On TRF, Kirk G posted:"So, after a couple of months of waiting, the Big Bertha kit is complete (or as much as the yellow base coat is going to get), and the weather is fine, clear, hot, sunny, NO wind....
And the club launch is a go on Saturday...
Despite a car accident blocking the highway, we get to the field late in the day, load up the Bertha, and get ready to launch...
And this was the result...""
https://www.facebook.com/#!/photo.ph...type=2&theater
"Everyone asks "What did you fly it on?" And I reply A8-3, just what the package recommends....
And they all laugh and gaphaw at me. "A8-3, that's NOTHING", they all say.
"But that's what was recommended on the package," I explain.
"That's cause they want to sell more kits," one opines.
SELL MORE KITS? HOW DOES THAT FOLLOW?"
Why would Estes label the classic kit to be an A8-3 if it produces this type of flight?
Any opinions welcome. (Later flights on an B6-4 and C6-3 and C6-5 went off just fine!
My response:
I was curious and looked up the Big Bertha recommended engines in the earlier Estes catalogs:
1967 Catalog, Big Bertha
B.8-2
1968, 69 and 70 Catalog, Big Bertha
A5-2, A8-3, B4-2, B6-4, C6-5
1971 and 1972 Catalog, Big Bertha
A5-2, A8-3, B4-2, B6-4, C6-5
Adds “Use B6-4 for first flights”
1973, 74 and 75 Catalog, Big Bertha
A8-3, B4-2, B6-2, B6-4, C6-5
“Use B6-2 for first flights”
1976, 77, 78 and 79 Catalog, Big Bertha
A8-3, B4-2, B6-2 (First flight), B6-4, C6-5
1980 Catalog, Big Bertha
A8-3, B4-2, B6-2 (First flight), B6-4, B8-5, B14-5, C6-5
From 1968 through 1972 they even listed the A5-2 engine for the Big Bertha.
Other recommended engines included a A8-3 for the Trident.
The Trident is 6" longer and weighs 1/2 ounce more!
I launched my Semroc Centurion with an A8-3 - once. The flight looked a lot like your Big Bertha with the A8-3.
The parachute didn't even have time to open before it hit the ground.
Fred Shector's response:
"MY GOD!!! This will be a serious safety problem for the millions of rocket flying folks who get into a time machine and travel back to 1990 and choose their motors from a catalog and ignore the instructions!!!!!!!!!!!!"
Relax Fred, I was curious and always wondered why Estes would recommend a under powered engine on a large model.
Be69ar (Mike from Estes) response:
"...1996 is the last year I can find that referenced using an A8-3 in the 1948 Big Bertha...been B motors and above since then. As for weights on the packaging, we actually use finished models but with light primer and paint jobs. With kits we state "Estimated Weight" as we don't know how much finish a modeler will apply and we with fair packaging requirements, we have to be within a certain allowed percentage of actual weight."
Mike
At least we have the official answer about kit weights.
People have been asking for years - Is that just the weight of the parts (for shipping) or the finished model weight?
Personally, I think it's the fat, puffy decal. That extra weight has to slow it down some.
Personally I think Estes A10-3T's are more powerful than the A8. I don't use A8's at all anymore.
ReplyDeleteSomebody a few SEVRA launches back launched a Big Bertha on an A8-3. The durned thing actually hovered at about 35' like the SpaceX Grasshopper
ReplyDeleteHi Phill,
DeleteI only launched my Centurion (about the same size as the Big Bertha) once with an A8-3. Never again!
I was surprised how long the A8-3 was listed as a recommended engine for the Bertha. In the old catalogs there are some other questionable engine choices.
Anonymous,
ReplyDeleteI do the same thing!
A few years back, Blackshire first posted on TRF about using A10-3t engines in place of A8-3s.
Why not? Four A10 engines for the same price as three A8-3s. The 2050 engine mount adapters are easy to make. Both engines are close in performance.
Anonymous,
ReplyDeleteI knew I'd done a thrust curve comparison between the A10 and A8 engines:
http://modelrocketbuilding.blogspot.mx/2014/02/a10-to-a8-engine-comparison.html
Pretty interesting that the 13mm A10 has more propellant and a higher peak thrust than the 18mm A8 engine.
I just glue the A10 inside an old 18mm casing to use it in that size engine mount. And you're right about getting four to a pack instead of three. For my size launch field the A10 is perfect.
DeleteI've noticed that some of the old catalogs show maximum liftoff weights of specific motors given in ounces. Several models in their catalog violate that rule. It is obvious that their recommendations are rounded to the nearest ounce, which is pretty crude resolution when some models typically weight only one or two ounces!
ReplyDeleteI would never fly my Bertha on an A. I would only use an A8 on a model weighting maybe 2 oz. at the most. I found that a parachute often needs at least 100 feet to be assured of it opening on time, with the motor delays +/- 1 second or more.
As for package specs from Estes and Quest, I consider them fairy tales and nothing more.