Joe,
Many thanks. I'm looking forward to what your investigation of the spar structure reveals.

So, what do people think about the advisability of electrifying this plane, given the apparent spar strength problems? I've wanted one for years...

The suitability of electrifying the BOT ARF depends on the maner in which it will be flown. If the airspeed is limited to air speeds not much above thermalling and climbing speeds it should be perfectly safe. However, if the air speed is allowed to build up too much and the plane hits a gust or is pulled out too sharply the wings will fail. After the wing strength is quantified, then a red line air speed can be estimated by calculation and you can determine if that speed limitation is acceptable. The downside is that Dynaflite has not shown any willingness to support any launch method besides a histart launch.

There are many potential benefits to knowing the specific wing strength.

An eastern european company makes an electric version called the Bird 3000, unfortunately I don't know who distributes this model.

http://www.pbmodel.cz/bird3000.html

Oh, and the website has a video which shows the model doing a few loops so it's wing should be fairly strong.

I think you can find the Bird 3000 on the following website:

www.espritmodel.com

I have the Bird 3000 and set it up for winch launch, instead of EP. I was attracted to the flat wing and airlerons.

Anyway, the spar on this model is simply lite ply and capped only with the very thin fiberglass D tube for the leading edge. The wings would bend noticibly under a moderate launch. I finally broke a wing while launching on a windy day.

It was a great looking model that I specked out many times, so I got another and added 1/4" CF spar caps and 1/4" shear webs sistered to the lite ply.

There is NO bending at launch now, and the ship flies great.

I have other ARF's and all required some strengthening in some areas.

If you buy an ARF, look for problem areas and beef up weak spots during the assembly stage. These units are assembly line work and will never have the attention to detail given scratch built or upscale ($500.00 and up) composites and better RTF models.

They save some time in getting to fly, but anything expected to go up on a winch should be thoroughly inspected and modified to handle the stress.

This Dynaflite BOT joiner and spar is simply not strong enough to handle a winch, the same as my Bird 3000. You can get several easy launches, but each will further weaken the assembly until it finally breaks, as in my case.

Modify it for the winch, or follow the manufacturer's launching advice without modifications. At least the process will give new modelers some building experience!

AJ

Folks,

Follow this great link that explains on how to install spoilers on the ARF version of the Dynaflite BOT. http://www.dozone.net/public/rcsoari...0of%20Time.htm

Equest

While people are opening up covering, perhaps some photos can be shot. If the grain is going the wrong way, and I personally don't know which way it should be going, I think publishing a few photos should put that to rest.

Let me provide the following. I don't know if it is useful in the discussion.

I use a NEsail standard hi-start to launch my GP Spirit 2M Select RTF. That is 1/2" rubber with 3/32 wall. It is really designed for much larger planes. The wings are two piece, joined with the standard joiner provided with the Spirit Select RTF. I tape them together at the start of each day's flying with 2" clear packing tape.

I measured the pull on the line with the NE Sail Hi-start I use. The most I could develop without crushing the body of the plane to hold on to it, was about 12 pounds, for whatever value that has to this discussion.

The Spirit has never complained even a little bit. The Spirit has been winch launched many times with a tap tap pedal.

I have flown it off of a dynaflite HD hi-start as well. That is 5/16 rubber with 1/16 wall. I never measured the pull but I don't think it ever exceeded 8 pounds no matter how far I pulled it, and may have been less. If that is the hi-start that the BOT is being targeted to, it provides a pretty soft gradual launch.

Again, I don't know if any of this info is relevent as this is a 2 meter Spirit Select RTF not a 3 meter BOT RTF.

Can anyone tell me if they have experienced wing failure after October, 2003 when Dynaflight post the below Tech Note?

http://www.dynaflite.com/techsupport/dyfa0500tech.html

The purpose, IMHO, for the webbing is to connect the upper and lower spars with something to significantly improve the strenght of this assy.

This will happen when the grain of the web piece is orineted vertically.

The BoT web is horizontal and does not add a significant support as the grain is separated easily in this condition.

Take care Jim

I did not know about the wing controversy (or this discussion group) when I ordered a BOT from Tower in June '04. I originally came here to ask about problems launching my BOT with an approx. 10 year old Dynaflite HD hi-start (DYFP 8302). I used to use it for my only other sailplane, a Bob Martin Pussycat which weighed about 1/4 as much as the BOT. The 3 BOT launches were very weak and slow and it popped off about 30 feet off the ground. I wanted to ask if high-starts get too weak to work after 10 years (stored in a dark closet in an air conditioned house). How much tension should I use? After reading about the wing, I took some covering off the middle wing section and discovered that the shear webbing is horizontal (which is wrong) and the spar caps look like medium hard 1/4" X 1/16" balsa. It may be some Chinese species that I am not familiar with. They are definitely not spruce as were the spar caps in the 6 kit planes I have built. I have never heard of a built up wing without spruce spar caps. There is one layer of 3/4" wide fiberglass or nylon cloth wrapped around inboard end of the joiner box. I don't see any point in adding vertical shear webs if the spar caps are just going to fail. I have thought about adding spruce spar caps behind the existing spar and filling in vertical grain balsa shear webs, but that would be as much work as starting from scratch. Adding CF to the bottom existing spar cap would help keep that spar from failing in tension, but the top spar will be in compression and CF won't help much there. It looks like Dynaflite has created a real lemon. I wish I had come to this discussion group before I ordered the BOT. Thinking about Chinese wood species made me think about bamboo. The spars are definitely not bamboo, but would bamboo be a good choice for spar caps? Has anybody ever tried that?

Hello,
I built the Bird of Time and have made a power pod for it. See pics. It has a OS Max 10 on it with a Hayes 2oz fuel tank and a servo for throttle control. The whole unit weighs
13oz. The glider weighs in at 63 oz plus 13 oz for the pod for a total of 76oz. The weight make the wing loading 10.30 oz per sq ft. The pod is held on with rubber bands. Next week you can go to my youtube page and see the build and flight review including building the power pod. Search rdawson55 at you tube aftar say 7-17-2009.
Here is the link for the webshot pics. http://rides.webshots.com/album/573406717BReylJ
Thanks, Roy

Hello,
Heres my ARF Bird of Time Youtube Build and flight review using a home made OS max Power pod. Lot of fun and easy to build

RC MODEL Bird of Time Sailplane Glider ARF by Dynaflite AIRCRAFT Roy Dawson Broker (8 min 30 sec)

Pics and a measured drawing of the power pod at my website
http://rides.webshots.com/album/573406717BReylJ

Bird of Time inflight video and flight review on youtube. See flying from a bird's eye view from the cockpit.

RC MODEL Bird of Time Sailplane Glider ARF Dynaflite Build Flight Review Aircraft by Roy Dawson (4 min 58 sec)