, it just makes the response more linear, which is good.

Hope this helps.

Edited By Mark Powell 2 on 12/08/2012 08:23:51

Edited By Mark Powell 2 on 12/08/2012 08:25:14

[Nick Chudley]

Thanks Mark:

"But then you move the stick a bit further as nothing much seems to have happened, and it all comes in at once."

That's exactly what happened to me when I tried it and it's the reason why I've avoided expo. However, something drastic is needed this time. I've got 12mm up and 8mm down on the ailerons. Following the best advice I have so far, I'm going to set up low rate at 70% of that and expo at 40%, and hope for the best.

Cheers

Nick

[Mark Powell 2]

Nick,

I had expo on the ailerons on my Great Planes OS 91 powered Little Tony (scale model of a 'hot' pylon racer) and on the maiden, when I moved the stick more than a little bit it rolled inverted unexpectedly very near the ground, only a few seconds after takeoff. My great skill (HoHo, totally luck) recovered it. I have avoided expo ever since.

[Nick Chudley]

Here's some advice I got on RCGroups from someone with loads of experience and heldpful ideas:

"Excessive aileron sensitivity is very common with such models and is one of the main causes of jerky flying and even crashes. So setting low rate at about 70% would be a good start. Expo is particularly helpful on aileron for such models -- I'd use about 35% on low rate and 40% on high rate."

This is my third version of the Vampire. The first two were smaller and twitchier and, after just enough fun and frollics to get me hooked, they bit the dust. This time I'll try the expo, carefully.

[graham kindberg1]

Posted by Mark Powell 2 on 12/08/2012 15:36:12:

Nick,

I had expo on the ailerons on my Great Planes OS 91 powered Little Tony (scale model of a 'hot' pylon racer) and on the maiden, when I moved the stick more than a little bit it rolled inverted unexpectedly very near the ground, only a few seconds after takeoff. My great skill (HoHo, totally luck) recovered it. I have avoided expo ever since.

Just a thought Mark, you didn't dial in negitive expo by mistake? Have seen it done before.

Graham

[Danny Fenton]

Expo I think is down to personal taste, however I go up to 60 or 70 percent to avoid the issue you are seeing, I have a super smooth flyer friend who goes to 80 percent. Low expo numbers and less than perfect c of g and you could end up suddenly over controlling. Mick Reeves uses up to 70 percent.

It is worth experimenting with switchable rates to see what you like.

As Graham says you do have to make sure you have the expo softening the centre travel easily confused with Futaba and JR having opposite numbering polarity.

Cheers

Danny

[Nick Chudley]

The 2 flights in this video represent before and after the use of expo. Both times, and also with my previous versions, I have 2 problems. First it's easy to get too much nose up on reducing power. Second it then stalls and goes into a very difficult spin. Seems to fly well at speed. The wing loading, in the end was 15-16oz /sq ft.

I have zero incidence for the wing, the stab and the thrust. The washout is 3 deg. I've checked and double checked the CoG by different routes. Following the published 3-views, I've broadened the wingtips slightly and also the horizontal and vertical stabs. I wonder if the exaggerated air intakes and the inboard part of the airfoil have a significant effect?

I would really like to learn from these mistakes. Any advice?

 

You certainly can't criticise the structural strength! With a long experience of crashing planes I was expecting to find a lot of matchwood after that first crash. The ground was pretty wet, but still...

hey-ho, another day, another lesson.

Edited By Chris Bott - Moderator on 06/09/2012 23:05:06

[Piers Bowlan]

Nick, the wing loading is not excessive, did you build in any washout in the wing, it will ensure the wing root stalls before the wing tips and so reduce the likelyhood of a spin should the aircraft stall. I also noticed in the video some gaps between the ailerons and the wing. you should seal these by covering the gaps with profilm/solarfilm or whatever. It will make the ailerons more effective although roll rate does not seem to be a problem!

Also did you dial in some differential aileron on your Tx.? It reduces adverse yaw and again will reduce the likelyhood of an incipient spin at low speeds. If you spin and you don't have any rudders you are doomed!

Just my ten penny worth.

Regards, Piers

[Nick Chudley]

Many thanks for your suggestions Piers.

Yes I did have washout - 3deg, which on the TLAR basis looked almost too much to me. Aileron differential was 2:1 up:down. Once the spin started I let the ailerons back to normal, kept the nose down, cut the throttle and waited for the correction which never came. I think that leaves me with moving CoG forward a bit and/or increasing the fins a bit more.

How does that sound?

Nick

[Ady Hayward]

Hi Nick,

I'm sorry to see the result of the last flight on the video, but it definately looks like you are flying it on or just behind the aft limit for the c/g as it appears very twitchy in pitch. The washout at 3 degrees should be fine and is the figure I use on my micro edf Vampires and they have flown without tip stalling issues. The wing loading is fine too as borne out by the slow flight. Increasing the fin area will help but it is at the cost of scale accuracy. I would try the forward c/g first and let the plane gather speed and turn smoothly and a bit wider so you don't bleed off speed by hauling on ther elevator.

Ady

[Piers Bowlan]

I agree with Ady, Nick, the C of G does appear to be rather too far aft, judging by the model's wayward behaviour in the video. I moved the C of G of my Durafly Vampire 21mm forward of the balance point indicated in the instructions (290mm rather than 311mm from the nose of the aircraft). I flew it last week and the model was transformed! My Vampire was tamed, very stable, no more 'roller-coaster ride' and no squirrely behaviour at all. The Vampire, both model and full sized, has quite a short tail moment so perhaps it has a narrow C of G band, being sensitive in pitch. A forward C of G would tend to calm things down or at least it did with my model.

The rest or your setup seems OK so I hope you are able to effect some repairs soon and try a more forward C of G. I don't really think the issue is the fins (although they are probably rather small).

Piers

[Nick Chudley]

Right then, at the risk of taking over your thread, here are some rebuild shots..

 

Edited By Nick Chudley on 07/09/2012 09:21:17

Edited By Nick Chudley on 07/09/2012 09:22:00

[Nick Chudley]

Success at last. Hooray

The CoG is now 20mm further forward. That seems to have solved the problems with the vertical forces.

I was still suspicious about the lateral forces so I added a little to the TE of the fins.

This time she flew as if she was on rails. And Fasssst! wahoo!

When I put her into a dive there was no sign of any tendency to climb out, so I think she'll tolerate a slightly more rearward CoG. The roll rate was slow, so I think I'll do away with the low rate and keep the expo.

AUW with a 2200 4S1P battery is 39oz. She glides forever.

Here's the video:

[Piers Bowlan]

Well done Nick your perseverance has paid off in spades. Amazing the difference a 2cm change in C of G makes.

Now come on Robin when are we going to see your T11 completed and airborne?

[Nick Chudley]

Thanks for all your help and encouragement, Piers, Mark and Ady. Now I need to make a cockpit and decals.

Robin, what are you going to do about a cockpit and decals? I have a simple vac forming outfit and a good source of waterbased decal paper. Would you like details, or copies?

Cheers

Nick

Edited By Nick Chudley on 12/09/2012 07:29:10

[RickenBangler]

Nick - good to see you finally got her sorted! Don't think I'm going to have too many problems with the decals - just roundels and letters really - will revisit when we are closer to the finishing stage! Our thread contributor Piers has some ideas about my cockpit canopy so I'll be passing some bits 'over the wall' to him to fiddle about with now I have the base of the cockpit faired in. The majority of it is do-able with flat sheet - just the central bubble over the pilots heads that may be 'interesting'. I think I mentioned earlier in this thread that I'd knocked up some art for the cockpit - here it is:

Feel free to print out and tweak if it's of any use - might need to be a bit creative as it's about right scale (and detail) wise to the real thing - unlike my cockpit...

I've now made a decision about the UC - I'm not having one. The physical weight of all the powered retracts scares me and I stalled completely trying to get the nosewheel sorted. That, coupled with the lack of a suitable runway, made me decide to go down the bungee launch route - or maybe just a good chuck...

It's getting there...

Cheers,

Robin

[Nick Chudley]

Thanks for those details Robin, I'll use them.

I found this quote from one of your early psotings:

"59" span - with the original target weight being around 2.5Kg." and I saw that you have the HK retracts. They'll certainly be ok. My model is a lot smaller and I have the E-flight retracts. Even so, as you can see, she flies out of my hand very well and lands in the long grass with the wheels retracted. It's a bit difficult to get hold of for a hand launch and I wouldn't want to try it with a bigger model. Are you going to have cheater holes underneath for air intakes? They could make it much easier. The trick with the bungee, I found, was to use about 10m of something much softer than the standard luggage bungee. My ramp is 2m long and 600mm at the high end. Sorry if that's all stuff that you already knew.

Good luck!

Nick

[Piers Bowlan]

Nick, it is true, I am going to have a go at producing a canopy for Robin's T11 as soon as my other project ( house painting) is finished! I have only made one canopy before and it was a bit hit or miss although one worked which was all that was needed. I have the proper perspex material for vac forming, Do you use a vacume pump or do you just heat the plastic and stretch it over a suitable plug? Any tips or suggestions gratefully received.

Regards,

Piers

[Nick Chudley]

Here's a link to one I prepared earlier: **LINK**

Cheers

Nick

[Piers Bowlan]

That looks great Nick. What did you make the plug (male mold) out of? Was it balsa or a hardwood and did you finish it with anything?

[AMC]

Well, What happend, How did it turn out!!