I agree. The sketched in line will help fill the prop and probably not hurt much on drag. All the other bumps, chines, and depressions though, they really should all be one big smooth curve. Carve down the high spots and/or fill in the low spots.
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Armilite
Well-Known Member
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Look at the Cessna 337. If you use a Cowling to cover everything how much difference will that make in Speed? How much is that going to affect your Overall Cooling? The Trouble with Water Cooled Engines is Pressure from the Coolant Heating up, not Heat itself. Take the Water out of the equation and use something like Evans Waterless Coolant.
Using all the different Ceramic and Moly Coatings can also reduce HEAT going into the Engine. They have Coatings for Pistons, Heads, Valves, Exhaust Ports, Exhaust, Bearings, etc! Which drop your overall Heat by 20%.
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WINGITIS
Well-Known Member
Another pusher, just for reference, AMBROSINI SS4.
Found large enough paper to complete my 4 : 1 sketch. I am pretty happy with new tail. Old tail arm and tail boom look very short in comparison. I am getting approximately 16° tail clearance for landing. But I have no idea at this point how correct tailboom supposed to be shaped like.
You might be interested to find that the first cowlings added to radial engines both improved cooling and reduced drag. Our knowledge has improved from there...
A cowling has multiple purposes in Eugene's airplane and has been talked of elsewhere in this thread and on the forum. First and foremost is the forest of disturbed air at the center of the wing, which messes with the entirety of airplane performance. A cowling will clean up wing airflow considerably and generally transform the airplane.
Once we have the idea of good airflow over the wing, yes, any cowling has to provide adequate airflow through the HX's and over the hot points of the engine. A proper pressure cowl to the HX can easily do this with less total drag than by just sticking HX out in the airflow. This concept has been demonstrated for over 90 years. Eugene is planning for all of this. If it adds to speed terrific, but that is not the biggest purpose.
It would be nice to avoid pressurized cooling systems, but we will have a hard time approaching a more reliable and durable cooling system than what is in Rotax 912 powered ships. The problem with straight glycol coolants is that they do not extract heat from the engine as well as water-glycol coolants do. In order to remove as much heat as our water-glycol mixes do, these straight glycol coolants must run at higher temperatures, and extant engines simply are not reliable and durable up there. The biggest issues include thermal tolerance of many of our common materials and thermal expansion of parts. Straight glycol approaches have been tried and abandoned repeatedly for these reasons.
What do you mean by "drop your overall Heat by 20%"? We are using approximately stoichiometric mixtures for the amount of air we are flowing, so the energy liberated in the combustion chamber is unchanged. Modest insulation of the combustion chamber with these coatings will reduce heating of heads and piston crowns, allowing the combustion gases to remain at somewhat higher temperatures through the power stroke. 20% reduction in heat flow to the head and piston is huge and probably not attainable with a coating a few thousandths of an inch thick. Less heat lost to piston and crown means EGTs will be increased, with negative impact upon exhaust valve life. Admittedly, the Rotax 912 does not appear to be life limited in the exhaust valves, but it is in most other aviation engines. I suspect that the margins on the Rotax to tolerate increased EGT's is not large...
Eugene already has a pretty full plate in addressing the airframe issues - trying to improve upon what Rotax supplies so reliably is asking a bit much of him at this point. Maybe after his airframe mods have been wrung out, he could explore coatings and coolants as a means to further reduce cooling drag in his airplane.
Billski
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Here is new tail versus old tail visual comparison.
I don't know that it's the best look for a pilot, but some folks who encounter issues with overall cooling just go without a shirt.
Here is my first attempt to build tail boom. I made about 12 inches vertical height underneath propeller and about 6 inches in front of horizontal stabilizer
That new tail lifts the hstab much more into the prop slipstream - you may find the controls more sensitive.
I'm not saying that's bad, but it will probably feel different to fly than the present arrangement.
Keep up the good work.
I'm not saying that's bad, but it will probably feel different to fly than the present arrangement.
Keep up the good work.
Made some progress and really like general shape. Unless I don't see something very important that you guys do. Now all I have to do is to make it perfect. How hard can that be!!??
This is looking really great, Eugene. You might consider making the fillet on the top side as an expanding radius (as it appears you have done on the bottom). As a way to finish off the fillets at the back (where we see a little pink foam), you could consider an extension that completes itself something like this:
Fillet(s) look aerodynamic, looks can be deceiving.
Thank you!!! I was already wondering what are you supposed to do with this corner when my first coat will dry out. That is why I wanted input from someone who "can see the air". Thanks again!
Air intake on this two pictures below is slightly angled. I wonder why and should I do the same thing?
jedi
Well-Known Member
The angle is more of a high speed Mach thing but it does not hurt. It is like a swept wing.
Others have found the the R-912 in the pusher configuration tend to run cool. That should make your job easier. Look and ram ar inlet sizes on tractor 912 instillations but realize your inlet is in the low pressure area of the wing.
The pressure recovery towards the rear of the wing is a significant issue that needs to be reckoned with. Don't expect the air to stay attached if it has to recover the pressure from both the cowl and the wing. Add a big fillet to help the air by not being trapped in a corner. This is a good spot to add some vortex flow to add energy at the surface.
Others have found the the R-912 in the pusher configuration tend to run cool. That should make your job easier. Look and ram ar inlet sizes on tractor 912 instillations but realize your inlet is in the low pressure area of the wing.
The pressure recovery towards the rear of the wing is a significant issue that needs to be reckoned with. Don't expect the air to stay attached if it has to recover the pressure from both the cowl and the wing. Add a big fillet to help the air by not being trapped in a corner. This is a good spot to add some vortex flow to add energy at the surface.
No, I don't think so.
The Boom is supersonic, and I'm sure it's dealing with all kinds of issues that are way above our pay grade (possibly variable inlet geometry etc.). Looks a lot like an F-14 inlet turned upside down, doesn't it? The Global Hawk, while not supersonic, might get a little reduced observability benefit from sloping the inlet.
For what you're doing, the inlet should be placed just far enough forward that a diverging duct (which might just be the inside surface of the cowling) can recover a reasonable amount of pressure. Tilting the top back eats away at that; pushing the bottom lip forward just adds more surface area (weight and drag). I think you're doing it right.
I don't remember whether inlet lip profile has been discussed in this thread, but you'll want it to have a healthy radius to help the air around the edge. (You could also have a separate duct in some applications).
I've just been working on the upper cowl cooling air inlets for my project - want them to be close to the middle example - limited space precludes the bottom example.
BJC
While not a pusher you can see the straight sides of this cowling on a successful design. I would be wary of fillets.
Yes, I remember, we talked about it and we decided that lips for air inlet supposed to be about 1 inch thick. Or about half inch radius.
In my case whole air intake supposed to be able to fly away during parachute deployment. Which makes it very interesting. I will cross that bridge when I get there. I hope
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