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New Hangar 9 P-51 60cc

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New Hangar 9 P-51 60cc

Old 06-08-2015, 03:19 PM
  #926  
fhollahan
 
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Originally Posted by old p47
If you go back in this thread a Horizon pilot pointed out you need to put a spoiler in front of you air exit hole to create a low pressure area to draw out the hot air. I fly in phx and have 9 flights so far. I followed his example and have no heating issues at all and we are in the hot part of the country.
Is your muffler completely inside the cowl as well? What engine are you using? Just curious.
Old 06-08-2015, 05:03 PM
  #927  
old p47
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yes it is completely inside. It is a DLE
Old 06-08-2015, 05:17 PM
  #928  
185skywagon
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Originally Posted by fhollahan
Is your muffler completely inside the cowl as well? What engine are you using? Just curious.
fhollahan Can you tell me the rough air temperatures you have been flying in ? I'm looking at the same setup, don't want those problems.
Old 06-08-2015, 05:46 PM
  #929  
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Originally Posted by 185skywagon
fhollahan Can you tell me the rough air temperatures you have been flying in ? I'm looking at the same setup, don't want those problems.
I'm flying in 80-85 degrees. I have DA and DLEs in several planes that all run well. I noticed the DAs I bought new from the factory are set a bit lean for peak performance right out-of-the-box so you may want to make it more rich to start thru a break-in period at least in this plane. It keeps the motor running but a lot more "burble" and sacrifices some power. I opened the front of the cowl right at the cooling fins a bit more as well. You can try the "spoiler" in front of the rear opening that is mentioned but I am not sure this is the only thing you should or need to do. It would be nice to see some temperature data with a spoiler and without on the same setup. I am going to use the higher octane leaded fuel, that will help. I'll report back my results in a week.
Old 06-08-2015, 05:52 PM
  #930  
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Originally Posted by 185skywagon
fhollahan Can you tell me the rough air temperatures you have been flying in ? I'm looking at the same setup, don't want those problems.
My overheat issues were in temps anywhere from 65° to 80°. After switching fuel, I have since flown in 80°-90° temps with no issues.

I I have noticed that if I shut down right after landing and taxiing back, after shutdown the temps will spike like crazy up to 330-340°. If I let it sit at idle for 30 seconds or so before shutdown the temps won't break 300° after shutdown. I don't know if the heat has any effect on it or not when it's not running, but it triggers my telemetry alarm and people usually approach me shortly after landing to talk about the plane and the alarm gets annoying. lol.
Old 06-08-2015, 10:35 PM
  #931  
185skywagon
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Thanks guys. Can you both confirm with me the fuel you use / will be using ? I think DA talk about voiding warranty with high octane fuels, I would like to know the disadvantages to using those fuels as I assume there are some ?

Anyway I only have access to 91 & 95 unleaded here and 100LL avgas. I run currently run all my gassers on 91. Recommendations ?

I know the science behind a spoiler / deflector works, its used on full size aircraft and I've seen it on other RC warbirds as well.
Old 06-09-2015, 12:36 AM
  #932  
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I use Sunoco super premium in my Da 50R, I think the octane is around 93 and it is advertised as not having ethanol additives. Internal combustion engineers will tell you that octane rating only matters when cylinder bore is larger than 2.5 inches when pre-ignition becomes a problem with engines that have compression ratios higher than 9 to 1. Most engines built today are less than 9 to 1 compression ratio. The single biggest performance factor model engines are concerned with is the ethanol mix. Manufacturers say that there are no negative issues with ethanol gas but my many years of repairing motorcycles, cars, and trucks working for dealerships proved to me that there are some expensive fuel system problems caused by ethanol. Even the Walbro carbs we get with our gas engines are fitted with ethanol "resistant" seals and gaskets. Unfortunately the corrosive effects of ethanol fuel can destroy the metal body castings if any gas is left in the fuel system after flying,
There is a reason that ethanol is not transported by pipeline and is mixed with gasoline at the distributor level- it destroys almost everything it comes in contact with. If you run your motor dry after flying sessions you won't have any problems. When gasohol absorbs moisture in the air it forms acid compounds.
At the time when all the local gas stations were switching to gasohol I began buying Coleman camp stove fuel. It is expensive by the gallon but there are no engine problems caused by its use in model engines, only a distinctive smell. Colman fuel is around 50-60 octane. When the Sunoco ethanol-free gas became available I switched to it and a lot of my friends are full scale pilots so they get their gas from the local airport. Airport fuel is 100LL and they don't have problems with it either.
If you buy midgrade or premium from gas stations it has ethanol mix in it unless labeled otherwise. I don't believe you will have fuel problems with any type of fuel in your model engines as long as you run it dry after flying sessions. I have found that the fuel tubing the hobby industry supplies is affected and will get hard after 5-6 weeks when exposed to gasohol-even TYGON tubing.
There is a type of tubing that is black in color that is claimed to be unaffected by gasohol but the only time I got any was when a hobby supplier gave 3 feet of it to every entrant at a local event.
A lot of overheating problems are cause by incorrectly set ignition timing(both retarded and over advanced). You can make an overheating engine cool down by going rich on the carb fuel needles. The most important fact is to have 3-4 times more cooling exhaust than intake area.
I don't have cooling problems with my model engine setups and I have never used spoilers on any of my planes. The guys who fly with me will tell you that I run my motors hard and use large high pitch props on gas and electric. Field temperatures here in Florida get to 100 degrees.
Old 06-09-2015, 04:16 AM
  #933  
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Viton is the tubing I use in all my tanks because it doesn't harden like Tygon
Old 06-09-2015, 04:16 AM
  #934  
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+1 on the ethanol-free gas! Is this your current setup in the h9 p-51? If so, is your muffler completely enclosed in the cowl? Just want to compare apples to apples.

I've never had a cooling issue on several gassers that I own, just this one. It was also unable to be tuned out, no matter how rich I went on the needles.
Old 06-09-2015, 07:32 AM
  #935  
CRG
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Originally Posted by sjhanc
The most important fact is to have 3-4 times more cooling exhaust than intake area.
This is just not true. The most important requirement is to force cooling air through the cylinder fins. Equally important is providing a mechanism to extract the hot air, typically this is achieved with a low-pressure area outside the cooling exit location. The size of the exit opening alone is not nearly as important, and there is no magic to the often-stated 1:3-4 ratio. Using a spoiler, ramp or louvers are common ways to create a low-pressure area.

The 60cc Mustang is a challenging airplane to cool effectively but it can be done with some baffling and the exit ramp. Prior to doing this we would see occasional overheating, and frequent vapor locking after shut down.

The baffle in the image is unfinished but note that it has a 'return' to guide air beyond just the side fins. The spoiler on the cowl lip needs to be larger than shown.
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Last edited by CRG; 06-09-2015 at 07:34 AM.
Old 06-09-2015, 07:38 AM
  #936  
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I am still assembling the H-9 P 51 and just getting to the muffler installation. It will be completely enclosed exactly like all of my other P 51 models. The muffler is steel construction I welded up myself. I got tired of paying $150+ for aluminum exhaust that sometimes cracked after a few flights. It is heavier than the hobby stuff but I need weight in the nose of this plane anyway.
The carb air filter is behind the firewall so it draws its air from the inside of the fuse. Some openings are required in the belly scoop and radiator exhaust to supply air. I glue a balsa block in the carb air opening under the spinner, then route out an aerodynamically shaped cooling air passage back to the upper cylinder. This keeps all the incoming air directed at the hot parts. The next step is a shaped cooling exhaust that is notched in the lower firewall. A wedge-shaped passage allows hot air to flow straight back and out under the fuse belly in front of the wing. High speed air flowing pass the cooling exhaust creates suction that helps pull the hot air out. I have never needed a dam or spoiler here so I don't bother with that.
I drill out most of the scale exhaust to the inside of the engine cowl, they are angled back into the airstream so there is a natural suction to remove heat from the upper engine compartment.
Most modelers just cut holes where it is convenient and trust the opening to do all the work of moving hot air. The heated air off of the cylinder and exhaust system has to have some space to expand two or three times its volume and then naturally keep moving without restriction out of the plane. A simple hole in a flat surface that is in line with the air stream won't guide hot air out and usually creates a restriction to air flow. That causes the overheating and dead stick landings.
Modelers want to keep it simple and not spend the time and labor to make it work. It is, after all just a toy. I had some extensive aircraft mechanic training both in the US Army and later for Bell Helicopter. I am used to seeing air intake and exhaust handling solutions in full scale aircraft and helicopters. I try to keep the scale models as simple as possible but a certain minimum of design and construction effort is necessary in order to have a nice flying day. In my military job as a crew chief I had to pay attention to the details so that others would not pay for a mistake with their lives. And I was along for the ride with them. I didn't have anything to do with the design of the aircraft I flew in but I got to take them apart every day and just got used to the way it needs to be. I flew up to 14 hours each day and pulled maintenance inspections all night with my gunner. When I needed extra manpower they got line mechanics out of bed to help us do a week's work in one night. When that happened I had to inspect all the other's work too. I got to sleep every time the pilots shut it down to go to a meeting for their mission orders (usually 10-15 minutes unless we were in a hot LZ being shot at).
Old 06-09-2015, 08:23 AM
  #937  
CRG
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You would need an incredible heat exchange to require anywhere near a 2-3x volume increase (assuming you wanted to maintain pressure). If my math is correct, warming 75degF air to 300degF would increase the volume less than 50%.
Old 06-09-2015, 08:57 AM
  #938  
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Originally Posted by Len Todd
I put telemetry in all my gas planes. My first plane (existing and later put in telemetry) was running over 300 degrees F and I was able to get that down to 230 with baffles and more air outlets. Most of mine run about 225 - 250 give or take ambient air temps. Also, I use the telemetry RPM readings in the air to figure the best prop that gets the engine in the power band. There is quite a bit of difference between running on the ground and in the air. RPMs also help tune for that slightly rich sweet spot. But you can get a hand tach too for that.
Len what're you using to obtain the RPM figures in the air? Are you piping it back to your receiver through some sort of optical RPM gauge, or through the ignition...?
Old 06-09-2015, 09:04 AM
  #939  
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Originally Posted by chorner
Len what're you using to obtain the RPM figures in the air? Are you piping it back to your receiver through some sort of optical RPM gauge, or through the ignition...?
The way I do it is with a spektrum receiver and a tm1000 telemetry unit. I then put a y-connector in-line between the hall sensor and the ignition module. That extra wire needs a ferrite choke on it, then changed into a telemetry connector on the other end and plugged into the rpm port on the tm100 telemetry module. Works great. Rpms will unload in flight close to 1000rpms (I.e. 6100 tpms on the ground will yield close to 7100 in the air)

nick
Old 06-09-2015, 10:36 AM
  #940  
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Awesome - I wanted to try that on my Spektrum telemetry unit. Was just worried about ignition interference; the ferrite choke takes care of that then and you haven't had any RF issues at all?
Old 06-09-2015, 11:27 AM
  #941  
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The muffler produces far more heat than the cylinder.
Old 06-09-2015, 11:31 AM
  #942  
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I have not had any rf issues. Without the choke, the tm1000 would lock up and stop working shortly after engine start. With the choke, it works just fine.
Old 06-09-2015, 01:18 PM
  #943  
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In order to have the cooling air flow or move through the cowling, you must have a pressure differential. Higher pressure where the air enters the cowling, and lower pressure where it exits the cowling. In some cases, this can be done with different sized inlet and outlet holes on the cowling... a small inlet and larger outlet. BUT.... depending on where that outlet is located on the airplane, and the angle of the surface that it is cut out from, you can have very little or no pressure difference and thus poor flow of cooling air. I have even seen reverse flow thru the cowl if the cooling air exit is located poorly. In some cases, making the exit hole bigger and bigger can make the problem worse.

In the case of the bottom of the Mustang cowl, the bottom surface is angled so that a hole cut in the bottom will actually scoop some of the air passing over it into the cowl, making high pressure in the area where you are trying to extract the cooling air. This applies to other Mustang kits such as the Aeroworks too. The solution isn't a bigger hole, it is a spoiler or cowl flap located at the front edge of the opening. This will create a low pressure area and allow the air to flow through the cowling.

KennyMac
Old 06-09-2015, 05:01 PM
  #944  
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This is the nose exhaust of my TF GS P 51 B. You need to really look at a Mustang's shape. Because the air flow around the entire aircraft is spiral (due to the prop dragging air around with it), centrifugal force causes air to move out away from the skin creating a low pressure air mass that reattaches further back near the wing. Openings near the front (back to a few feet behind the nose of the full scale) are under pressure and openings behind the curve (where an opening can't see the spinner) are in low pressure. The area of this opening is approximately 2.5 times the chin scoop.
The main body of spiral airflow (spiral air flow is the reason the leading edge of the vertical fin is offset a few degrees to the left) is forced by the air that it compressed when the spinner charged through it to rebound, pushing the boundary layers against the fuselage and forcefully squeezing the rear of the aircraft and recovering a lot of the original energy that the nose expended when it pushed through. This is some times called the "Pumpkin seed effect", and is the point in the airframe's operating envelope that, having reached this speed (fast cruise), it takes less power to maintain this speed (best cruise speed for fuel economy), a feature the P 51 had that a lot of other planes could not duplicate. It took some pretty smart guys to design this plane and they didn't get it completely right until the B-C models were produced.
Changes made to the design for the D model (visibility(bubble canopy), thicker wing (6 upright machine guns), and the chin carb-air-scoop (Packard-Merlin)), made it a better gunfighter but actually slowed top speed under 10,000 feet.
The common P 51 model designs have a box fuselage and these airflow factors are minimal.
The H-9 P 51 design has an almost constant curve to the fuse from nose to tail (except the area around the sides of the cockpit, this area is also the flattest part of the full scale fuse) and should show better efficiency than its competitors.
The above picture shows the simple hot air exhaust I have been using for about ten years on 5 of the 6 TF GS Mustangs I have flown in the last 11 years. It is cut out of the lower firewall and is 1.5 inches deep and 3 inches wide. It has rounded edges inside except for the front edge on the back of the cowl. High velocity air flowing past the opening exerts a drag effect that pulls the slower air coming out of this vent. The same aerodynamic principle used for slotted and fowler flaps on wings. If you put a spoiler here you upset the air flow and create drag.
The engine cowling in the picture is for the large electric motor I'm flying now. I have used this same exhaust on a Fox 2.4, A ZDZ 80, And twice with my DA 50R. The other cowls for the gas engines had exhaust stack openings that were just large enough to avoid damage from hot mufflers and of course the top of the gas engine cylinder. I also filled in the area behind the chin scoop with block balsa and created an aerodynamic air passage to carry the cool air directly to the engine cylinder. No overheating. And it is not visible unless you look at it from this angle.
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Last edited by sjhanc; 06-09-2015 at 05:05 PM. Reason: reply to engine cooling questions
Old 06-09-2015, 06:16 PM
  #945  
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Originally Posted by chorner
Len what're you using to obtain the RPM figures in the air? Are you piping it back to your receiver through some sort of optical RPM gauge, or through the ignition...?
I use one of HH's optical RPM couplers pluged into the DLE ignition module's RPM output. They work great. Then the coupler goes to a TM1000 telemetry module. The Telemetry module sends a signal back to the transmitter with all the data that I am measuring. I usually monitor Head/cylinder Temps, RPM and Battery voltages. I have alarms set on various parameters including temps, voltage, frame losses and holds. When I get an alarm, my observer typically takes a quick look to see what is going on. On the Jet, it monitors all kinds of parameters. But I only have an alarm on flameouts and battery voltages. Once I get all the bugs shook out, then I don't monitor telemetry that closely. I just listen for alarms which I seldom get becuase I got all the bugs worked out and the thing is running cool and correctly. Once you try telemetry, you will never fly an expensive plane w/o it. It is an outstanding tuning tool. I also use it to find the right prop.

On the air dams in front of the exit holes: A 1/2" dam angled at a 45 degree angle back added 30-45 degrees of added cooling on the same exit hole. This was on one of giant Extras with DLE 111. The faster I went it seemed to have even more positive effect.
Old 06-09-2015, 06:23 PM
  #946  
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With you set up you have a direct circuit tie from the Receiver to the Ignition Module via the TM1000. You ought to put a UHF scope on that circuit. You would be surprised what is on that circuit. The choke may take out the common mode currents. But depending on the material of the choke and the number of turns through it, various RF signals still made it down my circuit. I tried it several ways. That is why I went to HH's optical RPM coupler. It is made to plug into the ignition module's RPM port. It totally isolates the Receiver and Tm 1000 from the ignition module.
Old 06-09-2015, 07:23 PM
  #947  
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That is a good note. I haven't had any signal issues, fades or holds with it in place. I tried the optical sensor and couldn't get any decent readings at all with it.



Originally Posted by Len Todd
With you set up you have a direct circuit tie from the Receiver to the Ignition Module via the TM1000. You ought to put a UHF scope on that circuit. You would be surprised what is on that circuit. The choke may take out the common mode currents. But depending on the material of the choke and the number of turns through it, various RF signals still made it down my circuit. I tried it several ways. That is why I went to HH's optical RPM coupler. It is made to plug into the ignition module's RPM port. It totally isolates the Receiver and Tm 1000 from the ignition module.
Old 06-09-2015, 07:33 PM
  #948  
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I have the Evolution RPM sensor on every RCEXL based iginition (DLE, Saito, VVRC) I own. Simply plug the RPM lead from ignition into the EVOA107, or newer EVOA113, then insert into the RPM port of the TM1000 - done. Great tool for establishing throttle curves, prop testing and tuning.

Good telemetry thread on RCG

Cheers
Old 06-10-2015, 06:50 AM
  #949  
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I have several HH optical couplers and they all work great!
Old 06-10-2015, 08:18 AM
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Gas engines have been used for years in large scale mustangs, spitfires, p-47's
Why is this particular p-51 any different when it comes to cooling??
Perhaps it is the DLA or DLE that is running hotter?

Anyone using a Roto Motor inline twin 4 stroke? 84cc in this bird?

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