Apr 16, 2012, 11:50 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
In the Jet Talk forum, Hofer had memtioned something about this, in building his Starfire V2. He didn't go into any detail, though. I'm sure someone here will help us out, and explain it.
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Apr 17, 2012, 12:27 AM
Capt. Z
falcon5's Avatar
Quote:
Originally Posted by CoolerByTheLake View Post
Do you have more details about it?
Stu Maxwel told me about the thrust tubes and said to make them constant then the last part make the taper. I will have to dig up the e-mail but I think the gist of it was as the air is compressed down a long tapered tube it develops friction and friction is drag so he suggested keeping the tubes constant for most of the length and then just the last part taper. I think you get better e-flux doing it this way. But the gurus I am sure can give a much better break down than this laymen can.
Apr 17, 2012, 12:35 AM
Capt. Z
falcon5's Avatar
Quote:
Originally Posted by Eddie P View Post
What are you using for thrust tube material (both the tapered aft nozzles and the constant volume exhaust tubes)?
.010 acetate sheet.
Apr 17, 2012, 12:40 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
Thanks, falcon5. I hadn't thought about friction, was thinking more of a pressure build up. Kinda goes back to the garden hose , nozzel thing. I guess we don't have to know why it works, as long as it does!
Apr 17, 2012, 12:47 AM
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bdelapen's Avatar
Quote:
Originally Posted by falcon5 View Post
Stu Maxwel told me about the thrust tubes and said to make them constant then the last part make the taper. I will have to dig up the e-mail but I think the gist of it was as the air is compressed down a long tapered tube it develops friction and friction is drag so he suggested keeping the tubes constant for most of the length and then just the last part taper. I think you get better e-flux doing it this way. But the gurus I am sure can give a much better break down than this laymen can.
I believe that the best geometry (and the hardest to achieve without molds and layups) is actually an exponential taper. Straight for the larger part of the tube and then getting increasingly narrower towards the end in a more continuous fluid curve. I'm not sure if that made any sense but here is a good example of what I'm trying to describe:

https://www.rcgroups.com/forums/show...0#post19663559

- Birger
Apr 17, 2012, 02:20 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
That looks easy enough! Not to complicate things further, but is there a rule of thumb, reguarding taper lenght? Another thought, at the point where straight tube meets the section to be tapered, you use a ships curve, to get a nice curve up to the exit dia. A smoother transition. Works on intakes.
Apr 17, 2012, 06:37 AM
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bdelapen's Avatar
Quote:
Originally Posted by CoolerByTheLake View Post
That looks easy enough! Not to complicate things further, but is there a rule of thumb, reguarding taper lenght? Another thought, at the point where straight tube meets the section to be tapered, you use a ships curve, to get a nice curve up to the exit dia. A smoother transition. Works on intakes.
I'm sure there are some really complicated formulas that involve all kinds of variables but I would say that ultimately it depends on the overall length of your thrust tube. I'm sure that there should be a range, something like 50/50 for short tubes (straight vs. tapered) up to possibly 90/10 for long tubes but this is not empirical information. I would use the TLAR principle, that should get you close enough.

- Birger
Apr 17, 2012, 07:12 AM
Have Fun! Land, Sea or Air
jetcaptain's Avatar
Hi Falcon, just curious is to when you will make the canopy? Maybe Mr. Morgan can pull you one?
Apr 17, 2012, 08:48 AM
RC Fanatic
Reco's Avatar
I love this so much I want to take it out behind the high school and get it pregnant.....
Apr 17, 2012, 09:02 AM
fly like an EAGLE ;)
corsair nut's Avatar
i am making the canopy plug and sparky is going to make the pulls for us.


Quote:
Originally Posted by jetcaptain View Post
Hi Falcon, just curious is to when you will make the canopy? Maybe Mr. Morgan can pull you one?
Apr 17, 2012, 09:40 AM
Capt. Z
falcon5's Avatar
Quote:
Originally Posted by Reco View Post
I love this so much I want to take it out behind the high school and get it pregnant.....
Chaperoned dates only. But a litter of Talons would make grampa very proud.
Apr 17, 2012, 10:08 AM
Registered User
Quote:
Originally Posted by falcon5 View Post
Chaperoned dates only. But a litter of Talons would make grampa very proud.
After this thread seeing some copies might be the case or at least some cousins.

I see a some REALLY good benefits from using blue foam with SS1K for large scratch jet builds now.

- Maybe easier build and shorter build times (don't know what kinda time this model would take if it were not done with other materials)
- Low power needs, Lighter wing load, longer flight times, easier landings
- Lower overall cost if you have access to 2inch blue\pink foam (maybe)
- Easier covering with SS1K

The A-4 build I was doing is on hold right now and I've had the wing in the garage, picked it up the other day and the non glass 2 layer outer SS1K shell is hard as nails, not as hard as the sheeted Byron F16 wings but the caparisons are too close to quibble. The SS1K stuff alone brings down build complexity I just don't know how to get it harder quicker...I didn't use the vaporizer though.

If foam based scratch builds could be taken seriously by scale competitions I think we'd see more...dunno...I've not seen a 12flt long jet in JWM or NATs that wasn't a static ground model.
Apr 17, 2012, 03:04 PM
Official Boat Bum
Eddie P's Avatar
Quote:
Originally Posted by erh7771 View Post
If foam based scratch builds could be taken seriously by scale competitions I think we'd see more...dunno...I've not seen a 12flt long jet in JWM or NATs that wasn't a static ground model.
I can't see one single solitary reason why composite foam based scratch builds "should" be taken any less seriously than a plant based scratch build. (plant based = balsa tree... and balsa is actually a big weed by the way).

I know exactly why you mention this though, as there has been a bias in the past against foam. But when you have foam that is used as a composite, and it's engineered, finished, painted and detailed - I can see no reason why it would be any less marvelous than any other jet once it's a jet. In fact I see it the other way around. But that's me.
Apr 17, 2012, 03:11 PM
Registered User
Quote:
Originally Posted by Eddie P View Post
...I know exactly why you mention this though, as there has been a bias in the past against foam. But when you have foam that is used as a composite, and it's engineered, finished, painted and detailed - I can see no reason why it would be any less marvelous than any other jet once it's a jet. In fact I see it the other way around. But that's me.
Yeap, this is what I've heard from other modelers who've done scale comps with foam some time ago....the foam gets ignored as "toy" while the extra heavy 'weed" (lol) based planes gets all the attention.
Apr 17, 2012, 03:32 PM
fly like an EAGLE ;)
corsair nut's Avatar
i love when people find out my models are foam....the reaction is priceless. foam? really??? wow.


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