Tip Rocket Pre-Rotation

[Brent_Brown]

Erik; I think he was asking who makes a hollow torque tube not if it changes anything.

[darrellwittke]

Brent, just wondering who still makes a hollow torque tube or if it would be cheaper than having mine machined. (Have to do some calls and checking on machine work, etc for complete system cost.)

Thanks for answering the questions Erik. I appreciate your style of open honesty and no marketing hype or lies.

Glad to hear about the fail safe of pressure bleed off also.

We need some input (or I do, and probaly many others) as to strengths of hollow main bolt and impact of slightly aft cg of rotor blade and probaly half a dozen other things I haven't thought of yet!

(Chuck Beaty, if you would kind sir, please make your knowledgeable comments regarding Erik's design and I promise I'll get off my procrastinating butt and send in dues to rejoin PRA! (And/or any other engineers) How about that for an unfair trade ($40 bucks for a lifetime's knowledge of design assessment.))

Some general background and comments: A cg (as I recall, may be wrong and probaly am) behind the 1/4 chord of the rotor blade is somewhat equivalent to an aft cg in a fixed wing, but without a torsionally flexible rotor spar, not as dire as an aerodynamic center of lift aft of the cg (ie. far better of have cg behind aerodynamic center rather than aerodynamic center behind center of gravity, which leads to flutter or blade weave, although tail feathers (or reflex in this case) can compensate.) I suspect that the chambers weight will be okay, anecdotally, since Erik states he hasn't seen any blade weave.

I confess to being ignorant of my rotor head dimensions and bolt sizes, but I'll dig out my bensen plans and send the rotor head blueprints to you Erik, if somebody on the forum doesn't beat me to it...which just made me think of another good question (well, a question anyways.) Does the added height cause enough of an increase in the overturning moment to warrant a double bearing rotor head?

I am really excited about this system since the cost isn't out of my range, I have the resources to fly it and store it (and the H2O2) at my disposal, and I am having a lot of fantasies about places I have flown over but wanted to land and check out. I believe I could with Erik's system.

But I'm really ignorant as to if it is possible to modify my bensen/brock rotor head to make it work (I can probaly handle fitting the pipes, having them welded, etc.)

Any qualified people out there willing to state their analyses?

(I'm going back to work on my railroad bicycle project (got an abandoned line close to me) and let this percolate in my mind for awhile, thanks for reading these meanderings.)

[PeroxidePropuls]

Ben Mullet, an honored member of this forum, has written an interesting article about PPR, Partially Powred Rotor in the February issue of the PRA Rotorcraft magazine.

If my rotor tip rockets are not shut off after take-off but instead let idling, there will be a PPR effect.

Ben has found that PPR gives several positive improvements of the performence, like the rotor is travelling flatter. The climb is faster. (My conclusion from this is that my previous assumption, that one can use a smaller propeller engine when having tip rockets, is correct).
Other benefits mentioned by Ben is shallower glide and STOL. In low G, the rotor RPM decay is reduced or eliminated. -a major safety benefit.
Ben tells that already Dr. Igor Bensen used PPR. -Truly a remarkle man and pioneer!
I recommend everyone to visit Ben Mullets website: www.braggroup.com
Thank you for your article, Ben
Erik

[Victor Duarte]

Hi Erik
all said previously is right. at a moment i wanted tip jets on the rotor.
it's achievable with a good centrifugal compressor.. the peoblem is that you have to fint the KW to feed it and it takes about 80 HPto have a tip jet PPR (with quite helicoptering capabilities)..

I asked you if our system coud have a "slow mode" where the h202 if released in order to produce a ppr effect, or if it could be injected in a cold compressed air circuit..if so, the compressor could be much smaller and the h2o2 have a role of booster.

for example, the DJINN blades were feeded with 1.14 kg / sec at 3 bars (fully powered rotor), a big turbo can give 1 kg/sec at 2.5 bars.. a small one 0.4 kg/sec at 2 bars, you could imagine to produce the extra airmass with a slow release h2o2 injected after the compression..
what do you think ?
thanks

[PeroxidePropuls]

Hi Victor,
Even if you are making things more complicated than they need to be, in my taste, I guess you can combine peroxide tip rockets and cold jet nozzles. I do not know in detail, exactly how you would like to do it, though.

You would have to try it out yourself, because I am pretty full booked up myself. Unfortenatelly, sometimes I have to work for a living also, not only with rockets.

I could send you peroxide for your own testing, without problems I believe, because I have now sent rocket grade hydrogen peroxide two times to my rocketbelt friend Stuart Ross in England. Recently I sent peroxide to Visa Paivianen in Finland. Transport at least inside EU is no problem. Visa is working with a quite thrilling peroxide rocket project! I will report about it soon.
Erik

[Victor Duarte]

Thanks Erik for your kind proposition, i understand you need to fund your life, so i won't ask you to do anything
Having someone working with h2o2 and reporting here is great !

for now i've dropped the tip jet thing (too much hp needed) but , later i may try something, and i just wanted to know in witch way, a kind of "expanding" substance could be used to increase airmass... the first solution if burning fuel... the second could be the use of a small percent of h2o2 to double the airmass/pressure..almost like in a steam machine..
thanks and good fortune in your venture.

[darrellwittke]

at least to me. Regarding www.peroxidepropulsion under shop. Took me awhile to do just a little bit of research (told you I procrastinate! ) and called Ernie B. and looked for rotorhead drawings and priced stainless steel piping and welding.

So, first off, talking with Ernie Boyette was enlightening as to why none of the technically knowledgeable heavyweights have chimed in on this thread. Ernie suggested (and Chuck B suggested to him)to stay away from this system primarily because of the oxidative nature of hydrogen peroxide and that there are mechanical systems to accomplish the same thing without some of the drawbacks.

I personally like the system (from a non-educated glance from a distance) for its "keep it simple" straightforward design. Ernie and I simply agreed to disagree on this primary difference in design philosophy.

Ernie brought up other points in our brief phone conversation I hadn't thought about though, namely properly securing the piping and rocket chambers to secure against the 10,000 lbs centrifugal force trying to sling it, and also pointing out I would basically need a new rotorhead. He did state that it is possible that the 1 inch bolt drilled out may have sufficient strength if well polished on the inside (to prevent cracking), which was a big concern of mine. (just seems like a bolt with a hole in it would be 10 times more likely to crack than smaller same tensile strenth bolt with no hole, intuitively speaking)

Another gem of information was that you can raise the bensen teeter bolt by approx. 1 and 1/2 inch before the overturning moment (on a 5206 bearing) demands a two bearing setup. Of course that will change when you change to the bigger bearing to accomadate the 1 inch bolt so I do not know how relevant.

Ernie also stated Erik had talked to him before about the system. So I suspect that, for legal reasons, liability reasons, and basic distrust and/or disinterest in the H2O2 system, our best and brightest minds on the rotorcraft conference will not be posting valuable insights to get a operating system up and running. (I will call J. Vanek sometime, however, and see if he has any interest in building a modified rotorhead.)

I do suspect now that Erik has had some engineering work done on the rotorhead and rotor bolt, also. If he has access to someone who is familiar with bolt strength calculations, then it follows the rotorhead modification probaly has had some professional looking at it. Also, Erik is in a professional world and seems like too hard a worker to let this critical part go without engineering analyses.

On other things, I found Aircraft Spruce is the cheapest place for stainless steel piping at approx. $80 dollars plus shipping. Pacific metal had a price of $157. Welding would be Tig at $25 dollars per hour with 1 hour minimum charge.

I couldn't find any drawings of my rotorhead, bensen didn't include them in his plans I remembered, I thought I had a line drawing from Ken Brock mfg. when they rebuilt my rotorhead but I can't find it. There are generic drawings available someplace, I remember some being posted here or on the old forum or maybe R. Taggarts site. Doesn't matter since you need a new torque bar, bearing, spacer blocks, etc which in the end pretty much adds up to a new rotorhead.

So in closing, I have to say I really like your system Erik, I think it has a lot of potential as a very effective, lightweight and powerful pre-rotator for our autogyro's. At this stage of my life, however, I do not have the financial resources to expend on a new (and untried) rotorhead along with the rocket chambers and fuel system. I think the best thing for me is to keep my nose in the books, earn my degree, delay my gratification, and then reward myself with your system (which may have proven it's potential by then.)

Please keep up the communication, especially regarding rotorheads and prices, if you would be so kind, Erik. Please do not be disheartened with the seemingly tepid response here. Your system has great potential, we just have to find answers to the rotorhead problem and rotorblade safety. Best wishes, darrellwittke

[JoeSwanton]

Darrell,
If the rotorhead is your main drawback keep the one you have now along with your present pre-rotator. Just mount a spherical aluminum tank to the top of the hub bar (centered above the rotor) Your present pre-rotator will povide the centriugal pumping action so the pressurized tank or the hand pump tank are not needed. You would need to add a slip ring set-up to the rotor head to turn on a electric solenoid to open the fuel valve, or better yet it could be wirelessly remote controlled. The REAL issue is getting Ernie to build you a custom set of blades. Without custom built blades to address the centrifugal loads on the fuel pipe and the 1/4 chord balance issue it is going to be an exercise in futility. Don't let the dream die ---Joe Swanton

[PeroxidePropuls]

Hello Darrel,
Any sign of the spring in Montana yet?
I hate to critisize your math, because you are my greatest supporter, but the centrifugal force from the rockets and the pipes must be in the order of magnitude of maximum 1000 lbs. The 10 000 lbs you mention is more reasonable for the centrifugal force from the whole rotor blade, I think.

The name of the guy that has made all mechanical strength calculations is Prof. Nils-Gunnar Ohlson. I presented him and the other project team members in the first report from 2003: www.peroxidepropulsion.com/article/15 .
There was no need to change out the original rotorhead bearing, because the shaft diameter allowed for the bigger bolt. Nils-Gunnar explained that if you compare two bolts with the same steel weight, the bigger diameter bolt with a hole is stronger than the massive bolt with smaller diameter. If one need a light and still strong shaft it is common to make it hollow.
If you can send a drawing of your rotorhead I can maybe convince Nils-Gunnar to calculate the modifications for you. (No promise) He has the latest computor software with impressive grafic colour drawings showing were the stress is located.

The first rotor I had on the gyroglider last summer, came with the steel rod for the chord c/l balancing delivered separatelly - for the customer to install it himself. It was easy to install the steel pipe in the hole intended for the rod. If one apply some epoxy resin when installing it, it will be an extremally strong bond, with no risk of slinging the rockets out. It would be nice if more rotor blade manufactorers could deliver the rod on the side.

To Joe:
Already at the first project meeting 2003 (see link at the beginning of this post) we discussed the possibility to install the tank on top of the rotor, but the more experienced gyro people said such a tank would probably induce "two times per revolotion" vibrations because of the drag force on the tank. One guy even thought it would be a hard time to hold the stick! It would be interesting if someone would like to test it though. One could make the tank with a good aerodynamic shape and not too big.
Erik

[PeroxidePropuls]

Joe,
If one want to test your idea, one could start with just installing a small and light dummy tank on top of the rotor and find out how it effects the flight characteristics.
Why don´t you do that Joe, because I know you are an experienced pilot and an instructor? You could tell the rest of us if you experienced any stick shaking or not.
Erik

[et3dotcom]

IMO a lens shaped tank with a void in the center to accommodate the teeter tower, rotor hub, and hub bar would greatly reduce rotor drag at high speed.

Then you could use the hollow bolt for a collective pitch control! I concur that a hollow bolt is stronger – yet potential for corrosion inside the bolt might be an inspection issue.

[darrellwittke]

I asked a mechanical engineer about the hollow bolt issue and he confirmed what you all have already posted. Good enough to allay my fears about that.

Sorry about the slow pace of posting lately gentlemen, I've been busy (still am) with other projects.

I will search out drawings of my rotorhead and get them to you Erik. If anybody reading this can direct me to the generic ones that were on the forum before, I would appreciate it. Thanks in advance, darrellwittke

(ps. no sign of spring here yet erik, snowing with 2 ft expected in mtns.)
(pps. hate math, that's why I flunked out of engineering.)

Found some rotorheads at wobblyflyers and [url]www.keskydee.com/aviation/rotorhead

[JoeSwanton]

Erik, Darrell & Daryl,
I always wanted to say that--he he he. The nice thing about a rotor mounted tank and the wireless fuel solenoid is that the whole set-up could be moved from one machine to another. A rotor manufacturer could build and sell the complete package. (Ernie are you listening??)
Let's see now, if we shape the tank to equal the profile drag of the rotor when the blades are at the 9 & 3 o'clock position and mount the broadside of the tank into the airsteam when the rotor is at the 12 & 6 o'clock position we have just cancelled out the 2 per-rev drag variation that has been a thorn in our sides forever. If there is someone out there who can tell me why this wouldn't be the case I'm all ears. I believe this would result in an even smoother rotor than before the tank installation.
Now don't get me wrong, I'm not saying everyone could just bolt this set-up on their gyro and expect to be doing jump take-offs in a few days. It would have to be learned step-by-step, a little at a time just like we all learned to fly gyros the first time. I would definately be contacting Dick Degraw to pick his brain about how he taught himself and his wife to jump.
If the tank was only big enough to overspeed the rotor after a standard mechanical pre-rotation to 150rpm, and then another 10 seconds reserve time that would be perfect. Jump take-off and when you wanted to land bring it down on a normal power off approach and again hit the H2O2 switch to have a helicopter touchdown. Sound neat?? Say goodbye to airports--Bye Bye

[JoeSwanton]

Erik,

I do intend to test this tank idea (cancelling the 2 per-rev drag variation) I've been thinking about this idea for years. The only problem is, it is getting into the farming season here in Iowa and with a full-time job as a mechanic and 1000 acres to farm, it will be June before I have a chance to try it out. Someone will beat me to it I'm sure. If not I will indeed give you a full report in June. I plan on incorporating a Centra-Matic truck tire balancer with this set-up. It will be mounted laid down centered on the rotor and at the level of the teeter bolt (vertical CG of the coned rotor in flight). This should give dynamic balancing of the rotor. They are actualy made to do their job in the same range of rpms that our rotors turn. Again, If there is someone out there who can tell me why this won't work I'm all ears. I don't have all the answers just some ideas that I want to try. The H2O2 tip rockets are the final piece to the puzzle--maybe

[Brent_Brown]

I was thinking of the tank that looked like a skywheel hub bar that is bolted to the real hub bar. If you plan on gettting the blades over 100 rrpm before starting in with the H2O2 you will only need a small amount of it to get the blade over 300. This tank would only be about 24" long to hold the needed H2O2.