Announcement

Collapse
No announcement yet.

Ask An Expert- Aviation

Collapse
This is a sticky topic.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • gf0012-aust
    replied
    Originally posted by gunnut View Post
    This is a general aviation question.

    I was just browsing Wikipedia (some people browse youtube, I browse wiki) and I came across the engines used in light aircraft like Pipers. I noticed the Piper Seneca uses 2 flat-6 engines with 220hp @ 2800rpm each. The displacement is 5.9L.

    Continental IO-360 - Wikipedia, the free encyclopedia

    My question is why such huge displacement for such low power rating? Is it possible to use more modern auto engines with higher power ratings with less displacement? Or even use some tricks in auto engines to boost power in these aero engines?
    There are a number of aircraft now using car engines. Largest I know of is a 5.7L alloy chev. but Subaru boxer engines are also becoming popular.

    Leave a comment:


  • desertswo
    replied
    Originally posted by Stitch View Post
    I will try and answer this one as best as I can.

    I used to regularly fly in a Cessna Super Skymaster that had two Conti O-360's in it (technically, IO-360's, actually); we used to rebuild them every few years, and one thing I noticed about aero engines is that they are "over-square", that is, the bore is greater than the stroke of the piston. IIRC, these engines wouldn't go much over 2,500 rpm. I suspect that aero engines, as opposed to vehicle engines, are optimized for reliability, rather than output, hence the rather pedestrian performance figures; losing your engine on the freeway means you just have to pull off the road; losing your engine in an aircraft is a bit more problematic.

    The most efficient engines I've heard of being used in aircraft were actually rotary ("Wankel") engines; their power-to-weight ratio was (is?) phenomenal.
    My brother-in-law flew both A-1 Skyraiders and A-4 Skyhawks over the course of several deployments to Vietnam. On one mission while flying the venerable "Spad," before he even began his attack profile, he took a couple of 20mm AAW rounds, one of which blew off his canopy and actually dinged his helmet, and the other essentially took out an entire bank of cylinders in that Wright R-3350 Duplex-Cyclone engine they sported. It took a lickin' and kept on tickin'. So much so that he went ahead and pressed home the strike. I asked him why, given that he was losing oil pressure and all of the other stuff that goes with something like that, and he looked at me as if I had three heads and said, "They really pissed me off!" Why indeed. :wors:

    Leave a comment:


  • Stitch
    replied
    Originally posted by gunnut View Post
    How much more reliable are aero engines?
    Both my father and my older brother had A&P certifications (that's Airframe & Powerplant) for aircraft, and my brother was actually in business for quite a while doing annuals on light aircraft and occasionally rebuilding an engine. There are a lot of redundancies on aero engines that aren't required on regular automobile engines. As I said earlier, losing an engine on an aircraft is a BIG DEAL, so a lot of effort goes into making sure the engine keeps turning, even if one or two things go wrong with it (my airline pilot father-in-law had a joke he used to tell; he said ETOPS stood for Engines Turn Or People Swim).

    For instance, the aircraft engine I was mostly exposed to was the Continental IO-360 (and an occasional radial engine), and they had TWO distributors (on aircraft engines they're called magnetos, since they operate a little differently than a distributor), and TWO spark plugs per cylinder, partly for improved combustion, but also in case one of the magnetos went bad you'd still have another set of spark plugs working. I remember one of the pre-flight checks we did was switch the magnetos on and off, one at a time, to make sure they both worked.

    Also, if you've ever looked closely at an aero engine, you will notice that ALL of the fasteners (nuts & bolts) have safety wire going through them to keep them from coming loose in-flight.



    Originally posted by gunnut View Post
    How about weight? Are aero engines really that much lighter than an auto engine with smaller displacement?

    How does an air-cooled flat aero engine shed heat fast enough idling on the ground?
    All of the aero engines I've been exposed to were aluminum or magnesium block; I think some of the high-power V-12's had steel blocks, but pretty much all of the radial engines and most of the light engines out there are aluminum or magnesium alloy, so they're definitely lighter than your average vehicle engine.

    There is often an issue with engines overheating on the ground; usually, there is enough airflow over the engine from the propeller (particularly with radial engines) to keep the engine cool, but I know the rear engine on the Skymaster often overheated on the ground (particularly on hot days) because it wasn't getting enough airflow (the front "tractor" propeller didn't provide enough airflow to cool both engines while on the ground; the rear engine was cooled by "ram" air flowing over the fuselage in flight). Most aircraft are equipped with what are called "cowl flaps", which control the flow of air over the engine to keep it cool; normally, when operating on the ground, the cowl flaps are open, allowing the maximum amount of air to flow over the engine (unless it's already below zero and you're trying to get the engine warmed up!). At cruising altitude and speed, they are normally closed to keep the engine operating at the most efficient temperature.
    Attached Files

    Leave a comment:


  • gunnut
    replied
    Ah very good. I knew I was missing something. Thanks guys.

    More question about reliability. Modern auto engines are extremely reliable already. How much more reliable are aero engines?

    I had some suspicions on the difference between the load on a car engine and an airplane engine. Modern auto engines generate greatest power at high RPM. They still generate, probably greater than 90% of rated max power, at relatively low 2800 RPM. I wonder how much load there is on an engine driving a 2-blade or 3-blade prop at 2800 RPM, compared to a car cruising at 2800 RPM?

    How about weight? Are aero engines really that much lighter than an auto engine with smaller displacement?

    How does an air-cooled flat aero engine shed heat fast enough idling on the ground?

    Leave a comment:


  • SteveDaPirate
    replied
    In addition to weight there are a couple other factors at play as well.

    For one, cars and aircraft tend to have different operating patterns for the engines. Cars will rev up to 60-70% power for a few seconds as they accelerate onto the highway, and then sit down around 15-20% as you cruise along. Aircraft engines often run near full power the entire flight. The engine in your car wouldn't last very long if you had it running flat out all the time.

    The second issue is RPM. The equation for Horsepower is (HP = Torque x RPM 5252) yet the prop on an aircraft is generally limited to about 2500 rpm. If you want more power, and you can't increase the RPM, you have two options. You can put in an high RPM engine and add additional hardware to gear it down before it gets to the prop, or you can increase the torque the engine produces.

    It would appear that building a large displacement engine that runs at a low RPM with lots of torque generally provides a better mix of reliability, weight, and performance than utilizing the kind of engine you might find in a car.

    Leave a comment:


  • Stitch
    replied
    Originally posted by gunnut View Post
    This is a general aviation question.

    I was just browsing Wikipedia (some people browse youtube, I browse wiki) and I came across the engines used in light aircraft like Pipers. I noticed the Piper Seneca uses 2 flat-6 engines with 220hp @ 2800rpm each. The displacement is 5.9L.

    Continental IO-360 - Wikipedia, the free encyclopedia

    My question is why such huge displacement for such low power rating? Is it possible to use more modern auto engines with higher power ratings with less displacement? Or even use some tricks in auto engines to boost power in these aero engines?
    I will try and answer this one as best as I can.

    I used to regularly fly in a Cessna Super Skymaster that had two Conti O-360's in it (technically, IO-360's, actually); we used to rebuild them every few years, and one thing I noticed about aero engines is that they are "over-square", that is, the bore is greater than the stroke of the piston. IIRC, these engines wouldn't go much over 2,500 rpm. I suspect that aero engines, as opposed to vehicle engines, are optimized for reliability, rather than output, hence the rather pedestrian performance figures; losing your engine on the freeway means you just have to pull off the road; losing your engine in an aircraft is a bit more problematic.

    The most efficient engines I've heard of being used in aircraft were actually rotary ("Wankel") engines; their power-to-weight ratio was (is?) phenomenal.

    Leave a comment:


  • 85 gt kid
    replied
    Speaking as a car nut the motor is very light for its time. The weight for my windsor is around 500 lbs and that same motor in the 60s made like 150hp so it's power to weight ratio is my guess why they used it.. Now a newer turbo four cylinder would be great in that :).

    Leave a comment:


  • gunnut
    replied
    This is a general aviation question.

    I was just browsing Wikipedia (some people browse youtube, I browse wiki) and I came across the engines used in light aircraft like Pipers. I noticed the Piper Seneca uses 2 flat-6 engines with 220hp @ 2800rpm each. The displacement is 5.9L.

    Continental IO-360 - Wikipedia, the free encyclopedia

    My question is why such huge displacement for such low power rating? Is it possible to use more modern auto engines with higher power ratings with less displacement? Or even use some tricks in auto engines to boost power in these aero engines?

    Leave a comment:


  • desertswo
    replied
    Originally posted by jrb1537 View Post
    There are some F-5s and F-104s in the US. Those all came from foreign surplus (Canada mostly) to dodge the sorts of issues the Collings Foundation ran into. I wouldn't count on ever seeing anything newer in civilian hands.
    I seem to recall reading once "back in the day" that Brig Gen Chuck Yeager, USAF(Ret) had access to, if not outright ownership of, a non-Air Force inventory F-5.

    Leave a comment:


  • 85 gt kid
    replied
    Yea that's what I thought. I knew it was easier to get Migs and Sukhois then US planes but figured I'd ask. I always thought it'd be cool to have someone make a clone of a Tomcat/Warthog (obviously built different then military ones so to avoid issues) but that'd have to be a big lottery :D

    Leave a comment:


  • gf0012-aust
    replied
    Originally posted by Alpha1 View Post
    this doesn't answer why even the F-35 has a non stealthy engine
    Late answer but still needs to be addressed

    no such thing as a "stealth engine"

    the signature management for the platform is not just about the shape of the nozzles - and the JSF rear end is also IR and signal management. Signal and signature management is not just about nozzle shape, its about an all aspect sig measurement or IR measurement from likely angles of attack and how you diffuse/disrupt/deter/degrade red sensors

    the nozzle shapes are all about how they play a part in the platforms ability to manouvre across various ranges - and TVC as in the F-22 is about an emphasis to energise manouvre in the vertical axis (ie to the planes centreline and horizon at any given moment)

    a "non stealthy" engine would be one such as a pod hanging below a wing without any heat shield around the nozzles and without the benefits of body shape management. note that every manned and unmanned publicly displayed image of a VLO/LO platform shows different techniques in signature management - the US literally has improved and changed the way it manages signature issues at every generation

    what that also emphasises and what seems to get missed by a whole pile of "pseudo experts" in the broader magazine and blogosphere is that VLO/LO is not a fixed construct - its not a single identtity or "feature" that can be countered at one generation of asset and works from that point on.

    "stealth" is one of the most overtalked and misunderstood capabilities around IMO

    Leave a comment:


  • gf0012-aust
    replied
    you won't be able to do anything once you hit components covered by ITARs

    a pointless exercise......

    Leave a comment:


  • zraver
    replied
    Originally posted by 85 gt kid View Post
    Hey guys random question but hypothetically speaking if you were a billionaire and wanted to buy something like a F-18/15 could you buy from a country that has licensing agreements to build them (Japan F-15/Canada F-18)? Or is it just like buying any "new" US fighter where it's a big fast no even if another country purchased them (F-111 comes to mind)?
    You probably could not buy it do to export controls the US has unless you had a valid reason. So Space X could probably buy a third gen early fourth gen plane since they could likely make the case for the need for a super sonic craft but they could just as easily buy surplus USAF stuff. But outside of something like that I think the answer is no.

    Leave a comment:


  • jrb1537
    replied
    Originally posted by 85 gt kid View Post
    Hey guys random question but hypothetically speaking if you were a billionaire and wanted to buy something like a F-18/15 could you buy from a country that has licensing agreements to build them (Japan F-15/Canada F-18)? Or is it just like buying any "new" US fighter where it's a big fast no even if another country purchased them (F-111 comes to mind)?
    Trying to bring any even close to modern fighter plane into the US is going to involve red tape from nearly every agency imaginable, taking months or years and piles of money. It took two literal acts of Congress for the Colllings Foundation to get their A-4 and F-4 out of the boneyard. When someone brought over those two Su-27s, State, Defense, FAA, etc. went over those birds with a fine tooth comb both in Ukraine and in the US to make sure they were completely demilled.

    There are some F-5s and F-104s in the US. Those all came from foreign surplus (Canada mostly) to dodge the sorts of issues the Collings Foundation ran into. I wouldn't count on ever seeing anything newer in civilian hands.

    Leave a comment:


  • 85 gt kid
    replied
    Hey guys random question but hypothetically speaking if you were a billionaire and wanted to buy something like a F-18/15 could you buy from a country that has licensing agreements to build them (Japan F-15/Canada F-18)? Or is it just like buying any "new" US fighter where it's a big fast no even if another country purchased them (F-111 comes to mind)?

    Leave a comment:

Working...
X