That's a great link, and very helpful information!
Good to have some reference numbers to guide us, even if they are generic.

Guess I better get an inch-oz clicker and verify it.

Wish you were right.
"Snug" loosens.
Loose bolts loosen more.
Bad stuff happens.

It will be interesting to get good comparitive numbers, and I'll do that ASAP.

"Tight" plus a half turn (the old mechanics' universal torque value) isn't good for these, that is for sure.

Haven't seen any torque numbers posted for either the DA or DL 50 prop bolts. Anyone seen those in print anywhere?

The value given by 3W of 40 inch/pounds is based on the ISO standard for the M5X.8 bolt and has nothing to do with the compressable material behind it. You can do a search on the net for a torque value chart which gives standard torque values for each size bolt. If you can't find a metric chart just look up a 10-32. Props made of European Beech Wood have the following properties. Note the low density and great difference in Compressive Yield Strength based on the attitude of the grain to the load. That's what causes the problem.

Physical Properties Metric English Comments
Density 0.660 - 0.780 g/cc 0.0238 - 0.0282 lb/in³
Cell Length 1.10 mm 0.0433 in Mature Wood

Mechanical Properties Metric English Comments
Hardness, Wood Indentation 4800 N 1080 lb (f) Side
Tensile Strength, Ultimate 3.50 MPa 508 psi Perpendicular to Grain
130 MPa 18900 psi Axial
Modulus of Rupture 0.104 GPa 15.1 ksi Static Bending
Flexural Modulus 13.13 GPa 1904 ksi Static Bending
Compressive Yield Strength 7.90 MPa 1150 psi Perpendicular to Grain
46.0 MPa 6670 psi Parallel to Grain
Machinability 100 % 100 % Good Relative to Other Wood
Shear Strength 12.3 MPa 1780 psi Orientation Unknown
Toughness 31.2 J 23.0 ft-lb 2 cm x 2 cm sample
Cleavage 9.10 kN/m 51.9 lb/in

Thermal Properties Metric English Comments
Shrinkage 0.100 - 1.10 % 0.100 - 1.10 % Axial; Green to Zero Moisture
8.60 - 18.2 % 8.60 - 18.2 % Tangential; Green to Zero Moisture
12.3 - 21.8 % 12.3 - 21.8 % Volumetric; Green to Zero Moisture
5.80 % 5.80 % Radial; Green to Zero Moisture

Descriptive Properties
Color Whitish to pale brown Usual for heartwood
Pinkish-red Steamed; Usual for heartwood

Now can we get back to the DL-50???

I tighten them the German way GUDNTIGHT

I didn't think my JXF prop question would bring this much heat! I'm gonna soak the holes in thin CA and then tighten them up, and check them from time to time. My JXF that came today is just for breakin. Then I'm goin 23B vess. Just so I can fit in with the cool kids!!! LAMO!!!


Lou, I think that torque spec you were looken for is GDT. Its in all the books if you look.LOL

If you're referring to Geometric Dimensioning and Tolerancing, it has nothing to do with the international torque specification standards for bolts. Now, Let's get back to the DL-50!!

Lou55 - So, to summarize....

"tighten the bolts"

Yes, in a sequence. And then repeat the sequence. You will find the second time that the first bolt is loose again. I usually go through the sequence three times. After this discussion I don't care if they make them finger tight! Never seen such a fuss over a fix. Reminds me of the tuning video Bob. LMAO!!!! See what your good ideas started!!! LOL

Aerobob, I did the twist test you said to do. My JXF is stiff.

That's GREAT! Some are stiffer than others; that's the only "gripe" I have on JXF is wood variation. However, to be objective, it's probably equally likely that others have as much variation, who knows?

I know if the prop you're using is difficult to untwist by hand, you probably will have good performance in the verticals. That's where the "untwisting" of a prop really shows.

I'm still gonna maiden my Obsession / DL 50 with the PT Models 22 x 8 N, just to see what happens.

Get video!!!! It will be short, but get it nonetheless!!!

I'm thinking about getting another DL soon, and was wondering if anyone had any suggestions on a good warbird ARF? ( other than the TF P-51)

It's interesting to note that you (like myself) have an engineering background and we concur on the risks involved in this process.

Aerobob, do you have an engineering background?

What we're talking about here is not a "certain failure" but a significant increase in the risk of failure. When we're talking about something with not insignificant mass, spinning at 7K+ RPMs within "striking" distance of bystanders, I don't think it's advisable to increase the risks any more than is absolutely necessary.

Hospital care (and law suits) are very expensive compared to buying a prop that isn't so soft that you need to mess around like this.

What rpms are you getting with that pt carbon, Aerobob?

Around 7100 or so. Haven't checked lately. Others have reported lots higher, like 7400 or so....

xjet - You are most certainly correct regarding risk mitigation. Good insights to keep in perspective.

Why don't you just do this? Compute the mass of an 1/8" hardwood dowel approx. 3/4 of an inch long and then compute the outward force it creates traveling around an approx 3" circumference at 7000 rpm. Then compute the strength of the European beech (most good prop makers use this) from a point approx 1/2" in from the outside of the hub (on a plane perpendicular to the grain) and tell me what the liklelihood is of that dowel busting through that hub with that much force (the torque of the bolts) capturing it at the two ends of the axis. Then get back to me. We have a saying where I work... There comes a time in every job when you come to the realization that you just have to shoot the engineer and get on with the job! What field of engineering are you in and what do you work on, if you don't mind me asking? I stand corrected, an approx. 2.3" circumference.

Al - the hardwood dowels are about 3/8" radius from center of rotation. The original disagreement with my suggested fix was that the dowels themselves would be absorbing all the "clamping" force from the hub face and hub washer, thus removing all the surface contact area of the REST of the hub.

I think this has wandered too far, and I apologize if I've insulted any sensitivities about this topic.

Will it be okay with everyone if I just "un-suggest" my suggestion ???

Won't hurt my feelings at all, and the props that I've fixed will still work....

Buddy, I'm good with that if you are! I just wish we could keep this thread on subject. You try and give a little help with a quick fix and it's three pages off subject. Let's all remember this is a thread about the DL-50 engine. Props are on another thread. Anybody get 8000 rpms yet??? LMAO

If you want to put something this powerful into a warbird I would suggest you go to the CMP website and check theirs out. They are historically heavy, I believe, but fly great and have great detail. http://cmpairplane.com/ I believe Raidentech is around the cheapest place to get them. http://www.raidentech.com/ I know they do a 50cc Zero and believe they do a 50cc Mustang. They do an 82" Texan. They use a fiberglass fuse so if you get one don't leave it out in direct sunlight too long. It tends to soften.

aerobob,

Would you post a link to your DL50 tuning video? I'm maidening my second DL50 tomorrow and want to tune the engine before it leaves the ground, minimizing the learning curve I had on the first one. It ran for 30 minutes this afternoon and it is interesting how it started to smooth out after about ten minutes of run time.

Chuck

We at Valley View RC have found a couple of the new DL engines that have little or no compression out of the box. Check your new engine when you take it out of the box for this problem. We check all engines before we ship them and have only found 2 DL’s with this problem but have found a few more SPE’s. This problem is normally caused by the final cylinder hone or lack of it.

Are you an authorized factory distributor or are you selling off seconds?

We buy direct from the factory, our engines are not seconds, nor do I think DL has seconds. Looks like you are close to us in Washington.
Thanks
Tom

Please understand that that was not an accusation but an inquiry. I know Bob Kramer is a factory distributor but we have been warned against people claiming to be factory distributors that are, in fact, selling factory seconds. No offense meant but it was my understanding that DLUSA was the sole factory distributor in the US. BTW I spoke to you on the phone a week or two ago about an SD Extra 260 spinner.