Pusher cowling ideas

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

AdrianS

Well-Known Member
Joined
Jul 5, 2014
Messages
719
Location
Australia
I completely agree. I fixed already some cracks, because I found them visually. If you have engine cowling, that already representing high risk of missing on something during preflight inspection. I don't know. Everything is compromise. I will try to find my own comfort zone. And if I get in trouble, I can always ask my wife for advice. She is normally willing to tell me what to do without hesitation.
I had the primary exhaust on my MR2 ceramic coated, and have been impressed by how little heat is radiated from it.

I have seen several wrapped exhausts that have got quite corroded, presumably from moisture trapped in the wrapping when not in use.
 
Last edited:

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
13,596
Location
97FL, Florida, USA
Wrapping exhausts or ceramic coating the outside of exhausts is done to reduce hest transfer to other components, and always ages the exhaust faster due to higher metal temperatures.


BJC
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,239
Location
Port Townsend WA
Metal heat shields with an open 1/2" air gap have protected my Honda car exhaust from corrosion for 30 years.
The corrosion starts directly at the end of the heat shields and needed repair. (I MiG welded finger patch doublers to last another 10-20 years)
 

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
Absolutely no fillets on engine cowling, but straight vertical walls against the wing. I wonder why? Is that because propeller is creating a lot of suction and it doesn't matter? There is fillets on fuselage. But relatively small.

Air intake is definitely piece of art, looks like with adjustable louvers

Screen Shot 2021-08-01 at 20.05.53.pngScreen Shot 2021-08-01 at 19.54.22.pngScreen Shot 2021-08-01 at 19.52.46.png
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
5,015
Location
capital district NY
You could try dimples.
MythBusters Stunned by Fuel Efficient 'Golf Ball' Car - Bing video

Theory is that the drag from dimples will decrease pressure drag but the increase in friction drag more than offsets any gain from that. If you consider that the problem is that you already have friction drag "aka the problem" and you subtract the existing friction drag then do you have a net gain in efficiency because of the decrease in pressure drag?
 
Last edited:

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
Do it, mock one up before you move on, 17 & 1/2 " hub.
From what I see on my pictures, I will not benefit from larger spinner. It will simply be higher than engine itself. Not sure how beneficial this would be. 14 inches looks pretty good to me. I was simply trying to defend my decision to go with larger spinner. It is next to impossible to find dimensions that will make everybody happy.

tempImage02LCIN.pngtempImageyxHHMp.png
 

WonderousMountain

Well-Known Member
Joined
Apr 10, 2010
Messages
2,406
Location
Clatsop, Or
You took this in another direction than I was expecting.
Closing out to a spinner is quite different than flat foil
like closeout. If you are content the issue is resolved.
Maybe six inches to the radiator, but I would not know why.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,796
Location
US
Also wondering what would be recommended distance from intake diffuser to the radiator itself.
At the risk of repetition, what I would do is stay clear of that BRS hatch. That might mean that the duct starts at the radiator face, but we already know that the radiator and oil cooler work fine with no nacelle at all, so the only cost of a non-optimum diffuser might be slightly more drag.
If I extended the nacelle over the BRS top, I'd make anything that extends over it of something frangible.
A BRS that we can't be 100% sure of operating could easily be worse than no BRS at all.
 

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
At the risk of repetition, what I would do is stay clear of that BRS hatch. That might mean that the duct starts at the radiator face, but we already know that the radiator and oil cooler work fine with no nacelle at all, so the only cost of a non-optimum diffuser might be slightly more drag.
If I extended the nacelle over the BRS top, I'd make anything that extends over it of something frangible.
A BRS that we can't be 100% sure of operating could easily be worse than no BRS at all.
Thank you, this will give me something to think about.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,226
Location
Saline Michigan
I DO NOT KNOW what the right answer is. I can frame the problem of getting the rocket and chute package out, and we can even frame the issue of figuring the duct.

First off, the BRS chute. When you pull the handle a sequence starts. The rocket starts the ejecta (parachute) moving. When the ejecta contacts the lid of the box, it has to have more kinetic energy than is required to break loose the lid so that it keeps moving out. If it stalls, the gadget fails. They probably have quite a bit more energy than needed for their box. What you would be adding is another system that is encountered later in the sequence. The ejecta gains some kinetic energy before hitting the lid, breaks the lid loose and sucks up some of the kinetic energy, then, if the rocket engine is still running, the ejecta plus the lid is accelerated to some higher kinetic energy before it hits the nose of the scoop. The scoop will break loose if there is more kinetic energy in the ejecta plus lid at contact than is required to blow the scoop. If there is then enough kinetic energy left plus enough rocket energy left to lift and deploy the chute, it has a chance at saving your butt. If you go through your rocket energy without blowing the lid then the scoop then the lift the chute, the gadget does not deploy, and your last hope fails.

I have NO IDEA if they put in enough excess to knock the scoop off. To give a reasonable chance of success, I would do some calcs about what it takes to blow the lid and make sure the scoop takes less, then maybe see what I could do about making the lid come off easier too. Do the calcs by integrating force over distance for each thing it has to do. For popping the lid or scoop, that is the area under the force vs distance curve. The ejecta has to go to a certain height, so that energy is weight times height, and then I presume some kinetic energy is required when the risers run out too. No idea what that is either. Have you seen any video of this particular product when fired? Careful analysis of video can give some idea of how much excess energy there is.

Second the duct. Hi

Best game for efficiency is small opening, long gentle expansion, sealed so all air goes through the radiator cores. This can run the HX's well with reduced inlet area to the point where you may not have enough cooling of other stuff further aft, so might then find a need to open the inlet some. This may require a lot of energy from the BRS to knock out of the way.

Second best is a short diffuser, otherwise sealed as above. It will still be more efficient than the wide open radiator you have now, but your inlet area may need to be bigger to become effective and most likely will need some guide vanes to "wet" and build pressure on the entire radiator face. It will likely have plenty of air to do the auxiliary cooling after the radiators. You would have to get this aft of the BRS ejecta launch path, so it might be short indeed.

One other path is to move the BRS further forward, replace the weatherproof lid with a breakaway portion of a forward extension of the cowling that is forward of the inlet, and then make sure that you still have a weathertight bag over the BRS. Make a single fair shape that goes from engine forward of the BRS and into the roof at the windshield, with a single breakaway panel for the BRS ejecta to travel through.

I emphasize again, I DO NOT KNOW enough of the details to know if there is enough energy to move more than the standard lid and still deploy the chute.

Only one thing is certain. You have a bunch of figuring and estimating and maybe development to do. Have fun.

Billski
 
Last edited:

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
I DO NOT KNOW what the right answer is. I can frame the problem of getting the rocket and chute package out, and we can even frame the issue of figuring the duct.

First off, the BRS chute. When you pull the handle a sequence starts. The rocket starts the ejecta (parachute) moving. When the ejecta contacts the lid of the box, it has to have more kinetic energy than is required to break loose the lid so that it keeps moving out. If it stalls, the gadget fails. They probably have quite a bit more energy than needed for their box. What you would be adding is another system that is encountered later in the sequence. The ejecta gains some kinetic energy before hitting the lid, breaks the lid loose and sucks up some of the kinetic energy, then, if the rocket engine is still running, the ejecta plus the lid is accelerated to some higher kinetic energy before it hits the nose of the scoop. The scoop will break loose if there is more kinetic energy in the ejecta plus lid at contact than is required to blow the scoop. If there is then enough kinetic energy left plus enough rocket energy left to lift and deploy the chute, it has a chance at saving your butt. If you go through your rocket energy without blowing the lid then the scoop then the lift the chute, the gadget does not deploy, and your last hope fails.

I have NO IDEA if they put in enough excess to knock the scoop off. To give a reasonable chance of success, I would do some calcs about what it takes to blow the lid and make sure the scoop takes less, then maybe see what I could do about making the lid come off easier too. Do the calcs by integrating force over distance for each thing it has to do. For popping the lid or scoop, that is the area under the force vs distance curve. The ejecta has to go to a certain height, so that energy is weight times height, and then I presume some kinetic energy is required when the risers run out too. No idea what that is either. Have you seen any video of this particular product when fired? Careful analysis of video can give some idea of how much excess energy there is.

Second the duct. Hi

Best game for efficiency is small opening, long gentle expansion, sealed so all air goes through the radiator cores. This can run the HX's well with reduced inlet area to the point where you may not have enough cooling of other stuff further aft, so might then find a need to open the inlet some. This may require a lot of energy from the BRS to knock out of the way.

Second best is a short diffuser, otherwise sealed as above. It will still be more efficient than the wide open radiator you have now, but your inlet area may need to be bigger to become effective and most likely will need some guide vanes to "wet" and build pressure on the entire radiator face. It will likely have plenty of air to do the auxiliary cooling after the radiators. You would have to get this aft of the BRS ejecta launch path, so it might be short indeed.

One other path is to move the BRS further forward, replace the weatherproof lid with a breakaway portion of a forward extension of the cowling that is forward of the inlet, and then make sure that you still have a weathertight bag over the BRS. Make a single fair shape that goes from engine forward of the BRS and into the roof at the windshield, with a single breakaway panel for the BRS ejecta to travel through.

I emphasize again, I DO NOT KNOW enough of the details to know if there is enough energy to move more than the standard lid and still deploy the chute.

Only one thing is certain. You have a bunch of figuring and estimating and maybe development to do. Have fun.

Billski

Thank you! I will try to send this question to BRS engineers in Minnesota. Just to make sure that there is no easy solution out there that I am missing. Something like maybe converting to soft pack and shoot the rocket forward instead of straight up. I am just making it up. I don't know.

Another issue that I didn't think about is two straps that parachute will be pulling out of the airframe. Without engine cowling it was easier thing to do. With everything covered will be a problem.

They do this every day and they see so many airplanes all the time. Who knows, maybe they will have a recipe for me.

IMG_5653.jpeg
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,226
Location
Saline Michigan
The parachute bridles are typically run in troughs in the skin of the airplane, wrapped in some sort of bag that epoxy won’t stick to, and then are faired in. The opening of the chute, breaks the fairing compound away, then the shrouds run from the expected spots up to the chute.
 

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
The parachute bridles are typically run in troughs in the skin of the airplane, wrapped in some sort of bag that epoxy won’t stick to, and then are faired in. The opening of the chute, breaks the fairing compound away, then the shrouds run from the expected spots up to the chute.
OK, so that's not going to be a problem? That's a good news! Softpack if I remember correctly have much smaller dimensions. Maybe I can hide it somewhere else instead of right in front of radiator? I don't know, just brainstorming at this point.

IMG_5790.jpeg
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,796
Location
US
Marginally relevant:
Accident report from a fatal Rans S-12XL (a high wing pusher) crash after BRS deployment.
Summaries

Take-aways:
- Do a thorough route study before flying up a canyon.
- If the BRS manufacturer provides a section of Kevlar harness to withstand a prop strike, use it.
- If the manufacturer requires that the engine be shut down before BRS deployment, do that.

These installations are pretty well worked out between the BRS manufacturer and the aircraft kit maker. I hope the BRS folks are receptive to providing advice/assistance to a builder who is making changes, but honestly it would be surprising to me.
 

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
Marginally relevant:
Accident report from a fatal Rans S-12XL (a high wing pusher) crash after BRS deployment.
Summaries

Take-aways:
- Do a thorough route study before flying up a canyon.
- If the BRS manufacturer provides a section of Kevlar harness to withstand a prop strike, use it.
- If the manufacturer requires that the engine be shut down before BRS deployment, do that.

These installations are pretty well worked out between the BRS manufacturer and the aircraft kit maker. I hope the BRS folks are receptive to providing advice/assistance to a builder who is making changes, but honestly it would be surprising to me.

Yes, you have to turn engine off!!! I was actually thinking to install electric killswitch and connect it to the deployment handle.
 

Eugene

Well-Known Member
Joined
May 26, 2017
Messages
1,675
Location
Merrill, Wisconsin, USA
I hope the BRS folks are receptive to providing advice/assistance to a builder who is making changes, but honestly it would be surprising to me.
They did talked to me and helped to install my unit after purchase. They send me recommendations based on their previous experience working with Skyboys. I had to convince them that my way is better and they agreed. Picture below is what I was sending to them. They want me to connect one strap to the front connection with only one 6mm bolt.

IMG_0645.JPG
 
Top