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Old 10-09-2018, 12:49 AM
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DA150 Engine- What is the effect of a prop strike on an engine

Hi fellow Motor-Heads!!!!

Recently a fellow member Rafigitar put an engine up for sale on this site. It is a drone engine manufactured by Desert Aircraft and used on drones manufactured by Griffon Aerospace.

Intrigued, I found two such engines and purchased them to inspect the affect of a prop strike on the components of the engine. I will take apart two engines: One with a high impact prop strike, and the other with minimal prop damage.

The question we all ask is whether or not an engine suffering this fate will be good after repair and what kind of damage will we see.
DA has built and designed a fantastic product. From my first inspection I believe the engines will have little to no internal damage. But this is why I am opening them up, to inspect and verify.

Please do not take apart an engine unless you have the correct tools and you know what you are doing. DA will not work on this engine or ones like it.

I will inspect the following:

Measure Prop Hub Run-out
Measure gap in between Prop Hub and Crank Case
Remove all components
Split Crank Case and press out Crank Shaft
Inspect wrist pins, needle bearings, head, piston, Crank bearings for damage during impact
Document Procedures


On initial inspection I found the following:

This engine is not cosmetically finished like the model you would purchase. It is a rough cut Crank Case
It weighs about 14 OZ more then a DA150L (8lb vs the 7 lbs 2oz advertised by DA for the L version). Never the less, this one engine pushes 100 lbs to 100 mph. Quite the Engine don't you think?
This drone crashed upside-down and had no damage to the head cooling fins.
Its muffler has a ceramic catalytic converter internal bundle. It is excellent for maximizing HP, and reduce smoke, but on vibration and impact it can disintegrate and the powder can drop in the piston head. See pictures. I guess if you use a military drone once, it does not matter.
The OEM version had a velocity stack mounted on the carburetor which was broken off on impact.
Last, the mounting bolt pattern is not the same as the 150-L

The first engine is the High Impact Prop Damage.

The Prop Hub had a .0025 wobble and .003" out of round. If the hub has a .0025" wobble at 1" away from the center, at 15 inches from the center the prop will have more than .040" wobble. This engine could not run at this condition. The prop spindle had 0 run-out. The hub is fitted on a taper and the high impact twisted the Prop Hub. The space in between the Prop Hub and Crank Case varied from .069" to .072". This is consistent with the indicator readings. A feeler gauge was used to measure the gap. Therefore, from the readings I conclude that the Prop Hub in no good and damaged.

More will come in the next few days after I measure all the components.

ChemE


Video courtesy of TOPDOGZRC
NAWCWD China Lake Ranges 2018 (5 min 12 sec)
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Old 10-09-2018, 12:57 PM
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Engine #2 Light prop damage

Engine # 2 arrived this morning and although the prop damage was light, the damage to the Prop Hub and Prop Spindle was extensive. This engine is bran new. I would be surprised if it has one hour of flight. There was extensive material sucked into the intake and material falling into the exhaust port. See the pictures. No Damage is evident in the cylinders and head. The shaft does not turn well indicating either a bent Crank Shaft or damaged bearings.

You can't see the damage on the prop because I asked the previous owner to cut it and save money on shipment. I will look for an original picture to compare to engine #1.

I took apart the engine to the point of splitting the Crank Case and pressing out the Crank Shaft like engine #1. Numerically, here is what I found:

Prop Spindle had a .028" run-out. It is bent.
Prop Hub had a .006 wobble and .006 out of round

This coincided with feeler gauge measurements of .062 to .069 in between the Hub and Crank Case.

This may indicate that the damage to an engine is not determined on force but that it hit at all and any prop strike can be damaging to an engine.

One of the mufflers was intact. It is elegant to say the least. There is virtually no pressure drop across the muffler as the surface area is very large.

The cooling manifold around the Cylinder Heads is made of a G10 like pre-preg form fitted glass impregnated with epoxy and cured to form in an oven. The two halves are held together by rivets and cable ties.

The reed block and muffler were damaged in this crash as well as a slightly bent cooling fin.

The weight of the engine came in at 8 lbs 3 oz

I will measure both engine components for wear and will take both Crank Cases apart this weekend.

The two engines have been cleaned and are ready for inspection and crank removal. See dirt in pan collected from engine 2. This is what was sucked into the engine during the crash and after.

I will post the numbers soon.

ChemE
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Last edited by ChemE; 10-09-2018 at 08:53 PM. Reason: add pictures
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Old 10-10-2018, 06:20 AM
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Thanks for the pictures, the cooling ducts look like they would be very effective.
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Old 10-10-2018, 11:10 AM
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Interesting thread. I rebuilt an engine in much worse shape than yours. Runs fine now.
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Old 10-10-2018, 11:48 AM
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Interesting! Keep at it. I would suspect that the catalyst material is ceramic and probably very very hard on things internally so turning it over with in in the cylinders probably is a bad idea..

I don't know if prop damage is a good indicator of the force that these hit the ground with. Its been a few years since I have seen a drone shot down but once hit they often would pull the throttle back and or kill the motor so it didn't travel so far..so your no prop damage could have went in with the motor idling. also you don't really know how they were handled after the were picked up.. the last range cleanup when I saw some of these the guys were picking up and they were turning them over like kids with a Christmas present..etc.. so debris inside may have nothing to do with it running or not on impact.
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Old 10-10-2018, 12:22 PM
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Thank you all for your feedback.

I do not fly anything greater than 35% or 120 size engines. I purchased these two engines as a lab experiment for my own training.

I am looking to see how much work it will take to repair and secondly, determining damage, developing a disassembly and assembly procedure, a tool list to do this type of work.

This is a hobby to me. Normally, i would be crazy to do this work since DA is reasonable in cost and exquisite in quality.

I want to share this with you all.

I am keeping a track of the time also. Just think for a second: I will need two bars that I will machine that will bolt into the crank case to press out the the crank shaft. This will take some time. I also have to build the press fixtures to press the bearings onto the shaft without compressing the balls into the races. I also need spacers to fit in between the crank section to spread the load evenly during pressing. You need about $700 worth of measuring equipment and an arbor press.

By the way, the catalyst in the mufflers are extruded as a paste and then baked in a kiln at 1400c. When i took one of the mufflers apart they disintegrated.

More to come tonight.
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Old 10-10-2018, 08:13 PM
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Bore dimensions of Cylinder Heads

I measured the Cylinder heads and saw no measurable wear in the heads of either engines. I tried to measure the bores with a bore gauge but was unable since the one I have at home can measure 2" bore and up. The bores on the heads are 49 mm or 1.9291 inches. I used a standard telescoping gauge instead and measured the compression with a caliper. This makes the readings accuracy to +/-.001 inch. The bore gauge is more accurate because you set the gauge against a 1.929 standard and then set the dial on the gauge to zero. When you place the instrument in the bore, the indicator will tell you if your hole is bigger or smaller than the set point. It is much more accurate. ( see pictures of instruments)

Engine 1 Engine 2
Left Cylinder Head Bore (mm) 48.98 48.96
Right Cylinder Head Bore (mm) 48.97 49.00
Left Ring (mm) 2.11 2.12
Right Ring (mm) 2.10 2.10


For all purposes these engines have no wear. The dirt must have got in there post crash as 2Walla mentioned in a previous post.

The piston heads are not damaged at all from the crashes with the wrist pins and needle bearings showing the same , no damage.

More measurements after I remove the crank shafts.
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Old 10-10-2018, 09:12 PM
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Lots of different ports in those pistons and cylinders,,,


BV
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Old 10-10-2018, 09:43 PM
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On the next science project I should compare a 3W 150 with the DA150.
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Old 10-11-2018, 12:05 AM
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Pre-Disassembly Gaps

Below are dimensions taken before the case is disassembled for the two engines.
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Old 10-11-2018, 08:24 AM
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Quote:
Originally Posted by G Heiman View Post
Interesting thread. I rebuilt an engine in much worse shape than yours. Runs fine now.


What did you have to replace to bring it into running condition?
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Old 10-11-2018, 10:09 AM
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I replaced a cylinder, c-clips, gaskets, rebuilt carb, crank assy, sensor (the original was for reverse rotation) and most screws. I also repaired the ignition module.
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Old 10-11-2018, 01:28 PM
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Lock-tite

In a conversation with G Heiman the subject of green loc-tite was brought out. He reminded me of this issue. DA puts loc-tite on the shaft and bearing in the crank case. This is usually done due to the fact that aluminum expands at a greater rate than the bearings. In order for the bearing to not spin on the shaft and bore, you would have to have a very tight press fit of the bearing into the housing. By using loc-tite you extend the life of the bearing by having a looser fit between bearing and housing.

This is why I would recommend a hand operated arbor press instead of hydraulic one, and you have to use a brazing torch and temperature stick so you don't overheat the case. It is not difficult but you can ruin an engine if you don't know what you are doing.

This is a picture of a DA100 crank shaft I took apart some time ago.
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Old 10-11-2018, 02:05 PM
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Done this myself a few times,just curious.What type of tool did you come up with to get between the counter balance of crank and the bearing to pull it off.I use a two piece clam shell that bolts together under the bearing.Then I use puller to grab onto the clam shell to pull the bearing.
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Old 10-11-2018, 02:33 PM
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I did not have any special tools. I will post a full set of pictures when I take it apart complete with procedure and tools. As you can see from the previous post, I used anything I had in the shop. For the 150 engine, I will have to machine some brackets to screw into the head mounting holes to straddle the press. This will keep the case stationary while pressure is applied to the shaft.
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Last edited by ChemE; 10-11-2018 at 09:52 PM.
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