Engine test stand problems

[Elwyn Aud]

[Garf]

Air mail special delevery.

[Russell Shaffer]

I had a 35 shake the c-clamps loose on a test stand.  That was plenty of excitement for me, and I got hold of the stand before anything departed.  Wow. 

[Al Rabe]

Many years ago, I had a Sea Fury's ST .60 start in my hand while casually fliffing the prop in my worksjhop.  The engine hadn't been run in months.  I think it happened to fire on its WD-40 lubrication.  There was no, had been no other fuel source.  The engine flew about 5 feet.  Scared the heck out of me.

Al

[PatRobinson]

Hi Guys,
Several years ago I was testing out some prop modification techniques I saw in a magazine. I wanted to see if it was possible to reduce the prop load on a 15"-16"to the point that an engine could turn it the same rpm as a 12"-13" prop.
I had an 60 OS RC engine that I got cheap at a swap meet, that I was willing to risk in the test. My test stand was always weighted down with a full-size concrete block and concrete bricks were placed in front of the stand to avoid any sliding.

I had made progressive changes and noted result. I had the prop in the final modification. I made the mistake of not moving the throttle to low to start the engine. I cranked the engine and the whole rig including concrete block jumped  forward about 18". That stand had never budged before so I was totally unprepared.  It happened so fast I couldn't move and the prop hit my left hand just before it would have hit my body and the engine stopped.
I received the second worst injury I have received in modeling.

So the lesson here is, "increasing prop diameter increases thrust" so make sure your test stand can safely handle that increased thrust level. Just a word to the wise, from someone who learned the hard way.

P.S. After a month and a half of healing, I built a bigger stand and successfully completed my testing.       
                                                       Pat Robinson


                                                                                                           

[john e. holliday]

I have an aluminum motor mount that my brother made when he was still with me.  The studs in the block come up thru the front holes of the motor lugs aith a clamp to hold the engine down on each side.  I can't remember how engines I have run on it with no problems.    Decided to mount and run a K&B 5.8 for profile carrier.  I started the engine and moved around behind it to set needle and use the throttle.  I was about set on the needle with high speed when the engine disappeared.  Seems the Rev Up 9-7 had a flaw and half of the blade came off.  The instant vibration sheared those studs off instantly.  Luckly the moun-t was aimed toward the basement wall and the engine quit immediately once it departed.  Have fun,  DOC Holliday

[don Burke]

That J-85 was a real OOPS!  Those things are held to their mounts with two teeny bolts/side clamping spherical radiused blocks around spherical bearings sticking out the side of the engine!  OK when nothing goes wrong.  That dude disappeared in a hurry!  Wonder what it hit!

[Charlie Pate]

Reminds me about the tale told of the TOYOTA folks getting into truck racing.
The story goes, they rented a wind tunnel for drag test; didn,t have the truck tied down properly and it
got loose in the tunnel during the test ,tearing up the truck ,but mainly tearing up the wind tunnel   

[Michael Boucher]

I remember at the airlines hearing about when the test cell crew were running up a newly overhaul JT-9. The mount bolt sheared and the engine well thru one set of doors bounced off the walls  and was approaching the second set of doors  .  Found out they had a box of mount bolts that they used over and over again.  This put an end to that!

[L0U CRANE]

I've used a wooden milk box, mounted on an X-type camp stool, for about 30, maybe more, years. ('Borrowed' the milk box from our supplier, back then. Please don't tell them?) The box top has mounted the old wooden motor mounts, the early Tatone mounts, and the later - countersunk from above - aluminum mounts. It has also been adapted to allow testing of pre-first-flight tank 'preferences' for unfamiliar engines.

This is portable, brings the prop to a comfortable height out of ground-level dust, and folds up to a storable size. When running engines of unknown thrust potential, I add "ballast" to the interior of the milk box - usually an additional full gallon can of fuel. Only once has the thrust tipped the rig over, and that was without added ballast. And, yes, I did take a whack or three on my hand. More cautious since...

Safety is in awareness of potential problems, and dealing with their most dire effects before they amputate or mangle parts of our bods. Arbitrary "rules" based on anything beyond sensible precautions can be deadly - really!