sorry about your crash pankaj!! My only doubt regarding this incident (provided the build is proper) is that you must have pulled up elevator before the plane picked up enough airspeed which would cause the exact behavior which you have described!! I could be wrong though!!

- Chan

Oops 

It would be better if you pick an area with tall grass next time to see if the craft is underpowered (as described by Ashta).  Launch it into the tall grass and see if there is enough power to continue flying.  If not, all that is going to happen is a soft crash into tall grass.

Should check the landing gear, the wings being level and aligned with the rest of the airframe and same for rudder, elevator. Why not post pics of the model now?

That model was too good to have a crash. As it is said in SPADs if it looks about right (TLAR) then it will fly.

As Chan said, I think you took off too early and the airspeed wasn't enough. It sounds like a tip stall and it could happen even in take-off esp when there isn't enough airspeed. Basically, one half of your wing is not producing the required lift. Did you do a take-off roll on cross wind?

-Ismail

Ismile/Chan,

Yesterday was a relatively no wind situation in the ground from where I was trying to take off. I applied half the throttle with 10x5 prop, it shot off like a bullet and then started wobbling left/right and it was lifting off the ground on its own when I applied little bit of elev and then I think, it stalled.

Now analysing, the possibilities I can think of are as follows
1) uneven runaway was causing the wobble
2) alternative, the aerofoil is uneven (hand made so at best could be an approx match) and/or the flaperons were not aligned.
3) I applied too much elev at low speed hence the stall. In an attempt to startoff, I did not even apply flaps which could have provided the necessary lift. This is the first attempt at RC and the feeling is totally different from when one is on sim.

While constructing, I had not fortified the firewall too much, so when the model cartwheeled and the prop hit the ground, the firewall broke and so did the cowl. With that it ripped off the 2-side tape holding the ESC. Also the undercarriage was held lightly so the base came off taking some thermocol with it. 

It seemed a mess at the first glance, but after my nerves calmed down, I noticed that the damage is very little. Have managed to get the firewall back in action in about 1 hour, rest should be done today/tomorrow kind of a timeframe

Now, I think I shall do the following -

First find a reasonably even surface and just let the model run along and observe and report back to the forum for ideas, OR, will try to hand-launch with full throttle and figure out what happens and report. Third option?? open to suggestions

dear pankaj,
i have the following suggestion.
1. Arm the Plane fully with the Battery/ RCVr etc.
2. Find a place with lot of grass to take the weight of the plane.
3. With all the control surface aligned, do a glide test, several times by just throwing the plane in to the wind, with out power and carefully see how it glides. By looking at it normally one can judge very well, how it will fly.
4. For example if the plane has a tendency to turn left/ nose down etc, you will get that indication when you throw the plane.
4. Once you sort out these issues, the plane will generally fly well,  If you do not have much thrust angle issues.
5. After this you can again throw the plane with Power say half the throttle (You will gradually get a feeling, when you hold the plane and give throttle about the thrust) and see how it goes and cut the throttle soon so that it will glide in to the grass.
6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta

Quote from: Ashta on December 07, 2009, 12:04:14 PM
dear pankaj,
i have the following suggestion.

6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta

Hmm......
Finding a suitable high-grass field is an issue in Delhi - at least not within 15km radius from where I stay

Beside, I am kind of worried about chucking a 1kg+ plane into ground, as a plane of this weight would require some speed even to glide.
Pankaj

This is what I had asked long back in another thread. How do ppl do the initial trimming of  big model planes. I agree, many hours of work and/or lots of Rs./- being tossed into the sky isn;t a great approach. 

While it may sound strange, the actual method used in our fields are something like this.

1) Make sure the CG is about right on the ground.  If not, fix it by moving things around, or adding weight.

2) If you are not confident about handling pretty much any emergency, hand it over to some really good flyer around.  He does the initial flight, and adjusts the trims till the plane flies level pretty much hands off.  A runway of good size (ie, long!) is a useful thing, since it helps to gauge the speed the model can attain on the ground itself.  BTW, this is usually for models that are .40 size or higher.

For nitro models, there is the additional checking of whether the engine will quit at different orientations by tilting the aircraft by hand in different directions as some high throttle.

For smaller models (electrics), it is just a matter of some one experienced gauging if there is enough thrust by holding the model in their hands at full throttle, and the other big checks are making sure the CG and control surfaces are aligned.  After that, the experienced flyer takes off, and deals with any issues with his thumbs.  After all "trim" is just the same as "certain amounts of appropriate controls kept applied". The flyer then puts in the appropriate amounts of whatever trim is needed on each control/channel in the TX, while the model is still in the air.

BTW, tall grass seems the best option if you are doing test flights on your own, and you are not experienced enough to handle eventualities.  We do not have that around us either

Quote from: PankajC on December 07, 2009, 12:10:17 PM

Quote from: Ashta on December 07, 2009, 12:04:14 PM
dear pankaj,
i have the following suggestion.

6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta

Hmm......
Finding a suitable high-grass field is an issue in Delhi - at least not within 15km radius from where I stay

Beside, I am kind of worried about chucking a 1kg+ plane into ground, as a plane of this weight would require some speed even to glide.
Pankaj

The idea is to throw the plane so that it can glide for say 10 -15 feet. You can use any thing like grass, a hay stack or even paddy field ( be carefull if it is watery). Prcatically what i do is sit down holding the plane up and slowly throw it and see..
As long as it is a trainer, it should fly say at 10KMH and is OK for test glide.

Repair update...

Finished the first round of repairs and took it for field testing. The idea was to try and let the model roll in the ground to see whether or not the wheels are aligned. Suddenly the model collapsed. That is when I noticed one major build flaw in the fuse ---- The mounting of undercarriage.

The basic flaw that I did not use spring steel/piano wire for UC, instead went ahead and got hold of hard plastic strips. This I joined using  3" x 1" x 3mm balsa  It simply does not have the holding strength to counter the force generated by the length of the UC - simply ripped off at the slightest jerk.

Since to insert a piano wire UC strut was not possible, I replaced the 3"x1" balsa mount with a bakelite peice of similar size, bolted the UC struts and then pasted 2 cycle spoke length wise across the fuse with epoxy and reinforced with 3" transparent tape. 

Another major issue discovered today is that the material I have used may not be biofoam/depron. I enquired with the BioPac office in Mumbai and they confirmed that they do not have resellers in Delhi. So, the vendor who sold me the foam sheet did not tell the truth (nothing new in Delhi) and all the while I have been building with a material that just another form of thermocol and hence is very very brittle.

I am just wondering whether I need to start all over again.....

Pankaj

Foam of any type needs bracing and let me add, depron is brittle, unlike thermocole which is much more flexible and the high density versions are even better.

  :headscratch:Something is wrong and I am unable to get a hang of it.

Last Sunday went in for another field trial, located a fairly flat ground and started to test for speed taxi. Somehow, still not able to come to terms of hand-launching this bird.

When I the model starts to move slowly, it is fine, the moment I apply substantial throttle - it spins to the left. Slight adjustment of the tail wheel and the model spins to right on throttle. I figure this could be a combination of 2 problems a) wheel alignment and b)motor alignment.

So I brought the plane back and tested the same without the wings on the home floor and without the tail wheel. This time the tendency was to waver to right. So I add washers on the right side mount and adjust the wheels slightly. Now, the plane still tries to turn right, but this tendency is when the speed is low, when I apply throttle, its almosts straight.

Question is that when building a scratch model, how does one get on with the alignments? Even when following a plan, the cuts and thickness is not 100% accurate. So what precaution one should take?


Pankaj

little right/ left/up/down thrust issues exist in all planes. What i do for a tractor set up is to give some 2 deg down and 1 or 2 degree right thrust and assemble.
Rest alignments problems if any gets corrected during the trim. so do not give toomuch focus for this.
just make the plane visually straight and clean.

What prop size are you using on this model? Not that this is important but usually the wing span should be more than 3 times the prop dia. This will avoid any torque effect on the model once the wing gains lift.

The motor mounting angle (5 deg or so) would not have any effect on the model when tracking on ground. I suspect that your landing gear wheel does not have enough toe-in. Go have a look behind a load carrying auto. (Ape from bajaj??) and you would clearly see what I mean. IOW, when you look at the face of the model the two wheels should converge at an angle of 5 to 10 degrees.

Here is a good picture to explain it better:
http://www.spadtothebone.com/misc/toein.htm

-Ismail

Thanks Izmile, I have an direct opposite of a toe in . I guess that needs to be corrected asap.

Pankaj

OK, corrected the wheel mount to give it a toe-in.

Noticed something peculiar. when it taxis slowly, the plane has a tendency to turn right sharply, but when i apply substantial throttle, then it goes almost straight.

Anyone knows what the problem is?

Pankaj

Check your tail wheel.

BTW, its very difficult to tune the landing gear. Of all my builds the weakest link is the landing gear. Once you fine tune it, it would not last forever. The next landing (or hard landing) it will change and you would keep tinkering with it. I would suggest you to go and fly rather than look for 100% perfection. It simply dosen't exist.

Quote from: izmile on December 15, 2009, 10:15:58 PM
BTW, its very difficult to tune the landing gear.

I would suggest you to go and fly rather than look for 100% perfection. It simply dosen't exist.

+1. 

My experience is that you can get a decent level of landing gear accuracy on the bigger planes. 

On the smaller ones, think of them as just something to prevent the belly from rubbing on the ground.  On these (especially foamies), rudder action is your friend in terms of steering on the ground (instead of relying on any wheel).

hand launch??

from my experienec on electrics, i never try to taxi it for long distance. i ensure that it takes off at max of 10 feet and more like 3-4 feet most of the times.
so only that much accuracy reqmnts, in terms of wheel alignments.
if the plane has enough thrust to weight ratio, that much should be good enough. mainly landing wheels in that case comes handy more for a proper landing and saving the props.
with a bit experience or with the help of an experienced pilot, one will easily get a feel about it once u hold the plane in your hand and slowly increase the throttle.
ashta

Quote from: PankajC on December 15, 2009, 10:05:39 PM
OK, corrected the wheel mount to give it a toe-in.

Noticed something peculiar. when it taxis slowly, the plane has a tendency to turn right sharply, but when i apply substantial throttle, then it goes almost straight.

Anyone knows what the problem is?

Pankaj

This model discarded ... another started here :

http://www.rcindia.org/self-designed-diy-and-college-projects/scratch-build-trainer-part2/

umm, pankaj sir, could u tell me the inclination angle of the wings with the horizontal?? 
the general stats like wingspan and weight would help too.