Bird of Time update

[rnorth]

Does anybody know if Dynaflite has dealt with the wing problems on the BOT ARF. I have read some very negative comments about this on rc groups and just wondered if anyone had an up to date report.

Richardup

[ejett]

I'll admit to not knowing for sure, but I don't believe they have made any significant changes. At least I haven't heard of any.

EJ

[StevenatorLTFO]

I've been flying my BOTarf all summer, with the majority of the launches being from club winches. (some pretty stout ones at that). You do have to take things easy on the pedal, you can break it if you try I'm sure....

With over 100 flights on mine this year, No problems with the wings.

I have found that I feel the fuselage is a bit softer then maybe I would like, it has cracked twice behind the wing, on landings that I thought there shouldn't be issues with. The one time that I did land it really hard, no damage to the stock part of the airframes, but I managed to eject both spoiler servos with their covers, so go figure.

My take on it so far is that its a decent value for the money.... but if you want something you can stand on the winch pedal with when launching, no, this isn't your bird.

I do recommend cutting spoilers in on it if you do get one, if you come into the landing area fast at all, it will float forever!!!

Steve

[StevenatorLTFO]

Just a followup, to better answer your question on the wing construction, yes, they did make some changes to the structure, from the early ones that were very prone to folding, to the more recently built airplanes. The early ones had grain in the shear webbing in the center section that ran parallel to the spar, that has been fixed.

I got your PM, and replied to it, hope that answers your other question fully.

In a nutshell, for the price, I think it is a decent value.

Steve

[rnorth]

Thanks Steve

[ChuckA]

I don't have a BOT but suspect it is at least as strong as 90% of the models we were flying when the BOT was designed. Back then we were flying with high starts and winches with 12 volt motors on 6 volts, not 6 volt motors with real balls on 12 volts. Even old timers seem to have forgot how to tap the model up.

[histarter]

I don't have a BOT but suspect it is at least as strong as 90% of the models we were flying when the BOT was designed. Back then we were flying with high starts and winches with 12 volt motors on 6 volts, not 6 volt motors with real balls on 12 volts. Even old timers seem to have forgot how to tap the model up.
Us old timers forgot to "float like a butterfly" and are totally unable to "sting like a bee" also!! :eek: :D

[sleep4]

I have just recently sold my BOT ARF that I flew for two years, without any launching difficulties off the winch. However because of the wing strength issue, when I bought it I took the covering off the center section and applied some .007in carbon fiber laminate to the spars, then recovered. In the process I noticed that the manufacturer had added some plywood sandwiching to reinforce the shearwebs so I could not tell if the web grain went the right way or not. It would take a stout winch launch with little or no flex in the wing after the mod. I also have heard of some injecting expandable foam to strengthen the fuse which is definitely weak behind the wing.

[StevenatorLTFO]

Chalk up 5 more launches off of the winch today, all of them 'real balls' winches....

I tapped :D

Steve

[chlee]

It's been pointed out on this forum by more knowledgeable folks, but if I may echo their advice:

Vertical grain shear webs do not have a clear advantage over spanwise grain. Both cases will fail under the same shear load. If the shear webs failed, it's more likely that they simply weren't thick enough (regardless of grain) or that they weren't glued or fit properly.

- Chung

[StevenatorLTFO]

I can neither confirm or deny that statement :D

[brokenspar]

FWIW, there was a technical analysis in one of the NFFS Symposium books a few years ago re grain direction in shear webs. The conclusion was that vertical grain webs were stronger, but only by about 10 percent or so. Sounds like wood selection and glue joint quality would be the deciding factors in most cases.


It's been pointed out on this forum by more knowledgeable folks, but if I may echo their advice:

Vertical grain shear webs do not have a clear advantage over spanwise grain. Both cases will fail under the same shear load. If the shear webs failed, it's more likely that they simply weren't thick enough (regardless of grain) or that they weren't glued or fit properly.

- Chung

[StevenatorLTFO]

I'm no engineer, but that sounds logical. Where is the Doc when you need him?

I'm gonna build a new center panel for mine this winter, it might be a few inches longer, with ballast tubes built in. It just has to survive one more weekend......

Steve

[ejett]

I believe the Doc's information is that you should use 45* shears. It must not be worth the trouble, because he uses vertical shears in his RES built up planes.

I made some shear webbing of 2 ply balsa based on his recommendations. However, this stock is yet to make it to any plane. Given a choice, I will always use vertical grain myself (except for the untried special balsaply mentioned above). When I build another BoT wing, I am going to use the balsaply webbing.

EJ

[chlee]

Ah, actually, I was but quoting the same Dr.! There was a nice .pdf file posted somewhere in which he explains all this.

I'll try to find that original post.

//////////////

Here are some of those earlier posts that explain it much better:
http://www.rcgroups.com/forums/showthread.php?p=3352147
http://www.rcgroups.com/forums/showthread.php?t=103755&page=2

- Chung

[rnorth]

Hey Guys,
Thanks for all the input. I am thinking of purchasing a BOT arf and installing a brushless motor with a folding prop. I feel like the torque on the wing will not be as much of an issue since I won't be using a winch or hi-start.

I don't want a hotliner, I just want to thermal. I plan on taking the BOT up at about a 45 degree angle and also avoid any dives that would create a lot of speed. I really like this bird for the price and the looks.

RN

[StevenatorLTFO]

Thanks for the link to the previous discussions Chung, there is some good stuff in there, that totally alters what I need to think about with my new project. Looks like time to get a really nice little table saw, and start making some balsa sammiches

Steve